Adding upstream version 14.5.upstream/14.5upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

12 files changed, 23923 insertions, 0 deletions

diff --git a/src/backend/access/heap/Makefile b/src/backend/access/heap/Makefile
new file mode 100644
index 0000000..af0bd18
--- /dev/null
+++ b/src/backend/access/heap/Makefile
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+#-------------------------------------------------------------------------
+#
+# Makefile--
+#    Makefile for access/heap
+#
+# IDENTIFICATION
+#    src/backend/access/heap/Makefile
+#
+#-------------------------------------------------------------------------
+
+subdir = src/backend/access/heap
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+
+OBJS = \
+	heapam.o \
+	heapam_handler.o \
+	heapam_visibility.o \
+	heaptoast.o \
+	hio.o \
+	pruneheap.o \
+	rewriteheap.o \
+	vacuumlazy.o \
+	visibilitymap.o
+
+include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/heap/README.HOT b/src/backend/access/heap/README.HOT
new file mode 100644
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--- /dev/null
+++ b/src/backend/access/heap/README.HOT
@@ -0,0 +1,499 @@
+src/backend/access/heap/README.HOT
+
+Heap Only Tuples (HOT)
+======================
+
+The Heap Only Tuple (HOT) feature eliminates redundant index entries and
+allows the re-use of space taken by DELETEd or obsoleted UPDATEd tuples
+without performing a table-wide vacuum.  It does this by allowing
+single-page vacuuming, also called "defragmentation".
+
+Note: there is a Glossary at the end of this document that may be helpful
+for first-time readers.
+
+
+Technical Challenges
+--------------------
+
+Page-at-a-time vacuuming is normally impractical because of the costs of
+finding and removing the index entries that link to the tuples to be
+reclaimed.  Standard vacuuming scans the indexes to ensure all such index
+entries are removed, amortizing the index scan cost across as many dead
+tuples as possible; this approach does not scale down well to the case of
+reclaiming just a few tuples.  In principle one could recompute the index
+keys and do standard index searches to find the index entries, but this is
+risky in the presence of possibly-buggy user-defined functions in
+functional indexes.  An allegedly immutable function that in fact is not
+immutable might prevent us from re-finding an index entry (and we cannot
+throw an error for not finding it, in view of the fact that dead index
+entries are sometimes reclaimed early).  That would lead to a seriously
+corrupt index, in the form of entries pointing to tuple slots that by now
+contain some unrelated content.  In any case we would prefer to be able
+to do vacuuming without invoking any user-written code.
+
+HOT solves this problem for a restricted but useful special case:
+where a tuple is repeatedly updated in ways that do not change its
+indexed columns.  (Here, "indexed column" means any column referenced
+at all in an index definition, including for example columns that are
+tested in a partial-index predicate but are not stored in the index.)
+
+An additional property of HOT is that it reduces index size by avoiding
+the creation of identically-keyed index entries.  This improves search
+speeds.
+
+
+Update Chains With a Single Index Entry
+---------------------------------------
+
+Without HOT, every version of a row in an update chain has its own index
+entries, even if all indexed columns are the same.  With HOT, a new tuple
+placed on the same page and with all indexed columns the same as its
+parent row version does not get new index entries.  This means there is
+only one index entry for the entire update chain on the heap page.
+An index-entry-less tuple is marked with the HEAP_ONLY_TUPLE flag.
+The prior row version is marked HEAP_HOT_UPDATED, and (as always in an
+update chain) its t_ctid field links forward to the newer version.
+
+For example:
+
+	Index points to 1
+	lp [1]  [2]
+
+	[111111111]->[2222222222]
+
+In the above diagram, the index points to line pointer 1, and tuple 1 is
+marked as HEAP_HOT_UPDATED.  Tuple 2 is a HOT tuple, meaning it has
+no index entry pointing to it, and is marked as HEAP_ONLY_TUPLE.
+Although tuple 2 is not directly referenced by the index, it can still be
+found by an index search: after traversing from the index to tuple 1,
+the index search proceeds forward to child tuples as long as it sees the
+HEAP_HOT_UPDATED flag set.  Since we restrict the HOT chain to lie within
+a single page, this requires no additional page fetches and doesn't
+introduce much performance penalty.
+
+Eventually, tuple 1 will no longer be visible to any transaction.
+At that point its space could be reclaimed, but its line pointer cannot,
+since the index still links to that line pointer and we still need to
+be able to find tuple 2 in an index search.  HOT handles this by turning
+line pointer 1 into a "redirecting line pointer", which links to tuple 2
+but has no actual tuple attached.  This state of affairs looks like
+
+	Index points to 1
+	lp [1]->[2]
+
+	[2222222222]
+
+If now the row is updated again, to version 3, the page looks like this:
+
+	Index points to 1
+	lp [1]->[2]  [3]
+
+	[2222222222]->[3333333333]
+
+At some later time when no transaction can see tuple 2 in its snapshot,
+tuple 2 and its line pointer can be pruned entirely:
+
+	Index points to 1
+	lp [1]------>[3]
+
+	[3333333333]
+
+This is safe because no index entry points to line pointer 2.  Subsequent
+insertions into the page can now recycle both line pointer 2 and the
+space formerly used by tuple 2.
+
+If an update changes any indexed column, or there is not room on the
+same page for the new tuple, then the HOT chain ends: the last member
+has a regular t_ctid link to the next version and is not marked
+HEAP_HOT_UPDATED.  (In principle we could continue a HOT chain across
+pages, but this would destroy the desired property of being able to
+reclaim space with just page-local manipulations.  Anyway, we don't
+want to have to chase through multiple heap pages to get from an index
+entry to the desired tuple, so it seems better to create a new index
+entry for the new tuple.)  If further updates occur, the next version
+could become the root of a new HOT chain.
+
+Line pointer 1 has to remain as long as there is any non-dead member of
+the chain on the page.  When there is not, it is marked "dead".
+This lets us reclaim the last child line pointer and associated tuple
+immediately.  The next regular VACUUM pass can reclaim the index entries
+pointing at the line pointer and then the line pointer itself.  Since a
+line pointer is small compared to a tuple, this does not represent an
+undue space cost.
+
+Note: we can use a "dead" line pointer for any DELETEd tuple,
+whether it was part of a HOT chain or not.  This allows space reclamation
+in advance of running VACUUM for plain DELETEs as well as HOT updates.
+
+The requirement for doing a HOT update is that none of the indexed
+columns are changed.  This is checked at execution time by comparing the
+binary representation of the old and new values.  We insist on bitwise
+equality rather than using datatype-specific equality routines.  The
+main reason to avoid the latter is that there might be multiple notions
+of equality for a datatype, and we don't know exactly which one is
+relevant for the indexes at hand.  We assume that bitwise equality
+guarantees equality for all purposes.
+
+
+Abort Cases
+-----------
+
+If a heap-only tuple's xmin is aborted, then it can be removed immediately:
+it was never visible to any other transaction, and all descendant row
+versions must be aborted as well.  Therefore we need not consider it part
+of a HOT chain.  By the same token, if a HOT-updated tuple's xmax is
+aborted, there is no need to follow the chain link.  However, there is a
+race condition here: the transaction that did the HOT update might abort
+between the time we inspect the HOT-updated tuple and the time we reach
+the descendant heap-only tuple.  It is conceivable that someone prunes
+the heap-only tuple before that, and even conceivable that the line pointer
+is re-used for another purpose.  Therefore, when following a HOT chain,
+it is always necessary to be prepared for the possibility that the
+linked-to line pointer is unused, dead, or redirected; and if it is a
+normal line pointer, we still have to check that XMIN of the tuple matches
+the XMAX of the tuple we left.  Otherwise we should assume that we have
+come to the end of the HOT chain.  Note that this sort of XMIN/XMAX
+matching is required when following ordinary update chains anyway.
+
+(Early versions of the HOT code assumed that holding pin on the page
+buffer while following a HOT link would prevent this type of problem,
+but checking XMIN/XMAX matching is a much more robust solution.)
+
+
+Index/Sequential Scans
+----------------------
+
+When doing an index scan, whenever we reach a HEAP_HOT_UPDATED tuple whose
+xmax is not aborted, we need to follow its t_ctid link and check that
+entry as well; possibly repeatedly until we reach the end of the HOT
+chain.  (When using an MVCC snapshot it is possible to optimize this a
+bit: there can be at most one visible tuple in the chain, so we can stop
+when we find it.  This rule does not work for non-MVCC snapshots, though.)
+
+Sequential scans do not need to pay attention to the HOT links because
+they scan every line pointer on the page anyway.  The same goes for a
+bitmap heap scan with a lossy bitmap.
+
+
+Pruning
+-------
+
+HOT pruning means updating line pointers so that HOT chains are
+reduced in length, by collapsing out line pointers for intermediate dead
+tuples.  Although this makes those line pointers available for re-use,
+it does not immediately make the space occupied by their tuples available.
+
+
+Defragmentation
+---------------
+
+Defragmentation centralizes unused space.  After we have converted root
+line pointers to redirected line pointers and pruned away any dead
+intermediate line pointers, the tuples they linked to are free space.
+But unless that space is adjacent to the central "hole" on the page
+(the pd_lower-to-pd_upper area) it cannot be used by tuple insertion.
+Defragmentation moves the surviving tuples to coalesce all the free
+space into one "hole".  This is done with the same PageRepairFragmentation
+function that regular VACUUM uses.
+
+
+When can/should we prune or defragment?
+---------------------------------------
+
+This is the most interesting question in HOT implementation, since there
+is no simple right answer: we must use heuristics to determine when it's
+most efficient to perform pruning and/or defragmenting.
+
+We cannot prune or defragment unless we can get a "buffer cleanup lock"
+on the target page; otherwise, pruning might destroy line pointers that
+other backends have live references to, and defragmenting might move
+tuples that other backends have live pointers to.  Thus the general
+approach must be to heuristically decide if we should try to prune
+or defragment, and if so try to acquire the buffer cleanup lock without
+blocking.  If we succeed we can proceed with our housekeeping work.
+If we cannot get the lock (which should not happen often, except under
+very heavy contention) then the housekeeping has to be postponed till
+some other time.  The worst-case consequence of this is only that an
+UPDATE cannot be made HOT but has to link to a new tuple version placed on
+some other page, for lack of centralized space on the original page.
+
+Ideally we would do defragmenting only when we are about to attempt
+heap_update on a HOT-safe tuple.  The difficulty with this approach
+is that the update query has certainly got a pin on the old tuple, and
+therefore our attempt to acquire a buffer cleanup lock will always fail.
+(This corresponds to the idea that we don't want to move the old tuple
+out from under where the query's HeapTuple pointer points.  It might
+be possible to finesse that, but it seems fragile.)
+
+Pruning, however, is potentially useful even when we are not about to
+insert a new tuple, since shortening a HOT chain reduces the cost of
+subsequent index searches.  However it is unclear that this gain is
+large enough to accept any extra maintenance burden for.
+
+The currently planned heuristic is to prune and defrag when first accessing
+a page that potentially has prunable tuples (as flagged by the pd_prune_xid
+page hint field) and that either has free space less than MAX(fillfactor
+target free space, BLCKSZ/10) *or* has recently had an UPDATE fail to
+find enough free space to store an updated tuple version.  (These rules
+are subject to change.)
+
+We have effectively implemented the "truncate dead tuples to just line
+pointer" idea that has been proposed and rejected before because of fear
+of line pointer bloat: we might end up with huge numbers of line pointers
+and just a few actual tuples on a page.  To limit the damage in the worst
+case, and to keep various work arrays as well as the bitmaps in bitmap
+scans reasonably sized, the maximum number of line pointers per page
+is arbitrarily capped at MaxHeapTuplesPerPage (the most tuples that
+could fit without HOT pruning).
+
+Effectively, space reclamation happens during tuple retrieval when the
+page is nearly full (<10% free) and a buffer cleanup lock can be
+acquired.  This means that UPDATE, DELETE, and SELECT can trigger space
+reclamation, but often not during INSERT ... VALUES because it does
+not retrieve a row.
+
+
+VACUUM
+------
+
+There is little change to regular vacuum.  It performs pruning to remove
+dead heap-only tuples, and cleans up any dead line pointers as if they were
+regular dead tuples.
+
+
+Statistics
+----------
+
+Currently, we count HOT updates the same as cold updates for statistics
+purposes, though there is an additional per-table counter that counts
+only HOT updates.  When a page pruning operation is able to remove a
+physical tuple by eliminating an intermediate heap-only tuple or
+replacing a physical root tuple by a redirect pointer, a decrement in
+the table's number of dead tuples is reported to pgstats, which may
+postpone autovacuuming.  Note that we do not count replacing a root tuple
+by a DEAD line pointer as decrementing n_dead_tuples; we still want
+autovacuum to run to clean up the index entries and DEAD item.
+
+This area probably needs further work ...
+
+
+CREATE INDEX
+------------
+
+CREATE INDEX presents a problem for HOT updates.  While the existing HOT
+chains all have the same index values for existing indexes, the columns
+in the new index might change within a pre-existing HOT chain, creating
+a "broken" chain that can't be indexed properly.
+
+To address this issue, regular (non-concurrent) CREATE INDEX makes the
+new index usable only by new transactions and transactions that don't
+have snapshots older than the CREATE INDEX command.  This prevents
+queries that can see the inconsistent HOT chains from trying to use the
+new index and getting incorrect results.  Queries that can see the index
+can only see the rows that were visible after the index was created,
+hence the HOT chains are consistent for them.
+
+Entries in the new index point to root tuples (tuples with current index
+pointers) so that our index uses the same index pointers as all other
+indexes on the table.  However the row we want to index is actually at
+the *end* of the chain, ie, the most recent live tuple on the HOT chain.
+That is the one we compute the index entry values for, but the TID
+we put into the index is that of the root tuple.  Since queries that
+will be allowed to use the new index cannot see any of the older tuple
+versions in the chain, the fact that they might not match the index entry
+isn't a problem.  (Such queries will check the tuple visibility
+information of the older versions and ignore them, without ever looking at
+their contents, so the content inconsistency is OK.)  Subsequent updates
+to the live tuple will be allowed to extend the HOT chain only if they are
+HOT-safe for all the indexes.
+
+Because we have ShareLock on the table, any DELETE_IN_PROGRESS or
+INSERT_IN_PROGRESS tuples should have come from our own transaction.
+Therefore we can consider them committed since if the CREATE INDEX
+commits, they will be committed, and if it aborts the index is discarded.
+An exception to this is that early lock release is customary for system
+catalog updates, and so we might find such tuples when reindexing a system
+catalog.  In that case we deal with it by waiting for the source
+transaction to commit or roll back.  (We could do that for user tables
+too, but since the case is unexpected we prefer to throw an error.)
+
+Practically, we prevent certain transactions from using the new index by
+setting pg_index.indcheckxmin to TRUE.  Transactions are allowed to use
+such an index only after pg_index.xmin is below their TransactionXmin
+horizon, thereby ensuring that any incompatible rows in HOT chains are
+dead to them. (pg_index.xmin will be the XID of the CREATE INDEX
+transaction.  The reason for using xmin rather than a normal column is
+that the regular vacuum freezing mechanism will take care of converting
+xmin to FrozenTransactionId before it can wrap around.)
+
+This means in particular that the transaction creating the index will be
+unable to use the index if the transaction has old snapshots.  We
+alleviate that problem somewhat by not setting indcheckxmin unless the
+table actually contains HOT chains with RECENTLY_DEAD members.
+
+Another unpleasant consequence is that it is now risky to use SnapshotAny
+in an index scan: if the index was created more recently than the last
+vacuum, it's possible that some of the visited tuples do not match the
+index entry they are linked to.  This does not seem to be a fatal
+objection, since there are few users of SnapshotAny and most use seqscans.
+The only exception at this writing is CLUSTER, which is okay because it
+does not require perfect ordering of the indexscan readout (and especially
+so because CLUSTER tends to write recently-dead tuples out of order anyway).
+
+
+CREATE INDEX CONCURRENTLY
+-------------------------
+
+In the concurrent case we must take a different approach.  We create the
+pg_index entry immediately, before we scan the table.  The pg_index entry
+is marked as "not ready for inserts".  Then we commit and wait for any
+transactions which have the table open to finish.  This ensures that no
+new HOT updates will change the key value for our new index, because all
+transactions will see the existence of the index and will respect its
+constraint on which updates can be HOT.  Other transactions must include
+such an index when determining HOT-safety of updates, even though they
+must ignore it for both insertion and searching purposes.
+
+We must do this to avoid making incorrect index entries.  For example,
+suppose we are building an index on column X and we make an index entry for
+a non-HOT tuple with X=1.  Then some other backend, unaware that X is an
+indexed column, HOT-updates the row to have X=2, and commits.  We now have
+an index entry for X=1 pointing at a HOT chain whose live row has X=2.
+We could make an index entry with X=2 during the validation pass, but
+there is no nice way to get rid of the wrong entry with X=1.  So we must
+have the HOT-safety property enforced before we start to build the new
+index.
+
+After waiting for transactions which had the table open, we build the index
+for all rows that are valid in a fresh snapshot.  Any tuples visible in the
+snapshot will have only valid forward-growing HOT chains.  (They might have
+older HOT updates behind them which are broken, but this is OK for the same
+reason it's OK in a regular index build.)  As above, we point the index
+entry at the root of the HOT-update chain but we use the key value from the
+live tuple.
+
+We mark the index open for inserts (but still not ready for reads) then
+we again wait for transactions which have the table open.  Then we take
+a second reference snapshot and validate the index.  This searches for
+tuples missing from the index, and inserts any missing ones.  Again,
+the index entries have to have TIDs equal to HOT-chain root TIDs, but
+the value to be inserted is the one from the live tuple.
+
+Then we wait until every transaction that could have a snapshot older than
+the second reference snapshot is finished.  This ensures that nobody is
+alive any longer who could need to see any tuples that might be missing
+from the index, as well as ensuring that no one can see any inconsistent
+rows in a broken HOT chain (the first condition is stronger than the
+second).  Finally, we can mark the index valid for searches.
+
+Note that we do not need to set pg_index.indcheckxmin in this code path,
+because we have outwaited any transactions that would need to avoid using
+the index.  (indcheckxmin is only needed because non-concurrent CREATE
+INDEX doesn't want to wait; its stronger lock would create too much risk of
+deadlock if it did.)
+
+
+DROP INDEX CONCURRENTLY
+-----------------------
+
+DROP INDEX CONCURRENTLY is sort of the reverse sequence of CREATE INDEX
+CONCURRENTLY.  We first mark the index as not indisvalid, and then wait for
+any transactions that could be using it in queries to end.  (During this
+time, index updates must still be performed as normal, since such
+transactions might expect freshly inserted tuples to be findable.)
+Then, we clear indisready and indislive, and again wait for transactions
+that could be updating the index to end.  Finally we can drop the index
+normally (though taking only ShareUpdateExclusiveLock on its parent table).
+
+The reason we need the pg_index.indislive flag is that after the second
+wait step begins, we don't want transactions to be touching the index at
+all; otherwise they might suffer errors if the DROP finally commits while
+they are reading catalog entries for the index.  If we had only indisvalid
+and indisready, this state would be indistinguishable from the first stage
+of CREATE INDEX CONCURRENTLY --- but in that state, we *do* want
+transactions to examine the index, since they must consider it in
+HOT-safety checks.
+
+
+Limitations and Restrictions
+----------------------------
+
+It is worth noting that HOT forever forecloses alternative approaches
+to vacuuming, specifically the recompute-the-index-keys approach alluded
+to in Technical Challenges above.  It'll be tough to recompute the index
+keys for a root line pointer you don't have data for anymore ...
+
+
+Glossary
+--------
+
+Broken HOT Chain
+
+	A HOT chain in which the key value for an index has changed.
+
+	This is not allowed to occur normally but if a new index is created
+	it can happen.  In that case various strategies are used to ensure
+	that no transaction for which the older tuples are visible can
+	use the index.
+
+Cold update
+
+	A normal, non-HOT update, in which index entries are made for
+	the new version of the tuple.
+
+Dead line pointer
+
+	A stub line pointer, that does not point to anything, but cannot
+	be removed or reused yet because there are index pointers to it.
+	Semantically same as a dead tuple.  It has state LP_DEAD.
+
+Heap-only tuple
+
+	A heap tuple with no index pointers, which can only be reached
+	from indexes indirectly through its ancestral root tuple.
+	Marked with HEAP_ONLY_TUPLE flag.
+
+HOT-safe
+
+	A proposed tuple update is said to be HOT-safe if it changes
+	none of the tuple's indexed columns.  It will only become an
+	actual HOT update if we can find room on the same page for
+	the new tuple version.
+
+HOT update
+
+	An UPDATE where the new tuple becomes a heap-only tuple, and no
+	new index entries are made.
+
+HOT-updated tuple
+
+	An updated tuple, for which the next tuple in the chain is a
+	heap-only tuple.  Marked with HEAP_HOT_UPDATED flag.
+
+Indexed column
+
+	A column used in an index definition.  The column might not
+	actually be stored in the index --- it could be used in a
+	functional index's expression, or used in a partial index
+	predicate.  HOT treats all these cases alike.
+
+Redirecting line pointer
+
+	A line pointer that points to another line pointer and has no
+	associated tuple.  It has the special lp_flags state LP_REDIRECT,
+	and lp_off is the OffsetNumber of the line pointer it links to.
+	This is used when a root tuple becomes dead but we cannot prune
+	the line pointer because there are non-dead heap-only tuples
+	further down the chain.
+
+Root tuple
+
+	The first tuple in a HOT update chain; the one that indexes point to.
+
+Update chain
+
+	A chain of updated tuples, in which each tuple's ctid points to
+	the next tuple in the chain. A HOT update chain is an update chain
+	(or portion of an update chain) that consists of a root tuple and
+	one or more heap-only tuples.  A complete update chain can contain
+	both HOT and non-HOT (cold) updated tuples.
diff --git a/src/backend/access/heap/README.tuplock b/src/backend/access/heap/README.tuplock
new file mode 100644
index 0000000..6441e8b
--- /dev/null
+++ b/src/backend/access/heap/README.tuplock
@@ -0,0 +1,155 @@
+Locking tuples
+--------------
+
+Locking tuples is not as easy as locking tables or other database objects.
+The problem is that transactions might want to lock large numbers of tuples at
+any one time, so it's not possible to keep the locks objects in shared memory.
+To work around this limitation, we use a two-level mechanism.  The first level
+is implemented by storing locking information in the tuple header: a tuple is
+marked as locked by setting the current transaction's XID as its XMAX, and
+setting additional infomask bits to distinguish this case from the more normal
+case of having deleted the tuple.  When multiple transactions concurrently
+lock a tuple, a MultiXact is used; see below.  This mechanism can accommodate
+arbitrarily large numbers of tuples being locked simultaneously.
+
+When it is necessary to wait for a tuple-level lock to be released, the basic
+delay is provided by XactLockTableWait or MultiXactIdWait on the contents of
+the tuple's XMAX.  However, that mechanism will release all waiters
+concurrently, so there would be a race condition as to which waiter gets the
+tuple, potentially leading to indefinite starvation of some waiters.  The
+possibility of share-locking makes the problem much worse --- a steady stream
+of share-lockers can easily block an exclusive locker forever.  To provide
+more reliable semantics about who gets a tuple-level lock first, we use the
+standard lock manager, which implements the second level mentioned above.  The
+protocol for waiting for a tuple-level lock is really
+
+     LockTuple()
+     XactLockTableWait()
+     mark tuple as locked by me
+     UnlockTuple()
+
+When there are multiple waiters, arbitration of who is to get the lock next
+is provided by LockTuple().  However, at most one tuple-level lock will
+be held or awaited per backend at any time, so we don't risk overflow
+of the lock table.  Note that incoming share-lockers are required to
+do LockTuple as well, if there is any conflict, to ensure that they don't
+starve out waiting exclusive-lockers.  However, if there is not any active
+conflict for a tuple, we don't incur any extra overhead.
+
+We make an exception to the above rule for those lockers that already hold
+some lock on a tuple and attempt to acquire a stronger one on it.  In that
+case, we skip the LockTuple() call even when there are conflicts, provided
+that the target tuple is being locked, updated or deleted by multiple sessions
+concurrently.  Failing to skip the lock would risk a deadlock, e.g., between a
+session that was first to record its weaker lock in the tuple header and would
+be waiting on the LockTuple() call to upgrade to the stronger lock level, and
+another session that has already done LockTuple() and is waiting for the first
+session transaction to release its tuple header-level lock.
+
+We provide four levels of tuple locking strength: SELECT FOR UPDATE obtains an
+exclusive lock which prevents any kind of modification of the tuple. This is
+the lock level that is implicitly taken by DELETE operations, and also by
+UPDATE operations if they modify any of the tuple's key fields. SELECT FOR NO
+KEY UPDATE likewise obtains an exclusive lock, but only prevents tuple removal
+and modifications which might alter the tuple's key. This is the lock that is
+implicitly taken by UPDATE operations which leave all key fields unchanged.
+SELECT FOR SHARE obtains a shared lock which prevents any kind of tuple
+modification. Finally, SELECT FOR KEY SHARE obtains a shared lock which only
+prevents tuple removal and modifications of key fields. This lock level is
+just strong enough to implement RI checks, i.e. it ensures that tuples do not
+go away from under a check, without blocking transactions that want to update
+the tuple without changing its key.
+
+The conflict table is:
+
+                  UPDATE       NO KEY UPDATE    SHARE        KEY SHARE
+UPDATE           conflict        conflict      conflict      conflict
+NO KEY UPDATE    conflict        conflict      conflict
+SHARE            conflict        conflict
+KEY SHARE        conflict
+
+When there is a single locker in a tuple, we can just store the locking info
+in the tuple itself.  We do this by storing the locker's Xid in XMAX, and
+setting infomask bits specifying the locking strength.  There is one exception
+here: since infomask space is limited, we do not provide a separate bit
+for SELECT FOR SHARE, so we have to use the extended info in a MultiXact in
+that case.  (The other cases, SELECT FOR UPDATE and SELECT FOR KEY SHARE, are
+presumably more commonly used due to being the standards-mandated locking
+mechanism, or heavily used by the RI code, so we want to provide fast paths
+for those.)
+
+MultiXacts
+----------
+
+A tuple header provides very limited space for storing information about tuple
+locking and updates: there is room only for a single Xid and a small number of
+infomask bits.  Whenever we need to store more than one lock, we replace the
+first locker's Xid with a new MultiXactId.  Each MultiXact provides extended
+locking data; it comprises an array of Xids plus some flags bits for each one.
+The flags are currently used to store the locking strength of each member
+transaction.  (The flags also distinguish a pure locker from an updater.)
+
+In earlier PostgreSQL releases, a MultiXact always meant that the tuple was
+locked in shared mode by multiple transactions.  This is no longer the case; a
+MultiXact may contain an update or delete Xid.  (Keep in mind that tuple locks
+in a transaction do not conflict with other tuple locks in the same
+transaction, so it's possible to have otherwise conflicting locks in a
+MultiXact if they belong to the same transaction).
+
+Note that each lock is attributed to the subtransaction that acquires it.
+This means that a subtransaction that aborts is seen as though it releases the
+locks it acquired; concurrent transactions can then proceed without having to
+wait for the main transaction to finish.  It also means that a subtransaction
+can upgrade to a stronger lock level than an earlier transaction had, and if
+the subxact aborts, the earlier, weaker lock is kept.
+
+The possibility of having an update within a MultiXact means that they must
+persist across crashes and restarts: a future reader of the tuple needs to
+figure out whether the update committed or aborted.  So we have a requirement
+that pg_multixact needs to retain pages of its data until we're certain that
+the MultiXacts in them are no longer of interest.
+
+VACUUM is in charge of removing old MultiXacts at the time of tuple freezing.
+The lower bound used by vacuum (that is, the value below which all multixacts
+are removed) is stored as pg_class.relminmxid for each table; the minimum of
+all such values is stored in pg_database.datminmxid.  The minimum across
+all databases, in turn, is recorded in checkpoint records, and CHECKPOINT
+removes pg_multixact/ segments older than that value once the checkpoint
+record has been flushed.
+
+Infomask Bits
+-------------
+
+The following infomask bits are applicable:
+
+- HEAP_XMAX_INVALID
+  Any tuple with this bit set does not have a valid value stored in XMAX.
+
+- HEAP_XMAX_IS_MULTI
+  This bit is set if the tuple's Xmax is a MultiXactId (as opposed to a
+  regular TransactionId).
+
+- HEAP_XMAX_LOCK_ONLY
+  This bit is set when the XMAX is a locker only; that is, if it's a
+  multixact, it does not contain an update among its members.  It's set when
+  the XMAX is a plain Xid that locked the tuple, as well.
+
+- HEAP_XMAX_KEYSHR_LOCK
+- HEAP_XMAX_SHR_LOCK
+- HEAP_XMAX_EXCL_LOCK
+  These bits indicate the strength of the lock acquired; they are useful when
+  the XMAX is not a MultiXactId.  If it's a multi, the info is to be found in
+  the member flags.  If HEAP_XMAX_IS_MULTI is not set and HEAP_XMAX_LOCK_ONLY
+  is set, then one of these *must* be set as well.
+
+  Note that HEAP_XMAX_EXCL_LOCK does not distinguish FOR NO KEY UPDATE from
+  FOR UPDATE; this is implemented by the HEAP_KEYS_UPDATED bit.
+
+- HEAP_KEYS_UPDATED
+  This bit lives in t_infomask2.  If set, indicates that the operation(s) done
+  by the XMAX compromise the tuple key, such as a SELECT FOR UPDATE, an UPDATE
+  that modifies the columns of the key, or a DELETE.  It's set regardless of
+  whether the XMAX is a TransactionId or a MultiXactId.
+
+We currently never set the HEAP_XMAX_COMMITTED when the HEAP_XMAX_IS_MULTI bit
+is set.
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
new file mode 100644
index 0000000..64b9ec0
--- /dev/null
+++ b/src/backend/access/heap/heapam.c
@@ -0,0 +1,9955 @@
+/*-------------------------------------------------------------------------
+ *
+ * heapam.c
+ *	  heap access method code
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/heap/heapam.c
+ *
+ *
+ * INTERFACE ROUTINES
+ *		heap_beginscan	- begin relation scan
+ *		heap_rescan		- restart a relation scan
+ *		heap_endscan	- end relation scan
+ *		heap_getnext	- retrieve next tuple in scan
+ *		heap_fetch		- retrieve tuple with given tid
+ *		heap_insert		- insert tuple into a relation
+ *		heap_multi_insert - insert multiple tuples into a relation
+ *		heap_delete		- delete a tuple from a relation
+ *		heap_update		- replace a tuple in a relation with another tuple
+ *
+ * NOTES
+ *	  This file contains the heap_ routines which implement
+ *	  the POSTGRES heap access method used for all POSTGRES
+ *	  relations.
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/bufmask.h"
+#include "access/genam.h"
+#include "access/heapam.h"
+#include "access/heapam_xlog.h"
+#include "access/heaptoast.h"
+#include "access/hio.h"
+#include "access/multixact.h"
+#include "access/parallel.h"
+#include "access/relscan.h"
+#include "access/subtrans.h"
+#include "access/syncscan.h"
+#include "access/sysattr.h"
+#include "access/tableam.h"
+#include "access/transam.h"
+#include "access/valid.h"
+#include "access/visibilitymap.h"
+#include "access/xact.h"
+#include "access/xlog.h"
+#include "access/xloginsert.h"
+#include "access/xlogutils.h"
+#include "catalog/catalog.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "port/atomics.h"
+#include "port/pg_bitutils.h"
+#include "storage/bufmgr.h"
+#include "storage/freespace.h"
+#include "storage/lmgr.h"
+#include "storage/predicate.h"
+#include "storage/procarray.h"
+#include "storage/smgr.h"
+#include "storage/spin.h"
+#include "storage/standby.h"
+#include "utils/datum.h"
+#include "utils/inval.h"
+#include "utils/lsyscache.h"
+#include "utils/relcache.h"
+#include "utils/snapmgr.h"
+#include "utils/spccache.h"
+
+
+static HeapTuple heap_prepare_insert(Relation relation, HeapTuple tup,
+									 TransactionId xid, CommandId cid, int options);
+static XLogRecPtr log_heap_update(Relation reln, Buffer oldbuf,
+								  Buffer newbuf, HeapTuple oldtup,
+								  HeapTuple newtup, HeapTuple old_key_tuple,
+								  bool all_visible_cleared, bool new_all_visible_cleared);
+static Bitmapset *HeapDetermineColumnsInfo(Relation relation,
+										   Bitmapset *interesting_cols,
+										   Bitmapset *external_cols,
+										   HeapTuple oldtup, HeapTuple newtup,
+										   bool *has_external);
+static bool heap_acquire_tuplock(Relation relation, ItemPointer tid,
+								 LockTupleMode mode, LockWaitPolicy wait_policy,
+								 bool *have_tuple_lock);
+static void compute_new_xmax_infomask(TransactionId xmax, uint16 old_infomask,
+									  uint16 old_infomask2, TransactionId add_to_xmax,
+									  LockTupleMode mode, bool is_update,
+									  TransactionId *result_xmax, uint16 *result_infomask,
+									  uint16 *result_infomask2);
+static TM_Result heap_lock_updated_tuple(Relation rel, HeapTuple tuple,
+										 ItemPointer ctid, TransactionId xid,
+										 LockTupleMode mode);
+static void GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
+								   uint16 *new_infomask2);
+static TransactionId MultiXactIdGetUpdateXid(TransactionId xmax,
+											 uint16 t_infomask);
+static bool DoesMultiXactIdConflict(MultiXactId multi, uint16 infomask,
+									LockTupleMode lockmode, bool *current_is_member);
+static void MultiXactIdWait(MultiXactId multi, MultiXactStatus status, uint16 infomask,
+							Relation rel, ItemPointer ctid, XLTW_Oper oper,
+							int *remaining);
+static bool ConditionalMultiXactIdWait(MultiXactId multi, MultiXactStatus status,
+									   uint16 infomask, Relation rel, int *remaining);
+static void index_delete_sort(TM_IndexDeleteOp *delstate);
+static int	bottomup_sort_and_shrink(TM_IndexDeleteOp *delstate);
+static XLogRecPtr log_heap_new_cid(Relation relation, HeapTuple tup);
+static HeapTuple ExtractReplicaIdentity(Relation rel, HeapTuple tup, bool key_required,
+										bool *copy);
+
+
+/*
+ * Each tuple lock mode has a corresponding heavyweight lock, and one or two
+ * corresponding MultiXactStatuses (one to merely lock tuples, another one to
+ * update them).  This table (and the macros below) helps us determine the
+ * heavyweight lock mode and MultiXactStatus values to use for any particular
+ * tuple lock strength.
+ *
+ * Don't look at lockstatus/updstatus directly!  Use get_mxact_status_for_lock
+ * instead.
+ */
+static const struct
+{
+	LOCKMODE	hwlock;
+	int			lockstatus;
+	int			updstatus;
+}
+
+			tupleLockExtraInfo[MaxLockTupleMode + 1] =
+{
+	{							/* LockTupleKeyShare */
+		AccessShareLock,
+		MultiXactStatusForKeyShare,
+		-1						/* KeyShare does not allow updating tuples */
+	},
+	{							/* LockTupleShare */
+		RowShareLock,
+		MultiXactStatusForShare,
+		-1						/* Share does not allow updating tuples */
+	},
+	{							/* LockTupleNoKeyExclusive */
+		ExclusiveLock,
+		MultiXactStatusForNoKeyUpdate,
+		MultiXactStatusNoKeyUpdate
+	},
+	{							/* LockTupleExclusive */
+		AccessExclusiveLock,
+		MultiXactStatusForUpdate,
+		MultiXactStatusUpdate
+	}
+};
+
+/* Get the LOCKMODE for a given MultiXactStatus */
+#define LOCKMODE_from_mxstatus(status) \
+			(tupleLockExtraInfo[TUPLOCK_from_mxstatus((status))].hwlock)
+
+/*
+ * Acquire heavyweight locks on tuples, using a LockTupleMode strength value.
+ * This is more readable than having every caller translate it to lock.h's
+ * LOCKMODE.
+ */
+#define LockTupleTuplock(rel, tup, mode) \
+	LockTuple((rel), (tup), tupleLockExtraInfo[mode].hwlock)
+#define UnlockTupleTuplock(rel, tup, mode) \
+	UnlockTuple((rel), (tup), tupleLockExtraInfo[mode].hwlock)
+#define ConditionalLockTupleTuplock(rel, tup, mode) \
+	ConditionalLockTuple((rel), (tup), tupleLockExtraInfo[mode].hwlock)
+
+#ifdef USE_PREFETCH
+/*
+ * heap_index_delete_tuples and index_delete_prefetch_buffer use this
+ * structure to coordinate prefetching activity
+ */
+typedef struct
+{
+	BlockNumber cur_hblkno;
+	int			next_item;
+	int			ndeltids;
+	TM_IndexDelete *deltids;
+} IndexDeletePrefetchState;
+#endif
+
+/* heap_index_delete_tuples bottom-up index deletion costing constants */
+#define BOTTOMUP_MAX_NBLOCKS			6
+#define BOTTOMUP_TOLERANCE_NBLOCKS		3
+
+/*
+ * heap_index_delete_tuples uses this when determining which heap blocks it
+ * must visit to help its bottom-up index deletion caller
+ */
+typedef struct IndexDeleteCounts
+{
+	int16		npromisingtids; /* Number of "promising" TIDs in group */
+	int16		ntids;			/* Number of TIDs in group */
+	int16		ifirsttid;		/* Offset to group's first deltid */
+} IndexDeleteCounts;
+
+/*
+ * This table maps tuple lock strength values for each particular
+ * MultiXactStatus value.
+ */
+static const int MultiXactStatusLock[MaxMultiXactStatus + 1] =
+{
+	LockTupleKeyShare,			/* ForKeyShare */
+	LockTupleShare,				/* ForShare */
+	LockTupleNoKeyExclusive,	/* ForNoKeyUpdate */
+	LockTupleExclusive,			/* ForUpdate */
+	LockTupleNoKeyExclusive,	/* NoKeyUpdate */
+	LockTupleExclusive			/* Update */
+};
+
+/* Get the LockTupleMode for a given MultiXactStatus */
+#define TUPLOCK_from_mxstatus(status) \
+			(MultiXactStatusLock[(status)])
+
+/* ----------------------------------------------------------------
+ *						 heap support routines
+ * ----------------------------------------------------------------
+ */
+
+/* ----------------
+ *		initscan - scan code common to heap_beginscan and heap_rescan
+ * ----------------
+ */
+static void
+initscan(HeapScanDesc scan, ScanKey key, bool keep_startblock)
+{
+	ParallelBlockTableScanDesc bpscan = NULL;
+	bool		allow_strat;
+	bool		allow_sync;
+
+	/*
+	 * Determine the number of blocks we have to scan.
+	 *
+	 * It is sufficient to do this once at scan start, since any tuples added
+	 * while the scan is in progress will be invisible to my snapshot anyway.
+	 * (That is not true when using a non-MVCC snapshot.  However, we couldn't
+	 * guarantee to return tuples added after scan start anyway, since they
+	 * might go into pages we already scanned.  To guarantee consistent
+	 * results for a non-MVCC snapshot, the caller must hold some higher-level
+	 * lock that ensures the interesting tuple(s) won't change.)
+	 */
+	if (scan->rs_base.rs_parallel != NULL)
+	{
+		bpscan = (ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
+		scan->rs_nblocks = bpscan->phs_nblocks;
+	}
+	else
+		scan->rs_nblocks = RelationGetNumberOfBlocks(scan->rs_base.rs_rd);
+
+	/*
+	 * If the table is large relative to NBuffers, use a bulk-read access
+	 * strategy and enable synchronized scanning (see syncscan.c).  Although
+	 * the thresholds for these features could be different, we make them the
+	 * same so that there are only two behaviors to tune rather than four.
+	 * (However, some callers need to be able to disable one or both of these
+	 * behaviors, independently of the size of the table; also there is a GUC
+	 * variable that can disable synchronized scanning.)
+	 *
+	 * Note that table_block_parallelscan_initialize has a very similar test;
+	 * if you change this, consider changing that one, too.
+	 */
+	if (!RelationUsesLocalBuffers(scan->rs_base.rs_rd) &&
+		scan->rs_nblocks > NBuffers / 4)
+	{
+		allow_strat = (scan->rs_base.rs_flags & SO_ALLOW_STRAT) != 0;
+		allow_sync = (scan->rs_base.rs_flags & SO_ALLOW_SYNC) != 0;
+	}
+	else
+		allow_strat = allow_sync = false;
+
+	if (allow_strat)
+	{
+		/* During a rescan, keep the previous strategy object. */
+		if (scan->rs_strategy == NULL)
+			scan->rs_strategy = GetAccessStrategy(BAS_BULKREAD);
+	}
+	else
+	{
+		if (scan->rs_strategy != NULL)
+			FreeAccessStrategy(scan->rs_strategy);
+		scan->rs_strategy = NULL;
+	}
+
+	if (scan->rs_base.rs_parallel != NULL)
+	{
+		/* For parallel scan, believe whatever ParallelTableScanDesc says. */
+		if (scan->rs_base.rs_parallel->phs_syncscan)
+			scan->rs_base.rs_flags |= SO_ALLOW_SYNC;
+		else
+			scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
+	}
+	else if (keep_startblock)
+	{
+		/*
+		 * When rescanning, we want to keep the previous startblock setting,
+		 * so that rewinding a cursor doesn't generate surprising results.
+		 * Reset the active syncscan setting, though.
+		 */
+		if (allow_sync && synchronize_seqscans)
+			scan->rs_base.rs_flags |= SO_ALLOW_SYNC;
+		else
+			scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
+	}
+	else if (allow_sync && synchronize_seqscans)
+	{
+		scan->rs_base.rs_flags |= SO_ALLOW_SYNC;
+		scan->rs_startblock = ss_get_location(scan->rs_base.rs_rd, scan->rs_nblocks);
+	}
+	else
+	{
+		scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
+		scan->rs_startblock = 0;
+	}
+
+	scan->rs_numblocks = InvalidBlockNumber;
+	scan->rs_inited = false;
+	scan->rs_ctup.t_data = NULL;
+	ItemPointerSetInvalid(&scan->rs_ctup.t_self);
+	scan->rs_cbuf = InvalidBuffer;
+	scan->rs_cblock = InvalidBlockNumber;
+
+	/* page-at-a-time fields are always invalid when not rs_inited */
+
+	/*
+	 * copy the scan key, if appropriate
+	 */
+	if (key != NULL && scan->rs_base.rs_nkeys > 0)
+		memcpy(scan->rs_base.rs_key, key, scan->rs_base.rs_nkeys * sizeof(ScanKeyData));
+
+	/*
+	 * Currently, we only have a stats counter for sequential heap scans (but
+	 * e.g for bitmap scans the underlying bitmap index scans will be counted,
+	 * and for sample scans we update stats for tuple fetches).
+	 */
+	if (scan->rs_base.rs_flags & SO_TYPE_SEQSCAN)
+		pgstat_count_heap_scan(scan->rs_base.rs_rd);
+}
+
+/*
+ * heap_setscanlimits - restrict range of a heapscan
+ *
+ * startBlk is the page to start at
+ * numBlks is number of pages to scan (InvalidBlockNumber means "all")
+ */
+void
+heap_setscanlimits(TableScanDesc sscan, BlockNumber startBlk, BlockNumber numBlks)
+{
+	HeapScanDesc scan = (HeapScanDesc) sscan;
+
+	Assert(!scan->rs_inited);	/* else too late to change */
+	/* else rs_startblock is significant */
+	Assert(!(scan->rs_base.rs_flags & SO_ALLOW_SYNC));
+
+	/* Check startBlk is valid (but allow case of zero blocks...) */
+	Assert(startBlk == 0 || startBlk < scan->rs_nblocks);
+
+	scan->rs_startblock = startBlk;
+	scan->rs_numblocks = numBlks;
+}
+
+/*
+ * heapgetpage - subroutine for heapgettup()
+ *
+ * This routine reads and pins the specified page of the relation.
+ * In page-at-a-time mode it performs additional work, namely determining
+ * which tuples on the page are visible.
+ */
+void
+heapgetpage(TableScanDesc sscan, BlockNumber page)
+{
+	HeapScanDesc scan = (HeapScanDesc) sscan;
+	Buffer		buffer;
+	Snapshot	snapshot;
+	Page		dp;
+	int			lines;
+	int			ntup;
+	OffsetNumber lineoff;
+	ItemId		lpp;
+	bool		all_visible;
+
+	Assert(page < scan->rs_nblocks);
+
+	/* release previous scan buffer, if any */
+	if (BufferIsValid(scan->rs_cbuf))
+	{
+		ReleaseBuffer(scan->rs_cbuf);
+		scan->rs_cbuf = InvalidBuffer;
+	}
+
+	/*
+	 * Be sure to check for interrupts at least once per page.  Checks at
+	 * higher code levels won't be able to stop a seqscan that encounters many
+	 * pages' worth of consecutive dead tuples.
+	 */
+	CHECK_FOR_INTERRUPTS();
+
+	/* read page using selected strategy */
+	scan->rs_cbuf = ReadBufferExtended(scan->rs_base.rs_rd, MAIN_FORKNUM, page,
+									   RBM_NORMAL, scan->rs_strategy);
+	scan->rs_cblock = page;
+
+	if (!(scan->rs_base.rs_flags & SO_ALLOW_PAGEMODE))
+		return;
+
+	buffer = scan->rs_cbuf;
+	snapshot = scan->rs_base.rs_snapshot;
+
+	/*
+	 * Prune and repair fragmentation for the whole page, if possible.
+	 */
+	heap_page_prune_opt(scan->rs_base.rs_rd, buffer);
+
+	/*
+	 * We must hold share lock on the buffer content while examining tuple
+	 * visibility.  Afterwards, however, the tuples we have found to be
+	 * visible are guaranteed good as long as we hold the buffer pin.
+	 */
+	LockBuffer(buffer, BUFFER_LOCK_SHARE);
+
+	dp = BufferGetPage(buffer);
+	TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, dp);
+	lines = PageGetMaxOffsetNumber(dp);
+	ntup = 0;
+
+	/*
+	 * If the all-visible flag indicates that all tuples on the page are
+	 * visible to everyone, we can skip the per-tuple visibility tests.
+	 *
+	 * Note: In hot standby, a tuple that's already visible to all
+	 * transactions on the primary might still be invisible to a read-only
+	 * transaction in the standby. We partly handle this problem by tracking
+	 * the minimum xmin of visible tuples as the cut-off XID while marking a
+	 * page all-visible on the primary and WAL log that along with the
+	 * visibility map SET operation. In hot standby, we wait for (or abort)
+	 * all transactions that can potentially may not see one or more tuples on
+	 * the page. That's how index-only scans work fine in hot standby. A
+	 * crucial difference between index-only scans and heap scans is that the
+	 * index-only scan completely relies on the visibility map where as heap
+	 * scan looks at the page-level PD_ALL_VISIBLE flag. We are not sure if
+	 * the page-level flag can be trusted in the same way, because it might
+	 * get propagated somehow without being explicitly WAL-logged, e.g. via a
+	 * full page write. Until we can prove that beyond doubt, let's check each
+	 * tuple for visibility the hard way.
+	 */
+	all_visible = PageIsAllVisible(dp) && !snapshot->takenDuringRecovery;
+
+	for (lineoff = FirstOffsetNumber, lpp = PageGetItemId(dp, lineoff);
+		 lineoff <= lines;
+		 lineoff++, lpp++)
+	{
+		if (ItemIdIsNormal(lpp))
+		{
+			HeapTupleData loctup;
+			bool		valid;
+
+			loctup.t_tableOid = RelationGetRelid(scan->rs_base.rs_rd);
+			loctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
+			loctup.t_len = ItemIdGetLength(lpp);
+			ItemPointerSet(&(loctup.t_self), page, lineoff);
+
+			if (all_visible)
+				valid = true;
+			else
+				valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer);
+
+			HeapCheckForSerializableConflictOut(valid, scan->rs_base.rs_rd,
+												&loctup, buffer, snapshot);
+
+			if (valid)
+				scan->rs_vistuples[ntup++] = lineoff;
+		}
+	}
+
+	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+
+	Assert(ntup <= MaxHeapTuplesPerPage);
+	scan->rs_ntuples = ntup;
+}
+
+/* ----------------
+ *		heapgettup - fetch next heap tuple
+ *
+ *		Initialize the scan if not already done; then advance to the next
+ *		tuple as indicated by "dir"; return the next tuple in scan->rs_ctup,
+ *		or set scan->rs_ctup.t_data = NULL if no more tuples.
+ *
+ * dir == NoMovementScanDirection means "re-fetch the tuple indicated
+ * by scan->rs_ctup".
+ *
+ * Note: the reason nkeys/key are passed separately, even though they are
+ * kept in the scan descriptor, is that the caller may not want us to check
+ * the scankeys.
+ *
+ * Note: when we fall off the end of the scan in either direction, we
+ * reset rs_inited.  This means that a further request with the same
+ * scan direction will restart the scan, which is a bit odd, but a
+ * request with the opposite scan direction will start a fresh scan
+ * in the proper direction.  The latter is required behavior for cursors,
+ * while the former case is generally undefined behavior in Postgres
+ * so we don't care too much.
+ * ----------------
+ */
+static void
+heapgettup(HeapScanDesc scan,
+		   ScanDirection dir,
+		   int nkeys,
+		   ScanKey key)
+{
+	HeapTuple	tuple = &(scan->rs_ctup);
+	Snapshot	snapshot = scan->rs_base.rs_snapshot;
+	bool		backward = ScanDirectionIsBackward(dir);
+	BlockNumber page;
+	bool		finished;
+	Page		dp;
+	int			lines;
+	OffsetNumber lineoff;
+	int			linesleft;
+	ItemId		lpp;
+
+	/*
+	 * calculate next starting lineoff, given scan direction
+	 */
+	if (ScanDirectionIsForward(dir))
+	{
+		if (!scan->rs_inited)
+		{
+			/*
+			 * return null immediately if relation is empty
+			 */
+			if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
+			{
+				Assert(!BufferIsValid(scan->rs_cbuf));
+				tuple->t_data = NULL;
+				return;
+			}
+			if (scan->rs_base.rs_parallel != NULL)
+			{
+				ParallelBlockTableScanDesc pbscan =
+				(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
+				ParallelBlockTableScanWorker pbscanwork =
+				scan->rs_parallelworkerdata;
+
+				table_block_parallelscan_startblock_init(scan->rs_base.rs_rd,
+														 pbscanwork, pbscan);
+
+				page = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
+														 pbscanwork, pbscan);
+
+				/* Other processes might have already finished the scan. */
+				if (page == InvalidBlockNumber)
+				{
+					Assert(!BufferIsValid(scan->rs_cbuf));
+					tuple->t_data = NULL;
+					return;
+				}
+			}
+			else
+				page = scan->rs_startblock; /* first page */
+			heapgetpage((TableScanDesc) scan, page);
+			lineoff = FirstOffsetNumber;	/* first offnum */
+			scan->rs_inited = true;
+		}
+		else
+		{
+			/* continue from previously returned page/tuple */
+			page = scan->rs_cblock; /* current page */
+			lineoff =			/* next offnum */
+				OffsetNumberNext(ItemPointerGetOffsetNumber(&(tuple->t_self)));
+		}
+
+		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
+
+		dp = BufferGetPage(scan->rs_cbuf);
+		TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, dp);
+		lines = PageGetMaxOffsetNumber(dp);
+		/* page and lineoff now reference the physically next tid */
+
+		linesleft = lines - lineoff + 1;
+	}
+	else if (backward)
+	{
+		/* backward parallel scan not supported */
+		Assert(scan->rs_base.rs_parallel == NULL);
+
+		if (!scan->rs_inited)
+		{
+			/*
+			 * return null immediately if relation is empty
+			 */
+			if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
+			{
+				Assert(!BufferIsValid(scan->rs_cbuf));
+				tuple->t_data = NULL;
+				return;
+			}
+
+			/*
+			 * Disable reporting to syncscan logic in a backwards scan; it's
+			 * not very likely anyone else is doing the same thing at the same
+			 * time, and much more likely that we'll just bollix things for
+			 * forward scanners.
+			 */
+			scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
+
+			/*
+			 * Start from last page of the scan.  Ensure we take into account
+			 * rs_numblocks if it's been adjusted by heap_setscanlimits().
+			 */
+			if (scan->rs_numblocks != InvalidBlockNumber)
+				page = (scan->rs_startblock + scan->rs_numblocks - 1) % scan->rs_nblocks;
+			else if (scan->rs_startblock > 0)
+				page = scan->rs_startblock - 1;
+			else
+				page = scan->rs_nblocks - 1;
+			heapgetpage((TableScanDesc) scan, page);
+		}
+		else
+		{
+			/* continue from previously returned page/tuple */
+			page = scan->rs_cblock; /* current page */
+		}
+
+		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
+
+		dp = BufferGetPage(scan->rs_cbuf);
+		TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, dp);
+		lines = PageGetMaxOffsetNumber(dp);
+
+		if (!scan->rs_inited)
+		{
+			lineoff = lines;	/* final offnum */
+			scan->rs_inited = true;
+		}
+		else
+		{
+			/*
+			 * The previous returned tuple may have been vacuumed since the
+			 * previous scan when we use a non-MVCC snapshot, so we must
+			 * re-establish the lineoff <= PageGetMaxOffsetNumber(dp)
+			 * invariant
+			 */
+			lineoff =			/* previous offnum */
+				Min(lines,
+					OffsetNumberPrev(ItemPointerGetOffsetNumber(&(tuple->t_self))));
+		}
+		/* page and lineoff now reference the physically previous tid */
+
+		linesleft = lineoff;
+	}
+	else
+	{
+		/*
+		 * ``no movement'' scan direction: refetch prior tuple
+		 */
+		if (!scan->rs_inited)
+		{
+			Assert(!BufferIsValid(scan->rs_cbuf));
+			tuple->t_data = NULL;
+			return;
+		}
+
+		page = ItemPointerGetBlockNumber(&(tuple->t_self));
+		if (page != scan->rs_cblock)
+			heapgetpage((TableScanDesc) scan, page);
+
+		/* Since the tuple was previously fetched, needn't lock page here */
+		dp = BufferGetPage(scan->rs_cbuf);
+		TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, dp);
+		lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
+		lpp = PageGetItemId(dp, lineoff);
+		Assert(ItemIdIsNormal(lpp));
+
+		tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
+		tuple->t_len = ItemIdGetLength(lpp);
+
+		return;
+	}
+
+	/*
+	 * advance the scan until we find a qualifying tuple or run out of stuff
+	 * to scan
+	 */
+	lpp = PageGetItemId(dp, lineoff);
+	for (;;)
+	{
+		/*
+		 * Only continue scanning the page while we have lines left.
+		 *
+		 * Note that this protects us from accessing line pointers past
+		 * PageGetMaxOffsetNumber(); both for forward scans when we resume the
+		 * table scan, and for when we start scanning a new page.
+		 */
+		while (linesleft > 0)
+		{
+			if (ItemIdIsNormal(lpp))
+			{
+				bool		valid;
+
+				tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
+				tuple->t_len = ItemIdGetLength(lpp);
+				ItemPointerSet(&(tuple->t_self), page, lineoff);
+
+				/*
+				 * if current tuple qualifies, return it.
+				 */
+				valid = HeapTupleSatisfiesVisibility(tuple,
+													 snapshot,
+													 scan->rs_cbuf);
+
+				HeapCheckForSerializableConflictOut(valid, scan->rs_base.rs_rd,
+													tuple, scan->rs_cbuf,
+													snapshot);
+
+				if (valid && key != NULL)
+					HeapKeyTest(tuple, RelationGetDescr(scan->rs_base.rs_rd),
+								nkeys, key, valid);
+
+				if (valid)
+				{
+					LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+					return;
+				}
+			}
+
+			/*
+			 * otherwise move to the next item on the page
+			 */
+			--linesleft;
+			if (backward)
+			{
+				--lpp;			/* move back in this page's ItemId array */
+				--lineoff;
+			}
+			else
+			{
+				++lpp;			/* move forward in this page's ItemId array */
+				++lineoff;
+			}
+		}
+
+		/*
+		 * if we get here, it means we've exhausted the items on this page and
+		 * it's time to move to the next.
+		 */
+		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+
+		/*
+		 * advance to next/prior page and detect end of scan
+		 */
+		if (backward)
+		{
+			finished = (page == scan->rs_startblock) ||
+				(scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
+			if (page == 0)
+				page = scan->rs_nblocks;
+			page--;
+		}
+		else if (scan->rs_base.rs_parallel != NULL)
+		{
+			ParallelBlockTableScanDesc pbscan =
+			(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
+			ParallelBlockTableScanWorker pbscanwork =
+			scan->rs_parallelworkerdata;
+
+			page = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
+													 pbscanwork, pbscan);
+			finished = (page == InvalidBlockNumber);
+		}
+		else
+		{
+			page++;
+			if (page >= scan->rs_nblocks)
+				page = 0;
+			finished = (page == scan->rs_startblock) ||
+				(scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
+
+			/*
+			 * Report our new scan position for synchronization purposes. We
+			 * don't do that when moving backwards, however. That would just
+			 * mess up any other forward-moving scanners.
+			 *
+			 * Note: we do this before checking for end of scan so that the
+			 * final state of the position hint is back at the start of the
+			 * rel.  That's not strictly necessary, but otherwise when you run
+			 * the same query multiple times the starting position would shift
+			 * a little bit backwards on every invocation, which is confusing.
+			 * We don't guarantee any specific ordering in general, though.
+			 */
+			if (scan->rs_base.rs_flags & SO_ALLOW_SYNC)
+				ss_report_location(scan->rs_base.rs_rd, page);
+		}
+
+		/*
+		 * return NULL if we've exhausted all the pages
+		 */
+		if (finished)
+		{
+			if (BufferIsValid(scan->rs_cbuf))
+				ReleaseBuffer(scan->rs_cbuf);
+			scan->rs_cbuf = InvalidBuffer;
+			scan->rs_cblock = InvalidBlockNumber;
+			tuple->t_data = NULL;
+			scan->rs_inited = false;
+			return;
+		}
+
+		heapgetpage((TableScanDesc) scan, page);
+
+		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
+
+		dp = BufferGetPage(scan->rs_cbuf);
+		TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, dp);
+		lines = PageGetMaxOffsetNumber((Page) dp);
+		linesleft = lines;
+		if (backward)
+		{
+			lineoff = lines;
+			lpp = PageGetItemId(dp, lines);
+		}
+		else
+		{
+			lineoff = FirstOffsetNumber;
+			lpp = PageGetItemId(dp, FirstOffsetNumber);
+		}
+	}
+}
+
+/* ----------------
+ *		heapgettup_pagemode - fetch next heap tuple in page-at-a-time mode
+ *
+ *		Same API as heapgettup, but used in page-at-a-time mode
+ *
+ * The internal logic is much the same as heapgettup's too, but there are some
+ * differences: we do not take the buffer content lock (that only needs to
+ * happen inside heapgetpage), and we iterate through just the tuples listed
+ * in rs_vistuples[] rather than all tuples on the page.  Notice that
+ * lineindex is 0-based, where the corresponding loop variable lineoff in
+ * heapgettup is 1-based.
+ * ----------------
+ */
+static void
+heapgettup_pagemode(HeapScanDesc scan,
+					ScanDirection dir,
+					int nkeys,
+					ScanKey key)
+{
+	HeapTuple	tuple = &(scan->rs_ctup);
+	bool		backward = ScanDirectionIsBackward(dir);
+	BlockNumber page;
+	bool		finished;
+	Page		dp;
+	int			lines;
+	int			lineindex;
+	OffsetNumber lineoff;
+	int			linesleft;
+	ItemId		lpp;
+
+	/*
+	 * calculate next starting lineindex, given scan direction
+	 */
+	if (ScanDirectionIsForward(dir))
+	{
+		if (!scan->rs_inited)
+		{
+			/*
+			 * return null immediately if relation is empty
+			 */
+			if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
+			{
+				Assert(!BufferIsValid(scan->rs_cbuf));
+				tuple->t_data = NULL;
+				return;
+			}
+			if (scan->rs_base.rs_parallel != NULL)
+			{
+				ParallelBlockTableScanDesc pbscan =
+				(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
+				ParallelBlockTableScanWorker pbscanwork =
+				scan->rs_parallelworkerdata;
+
+				table_block_parallelscan_startblock_init(scan->rs_base.rs_rd,
+														 pbscanwork, pbscan);
+
+				page = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
+														 pbscanwork, pbscan);
+
+				/* Other processes might have already finished the scan. */
+				if (page == InvalidBlockNumber)
+				{
+					Assert(!BufferIsValid(scan->rs_cbuf));
+					tuple->t_data = NULL;
+					return;
+				}
+			}
+			else
+				page = scan->rs_startblock; /* first page */
+			heapgetpage((TableScanDesc) scan, page);
+			lineindex = 0;
+			scan->rs_inited = true;
+		}
+		else
+		{
+			/* continue from previously returned page/tuple */
+			page = scan->rs_cblock; /* current page */
+			lineindex = scan->rs_cindex + 1;
+		}
+
+		dp = BufferGetPage(scan->rs_cbuf);
+		TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, dp);
+		lines = scan->rs_ntuples;
+		/* page and lineindex now reference the next visible tid */
+
+		linesleft = lines - lineindex;
+	}
+	else if (backward)
+	{
+		/* backward parallel scan not supported */
+		Assert(scan->rs_base.rs_parallel == NULL);
+
+		if (!scan->rs_inited)
+		{
+			/*
+			 * return null immediately if relation is empty
+			 */
+			if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
+			{
+				Assert(!BufferIsValid(scan->rs_cbuf));
+				tuple->t_data = NULL;
+				return;
+			}
+
+			/*
+			 * Disable reporting to syncscan logic in a backwards scan; it's
+			 * not very likely anyone else is doing the same thing at the same
+			 * time, and much more likely that we'll just bollix things for
+			 * forward scanners.
+			 */
+			scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
+
+			/*
+			 * Start from last page of the scan.  Ensure we take into account
+			 * rs_numblocks if it's been adjusted by heap_setscanlimits().
+			 */
+			if (scan->rs_numblocks != InvalidBlockNumber)
+				page = (scan->rs_startblock + scan->rs_numblocks - 1) % scan->rs_nblocks;
+			else if (scan->rs_startblock > 0)
+				page = scan->rs_startblock - 1;
+			else
+				page = scan->rs_nblocks - 1;
+			heapgetpage((TableScanDesc) scan, page);
+		}
+		else
+		{
+			/* continue from previously returned page/tuple */
+			page = scan->rs_cblock; /* current page */
+		}
+
+		dp = BufferGetPage(scan->rs_cbuf);
+		TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, dp);
+		lines = scan->rs_ntuples;
+
+		if (!scan->rs_inited)
+		{
+			lineindex = lines - 1;
+			scan->rs_inited = true;
+		}
+		else
+		{
+			lineindex = scan->rs_cindex - 1;
+		}
+		/* page and lineindex now reference the previous visible tid */
+
+		linesleft = lineindex + 1;
+	}
+	else
+	{
+		/*
+		 * ``no movement'' scan direction: refetch prior tuple
+		 */
+		if (!scan->rs_inited)
+		{
+			Assert(!BufferIsValid(scan->rs_cbuf));
+			tuple->t_data = NULL;
+			return;
+		}
+
+		page = ItemPointerGetBlockNumber(&(tuple->t_self));
+		if (page != scan->rs_cblock)
+			heapgetpage((TableScanDesc) scan, page);
+
+		/* Since the tuple was previously fetched, needn't lock page here */
+		dp = BufferGetPage(scan->rs_cbuf);
+		TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, dp);
+		lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
+		lpp = PageGetItemId(dp, lineoff);
+		Assert(ItemIdIsNormal(lpp));
+
+		tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
+		tuple->t_len = ItemIdGetLength(lpp);
+
+		/* check that rs_cindex is in sync */
+		Assert(scan->rs_cindex < scan->rs_ntuples);
+		Assert(lineoff == scan->rs_vistuples[scan->rs_cindex]);
+
+		return;
+	}
+
+	/*
+	 * advance the scan until we find a qualifying tuple or run out of stuff
+	 * to scan
+	 */
+	for (;;)
+	{
+		while (linesleft > 0)
+		{
+			lineoff = scan->rs_vistuples[lineindex];
+			lpp = PageGetItemId(dp, lineoff);
+			Assert(ItemIdIsNormal(lpp));
+
+			tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
+			tuple->t_len = ItemIdGetLength(lpp);
+			ItemPointerSet(&(tuple->t_self), page, lineoff);
+
+			/*
+			 * if current tuple qualifies, return it.
+			 */
+			if (key != NULL)
+			{
+				bool		valid;
+
+				HeapKeyTest(tuple, RelationGetDescr(scan->rs_base.rs_rd),
+							nkeys, key, valid);
+				if (valid)
+				{
+					scan->rs_cindex = lineindex;
+					return;
+				}
+			}
+			else
+			{
+				scan->rs_cindex = lineindex;
+				return;
+			}
+
+			/*
+			 * otherwise move to the next item on the page
+			 */
+			--linesleft;
+			if (backward)
+				--lineindex;
+			else
+				++lineindex;
+		}
+
+		/*
+		 * if we get here, it means we've exhausted the items on this page and
+		 * it's time to move to the next.
+		 */
+		if (backward)
+		{
+			finished = (page == scan->rs_startblock) ||
+				(scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
+			if (page == 0)
+				page = scan->rs_nblocks;
+			page--;
+		}
+		else if (scan->rs_base.rs_parallel != NULL)
+		{
+			ParallelBlockTableScanDesc pbscan =
+			(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
+			ParallelBlockTableScanWorker pbscanwork =
+			scan->rs_parallelworkerdata;
+
+			page = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
+													 pbscanwork, pbscan);
+			finished = (page == InvalidBlockNumber);
+		}
+		else
+		{
+			page++;
+			if (page >= scan->rs_nblocks)
+				page = 0;
+			finished = (page == scan->rs_startblock) ||
+				(scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
+
+			/*
+			 * Report our new scan position for synchronization purposes. We
+			 * don't do that when moving backwards, however. That would just
+			 * mess up any other forward-moving scanners.
+			 *
+			 * Note: we do this before checking for end of scan so that the
+			 * final state of the position hint is back at the start of the
+			 * rel.  That's not strictly necessary, but otherwise when you run
+			 * the same query multiple times the starting position would shift
+			 * a little bit backwards on every invocation, which is confusing.
+			 * We don't guarantee any specific ordering in general, though.
+			 */
+			if (scan->rs_base.rs_flags & SO_ALLOW_SYNC)
+				ss_report_location(scan->rs_base.rs_rd, page);
+		}
+
+		/*
+		 * return NULL if we've exhausted all the pages
+		 */
+		if (finished)
+		{
+			if (BufferIsValid(scan->rs_cbuf))
+				ReleaseBuffer(scan->rs_cbuf);
+			scan->rs_cbuf = InvalidBuffer;
+			scan->rs_cblock = InvalidBlockNumber;
+			tuple->t_data = NULL;
+			scan->rs_inited = false;
+			return;
+		}
+
+		heapgetpage((TableScanDesc) scan, page);
+
+		dp = BufferGetPage(scan->rs_cbuf);
+		TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, dp);
+		lines = scan->rs_ntuples;
+		linesleft = lines;
+		if (backward)
+			lineindex = lines - 1;
+		else
+			lineindex = 0;
+	}
+}
+
+
+#if defined(DISABLE_COMPLEX_MACRO)
+/*
+ * This is formatted so oddly so that the correspondence to the macro
+ * definition in access/htup_details.h is maintained.
+ */
+Datum
+fastgetattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
+			bool *isnull)
+{
+	return (
+			(attnum) > 0 ?
+			(
+			 (*(isnull) = false),
+			 HeapTupleNoNulls(tup) ?
+			 (
+			  TupleDescAttr((tupleDesc), (attnum) - 1)->attcacheoff >= 0 ?
+			  (
+			   fetchatt(TupleDescAttr((tupleDesc), (attnum) - 1),
+						(char *) (tup)->t_data + (tup)->t_data->t_hoff +
+						TupleDescAttr((tupleDesc), (attnum) - 1)->attcacheoff)
+			   )
+			  :
+			  nocachegetattr((tup), (attnum), (tupleDesc))
+			  )
+			 :
+			 (
+			  att_isnull((attnum) - 1, (tup)->t_data->t_bits) ?
+			  (
+			   (*(isnull) = true),
+			   (Datum) NULL
+			   )
+			  :
+			  (
+			   nocachegetattr((tup), (attnum), (tupleDesc))
+			   )
+			  )
+			 )
+			:
+			(
+			 (Datum) NULL
+			 )
+		);
+}
+#endif							/* defined(DISABLE_COMPLEX_MACRO) */
+
+
+/* ----------------------------------------------------------------
+ *					 heap access method interface
+ * ----------------------------------------------------------------
+ */
+
+
+TableScanDesc
+heap_beginscan(Relation relation, Snapshot snapshot,
+			   int nkeys, ScanKey key,
+			   ParallelTableScanDesc parallel_scan,
+			   uint32 flags)
+{
+	HeapScanDesc scan;
+
+	/*
+	 * increment relation ref count while scanning relation
+	 *
+	 * This is just to make really sure the relcache entry won't go away while
+	 * the scan has a pointer to it.  Caller should be holding the rel open
+	 * anyway, so this is redundant in all normal scenarios...
+	 */
+	RelationIncrementReferenceCount(relation);
+
+	/*
+	 * allocate and initialize scan descriptor
+	 */
+	scan = (HeapScanDesc) palloc(sizeof(HeapScanDescData));
+
+	scan->rs_base.rs_rd = relation;
+	scan->rs_base.rs_snapshot = snapshot;
+	scan->rs_base.rs_nkeys = nkeys;
+	scan->rs_base.rs_flags = flags;
+	scan->rs_base.rs_parallel = parallel_scan;
+	scan->rs_strategy = NULL;	/* set in initscan */
+
+	/*
+	 * Disable page-at-a-time mode if it's not a MVCC-safe snapshot.
+	 */
+	if (!(snapshot && IsMVCCSnapshot(snapshot)))
+		scan->rs_base.rs_flags &= ~SO_ALLOW_PAGEMODE;
+
+	/*
+	 * For seqscan and sample scans in a serializable transaction, acquire a
+	 * predicate lock on the entire relation. This is required not only to
+	 * lock all the matching tuples, but also to conflict with new insertions
+	 * into the table. In an indexscan, we take page locks on the index pages
+	 * covering the range specified in the scan qual, but in a heap scan there
+	 * is nothing more fine-grained to lock. A bitmap scan is a different
+	 * story, there we have already scanned the index and locked the index
+	 * pages covering the predicate. But in that case we still have to lock
+	 * any matching heap tuples. For sample scan we could optimize the locking
+	 * to be at least page-level granularity, but we'd need to add per-tuple
+	 * locking for that.
+	 */
+	if (scan->rs_base.rs_flags & (SO_TYPE_SEQSCAN | SO_TYPE_SAMPLESCAN))
+	{
+		/*
+		 * Ensure a missing snapshot is noticed reliably, even if the
+		 * isolation mode means predicate locking isn't performed (and
+		 * therefore the snapshot isn't used here).
+		 */
+		Assert(snapshot);
+		PredicateLockRelation(relation, snapshot);
+	}
+
+	/* we only need to set this up once */
+	scan->rs_ctup.t_tableOid = RelationGetRelid(relation);
+
+	/*
+	 * Allocate memory to keep track of page allocation for parallel workers
+	 * when doing a parallel scan.
+	 */
+	if (parallel_scan != NULL)
+		scan->rs_parallelworkerdata = palloc(sizeof(ParallelBlockTableScanWorkerData));
+	else
+		scan->rs_parallelworkerdata = NULL;
+
+	/*
+	 * we do this here instead of in initscan() because heap_rescan also calls
+	 * initscan() and we don't want to allocate memory again
+	 */
+	if (nkeys > 0)
+		scan->rs_base.rs_key = (ScanKey) palloc(sizeof(ScanKeyData) * nkeys);
+	else
+		scan->rs_base.rs_key = NULL;
+
+	initscan(scan, key, false);
+
+	return (TableScanDesc) scan;
+}
+
+void
+heap_rescan(TableScanDesc sscan, ScanKey key, bool set_params,
+			bool allow_strat, bool allow_sync, bool allow_pagemode)
+{
+	HeapScanDesc scan = (HeapScanDesc) sscan;
+
+	if (set_params)
+	{
+		if (allow_strat)
+			scan->rs_base.rs_flags |= SO_ALLOW_STRAT;
+		else
+			scan->rs_base.rs_flags &= ~SO_ALLOW_STRAT;
+
+		if (allow_sync)
+			scan->rs_base.rs_flags |= SO_ALLOW_SYNC;
+		else
+			scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
+
+		if (allow_pagemode && scan->rs_base.rs_snapshot &&
+			IsMVCCSnapshot(scan->rs_base.rs_snapshot))
+			scan->rs_base.rs_flags |= SO_ALLOW_PAGEMODE;
+		else
+			scan->rs_base.rs_flags &= ~SO_ALLOW_PAGEMODE;
+	}
+
+	/*
+	 * unpin scan buffers
+	 */
+	if (BufferIsValid(scan->rs_cbuf))
+		ReleaseBuffer(scan->rs_cbuf);
+
+	/*
+	 * reinitialize scan descriptor
+	 */
+	initscan(scan, key, true);
+}
+
+void
+heap_endscan(TableScanDesc sscan)
+{
+	HeapScanDesc scan = (HeapScanDesc) sscan;
+
+	/* Note: no locking manipulations needed */
+
+	/*
+	 * unpin scan buffers
+	 */
+	if (BufferIsValid(scan->rs_cbuf))
+		ReleaseBuffer(scan->rs_cbuf);
+
+	/*
+	 * decrement relation reference count and free scan descriptor storage
+	 */
+	RelationDecrementReferenceCount(scan->rs_base.rs_rd);
+
+	if (scan->rs_base.rs_key)
+		pfree(scan->rs_base.rs_key);
+
+	if (scan->rs_strategy != NULL)
+		FreeAccessStrategy(scan->rs_strategy);
+
+	if (scan->rs_parallelworkerdata != NULL)
+		pfree(scan->rs_parallelworkerdata);
+
+	if (scan->rs_base.rs_flags & SO_TEMP_SNAPSHOT)
+		UnregisterSnapshot(scan->rs_base.rs_snapshot);
+
+	pfree(scan);
+}
+
+HeapTuple
+heap_getnext(TableScanDesc sscan, ScanDirection direction)
+{
+	HeapScanDesc scan = (HeapScanDesc) sscan;
+
+	/*
+	 * This is still widely used directly, without going through table AM, so
+	 * add a safety check.  It's possible we should, at a later point,
+	 * downgrade this to an assert. The reason for checking the AM routine,
+	 * rather than the AM oid, is that this allows to write regression tests
+	 * that create another AM reusing the heap handler.
+	 */
+	if (unlikely(sscan->rs_rd->rd_tableam != GetHeapamTableAmRoutine()))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg_internal("only heap AM is supported")));
+
+	/*
+	 * We don't expect direct calls to heap_getnext with valid CheckXidAlive
+	 * for catalog or regular tables.  See detailed comments in xact.c where
+	 * these variables are declared.  Normally we have such a check at tableam
+	 * level API but this is called from many places so we need to ensure it
+	 * here.
+	 */
+	if (unlikely(TransactionIdIsValid(CheckXidAlive) && !bsysscan))
+		elog(ERROR, "unexpected heap_getnext call during logical decoding");
+
+	/* Note: no locking manipulations needed */
+
+	if (scan->rs_base.rs_flags & SO_ALLOW_PAGEMODE)
+		heapgettup_pagemode(scan, direction,
+							scan->rs_base.rs_nkeys, scan->rs_base.rs_key);
+	else
+		heapgettup(scan, direction,
+				   scan->rs_base.rs_nkeys, scan->rs_base.rs_key);
+
+	if (scan->rs_ctup.t_data == NULL)
+		return NULL;
+
+	/*
+	 * if we get here it means we have a new current scan tuple, so point to
+	 * the proper return buffer and return the tuple.
+	 */
+
+	pgstat_count_heap_getnext(scan->rs_base.rs_rd);
+
+	return &scan->rs_ctup;
+}
+
+bool
+heap_getnextslot(TableScanDesc sscan, ScanDirection direction, TupleTableSlot *slot)
+{
+	HeapScanDesc scan = (HeapScanDesc) sscan;
+
+	/* Note: no locking manipulations needed */
+
+	if (sscan->rs_flags & SO_ALLOW_PAGEMODE)
+		heapgettup_pagemode(scan, direction, sscan->rs_nkeys, sscan->rs_key);
+	else
+		heapgettup(scan, direction, sscan->rs_nkeys, sscan->rs_key);
+
+	if (scan->rs_ctup.t_data == NULL)
+	{
+		ExecClearTuple(slot);
+		return false;
+	}
+
+	/*
+	 * if we get here it means we have a new current scan tuple, so point to
+	 * the proper return buffer and return the tuple.
+	 */
+
+	pgstat_count_heap_getnext(scan->rs_base.rs_rd);
+
+	ExecStoreBufferHeapTuple(&scan->rs_ctup, slot,
+							 scan->rs_cbuf);
+	return true;
+}
+
+void
+heap_set_tidrange(TableScanDesc sscan, ItemPointer mintid,
+				  ItemPointer maxtid)
+{
+	HeapScanDesc scan = (HeapScanDesc) sscan;
+	BlockNumber startBlk;
+	BlockNumber numBlks;
+	ItemPointerData highestItem;
+	ItemPointerData lowestItem;
+
+	/*
+	 * For relations without any pages, we can simply leave the TID range
+	 * unset.  There will be no tuples to scan, therefore no tuples outside
+	 * the given TID range.
+	 */
+	if (scan->rs_nblocks == 0)
+		return;
+
+	/*
+	 * Set up some ItemPointers which point to the first and last possible
+	 * tuples in the heap.
+	 */
+	ItemPointerSet(&highestItem, scan->rs_nblocks - 1, MaxOffsetNumber);
+	ItemPointerSet(&lowestItem, 0, FirstOffsetNumber);
+
+	/*
+	 * If the given maximum TID is below the highest possible TID in the
+	 * relation, then restrict the range to that, otherwise we scan to the end
+	 * of the relation.
+	 */
+	if (ItemPointerCompare(maxtid, &highestItem) < 0)
+		ItemPointerCopy(maxtid, &highestItem);
+
+	/*
+	 * If the given minimum TID is above the lowest possible TID in the
+	 * relation, then restrict the range to only scan for TIDs above that.
+	 */
+	if (ItemPointerCompare(mintid, &lowestItem) > 0)
+		ItemPointerCopy(mintid, &lowestItem);
+
+	/*
+	 * Check for an empty range and protect from would be negative results
+	 * from the numBlks calculation below.
+	 */
+	if (ItemPointerCompare(&highestItem, &lowestItem) < 0)
+	{
+		/* Set an empty range of blocks to scan */
+		heap_setscanlimits(sscan, 0, 0);
+		return;
+	}
+
+	/*
+	 * Calculate the first block and the number of blocks we must scan. We
+	 * could be more aggressive here and perform some more validation to try
+	 * and further narrow the scope of blocks to scan by checking if the
+	 * lowerItem has an offset above MaxOffsetNumber.  In this case, we could
+	 * advance startBlk by one.  Likewise, if highestItem has an offset of 0
+	 * we could scan one fewer blocks.  However, such an optimization does not
+	 * seem worth troubling over, currently.
+	 */
+	startBlk = ItemPointerGetBlockNumberNoCheck(&lowestItem);
+
+	numBlks = ItemPointerGetBlockNumberNoCheck(&highestItem) -
+		ItemPointerGetBlockNumberNoCheck(&lowestItem) + 1;
+
+	/* Set the start block and number of blocks to scan */
+	heap_setscanlimits(sscan, startBlk, numBlks);
+
+	/* Finally, set the TID range in sscan */
+	ItemPointerCopy(&lowestItem, &sscan->rs_mintid);
+	ItemPointerCopy(&highestItem, &sscan->rs_maxtid);
+}
+
+bool
+heap_getnextslot_tidrange(TableScanDesc sscan, ScanDirection direction,
+						  TupleTableSlot *slot)
+{
+	HeapScanDesc scan = (HeapScanDesc) sscan;
+	ItemPointer mintid = &sscan->rs_mintid;
+	ItemPointer maxtid = &sscan->rs_maxtid;
+
+	/* Note: no locking manipulations needed */
+	for (;;)
+	{
+		if (sscan->rs_flags & SO_ALLOW_PAGEMODE)
+			heapgettup_pagemode(scan, direction, sscan->rs_nkeys, sscan->rs_key);
+		else
+			heapgettup(scan, direction, sscan->rs_nkeys, sscan->rs_key);
+
+		if (scan->rs_ctup.t_data == NULL)
+		{
+			ExecClearTuple(slot);
+			return false;
+		}
+
+		/*
+		 * heap_set_tidrange will have used heap_setscanlimits to limit the
+		 * range of pages we scan to only ones that can contain the TID range
+		 * we're scanning for.  Here we must filter out any tuples from these
+		 * pages that are outwith that range.
+		 */
+		if (ItemPointerCompare(&scan->rs_ctup.t_self, mintid) < 0)
+		{
+			ExecClearTuple(slot);
+
+			/*
+			 * When scanning backwards, the TIDs will be in descending order.
+			 * Future tuples in this direction will be lower still, so we can
+			 * just return false to indicate there will be no more tuples.
+			 */
+			if (ScanDirectionIsBackward(direction))
+				return false;
+
+			continue;
+		}
+
+		/*
+		 * Likewise for the final page, we must filter out TIDs greater than
+		 * maxtid.
+		 */
+		if (ItemPointerCompare(&scan->rs_ctup.t_self, maxtid) > 0)
+		{
+			ExecClearTuple(slot);
+
+			/*
+			 * When scanning forward, the TIDs will be in ascending order.
+			 * Future tuples in this direction will be higher still, so we can
+			 * just return false to indicate there will be no more tuples.
+			 */
+			if (ScanDirectionIsForward(direction))
+				return false;
+			continue;
+		}
+
+		break;
+	}
+
+	/*
+	 * if we get here it means we have a new current scan tuple, so point to
+	 * the proper return buffer and return the tuple.
+	 */
+	pgstat_count_heap_getnext(scan->rs_base.rs_rd);
+
+	ExecStoreBufferHeapTuple(&scan->rs_ctup, slot, scan->rs_cbuf);
+	return true;
+}
+
+/*
+ *	heap_fetch		- retrieve tuple with given tid
+ *
+ * On entry, tuple->t_self is the TID to fetch.  We pin the buffer holding
+ * the tuple, fill in the remaining fields of *tuple, and check the tuple
+ * against the specified snapshot.
+ *
+ * If successful (tuple found and passes snapshot time qual), then *userbuf
+ * is set to the buffer holding the tuple and true is returned.  The caller
+ * must unpin the buffer when done with the tuple.
+ *
+ * If the tuple is not found (ie, item number references a deleted slot),
+ * then tuple->t_data is set to NULL, *userbuf is set to InvalidBuffer,
+ * and false is returned.
+ *
+ * If the tuple is found but fails the time qual check, then false is returned
+ * and *userbuf is set to InvalidBuffer, but tuple->t_data is left pointing
+ * to the tuple.  (Note that it is unsafe to dereference tuple->t_data in
+ * this case, but callers might choose to test it for NULL-ness.)
+ *
+ * heap_fetch does not follow HOT chains: only the exact TID requested will
+ * be fetched.
+ *
+ * It is somewhat inconsistent that we ereport() on invalid block number but
+ * return false on invalid item number.  There are a couple of reasons though.
+ * One is that the caller can relatively easily check the block number for
+ * validity, but cannot check the item number without reading the page
+ * himself.  Another is that when we are following a t_ctid link, we can be
+ * reasonably confident that the page number is valid (since VACUUM shouldn't
+ * truncate off the destination page without having killed the referencing
+ * tuple first), but the item number might well not be good.
+ */
+bool
+heap_fetch(Relation relation,
+		   Snapshot snapshot,
+		   HeapTuple tuple,
+		   Buffer *userbuf)
+{
+	return heap_fetch_extended(relation, snapshot, tuple, userbuf, false);
+}
+
+/*
+ *	heap_fetch_extended		- fetch tuple even if it fails snapshot test
+ *
+ * If keep_buf is true, then upon finding a tuple that is valid but fails
+ * the snapshot check, we return the tuple pointer in tuple->t_data and the
+ * buffer ID in *userbuf, keeping the buffer pin, just as if it had passed
+ * the snapshot.  (The function result is still "false" though.)
+ * If keep_buf is false then this behaves identically to heap_fetch().
+ */
+bool
+heap_fetch_extended(Relation relation,
+					Snapshot snapshot,
+					HeapTuple tuple,
+					Buffer *userbuf,
+					bool keep_buf)
+{
+	ItemPointer tid = &(tuple->t_self);
+	ItemId		lp;
+	Buffer		buffer;
+	Page		page;
+	OffsetNumber offnum;
+	bool		valid;
+
+	/*
+	 * Fetch and pin the appropriate page of the relation.
+	 */
+	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
+
+	/*
+	 * Need share lock on buffer to examine tuple commit status.
+	 */
+	LockBuffer(buffer, BUFFER_LOCK_SHARE);
+	page = BufferGetPage(buffer);
+	TestForOldSnapshot(snapshot, relation, page);
+
+	/*
+	 * We'd better check for out-of-range offnum in case of VACUUM since the
+	 * TID was obtained.
+	 */
+	offnum = ItemPointerGetOffsetNumber(tid);
+	if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(page))
+	{
+		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+		ReleaseBuffer(buffer);
+		*userbuf = InvalidBuffer;
+		tuple->t_data = NULL;
+		return false;
+	}
+
+	/*
+	 * get the item line pointer corresponding to the requested tid
+	 */
+	lp = PageGetItemId(page, offnum);
+
+	/*
+	 * Must check for deleted tuple.
+	 */
+	if (!ItemIdIsNormal(lp))
+	{
+		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+		ReleaseBuffer(buffer);
+		*userbuf = InvalidBuffer;
+		tuple->t_data = NULL;
+		return false;
+	}
+
+	/*
+	 * fill in *tuple fields
+	 */
+	tuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
+	tuple->t_len = ItemIdGetLength(lp);
+	tuple->t_tableOid = RelationGetRelid(relation);
+
+	/*
+	 * check tuple visibility, then release lock
+	 */
+	valid = HeapTupleSatisfiesVisibility(tuple, snapshot, buffer);
+
+	if (valid)
+		PredicateLockTID(relation, &(tuple->t_self), snapshot,
+						 HeapTupleHeaderGetXmin(tuple->t_data));
+
+	HeapCheckForSerializableConflictOut(valid, relation, tuple, buffer, snapshot);
+
+	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+
+	if (valid)
+	{
+		/*
+		 * All checks passed, so return the tuple as valid. Caller is now
+		 * responsible for releasing the buffer.
+		 */
+		*userbuf = buffer;
+
+		return true;
+	}
+
+	/* Tuple failed time qual, but maybe caller wants to see it anyway. */
+	if (keep_buf)
+		*userbuf = buffer;
+	else
+	{
+		ReleaseBuffer(buffer);
+		*userbuf = InvalidBuffer;
+	}
+
+	return false;
+}
+
+/*
+ *	heap_hot_search_buffer	- search HOT chain for tuple satisfying snapshot
+ *
+ * On entry, *tid is the TID of a tuple (either a simple tuple, or the root
+ * of a HOT chain), and buffer is the buffer holding this tuple.  We search
+ * for the first chain member satisfying the given snapshot.  If one is
+ * found, we update *tid to reference that tuple's offset number, and
+ * return true.  If no match, return false without modifying *tid.
+ *
+ * heapTuple is a caller-supplied buffer.  When a match is found, we return
+ * the tuple here, in addition to updating *tid.  If no match is found, the
+ * contents of this buffer on return are undefined.
+ *
+ * If all_dead is not NULL, we check non-visible tuples to see if they are
+ * globally dead; *all_dead is set true if all members of the HOT chain
+ * are vacuumable, false if not.
+ *
+ * Unlike heap_fetch, the caller must already have pin and (at least) share
+ * lock on the buffer; it is still pinned/locked at exit.
+ */
+bool
+heap_hot_search_buffer(ItemPointer tid, Relation relation, Buffer buffer,
+					   Snapshot snapshot, HeapTuple heapTuple,
+					   bool *all_dead, bool first_call)
+{
+	Page		dp = (Page) BufferGetPage(buffer);
+	TransactionId prev_xmax = InvalidTransactionId;
+	BlockNumber blkno;
+	OffsetNumber offnum;
+	bool		at_chain_start;
+	bool		valid;
+	bool		skip;
+	GlobalVisState *vistest = NULL;
+
+	/* If this is not the first call, previous call returned a (live!) tuple */
+	if (all_dead)
+		*all_dead = first_call;
+
+	blkno = ItemPointerGetBlockNumber(tid);
+	offnum = ItemPointerGetOffsetNumber(tid);
+	at_chain_start = first_call;
+	skip = !first_call;
+
+	/* XXX: we should assert that a snapshot is pushed or registered */
+	Assert(TransactionIdIsValid(RecentXmin));
+	Assert(BufferGetBlockNumber(buffer) == blkno);
+
+	/* Scan through possible multiple members of HOT-chain */
+	for (;;)
+	{
+		ItemId		lp;
+
+		/* check for bogus TID */
+		if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(dp))
+			break;
+
+		lp = PageGetItemId(dp, offnum);
+
+		/* check for unused, dead, or redirected items */
+		if (!ItemIdIsNormal(lp))
+		{
+			/* We should only see a redirect at start of chain */
+			if (ItemIdIsRedirected(lp) && at_chain_start)
+			{
+				/* Follow the redirect */
+				offnum = ItemIdGetRedirect(lp);
+				at_chain_start = false;
+				continue;
+			}
+			/* else must be end of chain */
+			break;
+		}
+
+		/*
+		 * Update heapTuple to point to the element of the HOT chain we're
+		 * currently investigating. Having t_self set correctly is important
+		 * because the SSI checks and the *Satisfies routine for historical
+		 * MVCC snapshots need the correct tid to decide about the visibility.
+		 */
+		heapTuple->t_data = (HeapTupleHeader) PageGetItem(dp, lp);
+		heapTuple->t_len = ItemIdGetLength(lp);
+		heapTuple->t_tableOid = RelationGetRelid(relation);
+		ItemPointerSet(&heapTuple->t_self, blkno, offnum);
+
+		/*
+		 * Shouldn't see a HEAP_ONLY tuple at chain start.
+		 */
+		if (at_chain_start && HeapTupleIsHeapOnly(heapTuple))
+			break;
+
+		/*
+		 * The xmin should match the previous xmax value, else chain is
+		 * broken.
+		 */
+		if (TransactionIdIsValid(prev_xmax) &&
+			!TransactionIdEquals(prev_xmax,
+								 HeapTupleHeaderGetXmin(heapTuple->t_data)))
+			break;
+
+		/*
+		 * When first_call is true (and thus, skip is initially false) we'll
+		 * return the first tuple we find.  But on later passes, heapTuple
+		 * will initially be pointing to the tuple we returned last time.
+		 * Returning it again would be incorrect (and would loop forever), so
+		 * we skip it and return the next match we find.
+		 */
+		if (!skip)
+		{
+			/* If it's visible per the snapshot, we must return it */
+			valid = HeapTupleSatisfiesVisibility(heapTuple, snapshot, buffer);
+			HeapCheckForSerializableConflictOut(valid, relation, heapTuple,
+												buffer, snapshot);
+
+			if (valid)
+			{
+				ItemPointerSetOffsetNumber(tid, offnum);
+				PredicateLockTID(relation, &heapTuple->t_self, snapshot,
+								 HeapTupleHeaderGetXmin(heapTuple->t_data));
+				if (all_dead)
+					*all_dead = false;
+				return true;
+			}
+		}
+		skip = false;
+
+		/*
+		 * If we can't see it, maybe no one else can either.  At caller
+		 * request, check whether all chain members are dead to all
+		 * transactions.
+		 *
+		 * Note: if you change the criterion here for what is "dead", fix the
+		 * planner's get_actual_variable_range() function to match.
+		 */
+		if (all_dead && *all_dead)
+		{
+			if (!vistest)
+				vistest = GlobalVisTestFor(relation);
+
+			if (!HeapTupleIsSurelyDead(heapTuple, vistest))
+				*all_dead = false;
+		}
+
+		/*
+		 * Check to see if HOT chain continues past this tuple; if so fetch
+		 * the next offnum and loop around.
+		 */
+		if (HeapTupleIsHotUpdated(heapTuple))
+		{
+			Assert(ItemPointerGetBlockNumber(&heapTuple->t_data->t_ctid) ==
+				   blkno);
+			offnum = ItemPointerGetOffsetNumber(&heapTuple->t_data->t_ctid);
+			at_chain_start = false;
+			prev_xmax = HeapTupleHeaderGetUpdateXid(heapTuple->t_data);
+		}
+		else
+			break;				/* end of chain */
+	}
+
+	return false;
+}
+
+/*
+ *	heap_get_latest_tid -  get the latest tid of a specified tuple
+ *
+ * Actually, this gets the latest version that is visible according to the
+ * scan's snapshot.  Create a scan using SnapshotDirty to get the very latest,
+ * possibly uncommitted version.
+ *
+ * *tid is both an input and an output parameter: it is updated to
+ * show the latest version of the row.  Note that it will not be changed
+ * if no version of the row passes the snapshot test.
+ */
+void
+heap_get_latest_tid(TableScanDesc sscan,
+					ItemPointer tid)
+{
+	Relation	relation = sscan->rs_rd;
+	Snapshot	snapshot = sscan->rs_snapshot;
+	ItemPointerData ctid;
+	TransactionId priorXmax;
+
+	/*
+	 * table_tuple_get_latest_tid() verified that the passed in tid is valid.
+	 * Assume that t_ctid links are valid however - there shouldn't be invalid
+	 * ones in the table.
+	 */
+	Assert(ItemPointerIsValid(tid));
+
+	/*
+	 * Loop to chase down t_ctid links.  At top of loop, ctid is the tuple we
+	 * need to examine, and *tid is the TID we will return if ctid turns out
+	 * to be bogus.
+	 *
+	 * Note that we will loop until we reach the end of the t_ctid chain.
+	 * Depending on the snapshot passed, there might be at most one visible
+	 * version of the row, but we don't try to optimize for that.
+	 */
+	ctid = *tid;
+	priorXmax = InvalidTransactionId;	/* cannot check first XMIN */
+	for (;;)
+	{
+		Buffer		buffer;
+		Page		page;
+		OffsetNumber offnum;
+		ItemId		lp;
+		HeapTupleData tp;
+		bool		valid;
+
+		/*
+		 * Read, pin, and lock the page.
+		 */
+		buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&ctid));
+		LockBuffer(buffer, BUFFER_LOCK_SHARE);
+		page = BufferGetPage(buffer);
+		TestForOldSnapshot(snapshot, relation, page);
+
+		/*
+		 * Check for bogus item number.  This is not treated as an error
+		 * condition because it can happen while following a t_ctid link. We
+		 * just assume that the prior tid is OK and return it unchanged.
+		 */
+		offnum = ItemPointerGetOffsetNumber(&ctid);
+		if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(page))
+		{
+			UnlockReleaseBuffer(buffer);
+			break;
+		}
+		lp = PageGetItemId(page, offnum);
+		if (!ItemIdIsNormal(lp))
+		{
+			UnlockReleaseBuffer(buffer);
+			break;
+		}
+
+		/* OK to access the tuple */
+		tp.t_self = ctid;
+		tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
+		tp.t_len = ItemIdGetLength(lp);
+		tp.t_tableOid = RelationGetRelid(relation);
+
+		/*
+		 * After following a t_ctid link, we might arrive at an unrelated
+		 * tuple.  Check for XMIN match.
+		 */
+		if (TransactionIdIsValid(priorXmax) &&
+			!TransactionIdEquals(priorXmax, HeapTupleHeaderGetXmin(tp.t_data)))
+		{
+			UnlockReleaseBuffer(buffer);
+			break;
+		}
+
+		/*
+		 * Check tuple visibility; if visible, set it as the new result
+		 * candidate.
+		 */
+		valid = HeapTupleSatisfiesVisibility(&tp, snapshot, buffer);
+		HeapCheckForSerializableConflictOut(valid, relation, &tp, buffer, snapshot);
+		if (valid)
+			*tid = ctid;
+
+		/*
+		 * If there's a valid t_ctid link, follow it, else we're done.
+		 */
+		if ((tp.t_data->t_infomask & HEAP_XMAX_INVALID) ||
+			HeapTupleHeaderIsOnlyLocked(tp.t_data) ||
+			HeapTupleHeaderIndicatesMovedPartitions(tp.t_data) ||
+			ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid))
+		{
+			UnlockReleaseBuffer(buffer);
+			break;
+		}
+
+		ctid = tp.t_data->t_ctid;
+		priorXmax = HeapTupleHeaderGetUpdateXid(tp.t_data);
+		UnlockReleaseBuffer(buffer);
+	}							/* end of loop */
+}
+
+
+/*
+ * UpdateXmaxHintBits - update tuple hint bits after xmax transaction ends
+ *
+ * This is called after we have waited for the XMAX transaction to terminate.
+ * If the transaction aborted, we guarantee the XMAX_INVALID hint bit will
+ * be set on exit.  If the transaction committed, we set the XMAX_COMMITTED
+ * hint bit if possible --- but beware that that may not yet be possible,
+ * if the transaction committed asynchronously.
+ *
+ * Note that if the transaction was a locker only, we set HEAP_XMAX_INVALID
+ * even if it commits.
+ *
+ * Hence callers should look only at XMAX_INVALID.
+ *
+ * Note this is not allowed for tuples whose xmax is a multixact.
+ */
+static void
+UpdateXmaxHintBits(HeapTupleHeader tuple, Buffer buffer, TransactionId xid)
+{
+	Assert(TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple), xid));
+	Assert(!(tuple->t_infomask & HEAP_XMAX_IS_MULTI));
+
+	if (!(tuple->t_infomask & (HEAP_XMAX_COMMITTED | HEAP_XMAX_INVALID)))
+	{
+		if (!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask) &&
+			TransactionIdDidCommit(xid))
+			HeapTupleSetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
+								 xid);
+		else
+			HeapTupleSetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+								 InvalidTransactionId);
+	}
+}
+
+
+/*
+ * GetBulkInsertState - prepare status object for a bulk insert
+ */
+BulkInsertState
+GetBulkInsertState(void)
+{
+	BulkInsertState bistate;
+
+	bistate = (BulkInsertState) palloc(sizeof(BulkInsertStateData));
+	bistate->strategy = GetAccessStrategy(BAS_BULKWRITE);
+	bistate->current_buf = InvalidBuffer;
+	return bistate;
+}
+
+/*
+ * FreeBulkInsertState - clean up after finishing a bulk insert
+ */
+void
+FreeBulkInsertState(BulkInsertState bistate)
+{
+	if (bistate->current_buf != InvalidBuffer)
+		ReleaseBuffer(bistate->current_buf);
+	FreeAccessStrategy(bistate->strategy);
+	pfree(bistate);
+}
+
+/*
+ * ReleaseBulkInsertStatePin - release a buffer currently held in bistate
+ */
+void
+ReleaseBulkInsertStatePin(BulkInsertState bistate)
+{
+	if (bistate->current_buf != InvalidBuffer)
+		ReleaseBuffer(bistate->current_buf);
+	bistate->current_buf = InvalidBuffer;
+}
+
+
+/*
+ *	heap_insert		- insert tuple into a heap
+ *
+ * The new tuple is stamped with current transaction ID and the specified
+ * command ID.
+ *
+ * See table_tuple_insert for comments about most of the input flags, except
+ * that this routine directly takes a tuple rather than a slot.
+ *
+ * There's corresponding HEAP_INSERT_ options to all the TABLE_INSERT_
+ * options, and there additionally is HEAP_INSERT_SPECULATIVE which is used to
+ * implement table_tuple_insert_speculative().
+ *
+ * On return the header fields of *tup are updated to match the stored tuple;
+ * in particular tup->t_self receives the actual TID where the tuple was
+ * stored.  But note that any toasting of fields within the tuple data is NOT
+ * reflected into *tup.
+ */
+void
+heap_insert(Relation relation, HeapTuple tup, CommandId cid,
+			int options, BulkInsertState bistate)
+{
+	TransactionId xid = GetCurrentTransactionId();
+	HeapTuple	heaptup;
+	Buffer		buffer;
+	Buffer		vmbuffer = InvalidBuffer;
+	bool		all_visible_cleared = false;
+
+	/* Cheap, simplistic check that the tuple matches the rel's rowtype. */
+	Assert(HeapTupleHeaderGetNatts(tup->t_data) <=
+		   RelationGetNumberOfAttributes(relation));
+
+	/*
+	 * Fill in tuple header fields and toast the tuple if necessary.
+	 *
+	 * Note: below this point, heaptup is the data we actually intend to store
+	 * into the relation; tup is the caller's original untoasted data.
+	 */
+	heaptup = heap_prepare_insert(relation, tup, xid, cid, options);
+
+	/*
+	 * Find buffer to insert this tuple into.  If the page is all visible,
+	 * this will also pin the requisite visibility map page.
+	 */
+	buffer = RelationGetBufferForTuple(relation, heaptup->t_len,
+									   InvalidBuffer, options, bistate,
+									   &vmbuffer, NULL);
+
+	/*
+	 * We're about to do the actual insert -- but check for conflict first, to
+	 * avoid possibly having to roll back work we've just done.
+	 *
+	 * This is safe without a recheck as long as there is no possibility of
+	 * another process scanning the page between this check and the insert
+	 * being visible to the scan (i.e., an exclusive buffer content lock is
+	 * continuously held from this point until the tuple insert is visible).
+	 *
+	 * For a heap insert, we only need to check for table-level SSI locks. Our
+	 * new tuple can't possibly conflict with existing tuple locks, and heap
+	 * page locks are only consolidated versions of tuple locks; they do not
+	 * lock "gaps" as index page locks do.  So we don't need to specify a
+	 * buffer when making the call, which makes for a faster check.
+	 */
+	CheckForSerializableConflictIn(relation, NULL, InvalidBlockNumber);
+
+	/* NO EREPORT(ERROR) from here till changes are logged */
+	START_CRIT_SECTION();
+
+	RelationPutHeapTuple(relation, buffer, heaptup,
+						 (options & HEAP_INSERT_SPECULATIVE) != 0);
+
+	if (PageIsAllVisible(BufferGetPage(buffer)))
+	{
+		all_visible_cleared = true;
+		PageClearAllVisible(BufferGetPage(buffer));
+		visibilitymap_clear(relation,
+							ItemPointerGetBlockNumber(&(heaptup->t_self)),
+							vmbuffer, VISIBILITYMAP_VALID_BITS);
+	}
+
+	/*
+	 * XXX Should we set PageSetPrunable on this page ?
+	 *
+	 * The inserting transaction may eventually abort thus making this tuple
+	 * DEAD and hence available for pruning. Though we don't want to optimize
+	 * for aborts, if no other tuple in this page is UPDATEd/DELETEd, the
+	 * aborted tuple will never be pruned until next vacuum is triggered.
+	 *
+	 * If you do add PageSetPrunable here, add it in heap_xlog_insert too.
+	 */
+
+	MarkBufferDirty(buffer);
+
+	/* XLOG stuff */
+	if (RelationNeedsWAL(relation))
+	{
+		xl_heap_insert xlrec;
+		xl_heap_header xlhdr;
+		XLogRecPtr	recptr;
+		Page		page = BufferGetPage(buffer);
+		uint8		info = XLOG_HEAP_INSERT;
+		int			bufflags = 0;
+
+		/*
+		 * If this is a catalog, we need to transmit combo CIDs to properly
+		 * decode, so log that as well.
+		 */
+		if (RelationIsAccessibleInLogicalDecoding(relation))
+			log_heap_new_cid(relation, heaptup);
+
+		/*
+		 * If this is the single and first tuple on page, we can reinit the
+		 * page instead of restoring the whole thing.  Set flag, and hide
+		 * buffer references from XLogInsert.
+		 */
+		if (ItemPointerGetOffsetNumber(&(heaptup->t_self)) == FirstOffsetNumber &&
+			PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
+		{
+			info |= XLOG_HEAP_INIT_PAGE;
+			bufflags |= REGBUF_WILL_INIT;
+		}
+
+		xlrec.offnum = ItemPointerGetOffsetNumber(&heaptup->t_self);
+		xlrec.flags = 0;
+		if (all_visible_cleared)
+			xlrec.flags |= XLH_INSERT_ALL_VISIBLE_CLEARED;
+		if (options & HEAP_INSERT_SPECULATIVE)
+			xlrec.flags |= XLH_INSERT_IS_SPECULATIVE;
+		Assert(ItemPointerGetBlockNumber(&heaptup->t_self) == BufferGetBlockNumber(buffer));
+
+		/*
+		 * For logical decoding, we need the tuple even if we're doing a full
+		 * page write, so make sure it's included even if we take a full-page
+		 * image. (XXX We could alternatively store a pointer into the FPW).
+		 */
+		if (RelationIsLogicallyLogged(relation) &&
+			!(options & HEAP_INSERT_NO_LOGICAL))
+		{
+			xlrec.flags |= XLH_INSERT_CONTAINS_NEW_TUPLE;
+			bufflags |= REGBUF_KEEP_DATA;
+
+			if (IsToastRelation(relation))
+				xlrec.flags |= XLH_INSERT_ON_TOAST_RELATION;
+		}
+
+		XLogBeginInsert();
+		XLogRegisterData((char *) &xlrec, SizeOfHeapInsert);
+
+		xlhdr.t_infomask2 = heaptup->t_data->t_infomask2;
+		xlhdr.t_infomask = heaptup->t_data->t_infomask;
+		xlhdr.t_hoff = heaptup->t_data->t_hoff;
+
+		/*
+		 * note we mark xlhdr as belonging to buffer; if XLogInsert decides to
+		 * write the whole page to the xlog, we don't need to store
+		 * xl_heap_header in the xlog.
+		 */
+		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD | bufflags);
+		XLogRegisterBufData(0, (char *) &xlhdr, SizeOfHeapHeader);
+		/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
+		XLogRegisterBufData(0,
+							(char *) heaptup->t_data + SizeofHeapTupleHeader,
+							heaptup->t_len - SizeofHeapTupleHeader);
+
+		/* filtering by origin on a row level is much more efficient */
+		XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
+
+		recptr = XLogInsert(RM_HEAP_ID, info);
+
+		PageSetLSN(page, recptr);
+	}
+
+	END_CRIT_SECTION();
+
+	UnlockReleaseBuffer(buffer);
+	if (vmbuffer != InvalidBuffer)
+		ReleaseBuffer(vmbuffer);
+
+	/*
+	 * If tuple is cachable, mark it for invalidation from the caches in case
+	 * we abort.  Note it is OK to do this after releasing the buffer, because
+	 * the heaptup data structure is all in local memory, not in the shared
+	 * buffer.
+	 */
+	CacheInvalidateHeapTuple(relation, heaptup, NULL);
+
+	/* Note: speculative insertions are counted too, even if aborted later */
+	pgstat_count_heap_insert(relation, 1);
+
+	/*
+	 * If heaptup is a private copy, release it.  Don't forget to copy t_self
+	 * back to the caller's image, too.
+	 */
+	if (heaptup != tup)
+	{
+		tup->t_self = heaptup->t_self;
+		heap_freetuple(heaptup);
+	}
+}
+
+/*
+ * Subroutine for heap_insert(). Prepares a tuple for insertion. This sets the
+ * tuple header fields and toasts the tuple if necessary.  Returns a toasted
+ * version of the tuple if it was toasted, or the original tuple if not. Note
+ * that in any case, the header fields are also set in the original tuple.
+ */
+static HeapTuple
+heap_prepare_insert(Relation relation, HeapTuple tup, TransactionId xid,
+					CommandId cid, int options)
+{
+	/*
+	 * To allow parallel inserts, we need to ensure that they are safe to be
+	 * performed in workers. We have the infrastructure to allow parallel
+	 * inserts in general except for the cases where inserts generate a new
+	 * CommandId (eg. inserts into a table having a foreign key column).
+	 */
+	if (IsParallelWorker())
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_TRANSACTION_STATE),
+				 errmsg("cannot insert tuples in a parallel worker")));
+
+	tup->t_data->t_infomask &= ~(HEAP_XACT_MASK);
+	tup->t_data->t_infomask2 &= ~(HEAP2_XACT_MASK);
+	tup->t_data->t_infomask |= HEAP_XMAX_INVALID;
+	HeapTupleHeaderSetXmin(tup->t_data, xid);
+	if (options & HEAP_INSERT_FROZEN)
+		HeapTupleHeaderSetXminFrozen(tup->t_data);
+
+	HeapTupleHeaderSetCmin(tup->t_data, cid);
+	HeapTupleHeaderSetXmax(tup->t_data, 0); /* for cleanliness */
+	tup->t_tableOid = RelationGetRelid(relation);
+
+	/*
+	 * If the new tuple is too big for storage or contains already toasted
+	 * out-of-line attributes from some other relation, invoke the toaster.
+	 */
+	if (relation->rd_rel->relkind != RELKIND_RELATION &&
+		relation->rd_rel->relkind != RELKIND_MATVIEW)
+	{
+		/* toast table entries should never be recursively toasted */
+		Assert(!HeapTupleHasExternal(tup));
+		return tup;
+	}
+	else if (HeapTupleHasExternal(tup) || tup->t_len > TOAST_TUPLE_THRESHOLD)
+		return heap_toast_insert_or_update(relation, tup, NULL, options);
+	else
+		return tup;
+}
+
+/*
+ *	heap_multi_insert	- insert multiple tuples into a heap
+ *
+ * This is like heap_insert(), but inserts multiple tuples in one operation.
+ * That's faster than calling heap_insert() in a loop, because when multiple
+ * tuples can be inserted on a single page, we can write just a single WAL
+ * record covering all of them, and only need to lock/unlock the page once.
+ *
+ * Note: this leaks memory into the current memory context. You can create a
+ * temporary context before calling this, if that's a problem.
+ */
+void
+heap_multi_insert(Relation relation, TupleTableSlot **slots, int ntuples,
+				  CommandId cid, int options, BulkInsertState bistate)
+{
+	TransactionId xid = GetCurrentTransactionId();
+	HeapTuple  *heaptuples;
+	int			i;
+	int			ndone;
+	PGAlignedBlock scratch;
+	Page		page;
+	Buffer		vmbuffer = InvalidBuffer;
+	bool		needwal;
+	Size		saveFreeSpace;
+	bool		need_tuple_data = RelationIsLogicallyLogged(relation);
+	bool		need_cids = RelationIsAccessibleInLogicalDecoding(relation);
+
+	/* currently not needed (thus unsupported) for heap_multi_insert() */
+	AssertArg(!(options & HEAP_INSERT_NO_LOGICAL));
+
+	needwal = RelationNeedsWAL(relation);
+	saveFreeSpace = RelationGetTargetPageFreeSpace(relation,
+												   HEAP_DEFAULT_FILLFACTOR);
+
+	/* Toast and set header data in all the slots */
+	heaptuples = palloc(ntuples * sizeof(HeapTuple));
+	for (i = 0; i < ntuples; i++)
+	{
+		HeapTuple	tuple;
+
+		tuple = ExecFetchSlotHeapTuple(slots[i], true, NULL);
+		slots[i]->tts_tableOid = RelationGetRelid(relation);
+		tuple->t_tableOid = slots[i]->tts_tableOid;
+		heaptuples[i] = heap_prepare_insert(relation, tuple, xid, cid,
+											options);
+	}
+
+	/*
+	 * We're about to do the actual inserts -- but check for conflict first,
+	 * to minimize the possibility of having to roll back work we've just
+	 * done.
+	 *
+	 * A check here does not definitively prevent a serialization anomaly;
+	 * that check MUST be done at least past the point of acquiring an
+	 * exclusive buffer content lock on every buffer that will be affected,
+	 * and MAY be done after all inserts are reflected in the buffers and
+	 * those locks are released; otherwise there is a race condition.  Since
+	 * multiple buffers can be locked and unlocked in the loop below, and it
+	 * would not be feasible to identify and lock all of those buffers before
+	 * the loop, we must do a final check at the end.
+	 *
+	 * The check here could be omitted with no loss of correctness; it is
+	 * present strictly as an optimization.
+	 *
+	 * For heap inserts, we only need to check for table-level SSI locks. Our
+	 * new tuples can't possibly conflict with existing tuple locks, and heap
+	 * page locks are only consolidated versions of tuple locks; they do not
+	 * lock "gaps" as index page locks do.  So we don't need to specify a
+	 * buffer when making the call, which makes for a faster check.
+	 */
+	CheckForSerializableConflictIn(relation, NULL, InvalidBlockNumber);
+
+	ndone = 0;
+	while (ndone < ntuples)
+	{
+		Buffer		buffer;
+		bool		starting_with_empty_page;
+		bool		all_visible_cleared = false;
+		bool		all_frozen_set = false;
+		int			nthispage;
+
+		CHECK_FOR_INTERRUPTS();
+
+		/*
+		 * Find buffer where at least the next tuple will fit.  If the page is
+		 * all-visible, this will also pin the requisite visibility map page.
+		 *
+		 * Also pin visibility map page if COPY FREEZE inserts tuples into an
+		 * empty page. See all_frozen_set below.
+		 */
+		buffer = RelationGetBufferForTuple(relation, heaptuples[ndone]->t_len,
+										   InvalidBuffer, options, bistate,
+										   &vmbuffer, NULL);
+		page = BufferGetPage(buffer);
+
+		starting_with_empty_page = PageGetMaxOffsetNumber(page) == 0;
+
+		if (starting_with_empty_page && (options & HEAP_INSERT_FROZEN))
+			all_frozen_set = true;
+
+		/* NO EREPORT(ERROR) from here till changes are logged */
+		START_CRIT_SECTION();
+
+		/*
+		 * RelationGetBufferForTuple has ensured that the first tuple fits.
+		 * Put that on the page, and then as many other tuples as fit.
+		 */
+		RelationPutHeapTuple(relation, buffer, heaptuples[ndone], false);
+
+		/*
+		 * For logical decoding we need combo CIDs to properly decode the
+		 * catalog.
+		 */
+		if (needwal && need_cids)
+			log_heap_new_cid(relation, heaptuples[ndone]);
+
+		for (nthispage = 1; ndone + nthispage < ntuples; nthispage++)
+		{
+			HeapTuple	heaptup = heaptuples[ndone + nthispage];
+
+			if (PageGetHeapFreeSpace(page) < MAXALIGN(heaptup->t_len) + saveFreeSpace)
+				break;
+
+			RelationPutHeapTuple(relation, buffer, heaptup, false);
+
+			/*
+			 * For logical decoding we need combo CIDs to properly decode the
+			 * catalog.
+			 */
+			if (needwal && need_cids)
+				log_heap_new_cid(relation, heaptup);
+		}
+
+		/*
+		 * If the page is all visible, need to clear that, unless we're only
+		 * going to add further frozen rows to it.
+		 *
+		 * If we're only adding already frozen rows to a previously empty
+		 * page, mark it as all-visible.
+		 */
+		if (PageIsAllVisible(page) && !(options & HEAP_INSERT_FROZEN))
+		{
+			all_visible_cleared = true;
+			PageClearAllVisible(page);
+			visibilitymap_clear(relation,
+								BufferGetBlockNumber(buffer),
+								vmbuffer, VISIBILITYMAP_VALID_BITS);
+		}
+		else if (all_frozen_set)
+			PageSetAllVisible(page);
+
+		/*
+		 * XXX Should we set PageSetPrunable on this page ? See heap_insert()
+		 */
+
+		MarkBufferDirty(buffer);
+
+		/* XLOG stuff */
+		if (needwal)
+		{
+			XLogRecPtr	recptr;
+			xl_heap_multi_insert *xlrec;
+			uint8		info = XLOG_HEAP2_MULTI_INSERT;
+			char	   *tupledata;
+			int			totaldatalen;
+			char	   *scratchptr = scratch.data;
+			bool		init;
+			int			bufflags = 0;
+
+			/*
+			 * If the page was previously empty, we can reinit the page
+			 * instead of restoring the whole thing.
+			 */
+			init = starting_with_empty_page;
+
+			/* allocate xl_heap_multi_insert struct from the scratch area */
+			xlrec = (xl_heap_multi_insert *) scratchptr;
+			scratchptr += SizeOfHeapMultiInsert;
+
+			/*
+			 * Allocate offsets array. Unless we're reinitializing the page,
+			 * in that case the tuples are stored in order starting at
+			 * FirstOffsetNumber and we don't need to store the offsets
+			 * explicitly.
+			 */
+			if (!init)
+				scratchptr += nthispage * sizeof(OffsetNumber);
+
+			/* the rest of the scratch space is used for tuple data */
+			tupledata = scratchptr;
+
+			/* check that the mutually exclusive flags are not both set */
+			Assert(!(all_visible_cleared && all_frozen_set));
+
+			xlrec->flags = 0;
+			if (all_visible_cleared)
+				xlrec->flags = XLH_INSERT_ALL_VISIBLE_CLEARED;
+			if (all_frozen_set)
+				xlrec->flags = XLH_INSERT_ALL_FROZEN_SET;
+
+			xlrec->ntuples = nthispage;
+
+			/*
+			 * Write out an xl_multi_insert_tuple and the tuple data itself
+			 * for each tuple.
+			 */
+			for (i = 0; i < nthispage; i++)
+			{
+				HeapTuple	heaptup = heaptuples[ndone + i];
+				xl_multi_insert_tuple *tuphdr;
+				int			datalen;
+
+				if (!init)
+					xlrec->offsets[i] = ItemPointerGetOffsetNumber(&heaptup->t_self);
+				/* xl_multi_insert_tuple needs two-byte alignment. */
+				tuphdr = (xl_multi_insert_tuple *) SHORTALIGN(scratchptr);
+				scratchptr = ((char *) tuphdr) + SizeOfMultiInsertTuple;
+
+				tuphdr->t_infomask2 = heaptup->t_data->t_infomask2;
+				tuphdr->t_infomask = heaptup->t_data->t_infomask;
+				tuphdr->t_hoff = heaptup->t_data->t_hoff;
+
+				/* write bitmap [+ padding] [+ oid] + data */
+				datalen = heaptup->t_len - SizeofHeapTupleHeader;
+				memcpy(scratchptr,
+					   (char *) heaptup->t_data + SizeofHeapTupleHeader,
+					   datalen);
+				tuphdr->datalen = datalen;
+				scratchptr += datalen;
+			}
+			totaldatalen = scratchptr - tupledata;
+			Assert((scratchptr - scratch.data) < BLCKSZ);
+
+			if (need_tuple_data)
+				xlrec->flags |= XLH_INSERT_CONTAINS_NEW_TUPLE;
+
+			/*
+			 * Signal that this is the last xl_heap_multi_insert record
+			 * emitted by this call to heap_multi_insert(). Needed for logical
+			 * decoding so it knows when to cleanup temporary data.
+			 */
+			if (ndone + nthispage == ntuples)
+				xlrec->flags |= XLH_INSERT_LAST_IN_MULTI;
+
+			if (init)
+			{
+				info |= XLOG_HEAP_INIT_PAGE;
+				bufflags |= REGBUF_WILL_INIT;
+			}
+
+			/*
+			 * If we're doing logical decoding, include the new tuple data
+			 * even if we take a full-page image of the page.
+			 */
+			if (need_tuple_data)
+				bufflags |= REGBUF_KEEP_DATA;
+
+			XLogBeginInsert();
+			XLogRegisterData((char *) xlrec, tupledata - scratch.data);
+			XLogRegisterBuffer(0, buffer, REGBUF_STANDARD | bufflags);
+
+			XLogRegisterBufData(0, tupledata, totaldatalen);
+
+			/* filtering by origin on a row level is much more efficient */
+			XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
+
+			recptr = XLogInsert(RM_HEAP2_ID, info);
+
+			PageSetLSN(page, recptr);
+		}
+
+		END_CRIT_SECTION();
+
+		/*
+		 * If we've frozen everything on the page, update the visibilitymap.
+		 * We're already holding pin on the vmbuffer.
+		 */
+		if (all_frozen_set)
+		{
+			Assert(PageIsAllVisible(page));
+			Assert(visibilitymap_pin_ok(BufferGetBlockNumber(buffer), vmbuffer));
+
+			/*
+			 * It's fine to use InvalidTransactionId here - this is only used
+			 * when HEAP_INSERT_FROZEN is specified, which intentionally
+			 * violates visibility rules.
+			 */
+			visibilitymap_set(relation, BufferGetBlockNumber(buffer), buffer,
+							  InvalidXLogRecPtr, vmbuffer,
+							  InvalidTransactionId,
+							  VISIBILITYMAP_ALL_VISIBLE | VISIBILITYMAP_ALL_FROZEN);
+		}
+
+		UnlockReleaseBuffer(buffer);
+		ndone += nthispage;
+
+		/*
+		 * NB: Only release vmbuffer after inserting all tuples - it's fairly
+		 * likely that we'll insert into subsequent heap pages that are likely
+		 * to use the same vm page.
+		 */
+	}
+
+	/* We're done with inserting all tuples, so release the last vmbuffer. */
+	if (vmbuffer != InvalidBuffer)
+		ReleaseBuffer(vmbuffer);
+
+	/*
+	 * We're done with the actual inserts.  Check for conflicts again, to
+	 * ensure that all rw-conflicts in to these inserts are detected.  Without
+	 * this final check, a sequential scan of the heap may have locked the
+	 * table after the "before" check, missing one opportunity to detect the
+	 * conflict, and then scanned the table before the new tuples were there,
+	 * missing the other chance to detect the conflict.
+	 *
+	 * For heap inserts, we only need to check for table-level SSI locks. Our
+	 * new tuples can't possibly conflict with existing tuple locks, and heap
+	 * page locks are only consolidated versions of tuple locks; they do not
+	 * lock "gaps" as index page locks do.  So we don't need to specify a
+	 * buffer when making the call.
+	 */
+	CheckForSerializableConflictIn(relation, NULL, InvalidBlockNumber);
+
+	/*
+	 * If tuples are cachable, mark them for invalidation from the caches in
+	 * case we abort.  Note it is OK to do this after releasing the buffer,
+	 * because the heaptuples data structure is all in local memory, not in
+	 * the shared buffer.
+	 */
+	if (IsCatalogRelation(relation))
+	{
+		for (i = 0; i < ntuples; i++)
+			CacheInvalidateHeapTuple(relation, heaptuples[i], NULL);
+	}
+
+	/* copy t_self fields back to the caller's slots */
+	for (i = 0; i < ntuples; i++)
+		slots[i]->tts_tid = heaptuples[i]->t_self;
+
+	pgstat_count_heap_insert(relation, ntuples);
+}
+
+/*
+ *	simple_heap_insert - insert a tuple
+ *
+ * Currently, this routine differs from heap_insert only in supplying
+ * a default command ID and not allowing access to the speedup options.
+ *
+ * This should be used rather than using heap_insert directly in most places
+ * where we are modifying system catalogs.
+ */
+void
+simple_heap_insert(Relation relation, HeapTuple tup)
+{
+	heap_insert(relation, tup, GetCurrentCommandId(true), 0, NULL);
+}
+
+/*
+ * Given infomask/infomask2, compute the bits that must be saved in the
+ * "infobits" field of xl_heap_delete, xl_heap_update, xl_heap_lock,
+ * xl_heap_lock_updated WAL records.
+ *
+ * See fix_infomask_from_infobits.
+ */
+static uint8
+compute_infobits(uint16 infomask, uint16 infomask2)
+{
+	return
+		((infomask & HEAP_XMAX_IS_MULTI) != 0 ? XLHL_XMAX_IS_MULTI : 0) |
+		((infomask & HEAP_XMAX_LOCK_ONLY) != 0 ? XLHL_XMAX_LOCK_ONLY : 0) |
+		((infomask & HEAP_XMAX_EXCL_LOCK) != 0 ? XLHL_XMAX_EXCL_LOCK : 0) |
+	/* note we ignore HEAP_XMAX_SHR_LOCK here */
+		((infomask & HEAP_XMAX_KEYSHR_LOCK) != 0 ? XLHL_XMAX_KEYSHR_LOCK : 0) |
+		((infomask2 & HEAP_KEYS_UPDATED) != 0 ?
+		 XLHL_KEYS_UPDATED : 0);
+}
+
+/*
+ * Given two versions of the same t_infomask for a tuple, compare them and
+ * return whether the relevant status for a tuple Xmax has changed.  This is
+ * used after a buffer lock has been released and reacquired: we want to ensure
+ * that the tuple state continues to be the same it was when we previously
+ * examined it.
+ *
+ * Note the Xmax field itself must be compared separately.
+ */
+static inline bool
+xmax_infomask_changed(uint16 new_infomask, uint16 old_infomask)
+{
+	const uint16 interesting =
+	HEAP_XMAX_IS_MULTI | HEAP_XMAX_LOCK_ONLY | HEAP_LOCK_MASK;
+
+	if ((new_infomask & interesting) != (old_infomask & interesting))
+		return true;
+
+	return false;
+}
+
+/*
+ *	heap_delete - delete a tuple
+ *
+ * See table_tuple_delete() for an explanation of the parameters, except that
+ * this routine directly takes a tuple rather than a slot.
+ *
+ * In the failure cases, the routine fills *tmfd with the tuple's t_ctid,
+ * t_xmax (resolving a possible MultiXact, if necessary), and t_cmax (the last
+ * only for TM_SelfModified, since we cannot obtain cmax from a combo CID
+ * generated by another transaction).
+ */
+TM_Result
+heap_delete(Relation relation, ItemPointer tid,
+			CommandId cid, Snapshot crosscheck, bool wait,
+			TM_FailureData *tmfd, bool changingPart)
+{
+	TM_Result	result;
+	TransactionId xid = GetCurrentTransactionId();
+	ItemId		lp;
+	HeapTupleData tp;
+	Page		page;
+	BlockNumber block;
+	Buffer		buffer;
+	Buffer		vmbuffer = InvalidBuffer;
+	TransactionId new_xmax;
+	uint16		new_infomask,
+				new_infomask2;
+	bool		have_tuple_lock = false;
+	bool		iscombo;
+	bool		all_visible_cleared = false;
+	HeapTuple	old_key_tuple = NULL;	/* replica identity of the tuple */
+	bool		old_key_copied = false;
+
+	Assert(ItemPointerIsValid(tid));
+
+	/*
+	 * Forbid this during a parallel operation, lest it allocate a combo CID.
+	 * Other workers might need that combo CID for visibility checks, and we
+	 * have no provision for broadcasting it to them.
+	 */
+	if (IsInParallelMode())
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_TRANSACTION_STATE),
+				 errmsg("cannot delete tuples during a parallel operation")));
+
+	block = ItemPointerGetBlockNumber(tid);
+	buffer = ReadBuffer(relation, block);
+	page = BufferGetPage(buffer);
+
+	/*
+	 * Before locking the buffer, pin the visibility map page if it appears to
+	 * be necessary.  Since we haven't got the lock yet, someone else might be
+	 * in the middle of changing this, so we'll need to recheck after we have
+	 * the lock.
+	 */
+	if (PageIsAllVisible(page))
+		visibilitymap_pin(relation, block, &vmbuffer);
+
+	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
+	/*
+	 * If we didn't pin the visibility map page and the page has become all
+	 * visible while we were busy locking the buffer, we'll have to unlock and
+	 * re-lock, to avoid holding the buffer lock across an I/O.  That's a bit
+	 * unfortunate, but hopefully shouldn't happen often.
+	 */
+	if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
+	{
+		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+		visibilitymap_pin(relation, block, &vmbuffer);
+		LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+	}
+
+	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
+	Assert(ItemIdIsNormal(lp));
+
+	tp.t_tableOid = RelationGetRelid(relation);
+	tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
+	tp.t_len = ItemIdGetLength(lp);
+	tp.t_self = *tid;
+
+l1:
+	result = HeapTupleSatisfiesUpdate(&tp, cid, buffer);
+
+	if (result == TM_Invisible)
+	{
+		UnlockReleaseBuffer(buffer);
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("attempted to delete invisible tuple")));
+	}
+	else if (result == TM_BeingModified && wait)
+	{
+		TransactionId xwait;
+		uint16		infomask;
+
+		/* must copy state data before unlocking buffer */
+		xwait = HeapTupleHeaderGetRawXmax(tp.t_data);
+		infomask = tp.t_data->t_infomask;
+
+		/*
+		 * Sleep until concurrent transaction ends -- except when there's a
+		 * single locker and it's our own transaction.  Note we don't care
+		 * which lock mode the locker has, because we need the strongest one.
+		 *
+		 * Before sleeping, we need to acquire tuple lock to establish our
+		 * priority for the tuple (see heap_lock_tuple).  LockTuple will
+		 * release us when we are next-in-line for the tuple.
+		 *
+		 * If we are forced to "start over" below, we keep the tuple lock;
+		 * this arranges that we stay at the head of the line while rechecking
+		 * tuple state.
+		 */
+		if (infomask & HEAP_XMAX_IS_MULTI)
+		{
+			bool		current_is_member = false;
+
+			if (DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
+										LockTupleExclusive, &current_is_member))
+			{
+				LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+
+				/*
+				 * Acquire the lock, if necessary (but skip it when we're
+				 * requesting a lock and already have one; avoids deadlock).
+				 */
+				if (!current_is_member)
+					heap_acquire_tuplock(relation, &(tp.t_self), LockTupleExclusive,
+										 LockWaitBlock, &have_tuple_lock);
+
+				/* wait for multixact */
+				MultiXactIdWait((MultiXactId) xwait, MultiXactStatusUpdate, infomask,
+								relation, &(tp.t_self), XLTW_Delete,
+								NULL);
+				LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
+				/*
+				 * If xwait had just locked the tuple then some other xact
+				 * could update this tuple before we get to this point.  Check
+				 * for xmax change, and start over if so.
+				 */
+				if (xmax_infomask_changed(tp.t_data->t_infomask, infomask) ||
+					!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tp.t_data),
+										 xwait))
+					goto l1;
+			}
+
+			/*
+			 * You might think the multixact is necessarily done here, but not
+			 * so: it could have surviving members, namely our own xact or
+			 * other subxacts of this backend.  It is legal for us to delete
+			 * the tuple in either case, however (the latter case is
+			 * essentially a situation of upgrading our former shared lock to
+			 * exclusive).  We don't bother changing the on-disk hint bits
+			 * since we are about to overwrite the xmax altogether.
+			 */
+		}
+		else if (!TransactionIdIsCurrentTransactionId(xwait))
+		{
+			/*
+			 * Wait for regular transaction to end; but first, acquire tuple
+			 * lock.
+			 */
+			LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+			heap_acquire_tuplock(relation, &(tp.t_self), LockTupleExclusive,
+								 LockWaitBlock, &have_tuple_lock);
+			XactLockTableWait(xwait, relation, &(tp.t_self), XLTW_Delete);
+			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
+			/*
+			 * xwait is done, but if xwait had just locked the tuple then some
+			 * other xact could update this tuple before we get to this point.
+			 * Check for xmax change, and start over if so.
+			 */
+			if (xmax_infomask_changed(tp.t_data->t_infomask, infomask) ||
+				!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tp.t_data),
+									 xwait))
+				goto l1;
+
+			/* Otherwise check if it committed or aborted */
+			UpdateXmaxHintBits(tp.t_data, buffer, xwait);
+		}
+
+		/*
+		 * We may overwrite if previous xmax aborted, or if it committed but
+		 * only locked the tuple without updating it.
+		 */
+		if ((tp.t_data->t_infomask & HEAP_XMAX_INVALID) ||
+			HEAP_XMAX_IS_LOCKED_ONLY(tp.t_data->t_infomask) ||
+			HeapTupleHeaderIsOnlyLocked(tp.t_data))
+			result = TM_Ok;
+		else if (!ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid))
+			result = TM_Updated;
+		else
+			result = TM_Deleted;
+	}
+
+	if (crosscheck != InvalidSnapshot && result == TM_Ok)
+	{
+		/* Perform additional check for transaction-snapshot mode RI updates */
+		if (!HeapTupleSatisfiesVisibility(&tp, crosscheck, buffer))
+			result = TM_Updated;
+	}
+
+	if (result != TM_Ok)
+	{
+		Assert(result == TM_SelfModified ||
+			   result == TM_Updated ||
+			   result == TM_Deleted ||
+			   result == TM_BeingModified);
+		Assert(!(tp.t_data->t_infomask & HEAP_XMAX_INVALID));
+		Assert(result != TM_Updated ||
+			   !ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid));
+		tmfd->ctid = tp.t_data->t_ctid;
+		tmfd->xmax = HeapTupleHeaderGetUpdateXid(tp.t_data);
+		if (result == TM_SelfModified)
+			tmfd->cmax = HeapTupleHeaderGetCmax(tp.t_data);
+		else
+			tmfd->cmax = InvalidCommandId;
+		UnlockReleaseBuffer(buffer);
+		if (have_tuple_lock)
+			UnlockTupleTuplock(relation, &(tp.t_self), LockTupleExclusive);
+		if (vmbuffer != InvalidBuffer)
+			ReleaseBuffer(vmbuffer);
+		return result;
+	}
+
+	/*
+	 * We're about to do the actual delete -- check for conflict first, to
+	 * avoid possibly having to roll back work we've just done.
+	 *
+	 * This is safe without a recheck as long as there is no possibility of
+	 * another process scanning the page between this check and the delete
+	 * being visible to the scan (i.e., an exclusive buffer content lock is
+	 * continuously held from this point until the tuple delete is visible).
+	 */
+	CheckForSerializableConflictIn(relation, tid, BufferGetBlockNumber(buffer));
+
+	/* replace cid with a combo CID if necessary */
+	HeapTupleHeaderAdjustCmax(tp.t_data, &cid, &iscombo);
+
+	/*
+	 * Compute replica identity tuple before entering the critical section so
+	 * we don't PANIC upon a memory allocation failure.
+	 */
+	old_key_tuple = ExtractReplicaIdentity(relation, &tp, true, &old_key_copied);
+
+	/*
+	 * If this is the first possibly-multixact-able operation in the current
+	 * transaction, set my per-backend OldestMemberMXactId setting. We can be
+	 * certain that the transaction will never become a member of any older
+	 * MultiXactIds than that.  (We have to do this even if we end up just
+	 * using our own TransactionId below, since some other backend could
+	 * incorporate our XID into a MultiXact immediately afterwards.)
+	 */
+	MultiXactIdSetOldestMember();
+
+	compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(tp.t_data),
+							  tp.t_data->t_infomask, tp.t_data->t_infomask2,
+							  xid, LockTupleExclusive, true,
+							  &new_xmax, &new_infomask, &new_infomask2);
+
+	START_CRIT_SECTION();
+
+	/*
+	 * If this transaction commits, the tuple will become DEAD sooner or
+	 * later.  Set flag that this page is a candidate for pruning once our xid
+	 * falls below the OldestXmin horizon.  If the transaction finally aborts,
+	 * the subsequent page pruning will be a no-op and the hint will be
+	 * cleared.
+	 */
+	PageSetPrunable(page, xid);
+
+	if (PageIsAllVisible(page))
+	{
+		all_visible_cleared = true;
+		PageClearAllVisible(page);
+		visibilitymap_clear(relation, BufferGetBlockNumber(buffer),
+							vmbuffer, VISIBILITYMAP_VALID_BITS);
+	}
+
+	/* store transaction information of xact deleting the tuple */
+	tp.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
+	tp.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+	tp.t_data->t_infomask |= new_infomask;
+	tp.t_data->t_infomask2 |= new_infomask2;
+	HeapTupleHeaderClearHotUpdated(tp.t_data);
+	HeapTupleHeaderSetXmax(tp.t_data, new_xmax);
+	HeapTupleHeaderSetCmax(tp.t_data, cid, iscombo);
+	/* Make sure there is no forward chain link in t_ctid */
+	tp.t_data->t_ctid = tp.t_self;
+
+	/* Signal that this is actually a move into another partition */
+	if (changingPart)
+		HeapTupleHeaderSetMovedPartitions(tp.t_data);
+
+	MarkBufferDirty(buffer);
+
+	/*
+	 * XLOG stuff
+	 *
+	 * NB: heap_abort_speculative() uses the same xlog record and replay
+	 * routines.
+	 */
+	if (RelationNeedsWAL(relation))
+	{
+		xl_heap_delete xlrec;
+		xl_heap_header xlhdr;
+		XLogRecPtr	recptr;
+
+		/*
+		 * For logical decode we need combo CIDs to properly decode the
+		 * catalog
+		 */
+		if (RelationIsAccessibleInLogicalDecoding(relation))
+			log_heap_new_cid(relation, &tp);
+
+		xlrec.flags = 0;
+		if (all_visible_cleared)
+			xlrec.flags |= XLH_DELETE_ALL_VISIBLE_CLEARED;
+		if (changingPart)
+			xlrec.flags |= XLH_DELETE_IS_PARTITION_MOVE;
+		xlrec.infobits_set = compute_infobits(tp.t_data->t_infomask,
+											  tp.t_data->t_infomask2);
+		xlrec.offnum = ItemPointerGetOffsetNumber(&tp.t_self);
+		xlrec.xmax = new_xmax;
+
+		if (old_key_tuple != NULL)
+		{
+			if (relation->rd_rel->relreplident == REPLICA_IDENTITY_FULL)
+				xlrec.flags |= XLH_DELETE_CONTAINS_OLD_TUPLE;
+			else
+				xlrec.flags |= XLH_DELETE_CONTAINS_OLD_KEY;
+		}
+
+		XLogBeginInsert();
+		XLogRegisterData((char *) &xlrec, SizeOfHeapDelete);
+
+		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
+
+		/*
+		 * Log replica identity of the deleted tuple if there is one
+		 */
+		if (old_key_tuple != NULL)
+		{
+			xlhdr.t_infomask2 = old_key_tuple->t_data->t_infomask2;
+			xlhdr.t_infomask = old_key_tuple->t_data->t_infomask;
+			xlhdr.t_hoff = old_key_tuple->t_data->t_hoff;
+
+			XLogRegisterData((char *) &xlhdr, SizeOfHeapHeader);
+			XLogRegisterData((char *) old_key_tuple->t_data
+							 + SizeofHeapTupleHeader,
+							 old_key_tuple->t_len
+							 - SizeofHeapTupleHeader);
+		}
+
+		/* filtering by origin on a row level is much more efficient */
+		XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
+
+		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_DELETE);
+
+		PageSetLSN(page, recptr);
+	}
+
+	END_CRIT_SECTION();
+
+	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+
+	if (vmbuffer != InvalidBuffer)
+		ReleaseBuffer(vmbuffer);
+
+	/*
+	 * If the tuple has toasted out-of-line attributes, we need to delete
+	 * those items too.  We have to do this before releasing the buffer
+	 * because we need to look at the contents of the tuple, but it's OK to
+	 * release the content lock on the buffer first.
+	 */
+	if (relation->rd_rel->relkind != RELKIND_RELATION &&
+		relation->rd_rel->relkind != RELKIND_MATVIEW)
+	{
+		/* toast table entries should never be recursively toasted */
+		Assert(!HeapTupleHasExternal(&tp));
+	}
+	else if (HeapTupleHasExternal(&tp))
+		heap_toast_delete(relation, &tp, false);
+
+	/*
+	 * Mark tuple for invalidation from system caches at next command
+	 * boundary. We have to do this before releasing the buffer because we
+	 * need to look at the contents of the tuple.
+	 */
+	CacheInvalidateHeapTuple(relation, &tp, NULL);
+
+	/* Now we can release the buffer */
+	ReleaseBuffer(buffer);
+
+	/*
+	 * Release the lmgr tuple lock, if we had it.
+	 */
+	if (have_tuple_lock)
+		UnlockTupleTuplock(relation, &(tp.t_self), LockTupleExclusive);
+
+	pgstat_count_heap_delete(relation);
+
+	if (old_key_tuple != NULL && old_key_copied)
+		heap_freetuple(old_key_tuple);
+
+	return TM_Ok;
+}
+
+/*
+ *	simple_heap_delete - delete a tuple
+ *
+ * This routine may be used to delete a tuple when concurrent updates of
+ * the target tuple are not expected (for example, because we have a lock
+ * on the relation associated with the tuple).  Any failure is reported
+ * via ereport().
+ */
+void
+simple_heap_delete(Relation relation, ItemPointer tid)
+{
+	TM_Result	result;
+	TM_FailureData tmfd;
+
+	result = heap_delete(relation, tid,
+						 GetCurrentCommandId(true), InvalidSnapshot,
+						 true /* wait for commit */ ,
+						 &tmfd, false /* changingPart */ );
+	switch (result)
+	{
+		case TM_SelfModified:
+			/* Tuple was already updated in current command? */
+			elog(ERROR, "tuple already updated by self");
+			break;
+
+		case TM_Ok:
+			/* done successfully */
+			break;
+
+		case TM_Updated:
+			elog(ERROR, "tuple concurrently updated");
+			break;
+
+		case TM_Deleted:
+			elog(ERROR, "tuple concurrently deleted");
+			break;
+
+		default:
+			elog(ERROR, "unrecognized heap_delete status: %u", result);
+			break;
+	}
+}
+
+/*
+ *	heap_update - replace a tuple
+ *
+ * See table_tuple_update() for an explanation of the parameters, except that
+ * this routine directly takes a tuple rather than a slot.
+ *
+ * In the failure cases, the routine fills *tmfd with the tuple's t_ctid,
+ * t_xmax (resolving a possible MultiXact, if necessary), and t_cmax (the last
+ * only for TM_SelfModified, since we cannot obtain cmax from a combo CID
+ * generated by another transaction).
+ */
+TM_Result
+heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
+			CommandId cid, Snapshot crosscheck, bool wait,
+			TM_FailureData *tmfd, LockTupleMode *lockmode)
+{
+	TM_Result	result;
+	TransactionId xid = GetCurrentTransactionId();
+	Bitmapset  *hot_attrs;
+	Bitmapset  *key_attrs;
+	Bitmapset  *id_attrs;
+	Bitmapset  *interesting_attrs;
+	Bitmapset  *modified_attrs;
+	ItemId		lp;
+	HeapTupleData oldtup;
+	HeapTuple	heaptup;
+	HeapTuple	old_key_tuple = NULL;
+	bool		old_key_copied = false;
+	Page		page;
+	BlockNumber block;
+	MultiXactStatus mxact_status;
+	Buffer		buffer,
+				newbuf,
+				vmbuffer = InvalidBuffer,
+				vmbuffer_new = InvalidBuffer;
+	bool		need_toast;
+	Size		newtupsize,
+				pagefree;
+	bool		have_tuple_lock = false;
+	bool		iscombo;
+	bool		use_hot_update = false;
+	bool		hot_attrs_checked = false;
+	bool		key_intact;
+	bool		all_visible_cleared = false;
+	bool		all_visible_cleared_new = false;
+	bool		checked_lockers;
+	bool		locker_remains;
+	bool		id_has_external = false;
+	TransactionId xmax_new_tuple,
+				xmax_old_tuple;
+	uint16		infomask_old_tuple,
+				infomask2_old_tuple,
+				infomask_new_tuple,
+				infomask2_new_tuple;
+
+	Assert(ItemPointerIsValid(otid));
+
+	/* Cheap, simplistic check that the tuple matches the rel's rowtype. */
+	Assert(HeapTupleHeaderGetNatts(newtup->t_data) <=
+		   RelationGetNumberOfAttributes(relation));
+
+	/*
+	 * Forbid this during a parallel operation, lest it allocate a combo CID.
+	 * Other workers might need that combo CID for visibility checks, and we
+	 * have no provision for broadcasting it to them.
+	 */
+	if (IsInParallelMode())
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_TRANSACTION_STATE),
+				 errmsg("cannot update tuples during a parallel operation")));
+
+	/*
+	 * Fetch the list of attributes to be checked for various operations.
+	 *
+	 * For HOT considerations, this is wasted effort if we fail to update or
+	 * have to put the new tuple on a different page.  But we must compute the
+	 * list before obtaining buffer lock --- in the worst case, if we are
+	 * doing an update on one of the relevant system catalogs, we could
+	 * deadlock if we try to fetch the list later.  In any case, the relcache
+	 * caches the data so this is usually pretty cheap.
+	 *
+	 * We also need columns used by the replica identity and columns that are
+	 * considered the "key" of rows in the table.
+	 *
+	 * Note that we get copies of each bitmap, so we need not worry about
+	 * relcache flush happening midway through.
+	 */
+	hot_attrs = RelationGetIndexAttrBitmap(relation, INDEX_ATTR_BITMAP_ALL);
+	key_attrs = RelationGetIndexAttrBitmap(relation, INDEX_ATTR_BITMAP_KEY);
+	id_attrs = RelationGetIndexAttrBitmap(relation,
+										  INDEX_ATTR_BITMAP_IDENTITY_KEY);
+
+
+	block = ItemPointerGetBlockNumber(otid);
+	buffer = ReadBuffer(relation, block);
+	page = BufferGetPage(buffer);
+
+	interesting_attrs = NULL;
+
+	/*
+	 * If the page is already full, there is hardly any chance of doing a HOT
+	 * update on this page. It might be wasteful effort to look for index
+	 * column updates only to later reject HOT updates for lack of space in
+	 * the same page. So we be conservative and only fetch hot_attrs if the
+	 * page is not already full. Since we are already holding a pin on the
+	 * buffer, there is no chance that the buffer can get cleaned up
+	 * concurrently and even if that was possible, in the worst case we lose a
+	 * chance to do a HOT update.
+	 */
+	if (!PageIsFull(page))
+	{
+		interesting_attrs = bms_add_members(interesting_attrs, hot_attrs);
+		hot_attrs_checked = true;
+	}
+	interesting_attrs = bms_add_members(interesting_attrs, key_attrs);
+	interesting_attrs = bms_add_members(interesting_attrs, id_attrs);
+
+	/*
+	 * Before locking the buffer, pin the visibility map page if it appears to
+	 * be necessary.  Since we haven't got the lock yet, someone else might be
+	 * in the middle of changing this, so we'll need to recheck after we have
+	 * the lock.
+	 */
+	if (PageIsAllVisible(page))
+		visibilitymap_pin(relation, block, &vmbuffer);
+
+	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
+	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(otid));
+	Assert(ItemIdIsNormal(lp));
+
+	/*
+	 * Fill in enough data in oldtup for HeapDetermineColumnsInfo to work
+	 * properly.
+	 */
+	oldtup.t_tableOid = RelationGetRelid(relation);
+	oldtup.t_data = (HeapTupleHeader) PageGetItem(page, lp);
+	oldtup.t_len = ItemIdGetLength(lp);
+	oldtup.t_self = *otid;
+
+	/* the new tuple is ready, except for this: */
+	newtup->t_tableOid = RelationGetRelid(relation);
+
+	/*
+	 * Determine columns modified by the update.  Additionally, identify
+	 * whether any of the unmodified replica identity key attributes in the
+	 * old tuple is externally stored or not.  This is required because for
+	 * such attributes the flattened value won't be WAL logged as part of the
+	 * new tuple so we must include it as part of the old_key_tuple.  See
+	 * ExtractReplicaIdentity.
+	 */
+	modified_attrs = HeapDetermineColumnsInfo(relation, interesting_attrs,
+											  id_attrs, &oldtup,
+											  newtup, &id_has_external);
+
+	/*
+	 * If we're not updating any "key" column, we can grab a weaker lock type.
+	 * This allows for more concurrency when we are running simultaneously
+	 * with foreign key checks.
+	 *
+	 * Note that if a column gets detoasted while executing the update, but
+	 * the value ends up being the same, this test will fail and we will use
+	 * the stronger lock.  This is acceptable; the important case to optimize
+	 * is updates that don't manipulate key columns, not those that
+	 * serendipitously arrive at the same key values.
+	 */
+	if (!bms_overlap(modified_attrs, key_attrs))
+	{
+		*lockmode = LockTupleNoKeyExclusive;
+		mxact_status = MultiXactStatusNoKeyUpdate;
+		key_intact = true;
+
+		/*
+		 * If this is the first possibly-multixact-able operation in the
+		 * current transaction, set my per-backend OldestMemberMXactId
+		 * setting. We can be certain that the transaction will never become a
+		 * member of any older MultiXactIds than that.  (We have to do this
+		 * even if we end up just using our own TransactionId below, since
+		 * some other backend could incorporate our XID into a MultiXact
+		 * immediately afterwards.)
+		 */
+		MultiXactIdSetOldestMember();
+	}
+	else
+	{
+		*lockmode = LockTupleExclusive;
+		mxact_status = MultiXactStatusUpdate;
+		key_intact = false;
+	}
+
+	/*
+	 * Note: beyond this point, use oldtup not otid to refer to old tuple.
+	 * otid may very well point at newtup->t_self, which we will overwrite
+	 * with the new tuple's location, so there's great risk of confusion if we
+	 * use otid anymore.
+	 */
+
+l2:
+	checked_lockers = false;
+	locker_remains = false;
+	result = HeapTupleSatisfiesUpdate(&oldtup, cid, buffer);
+
+	/* see below about the "no wait" case */
+	Assert(result != TM_BeingModified || wait);
+
+	if (result == TM_Invisible)
+	{
+		UnlockReleaseBuffer(buffer);
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("attempted to update invisible tuple")));
+	}
+	else if (result == TM_BeingModified && wait)
+	{
+		TransactionId xwait;
+		uint16		infomask;
+		bool		can_continue = false;
+
+		/*
+		 * XXX note that we don't consider the "no wait" case here.  This
+		 * isn't a problem currently because no caller uses that case, but it
+		 * should be fixed if such a caller is introduced.  It wasn't a
+		 * problem previously because this code would always wait, but now
+		 * that some tuple locks do not conflict with one of the lock modes we
+		 * use, it is possible that this case is interesting to handle
+		 * specially.
+		 *
+		 * This may cause failures with third-party code that calls
+		 * heap_update directly.
+		 */
+
+		/* must copy state data before unlocking buffer */
+		xwait = HeapTupleHeaderGetRawXmax(oldtup.t_data);
+		infomask = oldtup.t_data->t_infomask;
+
+		/*
+		 * Now we have to do something about the existing locker.  If it's a
+		 * multi, sleep on it; we might be awakened before it is completely
+		 * gone (or even not sleep at all in some cases); we need to preserve
+		 * it as locker, unless it is gone completely.
+		 *
+		 * If it's not a multi, we need to check for sleeping conditions
+		 * before actually going to sleep.  If the update doesn't conflict
+		 * with the locks, we just continue without sleeping (but making sure
+		 * it is preserved).
+		 *
+		 * Before sleeping, we need to acquire tuple lock to establish our
+		 * priority for the tuple (see heap_lock_tuple).  LockTuple will
+		 * release us when we are next-in-line for the tuple.  Note we must
+		 * not acquire the tuple lock until we're sure we're going to sleep;
+		 * otherwise we're open for race conditions with other transactions
+		 * holding the tuple lock which sleep on us.
+		 *
+		 * If we are forced to "start over" below, we keep the tuple lock;
+		 * this arranges that we stay at the head of the line while rechecking
+		 * tuple state.
+		 */
+		if (infomask & HEAP_XMAX_IS_MULTI)
+		{
+			TransactionId update_xact;
+			int			remain;
+			bool		current_is_member = false;
+
+			if (DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
+										*lockmode, &current_is_member))
+			{
+				LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+
+				/*
+				 * Acquire the lock, if necessary (but skip it when we're
+				 * requesting a lock and already have one; avoids deadlock).
+				 */
+				if (!current_is_member)
+					heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
+										 LockWaitBlock, &have_tuple_lock);
+
+				/* wait for multixact */
+				MultiXactIdWait((MultiXactId) xwait, mxact_status, infomask,
+								relation, &oldtup.t_self, XLTW_Update,
+								&remain);
+				checked_lockers = true;
+				locker_remains = remain != 0;
+				LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
+				/*
+				 * If xwait had just locked the tuple then some other xact
+				 * could update this tuple before we get to this point.  Check
+				 * for xmax change, and start over if so.
+				 */
+				if (xmax_infomask_changed(oldtup.t_data->t_infomask,
+										  infomask) ||
+					!TransactionIdEquals(HeapTupleHeaderGetRawXmax(oldtup.t_data),
+										 xwait))
+					goto l2;
+			}
+
+			/*
+			 * Note that the multixact may not be done by now.  It could have
+			 * surviving members; our own xact or other subxacts of this
+			 * backend, and also any other concurrent transaction that locked
+			 * the tuple with LockTupleKeyShare if we only got
+			 * LockTupleNoKeyExclusive.  If this is the case, we have to be
+			 * careful to mark the updated tuple with the surviving members in
+			 * Xmax.
+			 *
+			 * Note that there could have been another update in the
+			 * MultiXact. In that case, we need to check whether it committed
+			 * or aborted. If it aborted we are safe to update it again;
+			 * otherwise there is an update conflict, and we have to return
+			 * TableTuple{Deleted, Updated} below.
+			 *
+			 * In the LockTupleExclusive case, we still need to preserve the
+			 * surviving members: those would include the tuple locks we had
+			 * before this one, which are important to keep in case this
+			 * subxact aborts.
+			 */
+			if (!HEAP_XMAX_IS_LOCKED_ONLY(oldtup.t_data->t_infomask))
+				update_xact = HeapTupleGetUpdateXid(oldtup.t_data);
+			else
+				update_xact = InvalidTransactionId;
+
+			/*
+			 * There was no UPDATE in the MultiXact; or it aborted. No
+			 * TransactionIdIsInProgress() call needed here, since we called
+			 * MultiXactIdWait() above.
+			 */
+			if (!TransactionIdIsValid(update_xact) ||
+				TransactionIdDidAbort(update_xact))
+				can_continue = true;
+		}
+		else if (TransactionIdIsCurrentTransactionId(xwait))
+		{
+			/*
+			 * The only locker is ourselves; we can avoid grabbing the tuple
+			 * lock here, but must preserve our locking information.
+			 */
+			checked_lockers = true;
+			locker_remains = true;
+			can_continue = true;
+		}
+		else if (HEAP_XMAX_IS_KEYSHR_LOCKED(infomask) && key_intact)
+		{
+			/*
+			 * If it's just a key-share locker, and we're not changing the key
+			 * columns, we don't need to wait for it to end; but we need to
+			 * preserve it as locker.
+			 */
+			checked_lockers = true;
+			locker_remains = true;
+			can_continue = true;
+		}
+		else
+		{
+			/*
+			 * Wait for regular transaction to end; but first, acquire tuple
+			 * lock.
+			 */
+			LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+			heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
+								 LockWaitBlock, &have_tuple_lock);
+			XactLockTableWait(xwait, relation, &oldtup.t_self,
+							  XLTW_Update);
+			checked_lockers = true;
+			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
+			/*
+			 * xwait is done, but if xwait had just locked the tuple then some
+			 * other xact could update this tuple before we get to this point.
+			 * Check for xmax change, and start over if so.
+			 */
+			if (xmax_infomask_changed(oldtup.t_data->t_infomask, infomask) ||
+				!TransactionIdEquals(xwait,
+									 HeapTupleHeaderGetRawXmax(oldtup.t_data)))
+				goto l2;
+
+			/* Otherwise check if it committed or aborted */
+			UpdateXmaxHintBits(oldtup.t_data, buffer, xwait);
+			if (oldtup.t_data->t_infomask & HEAP_XMAX_INVALID)
+				can_continue = true;
+		}
+
+		if (can_continue)
+			result = TM_Ok;
+		else if (!ItemPointerEquals(&oldtup.t_self, &oldtup.t_data->t_ctid))
+			result = TM_Updated;
+		else
+			result = TM_Deleted;
+	}
+
+	if (crosscheck != InvalidSnapshot && result == TM_Ok)
+	{
+		/* Perform additional check for transaction-snapshot mode RI updates */
+		if (!HeapTupleSatisfiesVisibility(&oldtup, crosscheck, buffer))
+		{
+			result = TM_Updated;
+			Assert(!ItemPointerEquals(&oldtup.t_self, &oldtup.t_data->t_ctid));
+		}
+	}
+
+	if (result != TM_Ok)
+	{
+		Assert(result == TM_SelfModified ||
+			   result == TM_Updated ||
+			   result == TM_Deleted ||
+			   result == TM_BeingModified);
+		Assert(!(oldtup.t_data->t_infomask & HEAP_XMAX_INVALID));
+		Assert(result != TM_Updated ||
+			   !ItemPointerEquals(&oldtup.t_self, &oldtup.t_data->t_ctid));
+		tmfd->ctid = oldtup.t_data->t_ctid;
+		tmfd->xmax = HeapTupleHeaderGetUpdateXid(oldtup.t_data);
+		if (result == TM_SelfModified)
+			tmfd->cmax = HeapTupleHeaderGetCmax(oldtup.t_data);
+		else
+			tmfd->cmax = InvalidCommandId;
+		UnlockReleaseBuffer(buffer);
+		if (have_tuple_lock)
+			UnlockTupleTuplock(relation, &(oldtup.t_self), *lockmode);
+		if (vmbuffer != InvalidBuffer)
+			ReleaseBuffer(vmbuffer);
+		bms_free(hot_attrs);
+		bms_free(key_attrs);
+		bms_free(id_attrs);
+		bms_free(modified_attrs);
+		bms_free(interesting_attrs);
+		return result;
+	}
+
+	/*
+	 * If we didn't pin the visibility map page and the page has become all
+	 * visible while we were busy locking the buffer, or during some
+	 * subsequent window during which we had it unlocked, we'll have to unlock
+	 * and re-lock, to avoid holding the buffer lock across an I/O.  That's a
+	 * bit unfortunate, especially since we'll now have to recheck whether the
+	 * tuple has been locked or updated under us, but hopefully it won't
+	 * happen very often.
+	 */
+	if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
+	{
+		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+		visibilitymap_pin(relation, block, &vmbuffer);
+		LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+		goto l2;
+	}
+
+	/* Fill in transaction status data */
+
+	/*
+	 * If the tuple we're updating is locked, we need to preserve the locking
+	 * info in the old tuple's Xmax.  Prepare a new Xmax value for this.
+	 */
+	compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(oldtup.t_data),
+							  oldtup.t_data->t_infomask,
+							  oldtup.t_data->t_infomask2,
+							  xid, *lockmode, true,
+							  &xmax_old_tuple, &infomask_old_tuple,
+							  &infomask2_old_tuple);
+
+	/*
+	 * And also prepare an Xmax value for the new copy of the tuple.  If there
+	 * was no xmax previously, or there was one but all lockers are now gone,
+	 * then use InvalidXid; otherwise, get the xmax from the old tuple.  (In
+	 * rare cases that might also be InvalidXid and yet not have the
+	 * HEAP_XMAX_INVALID bit set; that's fine.)
+	 */
+	if ((oldtup.t_data->t_infomask & HEAP_XMAX_INVALID) ||
+		HEAP_LOCKED_UPGRADED(oldtup.t_data->t_infomask) ||
+		(checked_lockers && !locker_remains))
+		xmax_new_tuple = InvalidTransactionId;
+	else
+		xmax_new_tuple = HeapTupleHeaderGetRawXmax(oldtup.t_data);
+
+	if (!TransactionIdIsValid(xmax_new_tuple))
+	{
+		infomask_new_tuple = HEAP_XMAX_INVALID;
+		infomask2_new_tuple = 0;
+	}
+	else
+	{
+		/*
+		 * If we found a valid Xmax for the new tuple, then the infomask bits
+		 * to use on the new tuple depend on what was there on the old one.
+		 * Note that since we're doing an update, the only possibility is that
+		 * the lockers had FOR KEY SHARE lock.
+		 */
+		if (oldtup.t_data->t_infomask & HEAP_XMAX_IS_MULTI)
+		{
+			GetMultiXactIdHintBits(xmax_new_tuple, &infomask_new_tuple,
+								   &infomask2_new_tuple);
+		}
+		else
+		{
+			infomask_new_tuple = HEAP_XMAX_KEYSHR_LOCK | HEAP_XMAX_LOCK_ONLY;
+			infomask2_new_tuple = 0;
+		}
+	}
+
+	/*
+	 * Prepare the new tuple with the appropriate initial values of Xmin and
+	 * Xmax, as well as initial infomask bits as computed above.
+	 */
+	newtup->t_data->t_infomask &= ~(HEAP_XACT_MASK);
+	newtup->t_data->t_infomask2 &= ~(HEAP2_XACT_MASK);
+	HeapTupleHeaderSetXmin(newtup->t_data, xid);
+	HeapTupleHeaderSetCmin(newtup->t_data, cid);
+	newtup->t_data->t_infomask |= HEAP_UPDATED | infomask_new_tuple;
+	newtup->t_data->t_infomask2 |= infomask2_new_tuple;
+	HeapTupleHeaderSetXmax(newtup->t_data, xmax_new_tuple);
+
+	/*
+	 * Replace cid with a combo CID if necessary.  Note that we already put
+	 * the plain cid into the new tuple.
+	 */
+	HeapTupleHeaderAdjustCmax(oldtup.t_data, &cid, &iscombo);
+
+	/*
+	 * If the toaster needs to be activated, OR if the new tuple will not fit
+	 * on the same page as the old, then we need to release the content lock
+	 * (but not the pin!) on the old tuple's buffer while we are off doing
+	 * TOAST and/or table-file-extension work.  We must mark the old tuple to
+	 * show that it's locked, else other processes may try to update it
+	 * themselves.
+	 *
+	 * We need to invoke the toaster if there are already any out-of-line
+	 * toasted values present, or if the new tuple is over-threshold.
+	 */
+	if (relation->rd_rel->relkind != RELKIND_RELATION &&
+		relation->rd_rel->relkind != RELKIND_MATVIEW)
+	{
+		/* toast table entries should never be recursively toasted */
+		Assert(!HeapTupleHasExternal(&oldtup));
+		Assert(!HeapTupleHasExternal(newtup));
+		need_toast = false;
+	}
+	else
+		need_toast = (HeapTupleHasExternal(&oldtup) ||
+					  HeapTupleHasExternal(newtup) ||
+					  newtup->t_len > TOAST_TUPLE_THRESHOLD);
+
+	pagefree = PageGetHeapFreeSpace(page);
+
+	newtupsize = MAXALIGN(newtup->t_len);
+
+	if (need_toast || newtupsize > pagefree)
+	{
+		TransactionId xmax_lock_old_tuple;
+		uint16		infomask_lock_old_tuple,
+					infomask2_lock_old_tuple;
+		bool		cleared_all_frozen = false;
+
+		/*
+		 * To prevent concurrent sessions from updating the tuple, we have to
+		 * temporarily mark it locked, while we release the page-level lock.
+		 *
+		 * To satisfy the rule that any xid potentially appearing in a buffer
+		 * written out to disk, we unfortunately have to WAL log this
+		 * temporary modification.  We can reuse xl_heap_lock for this
+		 * purpose.  If we crash/error before following through with the
+		 * actual update, xmax will be of an aborted transaction, allowing
+		 * other sessions to proceed.
+		 */
+
+		/*
+		 * Compute xmax / infomask appropriate for locking the tuple. This has
+		 * to be done separately from the combo that's going to be used for
+		 * updating, because the potentially created multixact would otherwise
+		 * be wrong.
+		 */
+		compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(oldtup.t_data),
+								  oldtup.t_data->t_infomask,
+								  oldtup.t_data->t_infomask2,
+								  xid, *lockmode, false,
+								  &xmax_lock_old_tuple, &infomask_lock_old_tuple,
+								  &infomask2_lock_old_tuple);
+
+		Assert(HEAP_XMAX_IS_LOCKED_ONLY(infomask_lock_old_tuple));
+
+		START_CRIT_SECTION();
+
+		/* Clear obsolete visibility flags ... */
+		oldtup.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
+		oldtup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+		HeapTupleClearHotUpdated(&oldtup);
+		/* ... and store info about transaction updating this tuple */
+		Assert(TransactionIdIsValid(xmax_lock_old_tuple));
+		HeapTupleHeaderSetXmax(oldtup.t_data, xmax_lock_old_tuple);
+		oldtup.t_data->t_infomask |= infomask_lock_old_tuple;
+		oldtup.t_data->t_infomask2 |= infomask2_lock_old_tuple;
+		HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
+
+		/* temporarily make it look not-updated, but locked */
+		oldtup.t_data->t_ctid = oldtup.t_self;
+
+		/*
+		 * Clear all-frozen bit on visibility map if needed. We could
+		 * immediately reset ALL_VISIBLE, but given that the WAL logging
+		 * overhead would be unchanged, that doesn't seem necessarily
+		 * worthwhile.
+		 */
+		if (PageIsAllVisible(page) &&
+			visibilitymap_clear(relation, block, vmbuffer,
+								VISIBILITYMAP_ALL_FROZEN))
+			cleared_all_frozen = true;
+
+		MarkBufferDirty(buffer);
+
+		if (RelationNeedsWAL(relation))
+		{
+			xl_heap_lock xlrec;
+			XLogRecPtr	recptr;
+
+			XLogBeginInsert();
+			XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
+
+			xlrec.offnum = ItemPointerGetOffsetNumber(&oldtup.t_self);
+			xlrec.locking_xid = xmax_lock_old_tuple;
+			xlrec.infobits_set = compute_infobits(oldtup.t_data->t_infomask,
+												  oldtup.t_data->t_infomask2);
+			xlrec.flags =
+				cleared_all_frozen ? XLH_LOCK_ALL_FROZEN_CLEARED : 0;
+			XLogRegisterData((char *) &xlrec, SizeOfHeapLock);
+			recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_LOCK);
+			PageSetLSN(page, recptr);
+		}
+
+		END_CRIT_SECTION();
+
+		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+
+		/*
+		 * Let the toaster do its thing, if needed.
+		 *
+		 * Note: below this point, heaptup is the data we actually intend to
+		 * store into the relation; newtup is the caller's original untoasted
+		 * data.
+		 */
+		if (need_toast)
+		{
+			/* Note we always use WAL and FSM during updates */
+			heaptup = heap_toast_insert_or_update(relation, newtup, &oldtup, 0);
+			newtupsize = MAXALIGN(heaptup->t_len);
+		}
+		else
+			heaptup = newtup;
+
+		/*
+		 * Now, do we need a new page for the tuple, or not?  This is a bit
+		 * tricky since someone else could have added tuples to the page while
+		 * we weren't looking.  We have to recheck the available space after
+		 * reacquiring the buffer lock.  But don't bother to do that if the
+		 * former amount of free space is still not enough; it's unlikely
+		 * there's more free now than before.
+		 *
+		 * What's more, if we need to get a new page, we will need to acquire
+		 * buffer locks on both old and new pages.  To avoid deadlock against
+		 * some other backend trying to get the same two locks in the other
+		 * order, we must be consistent about the order we get the locks in.
+		 * We use the rule "lock the lower-numbered page of the relation
+		 * first".  To implement this, we must do RelationGetBufferForTuple
+		 * while not holding the lock on the old page, and we must rely on it
+		 * to get the locks on both pages in the correct order.
+		 *
+		 * Another consideration is that we need visibility map page pin(s) if
+		 * we will have to clear the all-visible flag on either page.  If we
+		 * call RelationGetBufferForTuple, we rely on it to acquire any such
+		 * pins; but if we don't, we have to handle that here.  Hence we need
+		 * a loop.
+		 */
+		for (;;)
+		{
+			if (newtupsize > pagefree)
+			{
+				/* It doesn't fit, must use RelationGetBufferForTuple. */
+				newbuf = RelationGetBufferForTuple(relation, heaptup->t_len,
+												   buffer, 0, NULL,
+												   &vmbuffer_new, &vmbuffer);
+				/* We're all done. */
+				break;
+			}
+			/* Acquire VM page pin if needed and we don't have it. */
+			if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
+				visibilitymap_pin(relation, block, &vmbuffer);
+			/* Re-acquire the lock on the old tuple's page. */
+			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+			/* Re-check using the up-to-date free space */
+			pagefree = PageGetHeapFreeSpace(page);
+			if (newtupsize > pagefree ||
+				(vmbuffer == InvalidBuffer && PageIsAllVisible(page)))
+			{
+				/*
+				 * Rats, it doesn't fit anymore, or somebody just now set the
+				 * all-visible flag.  We must now unlock and loop to avoid
+				 * deadlock.  Fortunately, this path should seldom be taken.
+				 */
+				LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+			}
+			else
+			{
+				/* We're all done. */
+				newbuf = buffer;
+				break;
+			}
+		}
+	}
+	else
+	{
+		/* No TOAST work needed, and it'll fit on same page */
+		newbuf = buffer;
+		heaptup = newtup;
+	}
+
+	/*
+	 * We're about to do the actual update -- check for conflict first, to
+	 * avoid possibly having to roll back work we've just done.
+	 *
+	 * This is safe without a recheck as long as there is no possibility of
+	 * another process scanning the pages between this check and the update
+	 * being visible to the scan (i.e., exclusive buffer content lock(s) are
+	 * continuously held from this point until the tuple update is visible).
+	 *
+	 * For the new tuple the only check needed is at the relation level, but
+	 * since both tuples are in the same relation and the check for oldtup
+	 * will include checking the relation level, there is no benefit to a
+	 * separate check for the new tuple.
+	 */
+	CheckForSerializableConflictIn(relation, &oldtup.t_self,
+								   BufferGetBlockNumber(buffer));
+
+	/*
+	 * At this point newbuf and buffer are both pinned and locked, and newbuf
+	 * has enough space for the new tuple.  If they are the same buffer, only
+	 * one pin is held.
+	 */
+
+	if (newbuf == buffer)
+	{
+		/*
+		 * Since the new tuple is going into the same page, we might be able
+		 * to do a HOT update.  Check if any of the index columns have been
+		 * changed. If the page was already full, we may have skipped checking
+		 * for index columns, and also can't do a HOT update.
+		 */
+		if (hot_attrs_checked && !bms_overlap(modified_attrs, hot_attrs))
+			use_hot_update = true;
+	}
+	else
+	{
+		/* Set a hint that the old page could use prune/defrag */
+		PageSetFull(page);
+	}
+
+	/*
+	 * Compute replica identity tuple before entering the critical section so
+	 * we don't PANIC upon a memory allocation failure.
+	 * ExtractReplicaIdentity() will return NULL if nothing needs to be
+	 * logged.  Pass old key required as true only if the replica identity key
+	 * columns are modified or it has external data.
+	 */
+	old_key_tuple = ExtractReplicaIdentity(relation, &oldtup,
+										   bms_overlap(modified_attrs, id_attrs) ||
+										   id_has_external,
+										   &old_key_copied);
+
+	/* NO EREPORT(ERROR) from here till changes are logged */
+	START_CRIT_SECTION();
+
+	/*
+	 * If this transaction commits, the old tuple will become DEAD sooner or
+	 * later.  Set flag that this page is a candidate for pruning once our xid
+	 * falls below the OldestXmin horizon.  If the transaction finally aborts,
+	 * the subsequent page pruning will be a no-op and the hint will be
+	 * cleared.
+	 *
+	 * XXX Should we set hint on newbuf as well?  If the transaction aborts,
+	 * there would be a prunable tuple in the newbuf; but for now we choose
+	 * not to optimize for aborts.  Note that heap_xlog_update must be kept in
+	 * sync if this decision changes.
+	 */
+	PageSetPrunable(page, xid);
+
+	if (use_hot_update)
+	{
+		/* Mark the old tuple as HOT-updated */
+		HeapTupleSetHotUpdated(&oldtup);
+		/* And mark the new tuple as heap-only */
+		HeapTupleSetHeapOnly(heaptup);
+		/* Mark the caller's copy too, in case different from heaptup */
+		HeapTupleSetHeapOnly(newtup);
+	}
+	else
+	{
+		/* Make sure tuples are correctly marked as not-HOT */
+		HeapTupleClearHotUpdated(&oldtup);
+		HeapTupleClearHeapOnly(heaptup);
+		HeapTupleClearHeapOnly(newtup);
+	}
+
+	RelationPutHeapTuple(relation, newbuf, heaptup, false); /* insert new tuple */
+
+
+	/* Clear obsolete visibility flags, possibly set by ourselves above... */
+	oldtup.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
+	oldtup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+	/* ... and store info about transaction updating this tuple */
+	Assert(TransactionIdIsValid(xmax_old_tuple));
+	HeapTupleHeaderSetXmax(oldtup.t_data, xmax_old_tuple);
+	oldtup.t_data->t_infomask |= infomask_old_tuple;
+	oldtup.t_data->t_infomask2 |= infomask2_old_tuple;
+	HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
+
+	/* record address of new tuple in t_ctid of old one */
+	oldtup.t_data->t_ctid = heaptup->t_self;
+
+	/* clear PD_ALL_VISIBLE flags, reset all visibilitymap bits */
+	if (PageIsAllVisible(BufferGetPage(buffer)))
+	{
+		all_visible_cleared = true;
+		PageClearAllVisible(BufferGetPage(buffer));
+		visibilitymap_clear(relation, BufferGetBlockNumber(buffer),
+							vmbuffer, VISIBILITYMAP_VALID_BITS);
+	}
+	if (newbuf != buffer && PageIsAllVisible(BufferGetPage(newbuf)))
+	{
+		all_visible_cleared_new = true;
+		PageClearAllVisible(BufferGetPage(newbuf));
+		visibilitymap_clear(relation, BufferGetBlockNumber(newbuf),
+							vmbuffer_new, VISIBILITYMAP_VALID_BITS);
+	}
+
+	if (newbuf != buffer)
+		MarkBufferDirty(newbuf);
+	MarkBufferDirty(buffer);
+
+	/* XLOG stuff */
+	if (RelationNeedsWAL(relation))
+	{
+		XLogRecPtr	recptr;
+
+		/*
+		 * For logical decoding we need combo CIDs to properly decode the
+		 * catalog.
+		 */
+		if (RelationIsAccessibleInLogicalDecoding(relation))
+		{
+			log_heap_new_cid(relation, &oldtup);
+			log_heap_new_cid(relation, heaptup);
+		}
+
+		recptr = log_heap_update(relation, buffer,
+								 newbuf, &oldtup, heaptup,
+								 old_key_tuple,
+								 all_visible_cleared,
+								 all_visible_cleared_new);
+		if (newbuf != buffer)
+		{
+			PageSetLSN(BufferGetPage(newbuf), recptr);
+		}
+		PageSetLSN(BufferGetPage(buffer), recptr);
+	}
+
+	END_CRIT_SECTION();
+
+	if (newbuf != buffer)
+		LockBuffer(newbuf, BUFFER_LOCK_UNLOCK);
+	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+
+	/*
+	 * Mark old tuple for invalidation from system caches at next command
+	 * boundary, and mark the new tuple for invalidation in case we abort. We
+	 * have to do this before releasing the buffer because oldtup is in the
+	 * buffer.  (heaptup is all in local memory, but it's necessary to process
+	 * both tuple versions in one call to inval.c so we can avoid redundant
+	 * sinval messages.)
+	 */
+	CacheInvalidateHeapTuple(relation, &oldtup, heaptup);
+
+	/* Now we can release the buffer(s) */
+	if (newbuf != buffer)
+		ReleaseBuffer(newbuf);
+	ReleaseBuffer(buffer);
+	if (BufferIsValid(vmbuffer_new))
+		ReleaseBuffer(vmbuffer_new);
+	if (BufferIsValid(vmbuffer))
+		ReleaseBuffer(vmbuffer);
+
+	/*
+	 * Release the lmgr tuple lock, if we had it.
+	 */
+	if (have_tuple_lock)
+		UnlockTupleTuplock(relation, &(oldtup.t_self), *lockmode);
+
+	pgstat_count_heap_update(relation, use_hot_update);
+
+	/*
+	 * If heaptup is a private copy, release it.  Don't forget to copy t_self
+	 * back to the caller's image, too.
+	 */
+	if (heaptup != newtup)
+	{
+		newtup->t_self = heaptup->t_self;
+		heap_freetuple(heaptup);
+	}
+
+	if (old_key_tuple != NULL && old_key_copied)
+		heap_freetuple(old_key_tuple);
+
+	bms_free(hot_attrs);
+	bms_free(key_attrs);
+	bms_free(id_attrs);
+	bms_free(modified_attrs);
+	bms_free(interesting_attrs);
+
+	return TM_Ok;
+}
+
+/*
+ * Check if the specified attribute's values are the same.  Subroutine for
+ * HeapDetermineColumnsInfo.
+ */
+static bool
+heap_attr_equals(TupleDesc tupdesc, int attrnum, Datum value1, Datum value2,
+				 bool isnull1, bool isnull2)
+{
+	Form_pg_attribute att;
+
+	/*
+	 * If one value is NULL and other is not, then they are certainly not
+	 * equal
+	 */
+	if (isnull1 != isnull2)
+		return false;
+
+	/*
+	 * If both are NULL, they can be considered equal.
+	 */
+	if (isnull1)
+		return true;
+
+	/*
+	 * We do simple binary comparison of the two datums.  This may be overly
+	 * strict because there can be multiple binary representations for the
+	 * same logical value.  But we should be OK as long as there are no false
+	 * positives.  Using a type-specific equality operator is messy because
+	 * there could be multiple notions of equality in different operator
+	 * classes; furthermore, we cannot safely invoke user-defined functions
+	 * while holding exclusive buffer lock.
+	 */
+	if (attrnum <= 0)
+	{
+		/* The only allowed system columns are OIDs, so do this */
+		return (DatumGetObjectId(value1) == DatumGetObjectId(value2));
+	}
+	else
+	{
+		Assert(attrnum <= tupdesc->natts);
+		att = TupleDescAttr(tupdesc, attrnum - 1);
+		return datumIsEqual(value1, value2, att->attbyval, att->attlen);
+	}
+}
+
+/*
+ * Check which columns are being updated.
+ *
+ * Given an updated tuple, determine (and return into the output bitmapset),
+ * from those listed as interesting, the set of columns that changed.
+ *
+ * has_external indicates if any of the unmodified attributes (from those
+ * listed as interesting) of the old tuple is a member of external_cols and is
+ * stored externally.
+ *
+ * The input interesting_cols bitmapset is destructively modified; that is OK
+ * since this is invoked at most once in heap_update.
+ */
+static Bitmapset *
+HeapDetermineColumnsInfo(Relation relation,
+						 Bitmapset *interesting_cols,
+						 Bitmapset *external_cols,
+						 HeapTuple oldtup, HeapTuple newtup,
+						 bool *has_external)
+{
+	int			attrnum;
+	Bitmapset  *modified = NULL;
+	TupleDesc	tupdesc = RelationGetDescr(relation);
+
+	while ((attrnum = bms_first_member(interesting_cols)) >= 0)
+	{
+		Datum		value1,
+					value2;
+		bool		isnull1,
+					isnull2;
+
+		attrnum += FirstLowInvalidHeapAttributeNumber;
+
+		/*
+		 * If it's a whole-tuple reference, say "not equal".  It's not really
+		 * worth supporting this case, since it could only succeed after a
+		 * no-op update, which is hardly a case worth optimizing for.
+		 */
+		if (attrnum == 0)
+		{
+			modified = bms_add_member(modified,
+									  attrnum -
+									  FirstLowInvalidHeapAttributeNumber);
+			continue;
+		}
+
+		/*
+		 * Likewise, automatically say "not equal" for any system attribute
+		 * other than tableOID; we cannot expect these to be consistent in a
+		 * HOT chain, or even to be set correctly yet in the new tuple.
+		 */
+		if (attrnum < 0)
+		{
+			if (attrnum != TableOidAttributeNumber)
+			{
+				modified = bms_add_member(modified,
+										  attrnum -
+										  FirstLowInvalidHeapAttributeNumber);
+				continue;
+			}
+		}
+
+		/*
+		 * Extract the corresponding values.  XXX this is pretty inefficient
+		 * if there are many indexed columns.  Should we do a single
+		 * heap_deform_tuple call on each tuple, instead?	But that doesn't
+		 * work for system columns ...
+		 */
+		value1 = heap_getattr(oldtup, attrnum, tupdesc, &isnull1);
+		value2 = heap_getattr(newtup, attrnum, tupdesc, &isnull2);
+
+		if (!heap_attr_equals(tupdesc, attrnum, value1,
+							  value2, isnull1, isnull2))
+		{
+			modified = bms_add_member(modified,
+									  attrnum -
+									  FirstLowInvalidHeapAttributeNumber);
+			continue;
+		}
+
+		/*
+		 * No need to check attributes that can't be stored externally. Note
+		 * that system attributes can't be stored externally.
+		 */
+		if (attrnum < 0 || isnull1 ||
+			TupleDescAttr(tupdesc, attrnum - 1)->attlen != -1)
+			continue;
+
+		/*
+		 * Check if the old tuple's attribute is stored externally and is a
+		 * member of external_cols.
+		 */
+		if (VARATT_IS_EXTERNAL((struct varlena *) DatumGetPointer(value1)) &&
+			bms_is_member(attrnum - FirstLowInvalidHeapAttributeNumber,
+						  external_cols))
+			*has_external = true;
+	}
+
+	return modified;
+}
+
+/*
+ *	simple_heap_update - replace a tuple
+ *
+ * This routine may be used to update a tuple when concurrent updates of
+ * the target tuple are not expected (for example, because we have a lock
+ * on the relation associated with the tuple).  Any failure is reported
+ * via ereport().
+ */
+void
+simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
+{
+	TM_Result	result;
+	TM_FailureData tmfd;
+	LockTupleMode lockmode;
+
+	result = heap_update(relation, otid, tup,
+						 GetCurrentCommandId(true), InvalidSnapshot,
+						 true /* wait for commit */ ,
+						 &tmfd, &lockmode);
+	switch (result)
+	{
+		case TM_SelfModified:
+			/* Tuple was already updated in current command? */
+			elog(ERROR, "tuple already updated by self");
+			break;
+
+		case TM_Ok:
+			/* done successfully */
+			break;
+
+		case TM_Updated:
+			elog(ERROR, "tuple concurrently updated");
+			break;
+
+		case TM_Deleted:
+			elog(ERROR, "tuple concurrently deleted");
+			break;
+
+		default:
+			elog(ERROR, "unrecognized heap_update status: %u", result);
+			break;
+	}
+}
+
+
+/*
+ * Return the MultiXactStatus corresponding to the given tuple lock mode.
+ */
+static MultiXactStatus
+get_mxact_status_for_lock(LockTupleMode mode, bool is_update)
+{
+	int			retval;
+
+	if (is_update)
+		retval = tupleLockExtraInfo[mode].updstatus;
+	else
+		retval = tupleLockExtraInfo[mode].lockstatus;
+
+	if (retval == -1)
+		elog(ERROR, "invalid lock tuple mode %d/%s", mode,
+			 is_update ? "true" : "false");
+
+	return (MultiXactStatus) retval;
+}
+
+/*
+ *	heap_lock_tuple - lock a tuple in shared or exclusive mode
+ *
+ * Note that this acquires a buffer pin, which the caller must release.
+ *
+ * Input parameters:
+ *	relation: relation containing tuple (caller must hold suitable lock)
+ *	tid: TID of tuple to lock
+ *	cid: current command ID (used for visibility test, and stored into
+ *		tuple's cmax if lock is successful)
+ *	mode: indicates if shared or exclusive tuple lock is desired
+ *	wait_policy: what to do if tuple lock is not available
+ *	follow_updates: if true, follow the update chain to also lock descendant
+ *		tuples.
+ *
+ * Output parameters:
+ *	*tuple: all fields filled in
+ *	*buffer: set to buffer holding tuple (pinned but not locked at exit)
+ *	*tmfd: filled in failure cases (see below)
+ *
+ * Function results are the same as the ones for table_tuple_lock().
+ *
+ * In the failure cases other than TM_Invisible, the routine fills
+ * *tmfd with the tuple's t_ctid, t_xmax (resolving a possible MultiXact,
+ * if necessary), and t_cmax (the last only for TM_SelfModified,
+ * since we cannot obtain cmax from a combo CID generated by another
+ * transaction).
+ * See comments for struct TM_FailureData for additional info.
+ *
+ * See README.tuplock for a thorough explanation of this mechanism.
+ */
+TM_Result
+heap_lock_tuple(Relation relation, HeapTuple tuple,
+				CommandId cid, LockTupleMode mode, LockWaitPolicy wait_policy,
+				bool follow_updates,
+				Buffer *buffer, TM_FailureData *tmfd)
+{
+	TM_Result	result;
+	ItemPointer tid = &(tuple->t_self);
+	ItemId		lp;
+	Page		page;
+	Buffer		vmbuffer = InvalidBuffer;
+	BlockNumber block;
+	TransactionId xid,
+				xmax;
+	uint16		old_infomask,
+				new_infomask,
+				new_infomask2;
+	bool		first_time = true;
+	bool		skip_tuple_lock = false;
+	bool		have_tuple_lock = false;
+	bool		cleared_all_frozen = false;
+
+	*buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
+	block = ItemPointerGetBlockNumber(tid);
+
+	/*
+	 * Before locking the buffer, pin the visibility map page if it appears to
+	 * be necessary.  Since we haven't got the lock yet, someone else might be
+	 * in the middle of changing this, so we'll need to recheck after we have
+	 * the lock.
+	 */
+	if (PageIsAllVisible(BufferGetPage(*buffer)))
+		visibilitymap_pin(relation, block, &vmbuffer);
+
+	LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+
+	page = BufferGetPage(*buffer);
+	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
+	Assert(ItemIdIsNormal(lp));
+
+	tuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
+	tuple->t_len = ItemIdGetLength(lp);
+	tuple->t_tableOid = RelationGetRelid(relation);
+
+l3:
+	result = HeapTupleSatisfiesUpdate(tuple, cid, *buffer);
+
+	if (result == TM_Invisible)
+	{
+		/*
+		 * This is possible, but only when locking a tuple for ON CONFLICT
+		 * UPDATE.  We return this value here rather than throwing an error in
+		 * order to give that case the opportunity to throw a more specific
+		 * error.
+		 */
+		result = TM_Invisible;
+		goto out_locked;
+	}
+	else if (result == TM_BeingModified ||
+			 result == TM_Updated ||
+			 result == TM_Deleted)
+	{
+		TransactionId xwait;
+		uint16		infomask;
+		uint16		infomask2;
+		bool		require_sleep;
+		ItemPointerData t_ctid;
+
+		/* must copy state data before unlocking buffer */
+		xwait = HeapTupleHeaderGetRawXmax(tuple->t_data);
+		infomask = tuple->t_data->t_infomask;
+		infomask2 = tuple->t_data->t_infomask2;
+		ItemPointerCopy(&tuple->t_data->t_ctid, &t_ctid);
+
+		LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
+
+		/*
+		 * If any subtransaction of the current top transaction already holds
+		 * a lock as strong as or stronger than what we're requesting, we
+		 * effectively hold the desired lock already.  We *must* succeed
+		 * without trying to take the tuple lock, else we will deadlock
+		 * against anyone wanting to acquire a stronger lock.
+		 *
+		 * Note we only do this the first time we loop on the HTSU result;
+		 * there is no point in testing in subsequent passes, because
+		 * evidently our own transaction cannot have acquired a new lock after
+		 * the first time we checked.
+		 */
+		if (first_time)
+		{
+			first_time = false;
+
+			if (infomask & HEAP_XMAX_IS_MULTI)
+			{
+				int			i;
+				int			nmembers;
+				MultiXactMember *members;
+
+				/*
+				 * We don't need to allow old multixacts here; if that had
+				 * been the case, HeapTupleSatisfiesUpdate would have returned
+				 * MayBeUpdated and we wouldn't be here.
+				 */
+				nmembers =
+					GetMultiXactIdMembers(xwait, &members, false,
+										  HEAP_XMAX_IS_LOCKED_ONLY(infomask));
+
+				for (i = 0; i < nmembers; i++)
+				{
+					/* only consider members of our own transaction */
+					if (!TransactionIdIsCurrentTransactionId(members[i].xid))
+						continue;
+
+					if (TUPLOCK_from_mxstatus(members[i].status) >= mode)
+					{
+						pfree(members);
+						result = TM_Ok;
+						goto out_unlocked;
+					}
+					else
+					{
+						/*
+						 * Disable acquisition of the heavyweight tuple lock.
+						 * Otherwise, when promoting a weaker lock, we might
+						 * deadlock with another locker that has acquired the
+						 * heavyweight tuple lock and is waiting for our
+						 * transaction to finish.
+						 *
+						 * Note that in this case we still need to wait for
+						 * the multixact if required, to avoid acquiring
+						 * conflicting locks.
+						 */
+						skip_tuple_lock = true;
+					}
+				}
+
+				if (members)
+					pfree(members);
+			}
+			else if (TransactionIdIsCurrentTransactionId(xwait))
+			{
+				switch (mode)
+				{
+					case LockTupleKeyShare:
+						Assert(HEAP_XMAX_IS_KEYSHR_LOCKED(infomask) ||
+							   HEAP_XMAX_IS_SHR_LOCKED(infomask) ||
+							   HEAP_XMAX_IS_EXCL_LOCKED(infomask));
+						result = TM_Ok;
+						goto out_unlocked;
+					case LockTupleShare:
+						if (HEAP_XMAX_IS_SHR_LOCKED(infomask) ||
+							HEAP_XMAX_IS_EXCL_LOCKED(infomask))
+						{
+							result = TM_Ok;
+							goto out_unlocked;
+						}
+						break;
+					case LockTupleNoKeyExclusive:
+						if (HEAP_XMAX_IS_EXCL_LOCKED(infomask))
+						{
+							result = TM_Ok;
+							goto out_unlocked;
+						}
+						break;
+					case LockTupleExclusive:
+						if (HEAP_XMAX_IS_EXCL_LOCKED(infomask) &&
+							infomask2 & HEAP_KEYS_UPDATED)
+						{
+							result = TM_Ok;
+							goto out_unlocked;
+						}
+						break;
+				}
+			}
+		}
+
+		/*
+		 * Initially assume that we will have to wait for the locking
+		 * transaction(s) to finish.  We check various cases below in which
+		 * this can be turned off.
+		 */
+		require_sleep = true;
+		if (mode == LockTupleKeyShare)
+		{
+			/*
+			 * If we're requesting KeyShare, and there's no update present, we
+			 * don't need to wait.  Even if there is an update, we can still
+			 * continue if the key hasn't been modified.
+			 *
+			 * However, if there are updates, we need to walk the update chain
+			 * to mark future versions of the row as locked, too.  That way,
+			 * if somebody deletes that future version, we're protected
+			 * against the key going away.  This locking of future versions
+			 * could block momentarily, if a concurrent transaction is
+			 * deleting a key; or it could return a value to the effect that
+			 * the transaction deleting the key has already committed.  So we
+			 * do this before re-locking the buffer; otherwise this would be
+			 * prone to deadlocks.
+			 *
+			 * Note that the TID we're locking was grabbed before we unlocked
+			 * the buffer.  For it to change while we're not looking, the
+			 * other properties we're testing for below after re-locking the
+			 * buffer would also change, in which case we would restart this
+			 * loop above.
+			 */
+			if (!(infomask2 & HEAP_KEYS_UPDATED))
+			{
+				bool		updated;
+
+				updated = !HEAP_XMAX_IS_LOCKED_ONLY(infomask);
+
+				/*
+				 * If there are updates, follow the update chain; bail out if
+				 * that cannot be done.
+				 */
+				if (follow_updates && updated)
+				{
+					TM_Result	res;
+
+					res = heap_lock_updated_tuple(relation, tuple, &t_ctid,
+												  GetCurrentTransactionId(),
+												  mode);
+					if (res != TM_Ok)
+					{
+						result = res;
+						/* recovery code expects to have buffer lock held */
+						LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+						goto failed;
+					}
+				}
+
+				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+
+				/*
+				 * Make sure it's still an appropriate lock, else start over.
+				 * Also, if it wasn't updated before we released the lock, but
+				 * is updated now, we start over too; the reason is that we
+				 * now need to follow the update chain to lock the new
+				 * versions.
+				 */
+				if (!HeapTupleHeaderIsOnlyLocked(tuple->t_data) &&
+					((tuple->t_data->t_infomask2 & HEAP_KEYS_UPDATED) ||
+					 !updated))
+					goto l3;
+
+				/* Things look okay, so we can skip sleeping */
+				require_sleep = false;
+
+				/*
+				 * Note we allow Xmax to change here; other updaters/lockers
+				 * could have modified it before we grabbed the buffer lock.
+				 * However, this is not a problem, because with the recheck we
+				 * just did we ensure that they still don't conflict with the
+				 * lock we want.
+				 */
+			}
+		}
+		else if (mode == LockTupleShare)
+		{
+			/*
+			 * If we're requesting Share, we can similarly avoid sleeping if
+			 * there's no update and no exclusive lock present.
+			 */
+			if (HEAP_XMAX_IS_LOCKED_ONLY(infomask) &&
+				!HEAP_XMAX_IS_EXCL_LOCKED(infomask))
+			{
+				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+
+				/*
+				 * Make sure it's still an appropriate lock, else start over.
+				 * See above about allowing xmax to change.
+				 */
+				if (!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_data->t_infomask) ||
+					HEAP_XMAX_IS_EXCL_LOCKED(tuple->t_data->t_infomask))
+					goto l3;
+				require_sleep = false;
+			}
+		}
+		else if (mode == LockTupleNoKeyExclusive)
+		{
+			/*
+			 * If we're requesting NoKeyExclusive, we might also be able to
+			 * avoid sleeping; just ensure that there no conflicting lock
+			 * already acquired.
+			 */
+			if (infomask & HEAP_XMAX_IS_MULTI)
+			{
+				if (!DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
+											 mode, NULL))
+				{
+					/*
+					 * No conflict, but if the xmax changed under us in the
+					 * meantime, start over.
+					 */
+					LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+					if (xmax_infomask_changed(tuple->t_data->t_infomask, infomask) ||
+						!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
+											 xwait))
+						goto l3;
+
+					/* otherwise, we're good */
+					require_sleep = false;
+				}
+			}
+			else if (HEAP_XMAX_IS_KEYSHR_LOCKED(infomask))
+			{
+				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+
+				/* if the xmax changed in the meantime, start over */
+				if (xmax_infomask_changed(tuple->t_data->t_infomask, infomask) ||
+					!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
+										 xwait))
+					goto l3;
+				/* otherwise, we're good */
+				require_sleep = false;
+			}
+		}
+
+		/*
+		 * As a check independent from those above, we can also avoid sleeping
+		 * if the current transaction is the sole locker of the tuple.  Note
+		 * that the strength of the lock already held is irrelevant; this is
+		 * not about recording the lock in Xmax (which will be done regardless
+		 * of this optimization, below).  Also, note that the cases where we
+		 * hold a lock stronger than we are requesting are already handled
+		 * above by not doing anything.
+		 *
+		 * Note we only deal with the non-multixact case here; MultiXactIdWait
+		 * is well equipped to deal with this situation on its own.
+		 */
+		if (require_sleep && !(infomask & HEAP_XMAX_IS_MULTI) &&
+			TransactionIdIsCurrentTransactionId(xwait))
+		{
+			/* ... but if the xmax changed in the meantime, start over */
+			LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+			if (xmax_infomask_changed(tuple->t_data->t_infomask, infomask) ||
+				!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
+									 xwait))
+				goto l3;
+			Assert(HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_data->t_infomask));
+			require_sleep = false;
+		}
+
+		/*
+		 * Time to sleep on the other transaction/multixact, if necessary.
+		 *
+		 * If the other transaction is an update/delete that's already
+		 * committed, then sleeping cannot possibly do any good: if we're
+		 * required to sleep, get out to raise an error instead.
+		 *
+		 * By here, we either have already acquired the buffer exclusive lock,
+		 * or we must wait for the locking transaction or multixact; so below
+		 * we ensure that we grab buffer lock after the sleep.
+		 */
+		if (require_sleep && (result == TM_Updated || result == TM_Deleted))
+		{
+			LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+			goto failed;
+		}
+		else if (require_sleep)
+		{
+			/*
+			 * Acquire tuple lock to establish our priority for the tuple, or
+			 * die trying.  LockTuple will release us when we are next-in-line
+			 * for the tuple.  We must do this even if we are share-locking,
+			 * but not if we already have a weaker lock on the tuple.
+			 *
+			 * If we are forced to "start over" below, we keep the tuple lock;
+			 * this arranges that we stay at the head of the line while
+			 * rechecking tuple state.
+			 */
+			if (!skip_tuple_lock &&
+				!heap_acquire_tuplock(relation, tid, mode, wait_policy,
+									  &have_tuple_lock))
+			{
+				/*
+				 * This can only happen if wait_policy is Skip and the lock
+				 * couldn't be obtained.
+				 */
+				result = TM_WouldBlock;
+				/* recovery code expects to have buffer lock held */
+				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+				goto failed;
+			}
+
+			if (infomask & HEAP_XMAX_IS_MULTI)
+			{
+				MultiXactStatus status = get_mxact_status_for_lock(mode, false);
+
+				/* We only ever lock tuples, never update them */
+				if (status >= MultiXactStatusNoKeyUpdate)
+					elog(ERROR, "invalid lock mode in heap_lock_tuple");
+
+				/* wait for multixact to end, or die trying  */
+				switch (wait_policy)
+				{
+					case LockWaitBlock:
+						MultiXactIdWait((MultiXactId) xwait, status, infomask,
+										relation, &tuple->t_self, XLTW_Lock, NULL);
+						break;
+					case LockWaitSkip:
+						if (!ConditionalMultiXactIdWait((MultiXactId) xwait,
+														status, infomask, relation,
+														NULL))
+						{
+							result = TM_WouldBlock;
+							/* recovery code expects to have buffer lock held */
+							LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+							goto failed;
+						}
+						break;
+					case LockWaitError:
+						if (!ConditionalMultiXactIdWait((MultiXactId) xwait,
+														status, infomask, relation,
+														NULL))
+							ereport(ERROR,
+									(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
+									 errmsg("could not obtain lock on row in relation \"%s\"",
+											RelationGetRelationName(relation))));
+
+						break;
+				}
+
+				/*
+				 * Of course, the multixact might not be done here: if we're
+				 * requesting a light lock mode, other transactions with light
+				 * locks could still be alive, as well as locks owned by our
+				 * own xact or other subxacts of this backend.  We need to
+				 * preserve the surviving MultiXact members.  Note that it
+				 * isn't absolutely necessary in the latter case, but doing so
+				 * is simpler.
+				 */
+			}
+			else
+			{
+				/* wait for regular transaction to end, or die trying */
+				switch (wait_policy)
+				{
+					case LockWaitBlock:
+						XactLockTableWait(xwait, relation, &tuple->t_self,
+										  XLTW_Lock);
+						break;
+					case LockWaitSkip:
+						if (!ConditionalXactLockTableWait(xwait))
+						{
+							result = TM_WouldBlock;
+							/* recovery code expects to have buffer lock held */
+							LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+							goto failed;
+						}
+						break;
+					case LockWaitError:
+						if (!ConditionalXactLockTableWait(xwait))
+							ereport(ERROR,
+									(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
+									 errmsg("could not obtain lock on row in relation \"%s\"",
+											RelationGetRelationName(relation))));
+						break;
+				}
+			}
+
+			/* if there are updates, follow the update chain */
+			if (follow_updates && !HEAP_XMAX_IS_LOCKED_ONLY(infomask))
+			{
+				TM_Result	res;
+
+				res = heap_lock_updated_tuple(relation, tuple, &t_ctid,
+											  GetCurrentTransactionId(),
+											  mode);
+				if (res != TM_Ok)
+				{
+					result = res;
+					/* recovery code expects to have buffer lock held */
+					LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+					goto failed;
+				}
+			}
+
+			LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+
+			/*
+			 * xwait is done, but if xwait had just locked the tuple then some
+			 * other xact could update this tuple before we get to this point.
+			 * Check for xmax change, and start over if so.
+			 */
+			if (xmax_infomask_changed(tuple->t_data->t_infomask, infomask) ||
+				!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
+									 xwait))
+				goto l3;
+
+			if (!(infomask & HEAP_XMAX_IS_MULTI))
+			{
+				/*
+				 * Otherwise check if it committed or aborted.  Note we cannot
+				 * be here if the tuple was only locked by somebody who didn't
+				 * conflict with us; that would have been handled above.  So
+				 * that transaction must necessarily be gone by now.  But
+				 * don't check for this in the multixact case, because some
+				 * locker transactions might still be running.
+				 */
+				UpdateXmaxHintBits(tuple->t_data, *buffer, xwait);
+			}
+		}
+
+		/* By here, we're certain that we hold buffer exclusive lock again */
+
+		/*
+		 * We may lock if previous xmax aborted, or if it committed but only
+		 * locked the tuple without updating it; or if we didn't have to wait
+		 * at all for whatever reason.
+		 */
+		if (!require_sleep ||
+			(tuple->t_data->t_infomask & HEAP_XMAX_INVALID) ||
+			HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_data->t_infomask) ||
+			HeapTupleHeaderIsOnlyLocked(tuple->t_data))
+			result = TM_Ok;
+		else if (!ItemPointerEquals(&tuple->t_self, &tuple->t_data->t_ctid))
+			result = TM_Updated;
+		else
+			result = TM_Deleted;
+	}
+
+failed:
+	if (result != TM_Ok)
+	{
+		Assert(result == TM_SelfModified || result == TM_Updated ||
+			   result == TM_Deleted || result == TM_WouldBlock);
+
+		/*
+		 * When locking a tuple under LockWaitSkip semantics and we fail with
+		 * TM_WouldBlock above, it's possible for concurrent transactions to
+		 * release the lock and set HEAP_XMAX_INVALID in the meantime.  So
+		 * this assert is slightly different from the equivalent one in
+		 * heap_delete and heap_update.
+		 */
+		Assert((result == TM_WouldBlock) ||
+			   !(tuple->t_data->t_infomask & HEAP_XMAX_INVALID));
+		Assert(result != TM_Updated ||
+			   !ItemPointerEquals(&tuple->t_self, &tuple->t_data->t_ctid));
+		tmfd->ctid = tuple->t_data->t_ctid;
+		tmfd->xmax = HeapTupleHeaderGetUpdateXid(tuple->t_data);
+		if (result == TM_SelfModified)
+			tmfd->cmax = HeapTupleHeaderGetCmax(tuple->t_data);
+		else
+			tmfd->cmax = InvalidCommandId;
+		goto out_locked;
+	}
+
+	/*
+	 * If we didn't pin the visibility map page and the page has become all
+	 * visible while we were busy locking the buffer, or during some
+	 * subsequent window during which we had it unlocked, we'll have to unlock
+	 * and re-lock, to avoid holding the buffer lock across I/O.  That's a bit
+	 * unfortunate, especially since we'll now have to recheck whether the
+	 * tuple has been locked or updated under us, but hopefully it won't
+	 * happen very often.
+	 */
+	if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
+	{
+		LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
+		visibilitymap_pin(relation, block, &vmbuffer);
+		LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+		goto l3;
+	}
+
+	xmax = HeapTupleHeaderGetRawXmax(tuple->t_data);
+	old_infomask = tuple->t_data->t_infomask;
+
+	/*
+	 * If this is the first possibly-multixact-able operation in the current
+	 * transaction, set my per-backend OldestMemberMXactId setting. We can be
+	 * certain that the transaction will never become a member of any older
+	 * MultiXactIds than that.  (We have to do this even if we end up just
+	 * using our own TransactionId below, since some other backend could
+	 * incorporate our XID into a MultiXact immediately afterwards.)
+	 */
+	MultiXactIdSetOldestMember();
+
+	/*
+	 * Compute the new xmax and infomask to store into the tuple.  Note we do
+	 * not modify the tuple just yet, because that would leave it in the wrong
+	 * state if multixact.c elogs.
+	 */
+	compute_new_xmax_infomask(xmax, old_infomask, tuple->t_data->t_infomask2,
+							  GetCurrentTransactionId(), mode, false,
+							  &xid, &new_infomask, &new_infomask2);
+
+	START_CRIT_SECTION();
+
+	/*
+	 * Store transaction information of xact locking the tuple.
+	 *
+	 * Note: Cmax is meaningless in this context, so don't set it; this avoids
+	 * possibly generating a useless combo CID.  Moreover, if we're locking a
+	 * previously updated tuple, it's important to preserve the Cmax.
+	 *
+	 * Also reset the HOT UPDATE bit, but only if there's no update; otherwise
+	 * we would break the HOT chain.
+	 */
+	tuple->t_data->t_infomask &= ~HEAP_XMAX_BITS;
+	tuple->t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+	tuple->t_data->t_infomask |= new_infomask;
+	tuple->t_data->t_infomask2 |= new_infomask2;
+	if (HEAP_XMAX_IS_LOCKED_ONLY(new_infomask))
+		HeapTupleHeaderClearHotUpdated(tuple->t_data);
+	HeapTupleHeaderSetXmax(tuple->t_data, xid);
+
+	/*
+	 * Make sure there is no forward chain link in t_ctid.  Note that in the
+	 * cases where the tuple has been updated, we must not overwrite t_ctid,
+	 * because it was set by the updater.  Moreover, if the tuple has been
+	 * updated, we need to follow the update chain to lock the new versions of
+	 * the tuple as well.
+	 */
+	if (HEAP_XMAX_IS_LOCKED_ONLY(new_infomask))
+		tuple->t_data->t_ctid = *tid;
+
+	/* Clear only the all-frozen bit on visibility map if needed */
+	if (PageIsAllVisible(page) &&
+		visibilitymap_clear(relation, block, vmbuffer,
+							VISIBILITYMAP_ALL_FROZEN))
+		cleared_all_frozen = true;
+
+
+	MarkBufferDirty(*buffer);
+
+	/*
+	 * XLOG stuff.  You might think that we don't need an XLOG record because
+	 * there is no state change worth restoring after a crash.  You would be
+	 * wrong however: we have just written either a TransactionId or a
+	 * MultiXactId that may never have been seen on disk before, and we need
+	 * to make sure that there are XLOG entries covering those ID numbers.
+	 * Else the same IDs might be re-used after a crash, which would be
+	 * disastrous if this page made it to disk before the crash.  Essentially
+	 * we have to enforce the WAL log-before-data rule even in this case.
+	 * (Also, in a PITR log-shipping or 2PC environment, we have to have XLOG
+	 * entries for everything anyway.)
+	 */
+	if (RelationNeedsWAL(relation))
+	{
+		xl_heap_lock xlrec;
+		XLogRecPtr	recptr;
+
+		XLogBeginInsert();
+		XLogRegisterBuffer(0, *buffer, REGBUF_STANDARD);
+
+		xlrec.offnum = ItemPointerGetOffsetNumber(&tuple->t_self);
+		xlrec.locking_xid = xid;
+		xlrec.infobits_set = compute_infobits(new_infomask,
+											  tuple->t_data->t_infomask2);
+		xlrec.flags = cleared_all_frozen ? XLH_LOCK_ALL_FROZEN_CLEARED : 0;
+		XLogRegisterData((char *) &xlrec, SizeOfHeapLock);
+
+		/* we don't decode row locks atm, so no need to log the origin */
+
+		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_LOCK);
+
+		PageSetLSN(page, recptr);
+	}
+
+	END_CRIT_SECTION();
+
+	result = TM_Ok;
+
+out_locked:
+	LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
+
+out_unlocked:
+	if (BufferIsValid(vmbuffer))
+		ReleaseBuffer(vmbuffer);
+
+	/*
+	 * Don't update the visibility map here. Locking a tuple doesn't change
+	 * visibility info.
+	 */
+
+	/*
+	 * Now that we have successfully marked the tuple as locked, we can
+	 * release the lmgr tuple lock, if we had it.
+	 */
+	if (have_tuple_lock)
+		UnlockTupleTuplock(relation, tid, mode);
+
+	return result;
+}
+
+/*
+ * Acquire heavyweight lock on the given tuple, in preparation for acquiring
+ * its normal, Xmax-based tuple lock.
+ *
+ * have_tuple_lock is an input and output parameter: on input, it indicates
+ * whether the lock has previously been acquired (and this function does
+ * nothing in that case).  If this function returns success, have_tuple_lock
+ * has been flipped to true.
+ *
+ * Returns false if it was unable to obtain the lock; this can only happen if
+ * wait_policy is Skip.
+ */
+static bool
+heap_acquire_tuplock(Relation relation, ItemPointer tid, LockTupleMode mode,
+					 LockWaitPolicy wait_policy, bool *have_tuple_lock)
+{
+	if (*have_tuple_lock)
+		return true;
+
+	switch (wait_policy)
+	{
+		case LockWaitBlock:
+			LockTupleTuplock(relation, tid, mode);
+			break;
+
+		case LockWaitSkip:
+			if (!ConditionalLockTupleTuplock(relation, tid, mode))
+				return false;
+			break;
+
+		case LockWaitError:
+			if (!ConditionalLockTupleTuplock(relation, tid, mode))
+				ereport(ERROR,
+						(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
+						 errmsg("could not obtain lock on row in relation \"%s\"",
+								RelationGetRelationName(relation))));
+			break;
+	}
+	*have_tuple_lock = true;
+
+	return true;
+}
+
+/*
+ * Given an original set of Xmax and infomask, and a transaction (identified by
+ * add_to_xmax) acquiring a new lock of some mode, compute the new Xmax and
+ * corresponding infomasks to use on the tuple.
+ *
+ * Note that this might have side effects such as creating a new MultiXactId.
+ *
+ * Most callers will have called HeapTupleSatisfiesUpdate before this function;
+ * that will have set the HEAP_XMAX_INVALID bit if the xmax was a MultiXactId
+ * but it was not running anymore. There is a race condition, which is that the
+ * MultiXactId may have finished since then, but that uncommon case is handled
+ * either here, or within MultiXactIdExpand.
+ *
+ * There is a similar race condition possible when the old xmax was a regular
+ * TransactionId.  We test TransactionIdIsInProgress again just to narrow the
+ * window, but it's still possible to end up creating an unnecessary
+ * MultiXactId.  Fortunately this is harmless.
+ */
+static void
+compute_new_xmax_infomask(TransactionId xmax, uint16 old_infomask,
+						  uint16 old_infomask2, TransactionId add_to_xmax,
+						  LockTupleMode mode, bool is_update,
+						  TransactionId *result_xmax, uint16 *result_infomask,
+						  uint16 *result_infomask2)
+{
+	TransactionId new_xmax;
+	uint16		new_infomask,
+				new_infomask2;
+
+	Assert(TransactionIdIsCurrentTransactionId(add_to_xmax));
+
+l5:
+	new_infomask = 0;
+	new_infomask2 = 0;
+	if (old_infomask & HEAP_XMAX_INVALID)
+	{
+		/*
+		 * No previous locker; we just insert our own TransactionId.
+		 *
+		 * Note that it's critical that this case be the first one checked,
+		 * because there are several blocks below that come back to this one
+		 * to implement certain optimizations; old_infomask might contain
+		 * other dirty bits in those cases, but we don't really care.
+		 */
+		if (is_update)
+		{
+			new_xmax = add_to_xmax;
+			if (mode == LockTupleExclusive)
+				new_infomask2 |= HEAP_KEYS_UPDATED;
+		}
+		else
+		{
+			new_infomask |= HEAP_XMAX_LOCK_ONLY;
+			switch (mode)
+			{
+				case LockTupleKeyShare:
+					new_xmax = add_to_xmax;
+					new_infomask |= HEAP_XMAX_KEYSHR_LOCK;
+					break;
+				case LockTupleShare:
+					new_xmax = add_to_xmax;
+					new_infomask |= HEAP_XMAX_SHR_LOCK;
+					break;
+				case LockTupleNoKeyExclusive:
+					new_xmax = add_to_xmax;
+					new_infomask |= HEAP_XMAX_EXCL_LOCK;
+					break;
+				case LockTupleExclusive:
+					new_xmax = add_to_xmax;
+					new_infomask |= HEAP_XMAX_EXCL_LOCK;
+					new_infomask2 |= HEAP_KEYS_UPDATED;
+					break;
+				default:
+					new_xmax = InvalidTransactionId;	/* silence compiler */
+					elog(ERROR, "invalid lock mode");
+			}
+		}
+	}
+	else if (old_infomask & HEAP_XMAX_IS_MULTI)
+	{
+		MultiXactStatus new_status;
+
+		/*
+		 * Currently we don't allow XMAX_COMMITTED to be set for multis, so
+		 * cross-check.
+		 */
+		Assert(!(old_infomask & HEAP_XMAX_COMMITTED));
+
+		/*
+		 * A multixact together with LOCK_ONLY set but neither lock bit set
+		 * (i.e. a pg_upgraded share locked tuple) cannot possibly be running
+		 * anymore.  This check is critical for databases upgraded by
+		 * pg_upgrade; both MultiXactIdIsRunning and MultiXactIdExpand assume
+		 * that such multis are never passed.
+		 */
+		if (HEAP_LOCKED_UPGRADED(old_infomask))
+		{
+			old_infomask &= ~HEAP_XMAX_IS_MULTI;
+			old_infomask |= HEAP_XMAX_INVALID;
+			goto l5;
+		}
+
+		/*
+		 * If the XMAX is already a MultiXactId, then we need to expand it to
+		 * include add_to_xmax; but if all the members were lockers and are
+		 * all gone, we can do away with the IS_MULTI bit and just set
+		 * add_to_xmax as the only locker/updater.  If all lockers are gone
+		 * and we have an updater that aborted, we can also do without a
+		 * multi.
+		 *
+		 * The cost of doing GetMultiXactIdMembers would be paid by
+		 * MultiXactIdExpand if we weren't to do this, so this check is not
+		 * incurring extra work anyhow.
+		 */
+		if (!MultiXactIdIsRunning(xmax, HEAP_XMAX_IS_LOCKED_ONLY(old_infomask)))
+		{
+			if (HEAP_XMAX_IS_LOCKED_ONLY(old_infomask) ||
+				!TransactionIdDidCommit(MultiXactIdGetUpdateXid(xmax,
+																old_infomask)))
+			{
+				/*
+				 * Reset these bits and restart; otherwise fall through to
+				 * create a new multi below.
+				 */
+				old_infomask &= ~HEAP_XMAX_IS_MULTI;
+				old_infomask |= HEAP_XMAX_INVALID;
+				goto l5;
+			}
+		}
+
+		new_status = get_mxact_status_for_lock(mode, is_update);
+
+		new_xmax = MultiXactIdExpand((MultiXactId) xmax, add_to_xmax,
+									 new_status);
+		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
+	}
+	else if (old_infomask & HEAP_XMAX_COMMITTED)
+	{
+		/*
+		 * It's a committed update, so we need to preserve him as updater of
+		 * the tuple.
+		 */
+		MultiXactStatus status;
+		MultiXactStatus new_status;
+
+		if (old_infomask2 & HEAP_KEYS_UPDATED)
+			status = MultiXactStatusUpdate;
+		else
+			status = MultiXactStatusNoKeyUpdate;
+
+		new_status = get_mxact_status_for_lock(mode, is_update);
+
+		/*
+		 * since it's not running, it's obviously impossible for the old
+		 * updater to be identical to the current one, so we need not check
+		 * for that case as we do in the block above.
+		 */
+		new_xmax = MultiXactIdCreate(xmax, status, add_to_xmax, new_status);
+		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
+	}
+	else if (TransactionIdIsInProgress(xmax))
+	{
+		/*
+		 * If the XMAX is a valid, in-progress TransactionId, then we need to
+		 * create a new MultiXactId that includes both the old locker or
+		 * updater and our own TransactionId.
+		 */
+		MultiXactStatus new_status;
+		MultiXactStatus old_status;
+		LockTupleMode old_mode;
+
+		if (HEAP_XMAX_IS_LOCKED_ONLY(old_infomask))
+		{
+			if (HEAP_XMAX_IS_KEYSHR_LOCKED(old_infomask))
+				old_status = MultiXactStatusForKeyShare;
+			else if (HEAP_XMAX_IS_SHR_LOCKED(old_infomask))
+				old_status = MultiXactStatusForShare;
+			else if (HEAP_XMAX_IS_EXCL_LOCKED(old_infomask))
+			{
+				if (old_infomask2 & HEAP_KEYS_UPDATED)
+					old_status = MultiXactStatusForUpdate;
+				else
+					old_status = MultiXactStatusForNoKeyUpdate;
+			}
+			else
+			{
+				/*
+				 * LOCK_ONLY can be present alone only when a page has been
+				 * upgraded by pg_upgrade.  But in that case,
+				 * TransactionIdIsInProgress() should have returned false.  We
+				 * assume it's no longer locked in this case.
+				 */
+				elog(WARNING, "LOCK_ONLY found for Xid in progress %u", xmax);
+				old_infomask |= HEAP_XMAX_INVALID;
+				old_infomask &= ~HEAP_XMAX_LOCK_ONLY;
+				goto l5;
+			}
+		}
+		else
+		{
+			/* it's an update, but which kind? */
+			if (old_infomask2 & HEAP_KEYS_UPDATED)
+				old_status = MultiXactStatusUpdate;
+			else
+				old_status = MultiXactStatusNoKeyUpdate;
+		}
+
+		old_mode = TUPLOCK_from_mxstatus(old_status);
+
+		/*
+		 * If the lock to be acquired is for the same TransactionId as the
+		 * existing lock, there's an optimization possible: consider only the
+		 * strongest of both locks as the only one present, and restart.
+		 */
+		if (xmax == add_to_xmax)
+		{
+			/*
+			 * Note that it's not possible for the original tuple to be
+			 * updated: we wouldn't be here because the tuple would have been
+			 * invisible and we wouldn't try to update it.  As a subtlety,
+			 * this code can also run when traversing an update chain to lock
+			 * future versions of a tuple.  But we wouldn't be here either,
+			 * because the add_to_xmax would be different from the original
+			 * updater.
+			 */
+			Assert(HEAP_XMAX_IS_LOCKED_ONLY(old_infomask));
+
+			/* acquire the strongest of both */
+			if (mode < old_mode)
+				mode = old_mode;
+			/* mustn't touch is_update */
+
+			old_infomask |= HEAP_XMAX_INVALID;
+			goto l5;
+		}
+
+		/* otherwise, just fall back to creating a new multixact */
+		new_status = get_mxact_status_for_lock(mode, is_update);
+		new_xmax = MultiXactIdCreate(xmax, old_status,
+									 add_to_xmax, new_status);
+		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
+	}
+	else if (!HEAP_XMAX_IS_LOCKED_ONLY(old_infomask) &&
+			 TransactionIdDidCommit(xmax))
+	{
+		/*
+		 * It's a committed update, so we gotta preserve him as updater of the
+		 * tuple.
+		 */
+		MultiXactStatus status;
+		MultiXactStatus new_status;
+
+		if (old_infomask2 & HEAP_KEYS_UPDATED)
+			status = MultiXactStatusUpdate;
+		else
+			status = MultiXactStatusNoKeyUpdate;
+
+		new_status = get_mxact_status_for_lock(mode, is_update);
+
+		/*
+		 * since it's not running, it's obviously impossible for the old
+		 * updater to be identical to the current one, so we need not check
+		 * for that case as we do in the block above.
+		 */
+		new_xmax = MultiXactIdCreate(xmax, status, add_to_xmax, new_status);
+		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
+	}
+	else
+	{
+		/*
+		 * Can get here iff the locking/updating transaction was running when
+		 * the infomask was extracted from the tuple, but finished before
+		 * TransactionIdIsInProgress got to run.  Deal with it as if there was
+		 * no locker at all in the first place.
+		 */
+		old_infomask |= HEAP_XMAX_INVALID;
+		goto l5;
+	}
+
+	*result_infomask = new_infomask;
+	*result_infomask2 = new_infomask2;
+	*result_xmax = new_xmax;
+}
+
+/*
+ * Subroutine for heap_lock_updated_tuple_rec.
+ *
+ * Given a hypothetical multixact status held by the transaction identified
+ * with the given xid, does the current transaction need to wait, fail, or can
+ * it continue if it wanted to acquire a lock of the given mode?  "needwait"
+ * is set to true if waiting is necessary; if it can continue, then TM_Ok is
+ * returned.  If the lock is already held by the current transaction, return
+ * TM_SelfModified.  In case of a conflict with another transaction, a
+ * different HeapTupleSatisfiesUpdate return code is returned.
+ *
+ * The held status is said to be hypothetical because it might correspond to a
+ * lock held by a single Xid, i.e. not a real MultiXactId; we express it this
+ * way for simplicity of API.
+ */
+static TM_Result
+test_lockmode_for_conflict(MultiXactStatus status, TransactionId xid,
+						   LockTupleMode mode, HeapTuple tup,
+						   bool *needwait)
+{
+	MultiXactStatus wantedstatus;
+
+	*needwait = false;
+	wantedstatus = get_mxact_status_for_lock(mode, false);
+
+	/*
+	 * Note: we *must* check TransactionIdIsInProgress before
+	 * TransactionIdDidAbort/Commit; see comment at top of heapam_visibility.c
+	 * for an explanation.
+	 */
+	if (TransactionIdIsCurrentTransactionId(xid))
+	{
+		/*
+		 * The tuple has already been locked by our own transaction.  This is
+		 * very rare but can happen if multiple transactions are trying to
+		 * lock an ancient version of the same tuple.
+		 */
+		return TM_SelfModified;
+	}
+	else if (TransactionIdIsInProgress(xid))
+	{
+		/*
+		 * If the locking transaction is running, what we do depends on
+		 * whether the lock modes conflict: if they do, then we must wait for
+		 * it to finish; otherwise we can fall through to lock this tuple
+		 * version without waiting.
+		 */
+		if (DoLockModesConflict(LOCKMODE_from_mxstatus(status),
+								LOCKMODE_from_mxstatus(wantedstatus)))
+		{
+			*needwait = true;
+		}
+
+		/*
+		 * If we set needwait above, then this value doesn't matter;
+		 * otherwise, this value signals to caller that it's okay to proceed.
+		 */
+		return TM_Ok;
+	}
+	else if (TransactionIdDidAbort(xid))
+		return TM_Ok;
+	else if (TransactionIdDidCommit(xid))
+	{
+		/*
+		 * The other transaction committed.  If it was only a locker, then the
+		 * lock is completely gone now and we can return success; but if it
+		 * was an update, then what we do depends on whether the two lock
+		 * modes conflict.  If they conflict, then we must report error to
+		 * caller. But if they don't, we can fall through to allow the current
+		 * transaction to lock the tuple.
+		 *
+		 * Note: the reason we worry about ISUPDATE here is because as soon as
+		 * a transaction ends, all its locks are gone and meaningless, and
+		 * thus we can ignore them; whereas its updates persist.  In the
+		 * TransactionIdIsInProgress case, above, we don't need to check
+		 * because we know the lock is still "alive" and thus a conflict needs
+		 * always be checked.
+		 */
+		if (!ISUPDATE_from_mxstatus(status))
+			return TM_Ok;
+
+		if (DoLockModesConflict(LOCKMODE_from_mxstatus(status),
+								LOCKMODE_from_mxstatus(wantedstatus)))
+		{
+			/* bummer */
+			if (!ItemPointerEquals(&tup->t_self, &tup->t_data->t_ctid))
+				return TM_Updated;
+			else
+				return TM_Deleted;
+		}
+
+		return TM_Ok;
+	}
+
+	/* Not in progress, not aborted, not committed -- must have crashed */
+	return TM_Ok;
+}
+
+
+/*
+ * Recursive part of heap_lock_updated_tuple
+ *
+ * Fetch the tuple pointed to by tid in rel, and mark it as locked by the given
+ * xid with the given mode; if this tuple is updated, recurse to lock the new
+ * version as well.
+ */
+static TM_Result
+heap_lock_updated_tuple_rec(Relation rel, ItemPointer tid, TransactionId xid,
+							LockTupleMode mode)
+{
+	TM_Result	result;
+	ItemPointerData tupid;
+	HeapTupleData mytup;
+	Buffer		buf;
+	uint16		new_infomask,
+				new_infomask2,
+				old_infomask,
+				old_infomask2;
+	TransactionId xmax,
+				new_xmax;
+	TransactionId priorXmax = InvalidTransactionId;
+	bool		cleared_all_frozen = false;
+	bool		pinned_desired_page;
+	Buffer		vmbuffer = InvalidBuffer;
+	BlockNumber block;
+
+	ItemPointerCopy(tid, &tupid);
+
+	for (;;)
+	{
+		new_infomask = 0;
+		new_xmax = InvalidTransactionId;
+		block = ItemPointerGetBlockNumber(&tupid);
+		ItemPointerCopy(&tupid, &(mytup.t_self));
+
+		if (!heap_fetch(rel, SnapshotAny, &mytup, &buf))
+		{
+			/*
+			 * if we fail to find the updated version of the tuple, it's
+			 * because it was vacuumed/pruned away after its creator
+			 * transaction aborted.  So behave as if we got to the end of the
+			 * chain, and there's no further tuple to lock: return success to
+			 * caller.
+			 */
+			result = TM_Ok;
+			goto out_unlocked;
+		}
+
+l4:
+		CHECK_FOR_INTERRUPTS();
+
+		/*
+		 * Before locking the buffer, pin the visibility map page if it
+		 * appears to be necessary.  Since we haven't got the lock yet,
+		 * someone else might be in the middle of changing this, so we'll need
+		 * to recheck after we have the lock.
+		 */
+		if (PageIsAllVisible(BufferGetPage(buf)))
+		{
+			visibilitymap_pin(rel, block, &vmbuffer);
+			pinned_desired_page = true;
+		}
+		else
+			pinned_desired_page = false;
+
+		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
+
+		/*
+		 * If we didn't pin the visibility map page and the page has become
+		 * all visible while we were busy locking the buffer, we'll have to
+		 * unlock and re-lock, to avoid holding the buffer lock across I/O.
+		 * That's a bit unfortunate, but hopefully shouldn't happen often.
+		 *
+		 * Note: in some paths through this function, we will reach here
+		 * holding a pin on a vm page that may or may not be the one matching
+		 * this page.  If this page isn't all-visible, we won't use the vm
+		 * page, but we hold onto such a pin till the end of the function.
+		 */
+		if (!pinned_desired_page && PageIsAllVisible(BufferGetPage(buf)))
+		{
+			LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+			visibilitymap_pin(rel, block, &vmbuffer);
+			LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
+		}
+
+		/*
+		 * Check the tuple XMIN against prior XMAX, if any.  If we reached the
+		 * end of the chain, we're done, so return success.
+		 */
+		if (TransactionIdIsValid(priorXmax) &&
+			!TransactionIdEquals(HeapTupleHeaderGetXmin(mytup.t_data),
+								 priorXmax))
+		{
+			result = TM_Ok;
+			goto out_locked;
+		}
+
+		/*
+		 * Also check Xmin: if this tuple was created by an aborted
+		 * (sub)transaction, then we already locked the last live one in the
+		 * chain, thus we're done, so return success.
+		 */
+		if (TransactionIdDidAbort(HeapTupleHeaderGetXmin(mytup.t_data)))
+		{
+			result = TM_Ok;
+			goto out_locked;
+		}
+
+		old_infomask = mytup.t_data->t_infomask;
+		old_infomask2 = mytup.t_data->t_infomask2;
+		xmax = HeapTupleHeaderGetRawXmax(mytup.t_data);
+
+		/*
+		 * If this tuple version has been updated or locked by some concurrent
+		 * transaction(s), what we do depends on whether our lock mode
+		 * conflicts with what those other transactions hold, and also on the
+		 * status of them.
+		 */
+		if (!(old_infomask & HEAP_XMAX_INVALID))
+		{
+			TransactionId rawxmax;
+			bool		needwait;
+
+			rawxmax = HeapTupleHeaderGetRawXmax(mytup.t_data);
+			if (old_infomask & HEAP_XMAX_IS_MULTI)
+			{
+				int			nmembers;
+				int			i;
+				MultiXactMember *members;
+
+				/*
+				 * We don't need a test for pg_upgrade'd tuples: this is only
+				 * applied to tuples after the first in an update chain.  Said
+				 * first tuple in the chain may well be locked-in-9.2-and-
+				 * pg_upgraded, but that one was already locked by our caller,
+				 * not us; and any subsequent ones cannot be because our
+				 * caller must necessarily have obtained a snapshot later than
+				 * the pg_upgrade itself.
+				 */
+				Assert(!HEAP_LOCKED_UPGRADED(mytup.t_data->t_infomask));
+
+				nmembers = GetMultiXactIdMembers(rawxmax, &members, false,
+												 HEAP_XMAX_IS_LOCKED_ONLY(old_infomask));
+				for (i = 0; i < nmembers; i++)
+				{
+					result = test_lockmode_for_conflict(members[i].status,
+														members[i].xid,
+														mode,
+														&mytup,
+														&needwait);
+
+					/*
+					 * If the tuple was already locked by ourselves in a
+					 * previous iteration of this (say heap_lock_tuple was
+					 * forced to restart the locking loop because of a change
+					 * in xmax), then we hold the lock already on this tuple
+					 * version and we don't need to do anything; and this is
+					 * not an error condition either.  We just need to skip
+					 * this tuple and continue locking the next version in the
+					 * update chain.
+					 */
+					if (result == TM_SelfModified)
+					{
+						pfree(members);
+						goto next;
+					}
+
+					if (needwait)
+					{
+						LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+						XactLockTableWait(members[i].xid, rel,
+										  &mytup.t_self,
+										  XLTW_LockUpdated);
+						pfree(members);
+						goto l4;
+					}
+					if (result != TM_Ok)
+					{
+						pfree(members);
+						goto out_locked;
+					}
+				}
+				if (members)
+					pfree(members);
+			}
+			else
+			{
+				MultiXactStatus status;
+
+				/*
+				 * For a non-multi Xmax, we first need to compute the
+				 * corresponding MultiXactStatus by using the infomask bits.
+				 */
+				if (HEAP_XMAX_IS_LOCKED_ONLY(old_infomask))
+				{
+					if (HEAP_XMAX_IS_KEYSHR_LOCKED(old_infomask))
+						status = MultiXactStatusForKeyShare;
+					else if (HEAP_XMAX_IS_SHR_LOCKED(old_infomask))
+						status = MultiXactStatusForShare;
+					else if (HEAP_XMAX_IS_EXCL_LOCKED(old_infomask))
+					{
+						if (old_infomask2 & HEAP_KEYS_UPDATED)
+							status = MultiXactStatusForUpdate;
+						else
+							status = MultiXactStatusForNoKeyUpdate;
+					}
+					else
+					{
+						/*
+						 * LOCK_ONLY present alone (a pg_upgraded tuple marked
+						 * as share-locked in the old cluster) shouldn't be
+						 * seen in the middle of an update chain.
+						 */
+						elog(ERROR, "invalid lock status in tuple");
+					}
+				}
+				else
+				{
+					/* it's an update, but which kind? */
+					if (old_infomask2 & HEAP_KEYS_UPDATED)
+						status = MultiXactStatusUpdate;
+					else
+						status = MultiXactStatusNoKeyUpdate;
+				}
+
+				result = test_lockmode_for_conflict(status, rawxmax, mode,
+													&mytup, &needwait);
+
+				/*
+				 * If the tuple was already locked by ourselves in a previous
+				 * iteration of this (say heap_lock_tuple was forced to
+				 * restart the locking loop because of a change in xmax), then
+				 * we hold the lock already on this tuple version and we don't
+				 * need to do anything; and this is not an error condition
+				 * either.  We just need to skip this tuple and continue
+				 * locking the next version in the update chain.
+				 */
+				if (result == TM_SelfModified)
+					goto next;
+
+				if (needwait)
+				{
+					LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+					XactLockTableWait(rawxmax, rel, &mytup.t_self,
+									  XLTW_LockUpdated);
+					goto l4;
+				}
+				if (result != TM_Ok)
+				{
+					goto out_locked;
+				}
+			}
+		}
+
+		/* compute the new Xmax and infomask values for the tuple ... */
+		compute_new_xmax_infomask(xmax, old_infomask, mytup.t_data->t_infomask2,
+								  xid, mode, false,
+								  &new_xmax, &new_infomask, &new_infomask2);
+
+		if (PageIsAllVisible(BufferGetPage(buf)) &&
+			visibilitymap_clear(rel, block, vmbuffer,
+								VISIBILITYMAP_ALL_FROZEN))
+			cleared_all_frozen = true;
+
+		START_CRIT_SECTION();
+
+		/* ... and set them */
+		HeapTupleHeaderSetXmax(mytup.t_data, new_xmax);
+		mytup.t_data->t_infomask &= ~HEAP_XMAX_BITS;
+		mytup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+		mytup.t_data->t_infomask |= new_infomask;
+		mytup.t_data->t_infomask2 |= new_infomask2;
+
+		MarkBufferDirty(buf);
+
+		/* XLOG stuff */
+		if (RelationNeedsWAL(rel))
+		{
+			xl_heap_lock_updated xlrec;
+			XLogRecPtr	recptr;
+			Page		page = BufferGetPage(buf);
+
+			XLogBeginInsert();
+			XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
+
+			xlrec.offnum = ItemPointerGetOffsetNumber(&mytup.t_self);
+			xlrec.xmax = new_xmax;
+			xlrec.infobits_set = compute_infobits(new_infomask, new_infomask2);
+			xlrec.flags =
+				cleared_all_frozen ? XLH_LOCK_ALL_FROZEN_CLEARED : 0;
+
+			XLogRegisterData((char *) &xlrec, SizeOfHeapLockUpdated);
+
+			recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_LOCK_UPDATED);
+
+			PageSetLSN(page, recptr);
+		}
+
+		END_CRIT_SECTION();
+
+next:
+		/* if we find the end of update chain, we're done. */
+		if (mytup.t_data->t_infomask & HEAP_XMAX_INVALID ||
+			HeapTupleHeaderIndicatesMovedPartitions(mytup.t_data) ||
+			ItemPointerEquals(&mytup.t_self, &mytup.t_data->t_ctid) ||
+			HeapTupleHeaderIsOnlyLocked(mytup.t_data))
+		{
+			result = TM_Ok;
+			goto out_locked;
+		}
+
+		/* tail recursion */
+		priorXmax = HeapTupleHeaderGetUpdateXid(mytup.t_data);
+		ItemPointerCopy(&(mytup.t_data->t_ctid), &tupid);
+		UnlockReleaseBuffer(buf);
+	}
+
+	result = TM_Ok;
+
+out_locked:
+	UnlockReleaseBuffer(buf);
+
+out_unlocked:
+	if (vmbuffer != InvalidBuffer)
+		ReleaseBuffer(vmbuffer);
+
+	return result;
+}
+
+/*
+ * heap_lock_updated_tuple
+ *		Follow update chain when locking an updated tuple, acquiring locks (row
+ *		marks) on the updated versions.
+ *
+ * The initial tuple is assumed to be already locked.
+ *
+ * This function doesn't check visibility, it just unconditionally marks the
+ * tuple(s) as locked.  If any tuple in the updated chain is being deleted
+ * concurrently (or updated with the key being modified), sleep until the
+ * transaction doing it is finished.
+ *
+ * Note that we don't acquire heavyweight tuple locks on the tuples we walk
+ * when we have to wait for other transactions to release them, as opposed to
+ * what heap_lock_tuple does.  The reason is that having more than one
+ * transaction walking the chain is probably uncommon enough that risk of
+ * starvation is not likely: one of the preconditions for being here is that
+ * the snapshot in use predates the update that created this tuple (because we
+ * started at an earlier version of the tuple), but at the same time such a
+ * transaction cannot be using repeatable read or serializable isolation
+ * levels, because that would lead to a serializability failure.
+ */
+static TM_Result
+heap_lock_updated_tuple(Relation rel, HeapTuple tuple, ItemPointer ctid,
+						TransactionId xid, LockTupleMode mode)
+{
+	/*
+	 * If the tuple has not been updated, or has moved into another partition
+	 * (effectively a delete) stop here.
+	 */
+	if (!HeapTupleHeaderIndicatesMovedPartitions(tuple->t_data) &&
+		!ItemPointerEquals(&tuple->t_self, ctid))
+	{
+		/*
+		 * If this is the first possibly-multixact-able operation in the
+		 * current transaction, set my per-backend OldestMemberMXactId
+		 * setting. We can be certain that the transaction will never become a
+		 * member of any older MultiXactIds than that.  (We have to do this
+		 * even if we end up just using our own TransactionId below, since
+		 * some other backend could incorporate our XID into a MultiXact
+		 * immediately afterwards.)
+		 */
+		MultiXactIdSetOldestMember();
+
+		return heap_lock_updated_tuple_rec(rel, ctid, xid, mode);
+	}
+
+	/* nothing to lock */
+	return TM_Ok;
+}
+
+/*
+ *	heap_finish_speculative - mark speculative insertion as successful
+ *
+ * To successfully finish a speculative insertion we have to clear speculative
+ * token from tuple.  To do so the t_ctid field, which will contain a
+ * speculative token value, is modified in place to point to the tuple itself,
+ * which is characteristic of a newly inserted ordinary tuple.
+ *
+ * NB: It is not ok to commit without either finishing or aborting a
+ * speculative insertion.  We could treat speculative tuples of committed
+ * transactions implicitly as completed, but then we would have to be prepared
+ * to deal with speculative tokens on committed tuples.  That wouldn't be
+ * difficult - no-one looks at the ctid field of a tuple with invalid xmax -
+ * but clearing the token at completion isn't very expensive either.
+ * An explicit confirmation WAL record also makes logical decoding simpler.
+ */
+void
+heap_finish_speculative(Relation relation, ItemPointer tid)
+{
+	Buffer		buffer;
+	Page		page;
+	OffsetNumber offnum;
+	ItemId		lp = NULL;
+	HeapTupleHeader htup;
+
+	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
+	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+	page = (Page) BufferGetPage(buffer);
+
+	offnum = ItemPointerGetOffsetNumber(tid);
+	if (PageGetMaxOffsetNumber(page) >= offnum)
+		lp = PageGetItemId(page, offnum);
+
+	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
+		elog(ERROR, "invalid lp");
+
+	htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+	/* SpecTokenOffsetNumber should be distinguishable from any real offset */
+	StaticAssertStmt(MaxOffsetNumber < SpecTokenOffsetNumber,
+					 "invalid speculative token constant");
+
+	/* NO EREPORT(ERROR) from here till changes are logged */
+	START_CRIT_SECTION();
+
+	Assert(HeapTupleHeaderIsSpeculative(htup));
+
+	MarkBufferDirty(buffer);
+
+	/*
+	 * Replace the speculative insertion token with a real t_ctid, pointing to
+	 * itself like it does on regular tuples.
+	 */
+	htup->t_ctid = *tid;
+
+	/* XLOG stuff */
+	if (RelationNeedsWAL(relation))
+	{
+		xl_heap_confirm xlrec;
+		XLogRecPtr	recptr;
+
+		xlrec.offnum = ItemPointerGetOffsetNumber(tid);
+
+		XLogBeginInsert();
+
+		/* We want the same filtering on this as on a plain insert */
+		XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
+
+		XLogRegisterData((char *) &xlrec, SizeOfHeapConfirm);
+		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
+
+		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_CONFIRM);
+
+		PageSetLSN(page, recptr);
+	}
+
+	END_CRIT_SECTION();
+
+	UnlockReleaseBuffer(buffer);
+}
+
+/*
+ *	heap_abort_speculative - kill a speculatively inserted tuple
+ *
+ * Marks a tuple that was speculatively inserted in the same command as dead,
+ * by setting its xmin as invalid.  That makes it immediately appear as dead
+ * to all transactions, including our own.  In particular, it makes
+ * HeapTupleSatisfiesDirty() regard the tuple as dead, so that another backend
+ * inserting a duplicate key value won't unnecessarily wait for our whole
+ * transaction to finish (it'll just wait for our speculative insertion to
+ * finish).
+ *
+ * Killing the tuple prevents "unprincipled deadlocks", which are deadlocks
+ * that arise due to a mutual dependency that is not user visible.  By
+ * definition, unprincipled deadlocks cannot be prevented by the user
+ * reordering lock acquisition in client code, because the implementation level
+ * lock acquisitions are not under the user's direct control.  If speculative
+ * inserters did not take this precaution, then under high concurrency they
+ * could deadlock with each other, which would not be acceptable.
+ *
+ * This is somewhat redundant with heap_delete, but we prefer to have a
+ * dedicated routine with stripped down requirements.  Note that this is also
+ * used to delete the TOAST tuples created during speculative insertion.
+ *
+ * This routine does not affect logical decoding as it only looks at
+ * confirmation records.
+ */
+void
+heap_abort_speculative(Relation relation, ItemPointer tid)
+{
+	TransactionId xid = GetCurrentTransactionId();
+	ItemId		lp;
+	HeapTupleData tp;
+	Page		page;
+	BlockNumber block;
+	Buffer		buffer;
+	TransactionId prune_xid;
+
+	Assert(ItemPointerIsValid(tid));
+
+	block = ItemPointerGetBlockNumber(tid);
+	buffer = ReadBuffer(relation, block);
+	page = BufferGetPage(buffer);
+
+	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
+	/*
+	 * Page can't be all visible, we just inserted into it, and are still
+	 * running.
+	 */
+	Assert(!PageIsAllVisible(page));
+
+	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
+	Assert(ItemIdIsNormal(lp));
+
+	tp.t_tableOid = RelationGetRelid(relation);
+	tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
+	tp.t_len = ItemIdGetLength(lp);
+	tp.t_self = *tid;
+
+	/*
+	 * Sanity check that the tuple really is a speculatively inserted tuple,
+	 * inserted by us.
+	 */
+	if (tp.t_data->t_choice.t_heap.t_xmin != xid)
+		elog(ERROR, "attempted to kill a tuple inserted by another transaction");
+	if (!(IsToastRelation(relation) || HeapTupleHeaderIsSpeculative(tp.t_data)))
+		elog(ERROR, "attempted to kill a non-speculative tuple");
+	Assert(!HeapTupleHeaderIsHeapOnly(tp.t_data));
+
+	/*
+	 * No need to check for serializable conflicts here.  There is never a
+	 * need for a combo CID, either.  No need to extract replica identity, or
+	 * do anything special with infomask bits.
+	 */
+
+	START_CRIT_SECTION();
+
+	/*
+	 * The tuple will become DEAD immediately.  Flag that this page is a
+	 * candidate for pruning by setting xmin to TransactionXmin. While not
+	 * immediately prunable, it is the oldest xid we can cheaply determine
+	 * that's safe against wraparound / being older than the table's
+	 * relfrozenxid.  To defend against the unlikely case of a new relation
+	 * having a newer relfrozenxid than our TransactionXmin, use relfrozenxid
+	 * if so (vacuum can't subsequently move relfrozenxid to beyond
+	 * TransactionXmin, so there's no race here).
+	 */
+	Assert(TransactionIdIsValid(TransactionXmin));
+	if (TransactionIdPrecedes(TransactionXmin, relation->rd_rel->relfrozenxid))
+		prune_xid = relation->rd_rel->relfrozenxid;
+	else
+		prune_xid = TransactionXmin;
+	PageSetPrunable(page, prune_xid);
+
+	/* store transaction information of xact deleting the tuple */
+	tp.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
+	tp.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+
+	/*
+	 * Set the tuple header xmin to InvalidTransactionId.  This makes the
+	 * tuple immediately invisible everyone.  (In particular, to any
+	 * transactions waiting on the speculative token, woken up later.)
+	 */
+	HeapTupleHeaderSetXmin(tp.t_data, InvalidTransactionId);
+
+	/* Clear the speculative insertion token too */
+	tp.t_data->t_ctid = tp.t_self;
+
+	MarkBufferDirty(buffer);
+
+	/*
+	 * XLOG stuff
+	 *
+	 * The WAL records generated here match heap_delete().  The same recovery
+	 * routines are used.
+	 */
+	if (RelationNeedsWAL(relation))
+	{
+		xl_heap_delete xlrec;
+		XLogRecPtr	recptr;
+
+		xlrec.flags = XLH_DELETE_IS_SUPER;
+		xlrec.infobits_set = compute_infobits(tp.t_data->t_infomask,
+											  tp.t_data->t_infomask2);
+		xlrec.offnum = ItemPointerGetOffsetNumber(&tp.t_self);
+		xlrec.xmax = xid;
+
+		XLogBeginInsert();
+		XLogRegisterData((char *) &xlrec, SizeOfHeapDelete);
+		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
+
+		/* No replica identity & replication origin logged */
+
+		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_DELETE);
+
+		PageSetLSN(page, recptr);
+	}
+
+	END_CRIT_SECTION();
+
+	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+
+	if (HeapTupleHasExternal(&tp))
+	{
+		Assert(!IsToastRelation(relation));
+		heap_toast_delete(relation, &tp, true);
+	}
+
+	/*
+	 * Never need to mark tuple for invalidation, since catalogs don't support
+	 * speculative insertion
+	 */
+
+	/* Now we can release the buffer */
+	ReleaseBuffer(buffer);
+
+	/* count deletion, as we counted the insertion too */
+	pgstat_count_heap_delete(relation);
+}
+
+/*
+ * heap_inplace_update - update a tuple "in place" (ie, overwrite it)
+ *
+ * Overwriting violates both MVCC and transactional safety, so the uses
+ * of this function in Postgres are extremely limited.  Nonetheless we
+ * find some places to use it.
+ *
+ * The tuple cannot change size, and therefore it's reasonable to assume
+ * that its null bitmap (if any) doesn't change either.  So we just
+ * overwrite the data portion of the tuple without touching the null
+ * bitmap or any of the header fields.
+ *
+ * tuple is an in-memory tuple structure containing the data to be written
+ * over the target tuple.  Also, tuple->t_self identifies the target tuple.
+ *
+ * Note that the tuple updated here had better not come directly from the
+ * syscache if the relation has a toast relation as this tuple could
+ * include toast values that have been expanded, causing a failure here.
+ */
+void
+heap_inplace_update(Relation relation, HeapTuple tuple)
+{
+	Buffer		buffer;
+	Page		page;
+	OffsetNumber offnum;
+	ItemId		lp = NULL;
+	HeapTupleHeader htup;
+	uint32		oldlen;
+	uint32		newlen;
+
+	/*
+	 * For now, we don't allow parallel updates.  Unlike a regular update,
+	 * this should never create a combo CID, so it might be possible to relax
+	 * this restriction, but not without more thought and testing.  It's not
+	 * clear that it would be useful, anyway.
+	 */
+	if (IsInParallelMode())
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_TRANSACTION_STATE),
+				 errmsg("cannot update tuples during a parallel operation")));
+
+	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&(tuple->t_self)));
+	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+	page = (Page) BufferGetPage(buffer);
+
+	offnum = ItemPointerGetOffsetNumber(&(tuple->t_self));
+	if (PageGetMaxOffsetNumber(page) >= offnum)
+		lp = PageGetItemId(page, offnum);
+
+	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
+		elog(ERROR, "invalid lp");
+
+	htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+	oldlen = ItemIdGetLength(lp) - htup->t_hoff;
+	newlen = tuple->t_len - tuple->t_data->t_hoff;
+	if (oldlen != newlen || htup->t_hoff != tuple->t_data->t_hoff)
+		elog(ERROR, "wrong tuple length");
+
+	/* NO EREPORT(ERROR) from here till changes are logged */
+	START_CRIT_SECTION();
+
+	memcpy((char *) htup + htup->t_hoff,
+		   (char *) tuple->t_data + tuple->t_data->t_hoff,
+		   newlen);
+
+	MarkBufferDirty(buffer);
+
+	/* XLOG stuff */
+	if (RelationNeedsWAL(relation))
+	{
+		xl_heap_inplace xlrec;
+		XLogRecPtr	recptr;
+
+		xlrec.offnum = ItemPointerGetOffsetNumber(&tuple->t_self);
+
+		XLogBeginInsert();
+		XLogRegisterData((char *) &xlrec, SizeOfHeapInplace);
+
+		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
+		XLogRegisterBufData(0, (char *) htup + htup->t_hoff, newlen);
+
+		/* inplace updates aren't decoded atm, don't log the origin */
+
+		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_INPLACE);
+
+		PageSetLSN(page, recptr);
+	}
+
+	END_CRIT_SECTION();
+
+	UnlockReleaseBuffer(buffer);
+
+	/*
+	 * Send out shared cache inval if necessary.  Note that because we only
+	 * pass the new version of the tuple, this mustn't be used for any
+	 * operations that could change catcache lookup keys.  But we aren't
+	 * bothering with index updates either, so that's true a fortiori.
+	 */
+	if (!IsBootstrapProcessingMode())
+		CacheInvalidateHeapTuple(relation, tuple, NULL);
+}
+
+#define		FRM_NOOP				0x0001
+#define		FRM_INVALIDATE_XMAX		0x0002
+#define		FRM_RETURN_IS_XID		0x0004
+#define		FRM_RETURN_IS_MULTI		0x0008
+#define		FRM_MARK_COMMITTED		0x0010
+
+/*
+ * FreezeMultiXactId
+ *		Determine what to do during freezing when a tuple is marked by a
+ *		MultiXactId.
+ *
+ * NB -- this might have the side-effect of creating a new MultiXactId!
+ *
+ * "flags" is an output value; it's used to tell caller what to do on return.
+ * Possible flags are:
+ * FRM_NOOP
+ *		don't do anything -- keep existing Xmax
+ * FRM_INVALIDATE_XMAX
+ *		mark Xmax as InvalidTransactionId and set XMAX_INVALID flag.
+ * FRM_RETURN_IS_XID
+ *		The Xid return value is a single update Xid to set as xmax.
+ * FRM_MARK_COMMITTED
+ *		Xmax can be marked as HEAP_XMAX_COMMITTED
+ * FRM_RETURN_IS_MULTI
+ *		The return value is a new MultiXactId to set as new Xmax.
+ *		(caller must obtain proper infomask bits using GetMultiXactIdHintBits)
+ */
+static TransactionId
+FreezeMultiXactId(MultiXactId multi, uint16 t_infomask,
+				  TransactionId relfrozenxid, TransactionId relminmxid,
+				  TransactionId cutoff_xid, MultiXactId cutoff_multi,
+				  uint16 *flags)
+{
+	TransactionId xid = InvalidTransactionId;
+	int			i;
+	MultiXactMember *members;
+	int			nmembers;
+	bool		need_replace;
+	int			nnewmembers;
+	MultiXactMember *newmembers;
+	bool		has_lockers;
+	TransactionId update_xid;
+	bool		update_committed;
+
+	*flags = 0;
+
+	/* We should only be called in Multis */
+	Assert(t_infomask & HEAP_XMAX_IS_MULTI);
+
+	if (!MultiXactIdIsValid(multi) ||
+		HEAP_LOCKED_UPGRADED(t_infomask))
+	{
+		/* Ensure infomask bits are appropriately set/reset */
+		*flags |= FRM_INVALIDATE_XMAX;
+		return InvalidTransactionId;
+	}
+	else if (MultiXactIdPrecedes(multi, relminmxid))
+		ereport(ERROR,
+				(errcode(ERRCODE_DATA_CORRUPTED),
+				 errmsg_internal("found multixact %u from before relminmxid %u",
+								 multi, relminmxid)));
+	else if (MultiXactIdPrecedes(multi, cutoff_multi))
+	{
+		/*
+		 * This old multi cannot possibly have members still running, but
+		 * verify just in case.  If it was a locker only, it can be removed
+		 * without any further consideration; but if it contained an update,
+		 * we might need to preserve it.
+		 */
+		if (MultiXactIdIsRunning(multi,
+								 HEAP_XMAX_IS_LOCKED_ONLY(t_infomask)))
+			ereport(ERROR,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg_internal("multixact %u from before cutoff %u found to be still running",
+									 multi, cutoff_multi)));
+
+		if (HEAP_XMAX_IS_LOCKED_ONLY(t_infomask))
+		{
+			*flags |= FRM_INVALIDATE_XMAX;
+			xid = InvalidTransactionId; /* not strictly necessary */
+		}
+		else
+		{
+			/* replace multi by update xid */
+			xid = MultiXactIdGetUpdateXid(multi, t_infomask);
+
+			/* wasn't only a lock, xid needs to be valid */
+			Assert(TransactionIdIsValid(xid));
+
+			if (TransactionIdPrecedes(xid, relfrozenxid))
+				ereport(ERROR,
+						(errcode(ERRCODE_DATA_CORRUPTED),
+						 errmsg_internal("found update xid %u from before relfrozenxid %u",
+										 xid, relfrozenxid)));
+
+			/*
+			 * If the xid is older than the cutoff, it has to have aborted,
+			 * otherwise the tuple would have gotten pruned away.
+			 */
+			if (TransactionIdPrecedes(xid, cutoff_xid))
+			{
+				if (TransactionIdDidCommit(xid))
+					ereport(ERROR,
+							(errcode(ERRCODE_DATA_CORRUPTED),
+							 errmsg_internal("cannot freeze committed update xid %u", xid)));
+				*flags |= FRM_INVALIDATE_XMAX;
+				xid = InvalidTransactionId; /* not strictly necessary */
+			}
+			else
+			{
+				*flags |= FRM_RETURN_IS_XID;
+			}
+		}
+
+		return xid;
+	}
+
+	/*
+	 * This multixact might have or might not have members still running, but
+	 * we know it's valid and is newer than the cutoff point for multis.
+	 * However, some member(s) of it may be below the cutoff for Xids, so we
+	 * need to walk the whole members array to figure out what to do, if
+	 * anything.
+	 */
+
+	nmembers =
+		GetMultiXactIdMembers(multi, &members, false,
+							  HEAP_XMAX_IS_LOCKED_ONLY(t_infomask));
+	if (nmembers <= 0)
+	{
+		/* Nothing worth keeping */
+		*flags |= FRM_INVALIDATE_XMAX;
+		return InvalidTransactionId;
+	}
+
+	/* is there anything older than the cutoff? */
+	need_replace = false;
+	for (i = 0; i < nmembers; i++)
+	{
+		if (TransactionIdPrecedes(members[i].xid, cutoff_xid))
+		{
+			need_replace = true;
+			break;
+		}
+	}
+
+	/*
+	 * In the simplest case, there is no member older than the cutoff; we can
+	 * keep the existing MultiXactId as is.
+	 */
+	if (!need_replace)
+	{
+		*flags |= FRM_NOOP;
+		pfree(members);
+		return InvalidTransactionId;
+	}
+
+	/*
+	 * If the multi needs to be updated, figure out which members do we need
+	 * to keep.
+	 */
+	nnewmembers = 0;
+	newmembers = palloc(sizeof(MultiXactMember) * nmembers);
+	has_lockers = false;
+	update_xid = InvalidTransactionId;
+	update_committed = false;
+
+	for (i = 0; i < nmembers; i++)
+	{
+		/*
+		 * Determine whether to keep this member or ignore it.
+		 */
+		if (ISUPDATE_from_mxstatus(members[i].status))
+		{
+			TransactionId xid = members[i].xid;
+
+			Assert(TransactionIdIsValid(xid));
+			if (TransactionIdPrecedes(xid, relfrozenxid))
+				ereport(ERROR,
+						(errcode(ERRCODE_DATA_CORRUPTED),
+						 errmsg_internal("found update xid %u from before relfrozenxid %u",
+										 xid, relfrozenxid)));
+
+			/*
+			 * It's an update; should we keep it?  If the transaction is known
+			 * aborted or crashed then it's okay to ignore it, otherwise not.
+			 * Note that an updater older than cutoff_xid cannot possibly be
+			 * committed, because HeapTupleSatisfiesVacuum would have returned
+			 * HEAPTUPLE_DEAD and we would not be trying to freeze the tuple.
+			 *
+			 * As with all tuple visibility routines, it's critical to test
+			 * TransactionIdIsInProgress before TransactionIdDidCommit,
+			 * because of race conditions explained in detail in
+			 * heapam_visibility.c.
+			 */
+			if (TransactionIdIsCurrentTransactionId(xid) ||
+				TransactionIdIsInProgress(xid))
+			{
+				Assert(!TransactionIdIsValid(update_xid));
+				update_xid = xid;
+			}
+			else if (TransactionIdDidCommit(xid))
+			{
+				/*
+				 * The transaction committed, so we can tell caller to set
+				 * HEAP_XMAX_COMMITTED.  (We can only do this because we know
+				 * the transaction is not running.)
+				 */
+				Assert(!TransactionIdIsValid(update_xid));
+				update_committed = true;
+				update_xid = xid;
+			}
+			else
+			{
+				/*
+				 * Not in progress, not committed -- must be aborted or
+				 * crashed; we can ignore it.
+				 */
+			}
+
+			/*
+			 * Since the tuple wasn't marked HEAPTUPLE_DEAD by vacuum, the
+			 * update Xid cannot possibly be older than the xid cutoff. The
+			 * presence of such a tuple would cause corruption, so be paranoid
+			 * and check.
+			 */
+			if (TransactionIdIsValid(update_xid) &&
+				TransactionIdPrecedes(update_xid, cutoff_xid))
+				ereport(ERROR,
+						(errcode(ERRCODE_DATA_CORRUPTED),
+						 errmsg_internal("found update xid %u from before xid cutoff %u",
+										 update_xid, cutoff_xid)));
+
+			/*
+			 * If we determined that it's an Xid corresponding to an update
+			 * that must be retained, additionally add it to the list of
+			 * members of the new Multi, in case we end up using that.  (We
+			 * might still decide to use only an update Xid and not a multi,
+			 * but it's easier to maintain the list as we walk the old members
+			 * list.)
+			 */
+			if (TransactionIdIsValid(update_xid))
+				newmembers[nnewmembers++] = members[i];
+		}
+		else
+		{
+			/* We only keep lockers if they are still running */
+			if (TransactionIdIsCurrentTransactionId(members[i].xid) ||
+				TransactionIdIsInProgress(members[i].xid))
+			{
+				/* running locker cannot possibly be older than the cutoff */
+				Assert(!TransactionIdPrecedes(members[i].xid, cutoff_xid));
+				newmembers[nnewmembers++] = members[i];
+				has_lockers = true;
+			}
+		}
+	}
+
+	pfree(members);
+
+	if (nnewmembers == 0)
+	{
+		/* nothing worth keeping!? Tell caller to remove the whole thing */
+		*flags |= FRM_INVALIDATE_XMAX;
+		xid = InvalidTransactionId;
+	}
+	else if (TransactionIdIsValid(update_xid) && !has_lockers)
+	{
+		/*
+		 * If there's a single member and it's an update, pass it back alone
+		 * without creating a new Multi.  (XXX we could do this when there's a
+		 * single remaining locker, too, but that would complicate the API too
+		 * much; moreover, the case with the single updater is more
+		 * interesting, because those are longer-lived.)
+		 */
+		Assert(nnewmembers == 1);
+		*flags |= FRM_RETURN_IS_XID;
+		if (update_committed)
+			*flags |= FRM_MARK_COMMITTED;
+		xid = update_xid;
+	}
+	else
+	{
+		/*
+		 * Create a new multixact with the surviving members of the previous
+		 * one, to set as new Xmax in the tuple.
+		 */
+		xid = MultiXactIdCreateFromMembers(nnewmembers, newmembers);
+		*flags |= FRM_RETURN_IS_MULTI;
+	}
+
+	pfree(newmembers);
+
+	return xid;
+}
+
+/*
+ * heap_prepare_freeze_tuple
+ *
+ * Check to see whether any of the XID fields of a tuple (xmin, xmax, xvac)
+ * are older than the specified cutoff XID and cutoff MultiXactId.  If so,
+ * setup enough state (in the *frz output argument) to later execute and
+ * WAL-log what we would need to do, and return true.  Return false if nothing
+ * is to be changed.  In addition, set *totally_frozen_p to true if the tuple
+ * will be totally frozen after these operations are performed and false if
+ * more freezing will eventually be required.
+ *
+ * Caller is responsible for setting the offset field, if appropriate.
+ *
+ * It is assumed that the caller has checked the tuple with
+ * HeapTupleSatisfiesVacuum() and determined that it is not HEAPTUPLE_DEAD
+ * (else we should be removing the tuple, not freezing it).
+ *
+ * NB: cutoff_xid *must* be <= the current global xmin, to ensure that any
+ * XID older than it could neither be running nor seen as running by any
+ * open transaction.  This ensures that the replacement will not change
+ * anyone's idea of the tuple state.
+ * Similarly, cutoff_multi must be less than or equal to the smallest
+ * MultiXactId used by any transaction currently open.
+ *
+ * If the tuple is in a shared buffer, caller must hold an exclusive lock on
+ * that buffer.
+ *
+ * NB: It is not enough to set hint bits to indicate something is
+ * committed/invalid -- they might not be set on a standby, or after crash
+ * recovery.  We really need to remove old xids.
+ */
+bool
+heap_prepare_freeze_tuple(HeapTupleHeader tuple,
+						  TransactionId relfrozenxid, TransactionId relminmxid,
+						  TransactionId cutoff_xid, TransactionId cutoff_multi,
+						  xl_heap_freeze_tuple *frz, bool *totally_frozen_p)
+{
+	bool		changed = false;
+	bool		xmax_already_frozen = false;
+	bool		xmin_frozen;
+	bool		freeze_xmax;
+	TransactionId xid;
+
+	frz->frzflags = 0;
+	frz->t_infomask2 = tuple->t_infomask2;
+	frz->t_infomask = tuple->t_infomask;
+	frz->xmax = HeapTupleHeaderGetRawXmax(tuple);
+
+	/*
+	 * Process xmin.  xmin_frozen has two slightly different meanings: in the
+	 * !XidIsNormal case, it means "the xmin doesn't need any freezing" (it's
+	 * already a permanent value), while in the block below it is set true to
+	 * mean "xmin won't need freezing after what we do to it here" (false
+	 * otherwise).  In both cases we're allowed to set totally_frozen, as far
+	 * as xmin is concerned.
+	 */
+	xid = HeapTupleHeaderGetXmin(tuple);
+	if (!TransactionIdIsNormal(xid))
+		xmin_frozen = true;
+	else
+	{
+		if (TransactionIdPrecedes(xid, relfrozenxid))
+			ereport(ERROR,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg_internal("found xmin %u from before relfrozenxid %u",
+									 xid, relfrozenxid)));
+
+		xmin_frozen = TransactionIdPrecedes(xid, cutoff_xid);
+		if (xmin_frozen)
+		{
+			if (!TransactionIdDidCommit(xid))
+				ereport(ERROR,
+						(errcode(ERRCODE_DATA_CORRUPTED),
+						 errmsg_internal("uncommitted xmin %u from before xid cutoff %u needs to be frozen",
+										 xid, cutoff_xid)));
+
+			frz->t_infomask |= HEAP_XMIN_FROZEN;
+			changed = true;
+		}
+	}
+
+	/*
+	 * Process xmax.  To thoroughly examine the current Xmax value we need to
+	 * resolve a MultiXactId to its member Xids, in case some of them are
+	 * below the given cutoff for Xids.  In that case, those values might need
+	 * freezing, too.  Also, if a multi needs freezing, we cannot simply take
+	 * it out --- if there's a live updater Xid, it needs to be kept.
+	 *
+	 * Make sure to keep heap_tuple_needs_freeze in sync with this.
+	 */
+	xid = HeapTupleHeaderGetRawXmax(tuple);
+
+	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+	{
+		TransactionId newxmax;
+		uint16		flags;
+
+		newxmax = FreezeMultiXactId(xid, tuple->t_infomask,
+									relfrozenxid, relminmxid,
+									cutoff_xid, cutoff_multi, &flags);
+
+		freeze_xmax = (flags & FRM_INVALIDATE_XMAX);
+
+		if (flags & FRM_RETURN_IS_XID)
+		{
+			/*
+			 * NB -- some of these transformations are only valid because we
+			 * know the return Xid is a tuple updater (i.e. not merely a
+			 * locker.) Also note that the only reason we don't explicitly
+			 * worry about HEAP_KEYS_UPDATED is because it lives in
+			 * t_infomask2 rather than t_infomask.
+			 */
+			frz->t_infomask &= ~HEAP_XMAX_BITS;
+			frz->xmax = newxmax;
+			if (flags & FRM_MARK_COMMITTED)
+				frz->t_infomask |= HEAP_XMAX_COMMITTED;
+			changed = true;
+		}
+		else if (flags & FRM_RETURN_IS_MULTI)
+		{
+			uint16		newbits;
+			uint16		newbits2;
+
+			/*
+			 * We can't use GetMultiXactIdHintBits directly on the new multi
+			 * here; that routine initializes the masks to all zeroes, which
+			 * would lose other bits we need.  Doing it this way ensures all
+			 * unrelated bits remain untouched.
+			 */
+			frz->t_infomask &= ~HEAP_XMAX_BITS;
+			frz->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+			GetMultiXactIdHintBits(newxmax, &newbits, &newbits2);
+			frz->t_infomask |= newbits;
+			frz->t_infomask2 |= newbits2;
+
+			frz->xmax = newxmax;
+
+			changed = true;
+		}
+	}
+	else if (TransactionIdIsNormal(xid))
+	{
+		if (TransactionIdPrecedes(xid, relfrozenxid))
+			ereport(ERROR,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg_internal("found xmax %u from before relfrozenxid %u",
+									 xid, relfrozenxid)));
+
+		if (TransactionIdPrecedes(xid, cutoff_xid))
+		{
+			/*
+			 * If we freeze xmax, make absolutely sure that it's not an XID
+			 * that is important.  (Note, a lock-only xmax can be removed
+			 * independent of committedness, since a committed lock holder has
+			 * released the lock).
+			 */
+			if (!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask) &&
+				TransactionIdDidCommit(xid))
+				ereport(ERROR,
+						(errcode(ERRCODE_DATA_CORRUPTED),
+						 errmsg_internal("cannot freeze committed xmax %u",
+										 xid)));
+			freeze_xmax = true;
+		}
+		else
+			freeze_xmax = false;
+	}
+	else if ((tuple->t_infomask & HEAP_XMAX_INVALID) ||
+			 !TransactionIdIsValid(HeapTupleHeaderGetRawXmax(tuple)))
+	{
+		freeze_xmax = false;
+		xmax_already_frozen = true;
+	}
+	else
+		ereport(ERROR,
+				(errcode(ERRCODE_DATA_CORRUPTED),
+				 errmsg_internal("found xmax %u (infomask 0x%04x) not frozen, not multi, not normal",
+								 xid, tuple->t_infomask)));
+
+	if (freeze_xmax)
+	{
+		Assert(!xmax_already_frozen);
+
+		frz->xmax = InvalidTransactionId;
+
+		/*
+		 * The tuple might be marked either XMAX_INVALID or XMAX_COMMITTED +
+		 * LOCKED.  Normalize to INVALID just to be sure no one gets confused.
+		 * Also get rid of the HEAP_KEYS_UPDATED bit.
+		 */
+		frz->t_infomask &= ~HEAP_XMAX_BITS;
+		frz->t_infomask |= HEAP_XMAX_INVALID;
+		frz->t_infomask2 &= ~HEAP_HOT_UPDATED;
+		frz->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+		changed = true;
+	}
+
+	/*
+	 * Old-style VACUUM FULL is gone, but we have to keep this code as long as
+	 * we support having MOVED_OFF/MOVED_IN tuples in the database.
+	 */
+	if (tuple->t_infomask & HEAP_MOVED)
+	{
+		xid = HeapTupleHeaderGetXvac(tuple);
+
+		/*
+		 * For Xvac, we ignore the cutoff_xid and just always perform the
+		 * freeze operation.  The oldest release in which such a value can
+		 * actually be set is PostgreSQL 8.4, because old-style VACUUM FULL
+		 * was removed in PostgreSQL 9.0.  Note that if we were to respect
+		 * cutoff_xid here, we'd need to make surely to clear totally_frozen
+		 * when we skipped freezing on that basis.
+		 */
+		if (TransactionIdIsNormal(xid))
+		{
+			/*
+			 * If a MOVED_OFF tuple is not dead, the xvac transaction must
+			 * have failed; whereas a non-dead MOVED_IN tuple must mean the
+			 * xvac transaction succeeded.
+			 */
+			if (tuple->t_infomask & HEAP_MOVED_OFF)
+				frz->frzflags |= XLH_INVALID_XVAC;
+			else
+				frz->frzflags |= XLH_FREEZE_XVAC;
+
+			/*
+			 * Might as well fix the hint bits too; usually XMIN_COMMITTED
+			 * will already be set here, but there's a small chance not.
+			 */
+			Assert(!(tuple->t_infomask & HEAP_XMIN_INVALID));
+			frz->t_infomask |= HEAP_XMIN_COMMITTED;
+			changed = true;
+		}
+	}
+
+	*totally_frozen_p = (xmin_frozen &&
+						 (freeze_xmax || xmax_already_frozen));
+	return changed;
+}
+
+/*
+ * heap_execute_freeze_tuple
+ *		Execute the prepared freezing of a tuple.
+ *
+ * Caller is responsible for ensuring that no other backend can access the
+ * storage underlying this tuple, either by holding an exclusive lock on the
+ * buffer containing it (which is what lazy VACUUM does), or by having it be
+ * in private storage (which is what CLUSTER and friends do).
+ *
+ * Note: it might seem we could make the changes without exclusive lock, since
+ * TransactionId read/write is assumed atomic anyway.  However there is a race
+ * condition: someone who just fetched an old XID that we overwrite here could
+ * conceivably not finish checking the XID against pg_xact before we finish
+ * the VACUUM and perhaps truncate off the part of pg_xact he needs.  Getting
+ * exclusive lock ensures no other backend is in process of checking the
+ * tuple status.  Also, getting exclusive lock makes it safe to adjust the
+ * infomask bits.
+ *
+ * NB: All code in here must be safe to execute during crash recovery!
+ */
+void
+heap_execute_freeze_tuple(HeapTupleHeader tuple, xl_heap_freeze_tuple *frz)
+{
+	HeapTupleHeaderSetXmax(tuple, frz->xmax);
+
+	if (frz->frzflags & XLH_FREEZE_XVAC)
+		HeapTupleHeaderSetXvac(tuple, FrozenTransactionId);
+
+	if (frz->frzflags & XLH_INVALID_XVAC)
+		HeapTupleHeaderSetXvac(tuple, InvalidTransactionId);
+
+	tuple->t_infomask = frz->t_infomask;
+	tuple->t_infomask2 = frz->t_infomask2;
+}
+
+/*
+ * heap_freeze_tuple
+ *		Freeze tuple in place, without WAL logging.
+ *
+ * Useful for callers like CLUSTER that perform their own WAL logging.
+ */
+bool
+heap_freeze_tuple(HeapTupleHeader tuple,
+				  TransactionId relfrozenxid, TransactionId relminmxid,
+				  TransactionId cutoff_xid, TransactionId cutoff_multi)
+{
+	xl_heap_freeze_tuple frz;
+	bool		do_freeze;
+	bool		tuple_totally_frozen;
+
+	do_freeze = heap_prepare_freeze_tuple(tuple,
+										  relfrozenxid, relminmxid,
+										  cutoff_xid, cutoff_multi,
+										  &frz, &tuple_totally_frozen);
+
+	/*
+	 * Note that because this is not a WAL-logged operation, we don't need to
+	 * fill in the offset in the freeze record.
+	 */
+
+	if (do_freeze)
+		heap_execute_freeze_tuple(tuple, &frz);
+	return do_freeze;
+}
+
+/*
+ * For a given MultiXactId, return the hint bits that should be set in the
+ * tuple's infomask.
+ *
+ * Normally this should be called for a multixact that was just created, and
+ * so is on our local cache, so the GetMembers call is fast.
+ */
+static void
+GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
+					   uint16 *new_infomask2)
+{
+	int			nmembers;
+	MultiXactMember *members;
+	int			i;
+	uint16		bits = HEAP_XMAX_IS_MULTI;
+	uint16		bits2 = 0;
+	bool		has_update = false;
+	LockTupleMode strongest = LockTupleKeyShare;
+
+	/*
+	 * We only use this in multis we just created, so they cannot be values
+	 * pre-pg_upgrade.
+	 */
+	nmembers = GetMultiXactIdMembers(multi, &members, false, false);
+
+	for (i = 0; i < nmembers; i++)
+	{
+		LockTupleMode mode;
+
+		/*
+		 * Remember the strongest lock mode held by any member of the
+		 * multixact.
+		 */
+		mode = TUPLOCK_from_mxstatus(members[i].status);
+		if (mode > strongest)
+			strongest = mode;
+
+		/* See what other bits we need */
+		switch (members[i].status)
+		{
+			case MultiXactStatusForKeyShare:
+			case MultiXactStatusForShare:
+			case MultiXactStatusForNoKeyUpdate:
+				break;
+
+			case MultiXactStatusForUpdate:
+				bits2 |= HEAP_KEYS_UPDATED;
+				break;
+
+			case MultiXactStatusNoKeyUpdate:
+				has_update = true;
+				break;
+
+			case MultiXactStatusUpdate:
+				bits2 |= HEAP_KEYS_UPDATED;
+				has_update = true;
+				break;
+		}
+	}
+
+	if (strongest == LockTupleExclusive ||
+		strongest == LockTupleNoKeyExclusive)
+		bits |= HEAP_XMAX_EXCL_LOCK;
+	else if (strongest == LockTupleShare)
+		bits |= HEAP_XMAX_SHR_LOCK;
+	else if (strongest == LockTupleKeyShare)
+		bits |= HEAP_XMAX_KEYSHR_LOCK;
+
+	if (!has_update)
+		bits |= HEAP_XMAX_LOCK_ONLY;
+
+	if (nmembers > 0)
+		pfree(members);
+
+	*new_infomask = bits;
+	*new_infomask2 = bits2;
+}
+
+/*
+ * MultiXactIdGetUpdateXid
+ *
+ * Given a multixact Xmax and corresponding infomask, which does not have the
+ * HEAP_XMAX_LOCK_ONLY bit set, obtain and return the Xid of the updating
+ * transaction.
+ *
+ * Caller is expected to check the status of the updating transaction, if
+ * necessary.
+ */
+static TransactionId
+MultiXactIdGetUpdateXid(TransactionId xmax, uint16 t_infomask)
+{
+	TransactionId update_xact = InvalidTransactionId;
+	MultiXactMember *members;
+	int			nmembers;
+
+	Assert(!(t_infomask & HEAP_XMAX_LOCK_ONLY));
+	Assert(t_infomask & HEAP_XMAX_IS_MULTI);
+
+	/*
+	 * Since we know the LOCK_ONLY bit is not set, this cannot be a multi from
+	 * pre-pg_upgrade.
+	 */
+	nmembers = GetMultiXactIdMembers(xmax, &members, false, false);
+
+	if (nmembers > 0)
+	{
+		int			i;
+
+		for (i = 0; i < nmembers; i++)
+		{
+			/* Ignore lockers */
+			if (!ISUPDATE_from_mxstatus(members[i].status))
+				continue;
+
+			/* there can be at most one updater */
+			Assert(update_xact == InvalidTransactionId);
+			update_xact = members[i].xid;
+#ifndef USE_ASSERT_CHECKING
+
+			/*
+			 * in an assert-enabled build, walk the whole array to ensure
+			 * there's no other updater.
+			 */
+			break;
+#endif
+		}
+
+		pfree(members);
+	}
+
+	return update_xact;
+}
+
+/*
+ * HeapTupleGetUpdateXid
+ *		As above, but use a HeapTupleHeader
+ *
+ * See also HeapTupleHeaderGetUpdateXid, which can be used without previously
+ * checking the hint bits.
+ */
+TransactionId
+HeapTupleGetUpdateXid(HeapTupleHeader tuple)
+{
+	return MultiXactIdGetUpdateXid(HeapTupleHeaderGetRawXmax(tuple),
+								   tuple->t_infomask);
+}
+
+/*
+ * Does the given multixact conflict with the current transaction grabbing a
+ * tuple lock of the given strength?
+ *
+ * The passed infomask pairs up with the given multixact in the tuple header.
+ *
+ * If current_is_member is not NULL, it is set to 'true' if the current
+ * transaction is a member of the given multixact.
+ */
+static bool
+DoesMultiXactIdConflict(MultiXactId multi, uint16 infomask,
+						LockTupleMode lockmode, bool *current_is_member)
+{
+	int			nmembers;
+	MultiXactMember *members;
+	bool		result = false;
+	LOCKMODE	wanted = tupleLockExtraInfo[lockmode].hwlock;
+
+	if (HEAP_LOCKED_UPGRADED(infomask))
+		return false;
+
+	nmembers = GetMultiXactIdMembers(multi, &members, false,
+									 HEAP_XMAX_IS_LOCKED_ONLY(infomask));
+	if (nmembers >= 0)
+	{
+		int			i;
+
+		for (i = 0; i < nmembers; i++)
+		{
+			TransactionId memxid;
+			LOCKMODE	memlockmode;
+
+			if (result && (current_is_member == NULL || *current_is_member))
+				break;
+
+			memlockmode = LOCKMODE_from_mxstatus(members[i].status);
+
+			/* ignore members from current xact (but track their presence) */
+			memxid = members[i].xid;
+			if (TransactionIdIsCurrentTransactionId(memxid))
+			{
+				if (current_is_member != NULL)
+					*current_is_member = true;
+				continue;
+			}
+			else if (result)
+				continue;
+
+			/* ignore members that don't conflict with the lock we want */
+			if (!DoLockModesConflict(memlockmode, wanted))
+				continue;
+
+			if (ISUPDATE_from_mxstatus(members[i].status))
+			{
+				/* ignore aborted updaters */
+				if (TransactionIdDidAbort(memxid))
+					continue;
+			}
+			else
+			{
+				/* ignore lockers-only that are no longer in progress */
+				if (!TransactionIdIsInProgress(memxid))
+					continue;
+			}
+
+			/*
+			 * Whatever remains are either live lockers that conflict with our
+			 * wanted lock, and updaters that are not aborted.  Those conflict
+			 * with what we want.  Set up to return true, but keep going to
+			 * look for the current transaction among the multixact members,
+			 * if needed.
+			 */
+			result = true;
+		}
+		pfree(members);
+	}
+
+	return result;
+}
+
+/*
+ * Do_MultiXactIdWait
+ *		Actual implementation for the two functions below.
+ *
+ * 'multi', 'status' and 'infomask' indicate what to sleep on (the status is
+ * needed to ensure we only sleep on conflicting members, and the infomask is
+ * used to optimize multixact access in case it's a lock-only multi); 'nowait'
+ * indicates whether to use conditional lock acquisition, to allow callers to
+ * fail if lock is unavailable.  'rel', 'ctid' and 'oper' are used to set up
+ * context information for error messages.  'remaining', if not NULL, receives
+ * the number of members that are still running, including any (non-aborted)
+ * subtransactions of our own transaction.
+ *
+ * We do this by sleeping on each member using XactLockTableWait.  Any
+ * members that belong to the current backend are *not* waited for, however;
+ * this would not merely be useless but would lead to Assert failure inside
+ * XactLockTableWait.  By the time this returns, it is certain that all
+ * transactions *of other backends* that were members of the MultiXactId
+ * that conflict with the requested status are dead (and no new ones can have
+ * been added, since it is not legal to add members to an existing
+ * MultiXactId).
+ *
+ * But by the time we finish sleeping, someone else may have changed the Xmax
+ * of the containing tuple, so the caller needs to iterate on us somehow.
+ *
+ * Note that in case we return false, the number of remaining members is
+ * not to be trusted.
+ */
+static bool
+Do_MultiXactIdWait(MultiXactId multi, MultiXactStatus status,
+				   uint16 infomask, bool nowait,
+				   Relation rel, ItemPointer ctid, XLTW_Oper oper,
+				   int *remaining)
+{
+	bool		result = true;
+	MultiXactMember *members;
+	int			nmembers;
+	int			remain = 0;
+
+	/* for pre-pg_upgrade tuples, no need to sleep at all */
+	nmembers = HEAP_LOCKED_UPGRADED(infomask) ? -1 :
+		GetMultiXactIdMembers(multi, &members, false,
+							  HEAP_XMAX_IS_LOCKED_ONLY(infomask));
+
+	if (nmembers >= 0)
+	{
+		int			i;
+
+		for (i = 0; i < nmembers; i++)
+		{
+			TransactionId memxid = members[i].xid;
+			MultiXactStatus memstatus = members[i].status;
+
+			if (TransactionIdIsCurrentTransactionId(memxid))
+			{
+				remain++;
+				continue;
+			}
+
+			if (!DoLockModesConflict(LOCKMODE_from_mxstatus(memstatus),
+									 LOCKMODE_from_mxstatus(status)))
+			{
+				if (remaining && TransactionIdIsInProgress(memxid))
+					remain++;
+				continue;
+			}
+
+			/*
+			 * This member conflicts with our multi, so we have to sleep (or
+			 * return failure, if asked to avoid waiting.)
+			 *
+			 * Note that we don't set up an error context callback ourselves,
+			 * but instead we pass the info down to XactLockTableWait.  This
+			 * might seem a bit wasteful because the context is set up and
+			 * tore down for each member of the multixact, but in reality it
+			 * should be barely noticeable, and it avoids duplicate code.
+			 */
+			if (nowait)
+			{
+				result = ConditionalXactLockTableWait(memxid);
+				if (!result)
+					break;
+			}
+			else
+				XactLockTableWait(memxid, rel, ctid, oper);
+		}
+
+		pfree(members);
+	}
+
+	if (remaining)
+		*remaining = remain;
+
+	return result;
+}
+
+/*
+ * MultiXactIdWait
+ *		Sleep on a MultiXactId.
+ *
+ * By the time we finish sleeping, someone else may have changed the Xmax
+ * of the containing tuple, so the caller needs to iterate on us somehow.
+ *
+ * We return (in *remaining, if not NULL) the number of members that are still
+ * running, including any (non-aborted) subtransactions of our own transaction.
+ */
+static void
+MultiXactIdWait(MultiXactId multi, MultiXactStatus status, uint16 infomask,
+				Relation rel, ItemPointer ctid, XLTW_Oper oper,
+				int *remaining)
+{
+	(void) Do_MultiXactIdWait(multi, status, infomask, false,
+							  rel, ctid, oper, remaining);
+}
+
+/*
+ * ConditionalMultiXactIdWait
+ *		As above, but only lock if we can get the lock without blocking.
+ *
+ * By the time we finish sleeping, someone else may have changed the Xmax
+ * of the containing tuple, so the caller needs to iterate on us somehow.
+ *
+ * If the multixact is now all gone, return true.  Returns false if some
+ * transactions might still be running.
+ *
+ * We return (in *remaining, if not NULL) the number of members that are still
+ * running, including any (non-aborted) subtransactions of our own transaction.
+ */
+static bool
+ConditionalMultiXactIdWait(MultiXactId multi, MultiXactStatus status,
+						   uint16 infomask, Relation rel, int *remaining)
+{
+	return Do_MultiXactIdWait(multi, status, infomask, true,
+							  rel, NULL, XLTW_None, remaining);
+}
+
+/*
+ * heap_tuple_needs_eventual_freeze
+ *
+ * Check to see whether any of the XID fields of a tuple (xmin, xmax, xvac)
+ * will eventually require freezing.  Similar to heap_tuple_needs_freeze,
+ * but there's no cutoff, since we're trying to figure out whether freezing
+ * will ever be needed, not whether it's needed now.
+ */
+bool
+heap_tuple_needs_eventual_freeze(HeapTupleHeader tuple)
+{
+	TransactionId xid;
+
+	/*
+	 * If xmin is a normal transaction ID, this tuple is definitely not
+	 * frozen.
+	 */
+	xid = HeapTupleHeaderGetXmin(tuple);
+	if (TransactionIdIsNormal(xid))
+		return true;
+
+	/*
+	 * If xmax is a valid xact or multixact, this tuple is also not frozen.
+	 */
+	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+	{
+		MultiXactId multi;
+
+		multi = HeapTupleHeaderGetRawXmax(tuple);
+		if (MultiXactIdIsValid(multi))
+			return true;
+	}
+	else
+	{
+		xid = HeapTupleHeaderGetRawXmax(tuple);
+		if (TransactionIdIsNormal(xid))
+			return true;
+	}
+
+	if (tuple->t_infomask & HEAP_MOVED)
+	{
+		xid = HeapTupleHeaderGetXvac(tuple);
+		if (TransactionIdIsNormal(xid))
+			return true;
+	}
+
+	return false;
+}
+
+/*
+ * heap_tuple_needs_freeze
+ *
+ * Check to see whether any of the XID fields of a tuple (xmin, xmax, xvac)
+ * are older than the specified cutoff XID or MultiXactId.  If so, return true.
+ *
+ * It doesn't matter whether the tuple is alive or dead, we are checking
+ * to see if a tuple needs to be removed or frozen to avoid wraparound.
+ *
+ * NB: Cannot rely on hint bits here, they might not be set after a crash or
+ * on a standby.
+ */
+bool
+heap_tuple_needs_freeze(HeapTupleHeader tuple, TransactionId cutoff_xid,
+						MultiXactId cutoff_multi, Buffer buf)
+{
+	TransactionId xid;
+
+	xid = HeapTupleHeaderGetXmin(tuple);
+	if (TransactionIdIsNormal(xid) &&
+		TransactionIdPrecedes(xid, cutoff_xid))
+		return true;
+
+	/*
+	 * The considerations for multixacts are complicated; look at
+	 * heap_prepare_freeze_tuple for justifications.  This routine had better
+	 * be in sync with that one!
+	 */
+	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+	{
+		MultiXactId multi;
+
+		multi = HeapTupleHeaderGetRawXmax(tuple);
+		if (!MultiXactIdIsValid(multi))
+		{
+			/* no xmax set, ignore */
+			;
+		}
+		else if (HEAP_LOCKED_UPGRADED(tuple->t_infomask))
+			return true;
+		else if (MultiXactIdPrecedes(multi, cutoff_multi))
+			return true;
+		else
+		{
+			MultiXactMember *members;
+			int			nmembers;
+			int			i;
+
+			/* need to check whether any member of the mxact is too old */
+
+			nmembers = GetMultiXactIdMembers(multi, &members, false,
+											 HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask));
+
+			for (i = 0; i < nmembers; i++)
+			{
+				if (TransactionIdPrecedes(members[i].xid, cutoff_xid))
+				{
+					pfree(members);
+					return true;
+				}
+			}
+			if (nmembers > 0)
+				pfree(members);
+		}
+	}
+	else
+	{
+		xid = HeapTupleHeaderGetRawXmax(tuple);
+		if (TransactionIdIsNormal(xid) &&
+			TransactionIdPrecedes(xid, cutoff_xid))
+			return true;
+	}
+
+	if (tuple->t_infomask & HEAP_MOVED)
+	{
+		xid = HeapTupleHeaderGetXvac(tuple);
+		if (TransactionIdIsNormal(xid) &&
+			TransactionIdPrecedes(xid, cutoff_xid))
+			return true;
+	}
+
+	return false;
+}
+
+/*
+ * If 'tuple' contains any visible XID greater than latestRemovedXid,
+ * ratchet forwards latestRemovedXid to the greatest one found.
+ * This is used as the basis for generating Hot Standby conflicts, so
+ * if a tuple was never visible then removing it should not conflict
+ * with queries.
+ */
+void
+HeapTupleHeaderAdvanceLatestRemovedXid(HeapTupleHeader tuple,
+									   TransactionId *latestRemovedXid)
+{
+	TransactionId xmin = HeapTupleHeaderGetXmin(tuple);
+	TransactionId xmax = HeapTupleHeaderGetUpdateXid(tuple);
+	TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+	if (tuple->t_infomask & HEAP_MOVED)
+	{
+		if (TransactionIdPrecedes(*latestRemovedXid, xvac))
+			*latestRemovedXid = xvac;
+	}
+
+	/*
+	 * Ignore tuples inserted by an aborted transaction or if the tuple was
+	 * updated/deleted by the inserting transaction.
+	 *
+	 * Look for a committed hint bit, or if no xmin bit is set, check clog.
+	 */
+	if (HeapTupleHeaderXminCommitted(tuple) ||
+		(!HeapTupleHeaderXminInvalid(tuple) && TransactionIdDidCommit(xmin)))
+	{
+		if (xmax != xmin &&
+			TransactionIdFollows(xmax, *latestRemovedXid))
+			*latestRemovedXid = xmax;
+	}
+
+	/* *latestRemovedXid may still be invalid at end */
+}
+
+#ifdef USE_PREFETCH
+/*
+ * Helper function for heap_index_delete_tuples.  Issues prefetch requests for
+ * prefetch_count buffers.  The prefetch_state keeps track of all the buffers
+ * we can prefetch, and which have already been prefetched; each call to this
+ * function picks up where the previous call left off.
+ *
+ * Note: we expect the deltids array to be sorted in an order that groups TIDs
+ * by heap block, with all TIDs for each block appearing together in exactly
+ * one group.
+ */
+static void
+index_delete_prefetch_buffer(Relation rel,
+							 IndexDeletePrefetchState *prefetch_state,
+							 int prefetch_count)
+{
+	BlockNumber cur_hblkno = prefetch_state->cur_hblkno;
+	int			count = 0;
+	int			i;
+	int			ndeltids = prefetch_state->ndeltids;
+	TM_IndexDelete *deltids = prefetch_state->deltids;
+
+	for (i = prefetch_state->next_item;
+		 i < ndeltids && count < prefetch_count;
+		 i++)
+	{
+		ItemPointer htid = &deltids[i].tid;
+
+		if (cur_hblkno == InvalidBlockNumber ||
+			ItemPointerGetBlockNumber(htid) != cur_hblkno)
+		{
+			cur_hblkno = ItemPointerGetBlockNumber(htid);
+			PrefetchBuffer(rel, MAIN_FORKNUM, cur_hblkno);
+			count++;
+		}
+	}
+
+	/*
+	 * Save the prefetch position so that next time we can continue from that
+	 * position.
+	 */
+	prefetch_state->next_item = i;
+	prefetch_state->cur_hblkno = cur_hblkno;
+}
+#endif
+
+/*
+ * heapam implementation of tableam's index_delete_tuples interface.
+ *
+ * This helper function is called by index AMs during index tuple deletion.
+ * See tableam header comments for an explanation of the interface implemented
+ * here and a general theory of operation.  Note that each call here is either
+ * a simple index deletion call, or a bottom-up index deletion call.
+ *
+ * It's possible for this to generate a fair amount of I/O, since we may be
+ * deleting hundreds of tuples from a single index block.  To amortize that
+ * cost to some degree, this uses prefetching and combines repeat accesses to
+ * the same heap block.
+ */
+TransactionId
+heap_index_delete_tuples(Relation rel, TM_IndexDeleteOp *delstate)
+{
+	/* Initial assumption is that earlier pruning took care of conflict */
+	TransactionId latestRemovedXid = InvalidTransactionId;
+	BlockNumber blkno = InvalidBlockNumber;
+	Buffer		buf = InvalidBuffer;
+	Page		page = NULL;
+	OffsetNumber maxoff = InvalidOffsetNumber;
+	TransactionId priorXmax;
+#ifdef USE_PREFETCH
+	IndexDeletePrefetchState prefetch_state;
+	int			prefetch_distance;
+#endif
+	SnapshotData SnapshotNonVacuumable;
+	int			finalndeltids = 0,
+				nblocksaccessed = 0;
+
+	/* State that's only used in bottom-up index deletion case */
+	int			nblocksfavorable = 0;
+	int			curtargetfreespace = delstate->bottomupfreespace,
+				lastfreespace = 0,
+				actualfreespace = 0;
+	bool		bottomup_final_block = false;
+
+	InitNonVacuumableSnapshot(SnapshotNonVacuumable, GlobalVisTestFor(rel));
+
+	/* Sort caller's deltids array by TID for further processing */
+	index_delete_sort(delstate);
+
+	/*
+	 * Bottom-up case: resort deltids array in an order attuned to where the
+	 * greatest number of promising TIDs are to be found, and determine how
+	 * many blocks from the start of sorted array should be considered
+	 * favorable.  This will also shrink the deltids array in order to
+	 * eliminate completely unfavorable blocks up front.
+	 */
+	if (delstate->bottomup)
+		nblocksfavorable = bottomup_sort_and_shrink(delstate);
+
+#ifdef USE_PREFETCH
+	/* Initialize prefetch state. */
+	prefetch_state.cur_hblkno = InvalidBlockNumber;
+	prefetch_state.next_item = 0;
+	prefetch_state.ndeltids = delstate->ndeltids;
+	prefetch_state.deltids = delstate->deltids;
+
+	/*
+	 * Determine the prefetch distance that we will attempt to maintain.
+	 *
+	 * Since the caller holds a buffer lock somewhere in rel, we'd better make
+	 * sure that isn't a catalog relation before we call code that does
+	 * syscache lookups, to avoid risk of deadlock.
+	 */
+	if (IsCatalogRelation(rel))
+		prefetch_distance = maintenance_io_concurrency;
+	else
+		prefetch_distance =
+			get_tablespace_maintenance_io_concurrency(rel->rd_rel->reltablespace);
+
+	/* Cap initial prefetch distance for bottom-up deletion caller */
+	if (delstate->bottomup)
+	{
+		Assert(nblocksfavorable >= 1);
+		Assert(nblocksfavorable <= BOTTOMUP_MAX_NBLOCKS);
+		prefetch_distance = Min(prefetch_distance, nblocksfavorable);
+	}
+
+	/* Start prefetching. */
+	index_delete_prefetch_buffer(rel, &prefetch_state, prefetch_distance);
+#endif
+
+	/* Iterate over deltids, determine which to delete, check their horizon */
+	Assert(delstate->ndeltids > 0);
+	for (int i = 0; i < delstate->ndeltids; i++)
+	{
+		TM_IndexDelete *ideltid = &delstate->deltids[i];
+		TM_IndexStatus *istatus = delstate->status + ideltid->id;
+		ItemPointer htid = &ideltid->tid;
+		OffsetNumber offnum;
+
+		/*
+		 * Read buffer, and perform required extra steps each time a new block
+		 * is encountered.  Avoid refetching if it's the same block as the one
+		 * from the last htid.
+		 */
+		if (blkno == InvalidBlockNumber ||
+			ItemPointerGetBlockNumber(htid) != blkno)
+		{
+			/*
+			 * Consider giving up early for bottom-up index deletion caller
+			 * first. (Only prefetch next-next block afterwards, when it
+			 * becomes clear that we're at least going to access the next
+			 * block in line.)
+			 *
+			 * Sometimes the first block frees so much space for bottom-up
+			 * caller that the deletion process can end without accessing any
+			 * more blocks.  It is usually necessary to access 2 or 3 blocks
+			 * per bottom-up deletion operation, though.
+			 */
+			if (delstate->bottomup)
+			{
+				/*
+				 * We often allow caller to delete a few additional items
+				 * whose entries we reached after the point that space target
+				 * from caller was satisfied.  The cost of accessing the page
+				 * was already paid at that point, so it made sense to finish
+				 * it off.  When that happened, we finalize everything here
+				 * (by finishing off the whole bottom-up deletion operation
+				 * without needlessly paying the cost of accessing any more
+				 * blocks).
+				 */
+				if (bottomup_final_block)
+					break;
+
+				/*
+				 * Give up when we didn't enable our caller to free any
+				 * additional space as a result of processing the page that we
+				 * just finished up with.  This rule is the main way in which
+				 * we keep the cost of bottom-up deletion under control.
+				 */
+				if (nblocksaccessed >= 1 && actualfreespace == lastfreespace)
+					break;
+				lastfreespace = actualfreespace;	/* for next time */
+
+				/*
+				 * Deletion operation (which is bottom-up) will definitely
+				 * access the next block in line.  Prepare for that now.
+				 *
+				 * Decay target free space so that we don't hang on for too
+				 * long with a marginal case. (Space target is only truly
+				 * helpful when it allows us to recognize that we don't need
+				 * to access more than 1 or 2 blocks to satisfy caller due to
+				 * agreeable workload characteristics.)
+				 *
+				 * We are a bit more patient when we encounter contiguous
+				 * blocks, though: these are treated as favorable blocks.  The
+				 * decay process is only applied when the next block in line
+				 * is not a favorable/contiguous block.  This is not an
+				 * exception to the general rule; we still insist on finding
+				 * at least one deletable item per block accessed.  See
+				 * bottomup_nblocksfavorable() for full details of the theory
+				 * behind favorable blocks and heap block locality in general.
+				 *
+				 * Note: The first block in line is always treated as a
+				 * favorable block, so the earliest possible point that the
+				 * decay can be applied is just before we access the second
+				 * block in line.  The Assert() verifies this for us.
+				 */
+				Assert(nblocksaccessed > 0 || nblocksfavorable > 0);
+				if (nblocksfavorable > 0)
+					nblocksfavorable--;
+				else
+					curtargetfreespace /= 2;
+			}
+
+			/* release old buffer */
+			if (BufferIsValid(buf))
+				UnlockReleaseBuffer(buf);
+
+			blkno = ItemPointerGetBlockNumber(htid);
+			buf = ReadBuffer(rel, blkno);
+			nblocksaccessed++;
+			Assert(!delstate->bottomup ||
+				   nblocksaccessed <= BOTTOMUP_MAX_NBLOCKS);
+
+#ifdef USE_PREFETCH
+
+			/*
+			 * To maintain the prefetch distance, prefetch one more page for
+			 * each page we read.
+			 */
+			index_delete_prefetch_buffer(rel, &prefetch_state, 1);
+#endif
+
+			LockBuffer(buf, BUFFER_LOCK_SHARE);
+
+			page = BufferGetPage(buf);
+			maxoff = PageGetMaxOffsetNumber(page);
+		}
+
+		if (istatus->knowndeletable)
+			Assert(!delstate->bottomup && !istatus->promising);
+		else
+		{
+			ItemPointerData tmp = *htid;
+			HeapTupleData heapTuple;
+
+			/* Are any tuples from this HOT chain non-vacuumable? */
+			if (heap_hot_search_buffer(&tmp, rel, buf, &SnapshotNonVacuumable,
+									   &heapTuple, NULL, true))
+				continue;		/* can't delete entry */
+
+			/* Caller will delete, since whole HOT chain is vacuumable */
+			istatus->knowndeletable = true;
+
+			/* Maintain index free space info for bottom-up deletion case */
+			if (delstate->bottomup)
+			{
+				Assert(istatus->freespace > 0);
+				actualfreespace += istatus->freespace;
+				if (actualfreespace >= curtargetfreespace)
+					bottomup_final_block = true;
+			}
+		}
+
+		/*
+		 * Maintain latestRemovedXid value for deletion operation as a whole
+		 * by advancing current value using heap tuple headers.  This is
+		 * loosely based on the logic for pruning a HOT chain.
+		 */
+		offnum = ItemPointerGetOffsetNumber(htid);
+		priorXmax = InvalidTransactionId;	/* cannot check first XMIN */
+		for (;;)
+		{
+			ItemId		lp;
+			HeapTupleHeader htup;
+
+			/* Some sanity checks */
+			if (offnum < FirstOffsetNumber || offnum > maxoff)
+				break;
+
+			lp = PageGetItemId(page, offnum);
+			if (ItemIdIsRedirected(lp))
+			{
+				offnum = ItemIdGetRedirect(lp);
+				continue;
+			}
+
+			/*
+			 * We'll often encounter LP_DEAD line pointers (especially with an
+			 * entry marked knowndeletable by our caller up front).  No heap
+			 * tuple headers get examined for an htid that leads us to an
+			 * LP_DEAD item.  This is okay because the earlier pruning
+			 * operation that made the line pointer LP_DEAD in the first place
+			 * must have considered the original tuple header as part of
+			 * generating its own latestRemovedXid value.
+			 *
+			 * Relying on XLOG_HEAP2_PRUNE records like this is the same
+			 * strategy that index vacuuming uses in all cases.  Index VACUUM
+			 * WAL records don't even have a latestRemovedXid field of their
+			 * own for this reason.
+			 */
+			if (!ItemIdIsNormal(lp))
+				break;
+
+			htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+			/*
+			 * Check the tuple XMIN against prior XMAX, if any
+			 */
+			if (TransactionIdIsValid(priorXmax) &&
+				!TransactionIdEquals(HeapTupleHeaderGetXmin(htup), priorXmax))
+				break;
+
+			HeapTupleHeaderAdvanceLatestRemovedXid(htup, &latestRemovedXid);
+
+			/*
+			 * If the tuple is not HOT-updated, then we are at the end of this
+			 * HOT-chain.  No need to visit later tuples from the same update
+			 * chain (they get their own index entries) -- just move on to
+			 * next htid from index AM caller.
+			 */
+			if (!HeapTupleHeaderIsHotUpdated(htup))
+				break;
+
+			/* Advance to next HOT chain member */
+			Assert(ItemPointerGetBlockNumber(&htup->t_ctid) == blkno);
+			offnum = ItemPointerGetOffsetNumber(&htup->t_ctid);
+			priorXmax = HeapTupleHeaderGetUpdateXid(htup);
+		}
+
+		/* Enable further/final shrinking of deltids for caller */
+		finalndeltids = i + 1;
+	}
+
+	UnlockReleaseBuffer(buf);
+
+	/*
+	 * Shrink deltids array to exclude non-deletable entries at the end.  This
+	 * is not just a minor optimization.  Final deltids array size might be
+	 * zero for a bottom-up caller.  Index AM is explicitly allowed to rely on
+	 * ndeltids being zero in all cases with zero total deletable entries.
+	 */
+	Assert(finalndeltids > 0 || delstate->bottomup);
+	delstate->ndeltids = finalndeltids;
+
+	return latestRemovedXid;
+}
+
+/*
+ * Specialized inlineable comparison function for index_delete_sort()
+ */
+static inline int
+index_delete_sort_cmp(TM_IndexDelete *deltid1, TM_IndexDelete *deltid2)
+{
+	ItemPointer tid1 = &deltid1->tid;
+	ItemPointer tid2 = &deltid2->tid;
+
+	{
+		BlockNumber blk1 = ItemPointerGetBlockNumber(tid1);
+		BlockNumber blk2 = ItemPointerGetBlockNumber(tid2);
+
+		if (blk1 != blk2)
+			return (blk1 < blk2) ? -1 : 1;
+	}
+	{
+		OffsetNumber pos1 = ItemPointerGetOffsetNumber(tid1);
+		OffsetNumber pos2 = ItemPointerGetOffsetNumber(tid2);
+
+		if (pos1 != pos2)
+			return (pos1 < pos2) ? -1 : 1;
+	}
+
+	Assert(false);
+
+	return 0;
+}
+
+/*
+ * Sort deltids array from delstate by TID.  This prepares it for further
+ * processing by heap_index_delete_tuples().
+ *
+ * This operation becomes a noticeable consumer of CPU cycles with some
+ * workloads, so we go to the trouble of specialization/micro optimization.
+ * We use shellsort for this because it's easy to specialize, compiles to
+ * relatively few instructions, and is adaptive to presorted inputs/subsets
+ * (which are typical here).
+ */
+static void
+index_delete_sort(TM_IndexDeleteOp *delstate)
+{
+	TM_IndexDelete *deltids = delstate->deltids;
+	int			ndeltids = delstate->ndeltids;
+	int			low = 0;
+
+	/*
+	 * Shellsort gap sequence (taken from Sedgewick-Incerpi paper).
+	 *
+	 * This implementation is fast with array sizes up to ~4500.  This covers
+	 * all supported BLCKSZ values.
+	 */
+	const int	gaps[9] = {1968, 861, 336, 112, 48, 21, 7, 3, 1};
+
+	/* Think carefully before changing anything here -- keep swaps cheap */
+	StaticAssertStmt(sizeof(TM_IndexDelete) <= 8,
+					 "element size exceeds 8 bytes");
+
+	for (int g = 0; g < lengthof(gaps); g++)
+	{
+		for (int hi = gaps[g], i = low + hi; i < ndeltids; i++)
+		{
+			TM_IndexDelete d = deltids[i];
+			int			j = i;
+
+			while (j >= hi && index_delete_sort_cmp(&deltids[j - hi], &d) >= 0)
+			{
+				deltids[j] = deltids[j - hi];
+				j -= hi;
+			}
+			deltids[j] = d;
+		}
+	}
+}
+
+/*
+ * Returns how many blocks should be considered favorable/contiguous for a
+ * bottom-up index deletion pass.  This is a number of heap blocks that starts
+ * from and includes the first block in line.
+ *
+ * There is always at least one favorable block during bottom-up index
+ * deletion.  In the worst case (i.e. with totally random heap blocks) the
+ * first block in line (the only favorable block) can be thought of as a
+ * degenerate array of contiguous blocks that consists of a single block.
+ * heap_index_delete_tuples() will expect this.
+ *
+ * Caller passes blockgroups, a description of the final order that deltids
+ * will be sorted in for heap_index_delete_tuples() bottom-up index deletion
+ * processing.  Note that deltids need not actually be sorted just yet (caller
+ * only passes deltids to us so that we can interpret blockgroups).
+ *
+ * You might guess that the existence of contiguous blocks cannot matter much,
+ * since in general the main factor that determines which blocks we visit is
+ * the number of promising TIDs, which is a fixed hint from the index AM.
+ * We're not really targeting the general case, though -- the actual goal is
+ * to adapt our behavior to a wide variety of naturally occurring conditions.
+ * The effects of most of the heuristics we apply are only noticeable in the
+ * aggregate, over time and across many _related_ bottom-up index deletion
+ * passes.
+ *
+ * Deeming certain blocks favorable allows heapam to recognize and adapt to
+ * workloads where heap blocks visited during bottom-up index deletion can be
+ * accessed contiguously, in the sense that each newly visited block is the
+ * neighbor of the block that bottom-up deletion just finished processing (or
+ * close enough to it).  It will likely be cheaper to access more favorable
+ * blocks sooner rather than later (e.g. in this pass, not across a series of
+ * related bottom-up passes).  Either way it is probably only a matter of time
+ * (or a matter of further correlated version churn) before all blocks that
+ * appear together as a single large batch of favorable blocks get accessed by
+ * _some_ bottom-up pass.  Large batches of favorable blocks tend to either
+ * appear almost constantly or not even once (it all depends on per-index
+ * workload characteristics).
+ *
+ * Note that the blockgroups sort order applies a power-of-two bucketing
+ * scheme that creates opportunities for contiguous groups of blocks to get
+ * batched together, at least with workloads that are naturally amenable to
+ * being driven by heap block locality.  This doesn't just enhance the spatial
+ * locality of bottom-up heap block processing in the obvious way.  It also
+ * enables temporal locality of access, since sorting by heap block number
+ * naturally tends to make the bottom-up processing order deterministic.
+ *
+ * Consider the following example to get a sense of how temporal locality
+ * might matter: There is a heap relation with several indexes, each of which
+ * is low to medium cardinality.  It is subject to constant non-HOT updates.
+ * The updates are skewed (in one part of the primary key, perhaps).  None of
+ * the indexes are logically modified by the UPDATE statements (if they were
+ * then bottom-up index deletion would not be triggered in the first place).
+ * Naturally, each new round of index tuples (for each heap tuple that gets a
+ * heap_update() call) will have the same heap TID in each and every index.
+ * Since these indexes are low cardinality and never get logically modified,
+ * heapam processing during bottom-up deletion passes will access heap blocks
+ * in approximately sequential order.  Temporal locality of access occurs due
+ * to bottom-up deletion passes behaving very similarly across each of the
+ * indexes at any given moment.  This keeps the number of buffer misses needed
+ * to visit heap blocks to a minimum.
+ */
+static int
+bottomup_nblocksfavorable(IndexDeleteCounts *blockgroups, int nblockgroups,
+						  TM_IndexDelete *deltids)
+{
+	int64		lastblock = -1;
+	int			nblocksfavorable = 0;
+
+	Assert(nblockgroups >= 1);
+	Assert(nblockgroups <= BOTTOMUP_MAX_NBLOCKS);
+
+	/*
+	 * We tolerate heap blocks that will be accessed only slightly out of
+	 * physical order.  Small blips occur when a pair of almost-contiguous
+	 * blocks happen to fall into different buckets (perhaps due only to a
+	 * small difference in npromisingtids that the bucketing scheme didn't
+	 * quite manage to ignore).  We effectively ignore these blips by applying
+	 * a small tolerance.  The precise tolerance we use is a little arbitrary,
+	 * but it works well enough in practice.
+	 */
+	for (int b = 0; b < nblockgroups; b++)
+	{
+		IndexDeleteCounts *group = blockgroups + b;
+		TM_IndexDelete *firstdtid = deltids + group->ifirsttid;
+		BlockNumber block = ItemPointerGetBlockNumber(&firstdtid->tid);
+
+		if (lastblock != -1 &&
+			((int64) block < lastblock - BOTTOMUP_TOLERANCE_NBLOCKS ||
+			 (int64) block > lastblock + BOTTOMUP_TOLERANCE_NBLOCKS))
+			break;
+
+		nblocksfavorable++;
+		lastblock = block;
+	}
+
+	/* Always indicate that there is at least 1 favorable block */
+	Assert(nblocksfavorable >= 1);
+
+	return nblocksfavorable;
+}
+
+/*
+ * qsort comparison function for bottomup_sort_and_shrink()
+ */
+static int
+bottomup_sort_and_shrink_cmp(const void *arg1, const void *arg2)
+{
+	const IndexDeleteCounts *group1 = (const IndexDeleteCounts *) arg1;
+	const IndexDeleteCounts *group2 = (const IndexDeleteCounts *) arg2;
+
+	/*
+	 * Most significant field is npromisingtids (which we invert the order of
+	 * so as to sort in desc order).
+	 *
+	 * Caller should have already normalized npromisingtids fields into
+	 * power-of-two values (buckets).
+	 */
+	if (group1->npromisingtids > group2->npromisingtids)
+		return -1;
+	if (group1->npromisingtids < group2->npromisingtids)
+		return 1;
+
+	/*
+	 * Tiebreak: desc ntids sort order.
+	 *
+	 * We cannot expect power-of-two values for ntids fields.  We should
+	 * behave as if they were already rounded up for us instead.
+	 */
+	if (group1->ntids != group2->ntids)
+	{
+		uint32		ntids1 = pg_nextpower2_32((uint32) group1->ntids);
+		uint32		ntids2 = pg_nextpower2_32((uint32) group2->ntids);
+
+		if (ntids1 > ntids2)
+			return -1;
+		if (ntids1 < ntids2)
+			return 1;
+	}
+
+	/*
+	 * Tiebreak: asc offset-into-deltids-for-block (offset to first TID for
+	 * block in deltids array) order.
+	 *
+	 * This is equivalent to sorting in ascending heap block number order
+	 * (among otherwise equal subsets of the array).  This approach allows us
+	 * to avoid accessing the out-of-line TID.  (We rely on the assumption
+	 * that the deltids array was sorted in ascending heap TID order when
+	 * these offsets to the first TID from each heap block group were formed.)
+	 */
+	if (group1->ifirsttid > group2->ifirsttid)
+		return 1;
+	if (group1->ifirsttid < group2->ifirsttid)
+		return -1;
+
+	pg_unreachable();
+
+	return 0;
+}
+
+/*
+ * heap_index_delete_tuples() helper function for bottom-up deletion callers.
+ *
+ * Sorts deltids array in the order needed for useful processing by bottom-up
+ * deletion.  The array should already be sorted in TID order when we're
+ * called.  The sort process groups heap TIDs from deltids into heap block
+ * groupings.  Earlier/more-promising groups/blocks are usually those that are
+ * known to have the most "promising" TIDs.
+ *
+ * Sets new size of deltids array (ndeltids) in state.  deltids will only have
+ * TIDs from the BOTTOMUP_MAX_NBLOCKS most promising heap blocks when we
+ * return.  This often means that deltids will be shrunk to a small fraction
+ * of its original size (we eliminate many heap blocks from consideration for
+ * caller up front).
+ *
+ * Returns the number of "favorable" blocks.  See bottomup_nblocksfavorable()
+ * for a definition and full details.
+ */
+static int
+bottomup_sort_and_shrink(TM_IndexDeleteOp *delstate)
+{
+	IndexDeleteCounts *blockgroups;
+	TM_IndexDelete *reordereddeltids;
+	BlockNumber curblock = InvalidBlockNumber;
+	int			nblockgroups = 0;
+	int			ncopied = 0;
+	int			nblocksfavorable = 0;
+
+	Assert(delstate->bottomup);
+	Assert(delstate->ndeltids > 0);
+
+	/* Calculate per-heap-block count of TIDs */
+	blockgroups = palloc(sizeof(IndexDeleteCounts) * delstate->ndeltids);
+	for (int i = 0; i < delstate->ndeltids; i++)
+	{
+		TM_IndexDelete *ideltid = &delstate->deltids[i];
+		TM_IndexStatus *istatus = delstate->status + ideltid->id;
+		ItemPointer htid = &ideltid->tid;
+		bool		promising = istatus->promising;
+
+		if (curblock != ItemPointerGetBlockNumber(htid))
+		{
+			/* New block group */
+			nblockgroups++;
+
+			Assert(curblock < ItemPointerGetBlockNumber(htid) ||
+				   !BlockNumberIsValid(curblock));
+
+			curblock = ItemPointerGetBlockNumber(htid);
+			blockgroups[nblockgroups - 1].ifirsttid = i;
+			blockgroups[nblockgroups - 1].ntids = 1;
+			blockgroups[nblockgroups - 1].npromisingtids = 0;
+		}
+		else
+		{
+			blockgroups[nblockgroups - 1].ntids++;
+		}
+
+		if (promising)
+			blockgroups[nblockgroups - 1].npromisingtids++;
+	}
+
+	/*
+	 * We're about ready to sort block groups to determine the optimal order
+	 * for visiting heap blocks.  But before we do, round the number of
+	 * promising tuples for each block group up to the next power-of-two,
+	 * unless it is very low (less than 4), in which case we round up to 4.
+	 * npromisingtids is far too noisy to trust when choosing between a pair
+	 * of block groups that both have very low values.
+	 *
+	 * This scheme divides heap blocks/block groups into buckets.  Each bucket
+	 * contains blocks that have _approximately_ the same number of promising
+	 * TIDs as each other.  The goal is to ignore relatively small differences
+	 * in the total number of promising entries, so that the whole process can
+	 * give a little weight to heapam factors (like heap block locality)
+	 * instead.  This isn't a trade-off, really -- we have nothing to lose. It
+	 * would be foolish to interpret small differences in npromisingtids
+	 * values as anything more than noise.
+	 *
+	 * We tiebreak on nhtids when sorting block group subsets that have the
+	 * same npromisingtids, but this has the same issues as npromisingtids,
+	 * and so nhtids is subject to the same power-of-two bucketing scheme. The
+	 * only reason that we don't fix nhtids in the same way here too is that
+	 * we'll need accurate nhtids values after the sort.  We handle nhtids
+	 * bucketization dynamically instead (in the sort comparator).
+	 *
+	 * See bottomup_nblocksfavorable() for a full explanation of when and how
+	 * heap locality/favorable blocks can significantly influence when and how
+	 * heap blocks are accessed.
+	 */
+	for (int b = 0; b < nblockgroups; b++)
+	{
+		IndexDeleteCounts *group = blockgroups + b;
+
+		/* Better off falling back on nhtids with low npromisingtids */
+		if (group->npromisingtids <= 4)
+			group->npromisingtids = 4;
+		else
+			group->npromisingtids =
+				pg_nextpower2_32((uint32) group->npromisingtids);
+	}
+
+	/* Sort groups and rearrange caller's deltids array */
+	qsort(blockgroups, nblockgroups, sizeof(IndexDeleteCounts),
+		  bottomup_sort_and_shrink_cmp);
+	reordereddeltids = palloc(delstate->ndeltids * sizeof(TM_IndexDelete));
+
+	nblockgroups = Min(BOTTOMUP_MAX_NBLOCKS, nblockgroups);
+	/* Determine number of favorable blocks at the start of final deltids */
+	nblocksfavorable = bottomup_nblocksfavorable(blockgroups, nblockgroups,
+												 delstate->deltids);
+
+	for (int b = 0; b < nblockgroups; b++)
+	{
+		IndexDeleteCounts *group = blockgroups + b;
+		TM_IndexDelete *firstdtid = delstate->deltids + group->ifirsttid;
+
+		memcpy(reordereddeltids + ncopied, firstdtid,
+			   sizeof(TM_IndexDelete) * group->ntids);
+		ncopied += group->ntids;
+	}
+
+	/* Copy final grouped and sorted TIDs back into start of caller's array */
+	memcpy(delstate->deltids, reordereddeltids,
+		   sizeof(TM_IndexDelete) * ncopied);
+	delstate->ndeltids = ncopied;
+
+	pfree(reordereddeltids);
+	pfree(blockgroups);
+
+	return nblocksfavorable;
+}
+
+/*
+ * Perform XLogInsert for a heap-freeze operation.  Caller must have already
+ * modified the buffer and marked it dirty.
+ */
+XLogRecPtr
+log_heap_freeze(Relation reln, Buffer buffer, TransactionId cutoff_xid,
+				xl_heap_freeze_tuple *tuples, int ntuples)
+{
+	xl_heap_freeze_page xlrec;
+	XLogRecPtr	recptr;
+
+	/* Caller should not call me on a non-WAL-logged relation */
+	Assert(RelationNeedsWAL(reln));
+	/* nor when there are no tuples to freeze */
+	Assert(ntuples > 0);
+
+	xlrec.cutoff_xid = cutoff_xid;
+	xlrec.ntuples = ntuples;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfHeapFreezePage);
+
+	/*
+	 * The freeze plan array is not actually in the buffer, but pretend that
+	 * it is.  When XLogInsert stores the whole buffer, the freeze plan need
+	 * not be stored too.
+	 */
+	XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
+	XLogRegisterBufData(0, (char *) tuples,
+						ntuples * sizeof(xl_heap_freeze_tuple));
+
+	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_FREEZE_PAGE);
+
+	return recptr;
+}
+
+/*
+ * Perform XLogInsert for a heap-visible operation.  'block' is the block
+ * being marked all-visible, and vm_buffer is the buffer containing the
+ * corresponding visibility map block.  Both should have already been modified
+ * and dirtied.
+ *
+ * If checksums are enabled, we also generate a full-page image of
+ * heap_buffer, if necessary.
+ */
+XLogRecPtr
+log_heap_visible(RelFileNode rnode, Buffer heap_buffer, Buffer vm_buffer,
+				 TransactionId cutoff_xid, uint8 vmflags)
+{
+	xl_heap_visible xlrec;
+	XLogRecPtr	recptr;
+	uint8		flags;
+
+	Assert(BufferIsValid(heap_buffer));
+	Assert(BufferIsValid(vm_buffer));
+
+	xlrec.cutoff_xid = cutoff_xid;
+	xlrec.flags = vmflags;
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfHeapVisible);
+
+	XLogRegisterBuffer(0, vm_buffer, 0);
+
+	flags = REGBUF_STANDARD;
+	if (!XLogHintBitIsNeeded())
+		flags |= REGBUF_NO_IMAGE;
+	XLogRegisterBuffer(1, heap_buffer, flags);
+
+	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_VISIBLE);
+
+	return recptr;
+}
+
+/*
+ * Perform XLogInsert for a heap-update operation.  Caller must already
+ * have modified the buffer(s) and marked them dirty.
+ */
+static XLogRecPtr
+log_heap_update(Relation reln, Buffer oldbuf,
+				Buffer newbuf, HeapTuple oldtup, HeapTuple newtup,
+				HeapTuple old_key_tuple,
+				bool all_visible_cleared, bool new_all_visible_cleared)
+{
+	xl_heap_update xlrec;
+	xl_heap_header xlhdr;
+	xl_heap_header xlhdr_idx;
+	uint8		info;
+	uint16		prefix_suffix[2];
+	uint16		prefixlen = 0,
+				suffixlen = 0;
+	XLogRecPtr	recptr;
+	Page		page = BufferGetPage(newbuf);
+	bool		need_tuple_data = RelationIsLogicallyLogged(reln);
+	bool		init;
+	int			bufflags;
+
+	/* Caller should not call me on a non-WAL-logged relation */
+	Assert(RelationNeedsWAL(reln));
+
+	XLogBeginInsert();
+
+	if (HeapTupleIsHeapOnly(newtup))
+		info = XLOG_HEAP_HOT_UPDATE;
+	else
+		info = XLOG_HEAP_UPDATE;
+
+	/*
+	 * If the old and new tuple are on the same page, we only need to log the
+	 * parts of the new tuple that were changed.  That saves on the amount of
+	 * WAL we need to write.  Currently, we just count any unchanged bytes in
+	 * the beginning and end of the tuple.  That's quick to check, and
+	 * perfectly covers the common case that only one field is updated.
+	 *
+	 * We could do this even if the old and new tuple are on different pages,
+	 * but only if we don't make a full-page image of the old page, which is
+	 * difficult to know in advance.  Also, if the old tuple is corrupt for
+	 * some reason, it would allow the corruption to propagate the new page,
+	 * so it seems best to avoid.  Under the general assumption that most
+	 * updates tend to create the new tuple version on the same page, there
+	 * isn't much to be gained by doing this across pages anyway.
+	 *
+	 * Skip this if we're taking a full-page image of the new page, as we
+	 * don't include the new tuple in the WAL record in that case.  Also
+	 * disable if wal_level='logical', as logical decoding needs to be able to
+	 * read the new tuple in whole from the WAL record alone.
+	 */
+	if (oldbuf == newbuf && !need_tuple_data &&
+		!XLogCheckBufferNeedsBackup(newbuf))
+	{
+		char	   *oldp = (char *) oldtup->t_data + oldtup->t_data->t_hoff;
+		char	   *newp = (char *) newtup->t_data + newtup->t_data->t_hoff;
+		int			oldlen = oldtup->t_len - oldtup->t_data->t_hoff;
+		int			newlen = newtup->t_len - newtup->t_data->t_hoff;
+
+		/* Check for common prefix between old and new tuple */
+		for (prefixlen = 0; prefixlen < Min(oldlen, newlen); prefixlen++)
+		{
+			if (newp[prefixlen] != oldp[prefixlen])
+				break;
+		}
+
+		/*
+		 * Storing the length of the prefix takes 2 bytes, so we need to save
+		 * at least 3 bytes or there's no point.
+		 */
+		if (prefixlen < 3)
+			prefixlen = 0;
+
+		/* Same for suffix */
+		for (suffixlen = 0; suffixlen < Min(oldlen, newlen) - prefixlen; suffixlen++)
+		{
+			if (newp[newlen - suffixlen - 1] != oldp[oldlen - suffixlen - 1])
+				break;
+		}
+		if (suffixlen < 3)
+			suffixlen = 0;
+	}
+
+	/* Prepare main WAL data chain */
+	xlrec.flags = 0;
+	if (all_visible_cleared)
+		xlrec.flags |= XLH_UPDATE_OLD_ALL_VISIBLE_CLEARED;
+	if (new_all_visible_cleared)
+		xlrec.flags |= XLH_UPDATE_NEW_ALL_VISIBLE_CLEARED;
+	if (prefixlen > 0)
+		xlrec.flags |= XLH_UPDATE_PREFIX_FROM_OLD;
+	if (suffixlen > 0)
+		xlrec.flags |= XLH_UPDATE_SUFFIX_FROM_OLD;
+	if (need_tuple_data)
+	{
+		xlrec.flags |= XLH_UPDATE_CONTAINS_NEW_TUPLE;
+		if (old_key_tuple)
+		{
+			if (reln->rd_rel->relreplident == REPLICA_IDENTITY_FULL)
+				xlrec.flags |= XLH_UPDATE_CONTAINS_OLD_TUPLE;
+			else
+				xlrec.flags |= XLH_UPDATE_CONTAINS_OLD_KEY;
+		}
+	}
+
+	/* If new tuple is the single and first tuple on page... */
+	if (ItemPointerGetOffsetNumber(&(newtup->t_self)) == FirstOffsetNumber &&
+		PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
+	{
+		info |= XLOG_HEAP_INIT_PAGE;
+		init = true;
+	}
+	else
+		init = false;
+
+	/* Prepare WAL data for the old page */
+	xlrec.old_offnum = ItemPointerGetOffsetNumber(&oldtup->t_self);
+	xlrec.old_xmax = HeapTupleHeaderGetRawXmax(oldtup->t_data);
+	xlrec.old_infobits_set = compute_infobits(oldtup->t_data->t_infomask,
+											  oldtup->t_data->t_infomask2);
+
+	/* Prepare WAL data for the new page */
+	xlrec.new_offnum = ItemPointerGetOffsetNumber(&newtup->t_self);
+	xlrec.new_xmax = HeapTupleHeaderGetRawXmax(newtup->t_data);
+
+	bufflags = REGBUF_STANDARD;
+	if (init)
+		bufflags |= REGBUF_WILL_INIT;
+	if (need_tuple_data)
+		bufflags |= REGBUF_KEEP_DATA;
+
+	XLogRegisterBuffer(0, newbuf, bufflags);
+	if (oldbuf != newbuf)
+		XLogRegisterBuffer(1, oldbuf, REGBUF_STANDARD);
+
+	XLogRegisterData((char *) &xlrec, SizeOfHeapUpdate);
+
+	/*
+	 * Prepare WAL data for the new tuple.
+	 */
+	if (prefixlen > 0 || suffixlen > 0)
+	{
+		if (prefixlen > 0 && suffixlen > 0)
+		{
+			prefix_suffix[0] = prefixlen;
+			prefix_suffix[1] = suffixlen;
+			XLogRegisterBufData(0, (char *) &prefix_suffix, sizeof(uint16) * 2);
+		}
+		else if (prefixlen > 0)
+		{
+			XLogRegisterBufData(0, (char *) &prefixlen, sizeof(uint16));
+		}
+		else
+		{
+			XLogRegisterBufData(0, (char *) &suffixlen, sizeof(uint16));
+		}
+	}
+
+	xlhdr.t_infomask2 = newtup->t_data->t_infomask2;
+	xlhdr.t_infomask = newtup->t_data->t_infomask;
+	xlhdr.t_hoff = newtup->t_data->t_hoff;
+	Assert(SizeofHeapTupleHeader + prefixlen + suffixlen <= newtup->t_len);
+
+	/*
+	 * PG73FORMAT: write bitmap [+ padding] [+ oid] + data
+	 *
+	 * The 'data' doesn't include the common prefix or suffix.
+	 */
+	XLogRegisterBufData(0, (char *) &xlhdr, SizeOfHeapHeader);
+	if (prefixlen == 0)
+	{
+		XLogRegisterBufData(0,
+							((char *) newtup->t_data) + SizeofHeapTupleHeader,
+							newtup->t_len - SizeofHeapTupleHeader - suffixlen);
+	}
+	else
+	{
+		/*
+		 * Have to write the null bitmap and data after the common prefix as
+		 * two separate rdata entries.
+		 */
+		/* bitmap [+ padding] [+ oid] */
+		if (newtup->t_data->t_hoff - SizeofHeapTupleHeader > 0)
+		{
+			XLogRegisterBufData(0,
+								((char *) newtup->t_data) + SizeofHeapTupleHeader,
+								newtup->t_data->t_hoff - SizeofHeapTupleHeader);
+		}
+
+		/* data after common prefix */
+		XLogRegisterBufData(0,
+							((char *) newtup->t_data) + newtup->t_data->t_hoff + prefixlen,
+							newtup->t_len - newtup->t_data->t_hoff - prefixlen - suffixlen);
+	}
+
+	/* We need to log a tuple identity */
+	if (need_tuple_data && old_key_tuple)
+	{
+		/* don't really need this, but its more comfy to decode */
+		xlhdr_idx.t_infomask2 = old_key_tuple->t_data->t_infomask2;
+		xlhdr_idx.t_infomask = old_key_tuple->t_data->t_infomask;
+		xlhdr_idx.t_hoff = old_key_tuple->t_data->t_hoff;
+
+		XLogRegisterData((char *) &xlhdr_idx, SizeOfHeapHeader);
+
+		/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
+		XLogRegisterData((char *) old_key_tuple->t_data + SizeofHeapTupleHeader,
+						 old_key_tuple->t_len - SizeofHeapTupleHeader);
+	}
+
+	/* filtering by origin on a row level is much more efficient */
+	XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
+
+	recptr = XLogInsert(RM_HEAP_ID, info);
+
+	return recptr;
+}
+
+/*
+ * Perform XLogInsert of an XLOG_HEAP2_NEW_CID record
+ *
+ * This is only used in wal_level >= WAL_LEVEL_LOGICAL, and only for catalog
+ * tuples.
+ */
+static XLogRecPtr
+log_heap_new_cid(Relation relation, HeapTuple tup)
+{
+	xl_heap_new_cid xlrec;
+
+	XLogRecPtr	recptr;
+	HeapTupleHeader hdr = tup->t_data;
+
+	Assert(ItemPointerIsValid(&tup->t_self));
+	Assert(tup->t_tableOid != InvalidOid);
+
+	xlrec.top_xid = GetTopTransactionId();
+	xlrec.target_node = relation->rd_node;
+	xlrec.target_tid = tup->t_self;
+
+	/*
+	 * If the tuple got inserted & deleted in the same TX we definitely have a
+	 * combo CID, set cmin and cmax.
+	 */
+	if (hdr->t_infomask & HEAP_COMBOCID)
+	{
+		Assert(!(hdr->t_infomask & HEAP_XMAX_INVALID));
+		Assert(!HeapTupleHeaderXminInvalid(hdr));
+		xlrec.cmin = HeapTupleHeaderGetCmin(hdr);
+		xlrec.cmax = HeapTupleHeaderGetCmax(hdr);
+		xlrec.combocid = HeapTupleHeaderGetRawCommandId(hdr);
+	}
+	/* No combo CID, so only cmin or cmax can be set by this TX */
+	else
+	{
+		/*
+		 * Tuple inserted.
+		 *
+		 * We need to check for LOCK ONLY because multixacts might be
+		 * transferred to the new tuple in case of FOR KEY SHARE updates in
+		 * which case there will be an xmax, although the tuple just got
+		 * inserted.
+		 */
+		if (hdr->t_infomask & HEAP_XMAX_INVALID ||
+			HEAP_XMAX_IS_LOCKED_ONLY(hdr->t_infomask))
+		{
+			xlrec.cmin = HeapTupleHeaderGetRawCommandId(hdr);
+			xlrec.cmax = InvalidCommandId;
+		}
+		/* Tuple from a different tx updated or deleted. */
+		else
+		{
+			xlrec.cmin = InvalidCommandId;
+			xlrec.cmax = HeapTupleHeaderGetRawCommandId(hdr);
+
+		}
+		xlrec.combocid = InvalidCommandId;
+	}
+
+	/*
+	 * Note that we don't need to register the buffer here, because this
+	 * operation does not modify the page. The insert/update/delete that
+	 * called us certainly did, but that's WAL-logged separately.
+	 */
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfHeapNewCid);
+
+	/* will be looked at irrespective of origin */
+
+	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_NEW_CID);
+
+	return recptr;
+}
+
+/*
+ * Build a heap tuple representing the configured REPLICA IDENTITY to represent
+ * the old tuple in a UPDATE or DELETE.
+ *
+ * Returns NULL if there's no need to log an identity or if there's no suitable
+ * key defined.
+ *
+ * Pass key_required true if any replica identity columns changed value, or if
+ * any of them have any external data.  Delete must always pass true.
+ *
+ * *copy is set to true if the returned tuple is a modified copy rather than
+ * the same tuple that was passed in.
+ */
+static HeapTuple
+ExtractReplicaIdentity(Relation relation, HeapTuple tp, bool key_required,
+					   bool *copy)
+{
+	TupleDesc	desc = RelationGetDescr(relation);
+	char		replident = relation->rd_rel->relreplident;
+	Bitmapset  *idattrs;
+	HeapTuple	key_tuple;
+	bool		nulls[MaxHeapAttributeNumber];
+	Datum		values[MaxHeapAttributeNumber];
+
+	*copy = false;
+
+	if (!RelationIsLogicallyLogged(relation))
+		return NULL;
+
+	if (replident == REPLICA_IDENTITY_NOTHING)
+		return NULL;
+
+	if (replident == REPLICA_IDENTITY_FULL)
+	{
+		/*
+		 * When logging the entire old tuple, it very well could contain
+		 * toasted columns. If so, force them to be inlined.
+		 */
+		if (HeapTupleHasExternal(tp))
+		{
+			*copy = true;
+			tp = toast_flatten_tuple(tp, desc);
+		}
+		return tp;
+	}
+
+	/* if the key isn't required and we're only logging the key, we're done */
+	if (!key_required)
+		return NULL;
+
+	/* find out the replica identity columns */
+	idattrs = RelationGetIndexAttrBitmap(relation,
+										 INDEX_ATTR_BITMAP_IDENTITY_KEY);
+
+	/*
+	 * If there's no defined replica identity columns, treat as !key_required.
+	 * (This case should not be reachable from heap_update, since that should
+	 * calculate key_required accurately.  But heap_delete just passes
+	 * constant true for key_required, so we can hit this case in deletes.)
+	 */
+	if (bms_is_empty(idattrs))
+		return NULL;
+
+	/*
+	 * Construct a new tuple containing only the replica identity columns,
+	 * with nulls elsewhere.  While we're at it, assert that the replica
+	 * identity columns aren't null.
+	 */
+	heap_deform_tuple(tp, desc, values, nulls);
+
+	for (int i = 0; i < desc->natts; i++)
+	{
+		if (bms_is_member(i + 1 - FirstLowInvalidHeapAttributeNumber,
+						  idattrs))
+			Assert(!nulls[i]);
+		else
+			nulls[i] = true;
+	}
+
+	key_tuple = heap_form_tuple(desc, values, nulls);
+	*copy = true;
+
+	bms_free(idattrs);
+
+	/*
+	 * If the tuple, which by here only contains indexed columns, still has
+	 * toasted columns, force them to be inlined. This is somewhat unlikely
+	 * since there's limits on the size of indexed columns, so we don't
+	 * duplicate toast_flatten_tuple()s functionality in the above loop over
+	 * the indexed columns, even if it would be more efficient.
+	 */
+	if (HeapTupleHasExternal(key_tuple))
+	{
+		HeapTuple	oldtup = key_tuple;
+
+		key_tuple = toast_flatten_tuple(oldtup, desc);
+		heap_freetuple(oldtup);
+	}
+
+	return key_tuple;
+}
+
+/*
+ * Handles XLOG_HEAP2_PRUNE record type.
+ *
+ * Acquires a super-exclusive lock.
+ */
+static void
+heap_xlog_prune(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_prune *xlrec = (xl_heap_prune *) XLogRecGetData(record);
+	Buffer		buffer;
+	RelFileNode rnode;
+	BlockNumber blkno;
+	XLogRedoAction action;
+
+	XLogRecGetBlockTag(record, 0, &rnode, NULL, &blkno);
+
+	/*
+	 * We're about to remove tuples. In Hot Standby mode, ensure that there's
+	 * no queries running for which the removed tuples are still visible.
+	 */
+	if (InHotStandby)
+		ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid, rnode);
+
+	/*
+	 * If we have a full-page image, restore it (using a cleanup lock) and
+	 * we're done.
+	 */
+	action = XLogReadBufferForRedoExtended(record, 0, RBM_NORMAL, true,
+										   &buffer);
+	if (action == BLK_NEEDS_REDO)
+	{
+		Page		page = (Page) BufferGetPage(buffer);
+		OffsetNumber *end;
+		OffsetNumber *redirected;
+		OffsetNumber *nowdead;
+		OffsetNumber *nowunused;
+		int			nredirected;
+		int			ndead;
+		int			nunused;
+		Size		datalen;
+
+		redirected = (OffsetNumber *) XLogRecGetBlockData(record, 0, &datalen);
+
+		nredirected = xlrec->nredirected;
+		ndead = xlrec->ndead;
+		end = (OffsetNumber *) ((char *) redirected + datalen);
+		nowdead = redirected + (nredirected * 2);
+		nowunused = nowdead + ndead;
+		nunused = (end - nowunused);
+		Assert(nunused >= 0);
+
+		/* Update all line pointers per the record, and repair fragmentation */
+		heap_page_prune_execute(buffer,
+								redirected, nredirected,
+								nowdead, ndead,
+								nowunused, nunused);
+
+		/*
+		 * Note: we don't worry about updating the page's prunability hints.
+		 * At worst this will cause an extra prune cycle to occur soon.
+		 */
+
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(buffer);
+	}
+
+	if (BufferIsValid(buffer))
+	{
+		Size		freespace = PageGetHeapFreeSpace(BufferGetPage(buffer));
+
+		UnlockReleaseBuffer(buffer);
+
+		/*
+		 * After pruning records from a page, it's useful to update the FSM
+		 * about it, as it may cause the page become target for insertions
+		 * later even if vacuum decides not to visit it (which is possible if
+		 * gets marked all-visible.)
+		 *
+		 * Do this regardless of a full-page image being applied, since the
+		 * FSM data is not in the page anyway.
+		 */
+		XLogRecordPageWithFreeSpace(rnode, blkno, freespace);
+	}
+}
+
+/*
+ * Handles XLOG_HEAP2_VACUUM record type.
+ *
+ * Acquires an exclusive lock only.
+ */
+static void
+heap_xlog_vacuum(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_vacuum *xlrec = (xl_heap_vacuum *) XLogRecGetData(record);
+	Buffer		buffer;
+	BlockNumber blkno;
+	XLogRedoAction action;
+
+	/*
+	 * If we have a full-page image, restore it	(without using a cleanup lock)
+	 * and we're done.
+	 */
+	action = XLogReadBufferForRedoExtended(record, 0, RBM_NORMAL, false,
+										   &buffer);
+	if (action == BLK_NEEDS_REDO)
+	{
+		Page		page = (Page) BufferGetPage(buffer);
+		OffsetNumber *nowunused;
+		Size		datalen;
+		OffsetNumber *offnum;
+
+		nowunused = (OffsetNumber *) XLogRecGetBlockData(record, 0, &datalen);
+
+		/* Shouldn't be a record unless there's something to do */
+		Assert(xlrec->nunused > 0);
+
+		/* Update all now-unused line pointers */
+		offnum = nowunused;
+		for (int i = 0; i < xlrec->nunused; i++)
+		{
+			OffsetNumber off = *offnum++;
+			ItemId		lp = PageGetItemId(page, off);
+
+			Assert(ItemIdIsDead(lp) && !ItemIdHasStorage(lp));
+			ItemIdSetUnused(lp);
+		}
+
+		/* Attempt to truncate line pointer array now */
+		PageTruncateLinePointerArray(page);
+
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(buffer);
+	}
+
+	if (BufferIsValid(buffer))
+	{
+		Size		freespace = PageGetHeapFreeSpace(BufferGetPage(buffer));
+		RelFileNode rnode;
+
+		XLogRecGetBlockTag(record, 0, &rnode, NULL, &blkno);
+
+		UnlockReleaseBuffer(buffer);
+
+		/*
+		 * After vacuuming LP_DEAD items from a page, it's useful to update
+		 * the FSM about it, as it may cause the page become target for
+		 * insertions later even if vacuum decides not to visit it (which is
+		 * possible if gets marked all-visible.)
+		 *
+		 * Do this regardless of a full-page image being applied, since the
+		 * FSM data is not in the page anyway.
+		 */
+		XLogRecordPageWithFreeSpace(rnode, blkno, freespace);
+	}
+}
+
+/*
+ * Replay XLOG_HEAP2_VISIBLE record.
+ *
+ * The critical integrity requirement here is that we must never end up with
+ * a situation where the visibility map bit is set, and the page-level
+ * PD_ALL_VISIBLE bit is clear.  If that were to occur, then a subsequent
+ * page modification would fail to clear the visibility map bit.
+ */
+static void
+heap_xlog_visible(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_visible *xlrec = (xl_heap_visible *) XLogRecGetData(record);
+	Buffer		vmbuffer = InvalidBuffer;
+	Buffer		buffer;
+	Page		page;
+	RelFileNode rnode;
+	BlockNumber blkno;
+	XLogRedoAction action;
+
+	XLogRecGetBlockTag(record, 1, &rnode, NULL, &blkno);
+
+	/*
+	 * If there are any Hot Standby transactions running that have an xmin
+	 * horizon old enough that this page isn't all-visible for them, they
+	 * might incorrectly decide that an index-only scan can skip a heap fetch.
+	 *
+	 * NB: It might be better to throw some kind of "soft" conflict here that
+	 * forces any index-only scan that is in flight to perform heap fetches,
+	 * rather than killing the transaction outright.
+	 */
+	if (InHotStandby)
+		ResolveRecoveryConflictWithSnapshot(xlrec->cutoff_xid, rnode);
+
+	/*
+	 * Read the heap page, if it still exists. If the heap file has dropped or
+	 * truncated later in recovery, we don't need to update the page, but we'd
+	 * better still update the visibility map.
+	 */
+	action = XLogReadBufferForRedo(record, 1, &buffer);
+	if (action == BLK_NEEDS_REDO)
+	{
+		/*
+		 * We don't bump the LSN of the heap page when setting the visibility
+		 * map bit (unless checksums or wal_hint_bits is enabled, in which
+		 * case we must), because that would generate an unworkable volume of
+		 * full-page writes.  This exposes us to torn page hazards, but since
+		 * we're not inspecting the existing page contents in any way, we
+		 * don't care.
+		 *
+		 * However, all operations that clear the visibility map bit *do* bump
+		 * the LSN, and those operations will only be replayed if the XLOG LSN
+		 * follows the page LSN.  Thus, if the page LSN has advanced past our
+		 * XLOG record's LSN, we mustn't mark the page all-visible, because
+		 * the subsequent update won't be replayed to clear the flag.
+		 */
+		page = BufferGetPage(buffer);
+
+		PageSetAllVisible(page);
+
+		MarkBufferDirty(buffer);
+	}
+	else if (action == BLK_RESTORED)
+	{
+		/*
+		 * If heap block was backed up, we already restored it and there's
+		 * nothing more to do. (This can only happen with checksums or
+		 * wal_log_hints enabled.)
+		 */
+	}
+
+	if (BufferIsValid(buffer))
+	{
+		Size		space = PageGetFreeSpace(BufferGetPage(buffer));
+
+		UnlockReleaseBuffer(buffer);
+
+		/*
+		 * Since FSM is not WAL-logged and only updated heuristically, it
+		 * easily becomes stale in standbys.  If the standby is later promoted
+		 * and runs VACUUM, it will skip updating individual free space
+		 * figures for pages that became all-visible (or all-frozen, depending
+		 * on the vacuum mode,) which is troublesome when FreeSpaceMapVacuum
+		 * propagates too optimistic free space values to upper FSM layers;
+		 * later inserters try to use such pages only to find out that they
+		 * are unusable.  This can cause long stalls when there are many such
+		 * pages.
+		 *
+		 * Forestall those problems by updating FSM's idea about a page that
+		 * is becoming all-visible or all-frozen.
+		 *
+		 * Do this regardless of a full-page image being applied, since the
+		 * FSM data is not in the page anyway.
+		 */
+		if (xlrec->flags & VISIBILITYMAP_VALID_BITS)
+			XLogRecordPageWithFreeSpace(rnode, blkno, space);
+	}
+
+	/*
+	 * Even if we skipped the heap page update due to the LSN interlock, it's
+	 * still safe to update the visibility map.  Any WAL record that clears
+	 * the visibility map bit does so before checking the page LSN, so any
+	 * bits that need to be cleared will still be cleared.
+	 */
+	if (XLogReadBufferForRedoExtended(record, 0, RBM_ZERO_ON_ERROR, false,
+									  &vmbuffer) == BLK_NEEDS_REDO)
+	{
+		Page		vmpage = BufferGetPage(vmbuffer);
+		Relation	reln;
+
+		/* initialize the page if it was read as zeros */
+		if (PageIsNew(vmpage))
+			PageInit(vmpage, BLCKSZ, 0);
+
+		/*
+		 * XLogReadBufferForRedoExtended locked the buffer. But
+		 * visibilitymap_set will handle locking itself.
+		 */
+		LockBuffer(vmbuffer, BUFFER_LOCK_UNLOCK);
+
+		reln = CreateFakeRelcacheEntry(rnode);
+		visibilitymap_pin(reln, blkno, &vmbuffer);
+
+		/*
+		 * Don't set the bit if replay has already passed this point.
+		 *
+		 * It might be safe to do this unconditionally; if replay has passed
+		 * this point, we'll replay at least as far this time as we did
+		 * before, and if this bit needs to be cleared, the record responsible
+		 * for doing so should be again replayed, and clear it.  For right
+		 * now, out of an abundance of conservatism, we use the same test here
+		 * we did for the heap page.  If this results in a dropped bit, no
+		 * real harm is done; and the next VACUUM will fix it.
+		 */
+		if (lsn > PageGetLSN(vmpage))
+			visibilitymap_set(reln, blkno, InvalidBuffer, lsn, vmbuffer,
+							  xlrec->cutoff_xid, xlrec->flags);
+
+		ReleaseBuffer(vmbuffer);
+		FreeFakeRelcacheEntry(reln);
+	}
+	else if (BufferIsValid(vmbuffer))
+		UnlockReleaseBuffer(vmbuffer);
+}
+
+/*
+ * Replay XLOG_HEAP2_FREEZE_PAGE records
+ */
+static void
+heap_xlog_freeze_page(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_freeze_page *xlrec = (xl_heap_freeze_page *) XLogRecGetData(record);
+	TransactionId cutoff_xid = xlrec->cutoff_xid;
+	Buffer		buffer;
+	int			ntup;
+
+	/*
+	 * In Hot Standby mode, ensure that there's no queries running which still
+	 * consider the frozen xids as running.
+	 */
+	if (InHotStandby)
+	{
+		RelFileNode rnode;
+		TransactionId latestRemovedXid = cutoff_xid;
+
+		TransactionIdRetreat(latestRemovedXid);
+
+		XLogRecGetBlockTag(record, 0, &rnode, NULL, NULL);
+		ResolveRecoveryConflictWithSnapshot(latestRemovedXid, rnode);
+	}
+
+	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
+	{
+		Page		page = BufferGetPage(buffer);
+		xl_heap_freeze_tuple *tuples;
+
+		tuples = (xl_heap_freeze_tuple *) XLogRecGetBlockData(record, 0, NULL);
+
+		/* now execute freeze plan for each frozen tuple */
+		for (ntup = 0; ntup < xlrec->ntuples; ntup++)
+		{
+			xl_heap_freeze_tuple *xlrec_tp;
+			ItemId		lp;
+			HeapTupleHeader tuple;
+
+			xlrec_tp = &tuples[ntup];
+			lp = PageGetItemId(page, xlrec_tp->offset); /* offsets are one-based */
+			tuple = (HeapTupleHeader) PageGetItem(page, lp);
+
+			heap_execute_freeze_tuple(tuple, xlrec_tp);
+		}
+
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(buffer);
+	}
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
+}
+
+/*
+ * Given an "infobits" field from an XLog record, set the correct bits in the
+ * given infomask and infomask2 for the tuple touched by the record.
+ *
+ * (This is the reverse of compute_infobits).
+ */
+static void
+fix_infomask_from_infobits(uint8 infobits, uint16 *infomask, uint16 *infomask2)
+{
+	*infomask &= ~(HEAP_XMAX_IS_MULTI | HEAP_XMAX_LOCK_ONLY |
+				   HEAP_XMAX_KEYSHR_LOCK | HEAP_XMAX_EXCL_LOCK);
+	*infomask2 &= ~HEAP_KEYS_UPDATED;
+
+	if (infobits & XLHL_XMAX_IS_MULTI)
+		*infomask |= HEAP_XMAX_IS_MULTI;
+	if (infobits & XLHL_XMAX_LOCK_ONLY)
+		*infomask |= HEAP_XMAX_LOCK_ONLY;
+	if (infobits & XLHL_XMAX_EXCL_LOCK)
+		*infomask |= HEAP_XMAX_EXCL_LOCK;
+	/* note HEAP_XMAX_SHR_LOCK isn't considered here */
+	if (infobits & XLHL_XMAX_KEYSHR_LOCK)
+		*infomask |= HEAP_XMAX_KEYSHR_LOCK;
+
+	if (infobits & XLHL_KEYS_UPDATED)
+		*infomask2 |= HEAP_KEYS_UPDATED;
+}
+
+static void
+heap_xlog_delete(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_delete *xlrec = (xl_heap_delete *) XLogRecGetData(record);
+	Buffer		buffer;
+	Page		page;
+	ItemId		lp = NULL;
+	HeapTupleHeader htup;
+	BlockNumber blkno;
+	RelFileNode target_node;
+	ItemPointerData target_tid;
+
+	XLogRecGetBlockTag(record, 0, &target_node, NULL, &blkno);
+	ItemPointerSetBlockNumber(&target_tid, blkno);
+	ItemPointerSetOffsetNumber(&target_tid, xlrec->offnum);
+
+	/*
+	 * The visibility map may need to be fixed even if the heap page is
+	 * already up-to-date.
+	 */
+	if (xlrec->flags & XLH_DELETE_ALL_VISIBLE_CLEARED)
+	{
+		Relation	reln = CreateFakeRelcacheEntry(target_node);
+		Buffer		vmbuffer = InvalidBuffer;
+
+		visibilitymap_pin(reln, blkno, &vmbuffer);
+		visibilitymap_clear(reln, blkno, vmbuffer, VISIBILITYMAP_VALID_BITS);
+		ReleaseBuffer(vmbuffer);
+		FreeFakeRelcacheEntry(reln);
+	}
+
+	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
+	{
+		page = BufferGetPage(buffer);
+
+		if (PageGetMaxOffsetNumber(page) >= xlrec->offnum)
+			lp = PageGetItemId(page, xlrec->offnum);
+
+		if (PageGetMaxOffsetNumber(page) < xlrec->offnum || !ItemIdIsNormal(lp))
+			elog(PANIC, "invalid lp");
+
+		htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+		htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
+		htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+		HeapTupleHeaderClearHotUpdated(htup);
+		fix_infomask_from_infobits(xlrec->infobits_set,
+								   &htup->t_infomask, &htup->t_infomask2);
+		if (!(xlrec->flags & XLH_DELETE_IS_SUPER))
+			HeapTupleHeaderSetXmax(htup, xlrec->xmax);
+		else
+			HeapTupleHeaderSetXmin(htup, InvalidTransactionId);
+		HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
+
+		/* Mark the page as a candidate for pruning */
+		PageSetPrunable(page, XLogRecGetXid(record));
+
+		if (xlrec->flags & XLH_DELETE_ALL_VISIBLE_CLEARED)
+			PageClearAllVisible(page);
+
+		/* Make sure t_ctid is set correctly */
+		if (xlrec->flags & XLH_DELETE_IS_PARTITION_MOVE)
+			HeapTupleHeaderSetMovedPartitions(htup);
+		else
+			htup->t_ctid = target_tid;
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(buffer);
+	}
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
+}
+
+static void
+heap_xlog_insert(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_insert *xlrec = (xl_heap_insert *) XLogRecGetData(record);
+	Buffer		buffer;
+	Page		page;
+	union
+	{
+		HeapTupleHeaderData hdr;
+		char		data[MaxHeapTupleSize];
+	}			tbuf;
+	HeapTupleHeader htup;
+	xl_heap_header xlhdr;
+	uint32		newlen;
+	Size		freespace = 0;
+	RelFileNode target_node;
+	BlockNumber blkno;
+	ItemPointerData target_tid;
+	XLogRedoAction action;
+
+	XLogRecGetBlockTag(record, 0, &target_node, NULL, &blkno);
+	ItemPointerSetBlockNumber(&target_tid, blkno);
+	ItemPointerSetOffsetNumber(&target_tid, xlrec->offnum);
+
+	/*
+	 * The visibility map may need to be fixed even if the heap page is
+	 * already up-to-date.
+	 */
+	if (xlrec->flags & XLH_INSERT_ALL_VISIBLE_CLEARED)
+	{
+		Relation	reln = CreateFakeRelcacheEntry(target_node);
+		Buffer		vmbuffer = InvalidBuffer;
+
+		visibilitymap_pin(reln, blkno, &vmbuffer);
+		visibilitymap_clear(reln, blkno, vmbuffer, VISIBILITYMAP_VALID_BITS);
+		ReleaseBuffer(vmbuffer);
+		FreeFakeRelcacheEntry(reln);
+	}
+
+	/*
+	 * If we inserted the first and only tuple on the page, re-initialize the
+	 * page from scratch.
+	 */
+	if (XLogRecGetInfo(record) & XLOG_HEAP_INIT_PAGE)
+	{
+		buffer = XLogInitBufferForRedo(record, 0);
+		page = BufferGetPage(buffer);
+		PageInit(page, BufferGetPageSize(buffer), 0);
+		action = BLK_NEEDS_REDO;
+	}
+	else
+		action = XLogReadBufferForRedo(record, 0, &buffer);
+	if (action == BLK_NEEDS_REDO)
+	{
+		Size		datalen;
+		char	   *data;
+
+		page = BufferGetPage(buffer);
+
+		if (PageGetMaxOffsetNumber(page) + 1 < xlrec->offnum)
+			elog(PANIC, "invalid max offset number");
+
+		data = XLogRecGetBlockData(record, 0, &datalen);
+
+		newlen = datalen - SizeOfHeapHeader;
+		Assert(datalen > SizeOfHeapHeader && newlen <= MaxHeapTupleSize);
+		memcpy((char *) &xlhdr, data, SizeOfHeapHeader);
+		data += SizeOfHeapHeader;
+
+		htup = &tbuf.hdr;
+		MemSet((char *) htup, 0, SizeofHeapTupleHeader);
+		/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
+		memcpy((char *) htup + SizeofHeapTupleHeader,
+			   data,
+			   newlen);
+		newlen += SizeofHeapTupleHeader;
+		htup->t_infomask2 = xlhdr.t_infomask2;
+		htup->t_infomask = xlhdr.t_infomask;
+		htup->t_hoff = xlhdr.t_hoff;
+		HeapTupleHeaderSetXmin(htup, XLogRecGetXid(record));
+		HeapTupleHeaderSetCmin(htup, FirstCommandId);
+		htup->t_ctid = target_tid;
+
+		if (PageAddItem(page, (Item) htup, newlen, xlrec->offnum,
+						true, true) == InvalidOffsetNumber)
+			elog(PANIC, "failed to add tuple");
+
+		freespace = PageGetHeapFreeSpace(page); /* needed to update FSM below */
+
+		PageSetLSN(page, lsn);
+
+		if (xlrec->flags & XLH_INSERT_ALL_VISIBLE_CLEARED)
+			PageClearAllVisible(page);
+
+		/* XLH_INSERT_ALL_FROZEN_SET implies that all tuples are visible */
+		if (xlrec->flags & XLH_INSERT_ALL_FROZEN_SET)
+			PageSetAllVisible(page);
+
+		MarkBufferDirty(buffer);
+	}
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
+
+	/*
+	 * If the page is running low on free space, update the FSM as well.
+	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
+	 * better than that without knowing the fill-factor for the table.
+	 *
+	 * XXX: Don't do this if the page was restored from full page image. We
+	 * don't bother to update the FSM in that case, it doesn't need to be
+	 * totally accurate anyway.
+	 */
+	if (action == BLK_NEEDS_REDO && freespace < BLCKSZ / 5)
+		XLogRecordPageWithFreeSpace(target_node, blkno, freespace);
+}
+
+/*
+ * Handles MULTI_INSERT record type.
+ */
+static void
+heap_xlog_multi_insert(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_multi_insert *xlrec;
+	RelFileNode rnode;
+	BlockNumber blkno;
+	Buffer		buffer;
+	Page		page;
+	union
+	{
+		HeapTupleHeaderData hdr;
+		char		data[MaxHeapTupleSize];
+	}			tbuf;
+	HeapTupleHeader htup;
+	uint32		newlen;
+	Size		freespace = 0;
+	int			i;
+	bool		isinit = (XLogRecGetInfo(record) & XLOG_HEAP_INIT_PAGE) != 0;
+	XLogRedoAction action;
+
+	/*
+	 * Insertion doesn't overwrite MVCC data, so no conflict processing is
+	 * required.
+	 */
+	xlrec = (xl_heap_multi_insert *) XLogRecGetData(record);
+
+	XLogRecGetBlockTag(record, 0, &rnode, NULL, &blkno);
+
+	/* check that the mutually exclusive flags are not both set */
+	Assert(!((xlrec->flags & XLH_INSERT_ALL_VISIBLE_CLEARED) &&
+			 (xlrec->flags & XLH_INSERT_ALL_FROZEN_SET)));
+
+	/*
+	 * The visibility map may need to be fixed even if the heap page is
+	 * already up-to-date.
+	 */
+	if (xlrec->flags & XLH_INSERT_ALL_VISIBLE_CLEARED)
+	{
+		Relation	reln = CreateFakeRelcacheEntry(rnode);
+		Buffer		vmbuffer = InvalidBuffer;
+
+		visibilitymap_pin(reln, blkno, &vmbuffer);
+		visibilitymap_clear(reln, blkno, vmbuffer, VISIBILITYMAP_VALID_BITS);
+		ReleaseBuffer(vmbuffer);
+		FreeFakeRelcacheEntry(reln);
+	}
+
+	if (isinit)
+	{
+		buffer = XLogInitBufferForRedo(record, 0);
+		page = BufferGetPage(buffer);
+		PageInit(page, BufferGetPageSize(buffer), 0);
+		action = BLK_NEEDS_REDO;
+	}
+	else
+		action = XLogReadBufferForRedo(record, 0, &buffer);
+	if (action == BLK_NEEDS_REDO)
+	{
+		char	   *tupdata;
+		char	   *endptr;
+		Size		len;
+
+		/* Tuples are stored as block data */
+		tupdata = XLogRecGetBlockData(record, 0, &len);
+		endptr = tupdata + len;
+
+		page = (Page) BufferGetPage(buffer);
+
+		for (i = 0; i < xlrec->ntuples; i++)
+		{
+			OffsetNumber offnum;
+			xl_multi_insert_tuple *xlhdr;
+
+			/*
+			 * If we're reinitializing the page, the tuples are stored in
+			 * order from FirstOffsetNumber. Otherwise there's an array of
+			 * offsets in the WAL record, and the tuples come after that.
+			 */
+			if (isinit)
+				offnum = FirstOffsetNumber + i;
+			else
+				offnum = xlrec->offsets[i];
+			if (PageGetMaxOffsetNumber(page) + 1 < offnum)
+				elog(PANIC, "invalid max offset number");
+
+			xlhdr = (xl_multi_insert_tuple *) SHORTALIGN(tupdata);
+			tupdata = ((char *) xlhdr) + SizeOfMultiInsertTuple;
+
+			newlen = xlhdr->datalen;
+			Assert(newlen <= MaxHeapTupleSize);
+			htup = &tbuf.hdr;
+			MemSet((char *) htup, 0, SizeofHeapTupleHeader);
+			/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
+			memcpy((char *) htup + SizeofHeapTupleHeader,
+				   (char *) tupdata,
+				   newlen);
+			tupdata += newlen;
+
+			newlen += SizeofHeapTupleHeader;
+			htup->t_infomask2 = xlhdr->t_infomask2;
+			htup->t_infomask = xlhdr->t_infomask;
+			htup->t_hoff = xlhdr->t_hoff;
+			HeapTupleHeaderSetXmin(htup, XLogRecGetXid(record));
+			HeapTupleHeaderSetCmin(htup, FirstCommandId);
+			ItemPointerSetBlockNumber(&htup->t_ctid, blkno);
+			ItemPointerSetOffsetNumber(&htup->t_ctid, offnum);
+
+			offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
+			if (offnum == InvalidOffsetNumber)
+				elog(PANIC, "failed to add tuple");
+		}
+		if (tupdata != endptr)
+			elog(PANIC, "total tuple length mismatch");
+
+		freespace = PageGetHeapFreeSpace(page); /* needed to update FSM below */
+
+		PageSetLSN(page, lsn);
+
+		if (xlrec->flags & XLH_INSERT_ALL_VISIBLE_CLEARED)
+			PageClearAllVisible(page);
+
+		/* XLH_INSERT_ALL_FROZEN_SET implies that all tuples are visible */
+		if (xlrec->flags & XLH_INSERT_ALL_FROZEN_SET)
+			PageSetAllVisible(page);
+
+		MarkBufferDirty(buffer);
+	}
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
+
+	/*
+	 * If the page is running low on free space, update the FSM as well.
+	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
+	 * better than that without knowing the fill-factor for the table.
+	 *
+	 * XXX: Don't do this if the page was restored from full page image. We
+	 * don't bother to update the FSM in that case, it doesn't need to be
+	 * totally accurate anyway.
+	 */
+	if (action == BLK_NEEDS_REDO && freespace < BLCKSZ / 5)
+		XLogRecordPageWithFreeSpace(rnode, blkno, freespace);
+}
+
+/*
+ * Handles UPDATE and HOT_UPDATE
+ */
+static void
+heap_xlog_update(XLogReaderState *record, bool hot_update)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_update *xlrec = (xl_heap_update *) XLogRecGetData(record);
+	RelFileNode rnode;
+	BlockNumber oldblk;
+	BlockNumber newblk;
+	ItemPointerData newtid;
+	Buffer		obuffer,
+				nbuffer;
+	Page		page;
+	OffsetNumber offnum;
+	ItemId		lp = NULL;
+	HeapTupleData oldtup;
+	HeapTupleHeader htup;
+	uint16		prefixlen = 0,
+				suffixlen = 0;
+	char	   *newp;
+	union
+	{
+		HeapTupleHeaderData hdr;
+		char		data[MaxHeapTupleSize];
+	}			tbuf;
+	xl_heap_header xlhdr;
+	uint32		newlen;
+	Size		freespace = 0;
+	XLogRedoAction oldaction;
+	XLogRedoAction newaction;
+
+	/* initialize to keep the compiler quiet */
+	oldtup.t_data = NULL;
+	oldtup.t_len = 0;
+
+	XLogRecGetBlockTag(record, 0, &rnode, NULL, &newblk);
+	if (XLogRecGetBlockTag(record, 1, NULL, NULL, &oldblk))
+	{
+		/* HOT updates are never done across pages */
+		Assert(!hot_update);
+	}
+	else
+		oldblk = newblk;
+
+	ItemPointerSet(&newtid, newblk, xlrec->new_offnum);
+
+	/*
+	 * The visibility map may need to be fixed even if the heap page is
+	 * already up-to-date.
+	 */
+	if (xlrec->flags & XLH_UPDATE_OLD_ALL_VISIBLE_CLEARED)
+	{
+		Relation	reln = CreateFakeRelcacheEntry(rnode);
+		Buffer		vmbuffer = InvalidBuffer;
+
+		visibilitymap_pin(reln, oldblk, &vmbuffer);
+		visibilitymap_clear(reln, oldblk, vmbuffer, VISIBILITYMAP_VALID_BITS);
+		ReleaseBuffer(vmbuffer);
+		FreeFakeRelcacheEntry(reln);
+	}
+
+	/*
+	 * In normal operation, it is important to lock the two pages in
+	 * page-number order, to avoid possible deadlocks against other update
+	 * operations going the other way.  However, during WAL replay there can
+	 * be no other update happening, so we don't need to worry about that. But
+	 * we *do* need to worry that we don't expose an inconsistent state to Hot
+	 * Standby queries --- so the original page can't be unlocked before we've
+	 * added the new tuple to the new page.
+	 */
+
+	/* Deal with old tuple version */
+	oldaction = XLogReadBufferForRedo(record, (oldblk == newblk) ? 0 : 1,
+									  &obuffer);
+	if (oldaction == BLK_NEEDS_REDO)
+	{
+		page = BufferGetPage(obuffer);
+		offnum = xlrec->old_offnum;
+		if (PageGetMaxOffsetNumber(page) >= offnum)
+			lp = PageGetItemId(page, offnum);
+
+		if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
+			elog(PANIC, "invalid lp");
+
+		htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+		oldtup.t_data = htup;
+		oldtup.t_len = ItemIdGetLength(lp);
+
+		htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
+		htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+		if (hot_update)
+			HeapTupleHeaderSetHotUpdated(htup);
+		else
+			HeapTupleHeaderClearHotUpdated(htup);
+		fix_infomask_from_infobits(xlrec->old_infobits_set, &htup->t_infomask,
+								   &htup->t_infomask2);
+		HeapTupleHeaderSetXmax(htup, xlrec->old_xmax);
+		HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
+		/* Set forward chain link in t_ctid */
+		htup->t_ctid = newtid;
+
+		/* Mark the page as a candidate for pruning */
+		PageSetPrunable(page, XLogRecGetXid(record));
+
+		if (xlrec->flags & XLH_UPDATE_OLD_ALL_VISIBLE_CLEARED)
+			PageClearAllVisible(page);
+
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(obuffer);
+	}
+
+	/*
+	 * Read the page the new tuple goes into, if different from old.
+	 */
+	if (oldblk == newblk)
+	{
+		nbuffer = obuffer;
+		newaction = oldaction;
+	}
+	else if (XLogRecGetInfo(record) & XLOG_HEAP_INIT_PAGE)
+	{
+		nbuffer = XLogInitBufferForRedo(record, 0);
+		page = (Page) BufferGetPage(nbuffer);
+		PageInit(page, BufferGetPageSize(nbuffer), 0);
+		newaction = BLK_NEEDS_REDO;
+	}
+	else
+		newaction = XLogReadBufferForRedo(record, 0, &nbuffer);
+
+	/*
+	 * The visibility map may need to be fixed even if the heap page is
+	 * already up-to-date.
+	 */
+	if (xlrec->flags & XLH_UPDATE_NEW_ALL_VISIBLE_CLEARED)
+	{
+		Relation	reln = CreateFakeRelcacheEntry(rnode);
+		Buffer		vmbuffer = InvalidBuffer;
+
+		visibilitymap_pin(reln, newblk, &vmbuffer);
+		visibilitymap_clear(reln, newblk, vmbuffer, VISIBILITYMAP_VALID_BITS);
+		ReleaseBuffer(vmbuffer);
+		FreeFakeRelcacheEntry(reln);
+	}
+
+	/* Deal with new tuple */
+	if (newaction == BLK_NEEDS_REDO)
+	{
+		char	   *recdata;
+		char	   *recdata_end;
+		Size		datalen;
+		Size		tuplen;
+
+		recdata = XLogRecGetBlockData(record, 0, &datalen);
+		recdata_end = recdata + datalen;
+
+		page = BufferGetPage(nbuffer);
+
+		offnum = xlrec->new_offnum;
+		if (PageGetMaxOffsetNumber(page) + 1 < offnum)
+			elog(PANIC, "invalid max offset number");
+
+		if (xlrec->flags & XLH_UPDATE_PREFIX_FROM_OLD)
+		{
+			Assert(newblk == oldblk);
+			memcpy(&prefixlen, recdata, sizeof(uint16));
+			recdata += sizeof(uint16);
+		}
+		if (xlrec->flags & XLH_UPDATE_SUFFIX_FROM_OLD)
+		{
+			Assert(newblk == oldblk);
+			memcpy(&suffixlen, recdata, sizeof(uint16));
+			recdata += sizeof(uint16);
+		}
+
+		memcpy((char *) &xlhdr, recdata, SizeOfHeapHeader);
+		recdata += SizeOfHeapHeader;
+
+		tuplen = recdata_end - recdata;
+		Assert(tuplen <= MaxHeapTupleSize);
+
+		htup = &tbuf.hdr;
+		MemSet((char *) htup, 0, SizeofHeapTupleHeader);
+
+		/*
+		 * Reconstruct the new tuple using the prefix and/or suffix from the
+		 * old tuple, and the data stored in the WAL record.
+		 */
+		newp = (char *) htup + SizeofHeapTupleHeader;
+		if (prefixlen > 0)
+		{
+			int			len;
+
+			/* copy bitmap [+ padding] [+ oid] from WAL record */
+			len = xlhdr.t_hoff - SizeofHeapTupleHeader;
+			memcpy(newp, recdata, len);
+			recdata += len;
+			newp += len;
+
+			/* copy prefix from old tuple */
+			memcpy(newp, (char *) oldtup.t_data + oldtup.t_data->t_hoff, prefixlen);
+			newp += prefixlen;
+
+			/* copy new tuple data from WAL record */
+			len = tuplen - (xlhdr.t_hoff - SizeofHeapTupleHeader);
+			memcpy(newp, recdata, len);
+			recdata += len;
+			newp += len;
+		}
+		else
+		{
+			/*
+			 * copy bitmap [+ padding] [+ oid] + data from record, all in one
+			 * go
+			 */
+			memcpy(newp, recdata, tuplen);
+			recdata += tuplen;
+			newp += tuplen;
+		}
+		Assert(recdata == recdata_end);
+
+		/* copy suffix from old tuple */
+		if (suffixlen > 0)
+			memcpy(newp, (char *) oldtup.t_data + oldtup.t_len - suffixlen, suffixlen);
+
+		newlen = SizeofHeapTupleHeader + tuplen + prefixlen + suffixlen;
+		htup->t_infomask2 = xlhdr.t_infomask2;
+		htup->t_infomask = xlhdr.t_infomask;
+		htup->t_hoff = xlhdr.t_hoff;
+
+		HeapTupleHeaderSetXmin(htup, XLogRecGetXid(record));
+		HeapTupleHeaderSetCmin(htup, FirstCommandId);
+		HeapTupleHeaderSetXmax(htup, xlrec->new_xmax);
+		/* Make sure there is no forward chain link in t_ctid */
+		htup->t_ctid = newtid;
+
+		offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
+		if (offnum == InvalidOffsetNumber)
+			elog(PANIC, "failed to add tuple");
+
+		if (xlrec->flags & XLH_UPDATE_NEW_ALL_VISIBLE_CLEARED)
+			PageClearAllVisible(page);
+
+		freespace = PageGetHeapFreeSpace(page); /* needed to update FSM below */
+
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(nbuffer);
+	}
+
+	if (BufferIsValid(nbuffer) && nbuffer != obuffer)
+		UnlockReleaseBuffer(nbuffer);
+	if (BufferIsValid(obuffer))
+		UnlockReleaseBuffer(obuffer);
+
+	/*
+	 * If the new page is running low on free space, update the FSM as well.
+	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
+	 * better than that without knowing the fill-factor for the table.
+	 *
+	 * However, don't update the FSM on HOT updates, because after crash
+	 * recovery, either the old or the new tuple will certainly be dead and
+	 * prunable. After pruning, the page will have roughly as much free space
+	 * as it did before the update, assuming the new tuple is about the same
+	 * size as the old one.
+	 *
+	 * XXX: Don't do this if the page was restored from full page image. We
+	 * don't bother to update the FSM in that case, it doesn't need to be
+	 * totally accurate anyway.
+	 */
+	if (newaction == BLK_NEEDS_REDO && !hot_update && freespace < BLCKSZ / 5)
+		XLogRecordPageWithFreeSpace(rnode, newblk, freespace);
+}
+
+static void
+heap_xlog_confirm(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_confirm *xlrec = (xl_heap_confirm *) XLogRecGetData(record);
+	Buffer		buffer;
+	Page		page;
+	OffsetNumber offnum;
+	ItemId		lp = NULL;
+	HeapTupleHeader htup;
+
+	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
+	{
+		page = BufferGetPage(buffer);
+
+		offnum = xlrec->offnum;
+		if (PageGetMaxOffsetNumber(page) >= offnum)
+			lp = PageGetItemId(page, offnum);
+
+		if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
+			elog(PANIC, "invalid lp");
+
+		htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+		/*
+		 * Confirm tuple as actually inserted
+		 */
+		ItemPointerSet(&htup->t_ctid, BufferGetBlockNumber(buffer), offnum);
+
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(buffer);
+	}
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
+}
+
+static void
+heap_xlog_lock(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_lock *xlrec = (xl_heap_lock *) XLogRecGetData(record);
+	Buffer		buffer;
+	Page		page;
+	OffsetNumber offnum;
+	ItemId		lp = NULL;
+	HeapTupleHeader htup;
+
+	/*
+	 * The visibility map may need to be fixed even if the heap page is
+	 * already up-to-date.
+	 */
+	if (xlrec->flags & XLH_LOCK_ALL_FROZEN_CLEARED)
+	{
+		RelFileNode rnode;
+		Buffer		vmbuffer = InvalidBuffer;
+		BlockNumber block;
+		Relation	reln;
+
+		XLogRecGetBlockTag(record, 0, &rnode, NULL, &block);
+		reln = CreateFakeRelcacheEntry(rnode);
+
+		visibilitymap_pin(reln, block, &vmbuffer);
+		visibilitymap_clear(reln, block, vmbuffer, VISIBILITYMAP_ALL_FROZEN);
+
+		ReleaseBuffer(vmbuffer);
+		FreeFakeRelcacheEntry(reln);
+	}
+
+	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
+	{
+		page = (Page) BufferGetPage(buffer);
+
+		offnum = xlrec->offnum;
+		if (PageGetMaxOffsetNumber(page) >= offnum)
+			lp = PageGetItemId(page, offnum);
+
+		if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
+			elog(PANIC, "invalid lp");
+
+		htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+		htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
+		htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+		fix_infomask_from_infobits(xlrec->infobits_set, &htup->t_infomask,
+								   &htup->t_infomask2);
+
+		/*
+		 * Clear relevant update flags, but only if the modified infomask says
+		 * there's no update.
+		 */
+		if (HEAP_XMAX_IS_LOCKED_ONLY(htup->t_infomask))
+		{
+			HeapTupleHeaderClearHotUpdated(htup);
+			/* Make sure there is no forward chain link in t_ctid */
+			ItemPointerSet(&htup->t_ctid,
+						   BufferGetBlockNumber(buffer),
+						   offnum);
+		}
+		HeapTupleHeaderSetXmax(htup, xlrec->locking_xid);
+		HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(buffer);
+	}
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
+}
+
+static void
+heap_xlog_lock_updated(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_lock_updated *xlrec;
+	Buffer		buffer;
+	Page		page;
+	OffsetNumber offnum;
+	ItemId		lp = NULL;
+	HeapTupleHeader htup;
+
+	xlrec = (xl_heap_lock_updated *) XLogRecGetData(record);
+
+	/*
+	 * The visibility map may need to be fixed even if the heap page is
+	 * already up-to-date.
+	 */
+	if (xlrec->flags & XLH_LOCK_ALL_FROZEN_CLEARED)
+	{
+		RelFileNode rnode;
+		Buffer		vmbuffer = InvalidBuffer;
+		BlockNumber block;
+		Relation	reln;
+
+		XLogRecGetBlockTag(record, 0, &rnode, NULL, &block);
+		reln = CreateFakeRelcacheEntry(rnode);
+
+		visibilitymap_pin(reln, block, &vmbuffer);
+		visibilitymap_clear(reln, block, vmbuffer, VISIBILITYMAP_ALL_FROZEN);
+
+		ReleaseBuffer(vmbuffer);
+		FreeFakeRelcacheEntry(reln);
+	}
+
+	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
+	{
+		page = BufferGetPage(buffer);
+
+		offnum = xlrec->offnum;
+		if (PageGetMaxOffsetNumber(page) >= offnum)
+			lp = PageGetItemId(page, offnum);
+
+		if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
+			elog(PANIC, "invalid lp");
+
+		htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+		htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
+		htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+		fix_infomask_from_infobits(xlrec->infobits_set, &htup->t_infomask,
+								   &htup->t_infomask2);
+		HeapTupleHeaderSetXmax(htup, xlrec->xmax);
+
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(buffer);
+	}
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
+}
+
+static void
+heap_xlog_inplace(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_heap_inplace *xlrec = (xl_heap_inplace *) XLogRecGetData(record);
+	Buffer		buffer;
+	Page		page;
+	OffsetNumber offnum;
+	ItemId		lp = NULL;
+	HeapTupleHeader htup;
+	uint32		oldlen;
+	Size		newlen;
+
+	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
+	{
+		char	   *newtup = XLogRecGetBlockData(record, 0, &newlen);
+
+		page = BufferGetPage(buffer);
+
+		offnum = xlrec->offnum;
+		if (PageGetMaxOffsetNumber(page) >= offnum)
+			lp = PageGetItemId(page, offnum);
+
+		if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
+			elog(PANIC, "invalid lp");
+
+		htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+		oldlen = ItemIdGetLength(lp) - htup->t_hoff;
+		if (oldlen != newlen)
+			elog(PANIC, "wrong tuple length");
+
+		memcpy((char *) htup + htup->t_hoff, newtup, newlen);
+
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(buffer);
+	}
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
+}
+
+void
+heap_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	/*
+	 * These operations don't overwrite MVCC data so no conflict processing is
+	 * required. The ones in heap2 rmgr do.
+	 */
+
+	switch (info & XLOG_HEAP_OPMASK)
+	{
+		case XLOG_HEAP_INSERT:
+			heap_xlog_insert(record);
+			break;
+		case XLOG_HEAP_DELETE:
+			heap_xlog_delete(record);
+			break;
+		case XLOG_HEAP_UPDATE:
+			heap_xlog_update(record, false);
+			break;
+		case XLOG_HEAP_TRUNCATE:
+
+			/*
+			 * TRUNCATE is a no-op because the actions are already logged as
+			 * SMGR WAL records.  TRUNCATE WAL record only exists for logical
+			 * decoding.
+			 */
+			break;
+		case XLOG_HEAP_HOT_UPDATE:
+			heap_xlog_update(record, true);
+			break;
+		case XLOG_HEAP_CONFIRM:
+			heap_xlog_confirm(record);
+			break;
+		case XLOG_HEAP_LOCK:
+			heap_xlog_lock(record);
+			break;
+		case XLOG_HEAP_INPLACE:
+			heap_xlog_inplace(record);
+			break;
+		default:
+			elog(PANIC, "heap_redo: unknown op code %u", info);
+	}
+}
+
+void
+heap2_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	switch (info & XLOG_HEAP_OPMASK)
+	{
+		case XLOG_HEAP2_PRUNE:
+			heap_xlog_prune(record);
+			break;
+		case XLOG_HEAP2_VACUUM:
+			heap_xlog_vacuum(record);
+			break;
+		case XLOG_HEAP2_FREEZE_PAGE:
+			heap_xlog_freeze_page(record);
+			break;
+		case XLOG_HEAP2_VISIBLE:
+			heap_xlog_visible(record);
+			break;
+		case XLOG_HEAP2_MULTI_INSERT:
+			heap_xlog_multi_insert(record);
+			break;
+		case XLOG_HEAP2_LOCK_UPDATED:
+			heap_xlog_lock_updated(record);
+			break;
+		case XLOG_HEAP2_NEW_CID:
+
+			/*
+			 * Nothing to do on a real replay, only used during logical
+			 * decoding.
+			 */
+			break;
+		case XLOG_HEAP2_REWRITE:
+			heap_xlog_logical_rewrite(record);
+			break;
+		default:
+			elog(PANIC, "heap2_redo: unknown op code %u", info);
+	}
+}
+
+/*
+ * Mask a heap page before performing consistency checks on it.
+ */
+void
+heap_mask(char *pagedata, BlockNumber blkno)
+{
+	Page		page = (Page) pagedata;
+	OffsetNumber off;
+
+	mask_page_lsn_and_checksum(page);
+
+	mask_page_hint_bits(page);
+	mask_unused_space(page);
+
+	for (off = 1; off <= PageGetMaxOffsetNumber(page); off++)
+	{
+		ItemId		iid = PageGetItemId(page, off);
+		char	   *page_item;
+
+		page_item = (char *) (page + ItemIdGetOffset(iid));
+
+		if (ItemIdIsNormal(iid))
+		{
+			HeapTupleHeader page_htup = (HeapTupleHeader) page_item;
+
+			/*
+			 * If xmin of a tuple is not yet frozen, we should ignore
+			 * differences in hint bits, since they can be set without
+			 * emitting WAL.
+			 */
+			if (!HeapTupleHeaderXminFrozen(page_htup))
+				page_htup->t_infomask &= ~HEAP_XACT_MASK;
+			else
+			{
+				/* Still we need to mask xmax hint bits. */
+				page_htup->t_infomask &= ~HEAP_XMAX_INVALID;
+				page_htup->t_infomask &= ~HEAP_XMAX_COMMITTED;
+			}
+
+			/*
+			 * During replay, we set Command Id to FirstCommandId. Hence, mask
+			 * it. See heap_xlog_insert() for details.
+			 */
+			page_htup->t_choice.t_heap.t_field3.t_cid = MASK_MARKER;
+
+			/*
+			 * For a speculative tuple, heap_insert() does not set ctid in the
+			 * caller-passed heap tuple itself, leaving the ctid field to
+			 * contain a speculative token value - a per-backend monotonically
+			 * increasing identifier. Besides, it does not WAL-log ctid under
+			 * any circumstances.
+			 *
+			 * During redo, heap_xlog_insert() sets t_ctid to current block
+			 * number and self offset number. It doesn't care about any
+			 * speculative insertions on the primary. Hence, we set t_ctid to
+			 * current block number and self offset number to ignore any
+			 * inconsistency.
+			 */
+			if (HeapTupleHeaderIsSpeculative(page_htup))
+				ItemPointerSet(&page_htup->t_ctid, blkno, off);
+
+			/*
+			 * NB: Not ignoring ctid changes due to the tuple having moved
+			 * (i.e. HeapTupleHeaderIndicatesMovedPartitions), because that's
+			 * important information that needs to be in-sync between primary
+			 * and standby, and thus is WAL logged.
+			 */
+		}
+
+		/*
+		 * Ignore any padding bytes after the tuple, when the length of the
+		 * item is not MAXALIGNed.
+		 */
+		if (ItemIdHasStorage(iid))
+		{
+			int			len = ItemIdGetLength(iid);
+			int			padlen = MAXALIGN(len) - len;
+
+			if (padlen > 0)
+				memset(page_item + len, MASK_MARKER, padlen);
+		}
+	}
+}
+
+/*
+ * HeapCheckForSerializableConflictOut
+ *		We are reading a tuple.  If it's not visible, there may be a
+ *		rw-conflict out with the inserter.  Otherwise, if it is visible to us
+ *		but has been deleted, there may be a rw-conflict out with the deleter.
+ *
+ * We will determine the top level xid of the writing transaction with which
+ * we may be in conflict, and ask CheckForSerializableConflictOut() to check
+ * for overlap with our own transaction.
+ *
+ * This function should be called just about anywhere in heapam.c where a
+ * tuple has been read. The caller must hold at least a shared lock on the
+ * buffer, because this function might set hint bits on the tuple. There is
+ * currently no known reason to call this function from an index AM.
+ */
+void
+HeapCheckForSerializableConflictOut(bool visible, Relation relation,
+									HeapTuple tuple, Buffer buffer,
+									Snapshot snapshot)
+{
+	TransactionId xid;
+	HTSV_Result htsvResult;
+
+	if (!CheckForSerializableConflictOutNeeded(relation, snapshot))
+		return;
+
+	/*
+	 * Check to see whether the tuple has been written to by a concurrent
+	 * transaction, either to create it not visible to us, or to delete it
+	 * while it is visible to us.  The "visible" bool indicates whether the
+	 * tuple is visible to us, while HeapTupleSatisfiesVacuum checks what else
+	 * is going on with it.
+	 *
+	 * In the event of a concurrently inserted tuple that also happens to have
+	 * been concurrently updated (by a separate transaction), the xmin of the
+	 * tuple will be used -- not the updater's xid.
+	 */
+	htsvResult = HeapTupleSatisfiesVacuum(tuple, TransactionXmin, buffer);
+	switch (htsvResult)
+	{
+		case HEAPTUPLE_LIVE:
+			if (visible)
+				return;
+			xid = HeapTupleHeaderGetXmin(tuple->t_data);
+			break;
+		case HEAPTUPLE_RECENTLY_DEAD:
+		case HEAPTUPLE_DELETE_IN_PROGRESS:
+			if (visible)
+				xid = HeapTupleHeaderGetUpdateXid(tuple->t_data);
+			else
+				xid = HeapTupleHeaderGetXmin(tuple->t_data);
+
+			if (TransactionIdPrecedes(xid, TransactionXmin))
+			{
+				/* This is like the HEAPTUPLE_DEAD case */
+				Assert(!visible);
+				return;
+			}
+			break;
+		case HEAPTUPLE_INSERT_IN_PROGRESS:
+			xid = HeapTupleHeaderGetXmin(tuple->t_data);
+			break;
+		case HEAPTUPLE_DEAD:
+			Assert(!visible);
+			return;
+		default:
+
+			/*
+			 * The only way to get to this default clause is if a new value is
+			 * added to the enum type without adding it to this switch
+			 * statement.  That's a bug, so elog.
+			 */
+			elog(ERROR, "unrecognized return value from HeapTupleSatisfiesVacuum: %u", htsvResult);
+
+			/*
+			 * In spite of having all enum values covered and calling elog on
+			 * this default, some compilers think this is a code path which
+			 * allows xid to be used below without initialization. Silence
+			 * that warning.
+			 */
+			xid = InvalidTransactionId;
+	}
+
+	Assert(TransactionIdIsValid(xid));
+	Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));
+
+	/*
+	 * Find top level xid.  Bail out if xid is too early to be a conflict, or
+	 * if it's our own xid.
+	 */
+	if (TransactionIdEquals(xid, GetTopTransactionIdIfAny()))
+		return;
+	xid = SubTransGetTopmostTransaction(xid);
+	if (TransactionIdPrecedes(xid, TransactionXmin))
+		return;
+
+	CheckForSerializableConflictOut(relation, xid, snapshot);
+}
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
new file mode 100644
index 0000000..6633939
--- /dev/null
+++ b/src/backend/access/heap/heapam_handler.c
@@ -0,0 +1,2608 @@
+/*-------------------------------------------------------------------------
+ *
+ * heapam_handler.c
+ *	  heap table access method code
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/heap/heapam_handler.c
+ *
+ *
+ * NOTES
+ *	  This files wires up the lower level heapam.c et al routines with the
+ *	  tableam abstraction.
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/genam.h"
+#include "access/heapam.h"
+#include "access/heaptoast.h"
+#include "access/multixact.h"
+#include "access/rewriteheap.h"
+#include "access/syncscan.h"
+#include "access/tableam.h"
+#include "access/tsmapi.h"
+#include "access/xact.h"
+#include "catalog/catalog.h"
+#include "catalog/index.h"
+#include "catalog/storage.h"
+#include "catalog/storage_xlog.h"
+#include "commands/progress.h"
+#include "executor/executor.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "storage/bufmgr.h"
+#include "storage/bufpage.h"
+#include "storage/lmgr.h"
+#include "storage/predicate.h"
+#include "storage/procarray.h"
+#include "storage/smgr.h"
+#include "utils/builtins.h"
+#include "utils/rel.h"
+
+static void reform_and_rewrite_tuple(HeapTuple tuple,
+									 Relation OldHeap, Relation NewHeap,
+									 Datum *values, bool *isnull, RewriteState rwstate);
+
+static bool SampleHeapTupleVisible(TableScanDesc scan, Buffer buffer,
+								   HeapTuple tuple,
+								   OffsetNumber tupoffset);
+
+static BlockNumber heapam_scan_get_blocks_done(HeapScanDesc hscan);
+
+static const TableAmRoutine heapam_methods;
+
+
+/* ------------------------------------------------------------------------
+ * Slot related callbacks for heap AM
+ * ------------------------------------------------------------------------
+ */
+
+static const TupleTableSlotOps *
+heapam_slot_callbacks(Relation relation)
+{
+	return &TTSOpsBufferHeapTuple;
+}
+
+
+/* ------------------------------------------------------------------------
+ * Index Scan Callbacks for heap AM
+ * ------------------------------------------------------------------------
+ */
+
+static IndexFetchTableData *
+heapam_index_fetch_begin(Relation rel)
+{
+	IndexFetchHeapData *hscan = palloc0(sizeof(IndexFetchHeapData));
+
+	hscan->xs_base.rel = rel;
+	hscan->xs_cbuf = InvalidBuffer;
+
+	return &hscan->xs_base;
+}
+
+static void
+heapam_index_fetch_reset(IndexFetchTableData *scan)
+{
+	IndexFetchHeapData *hscan = (IndexFetchHeapData *) scan;
+
+	if (BufferIsValid(hscan->xs_cbuf))
+	{
+		ReleaseBuffer(hscan->xs_cbuf);
+		hscan->xs_cbuf = InvalidBuffer;
+	}
+}
+
+static void
+heapam_index_fetch_end(IndexFetchTableData *scan)
+{
+	IndexFetchHeapData *hscan = (IndexFetchHeapData *) scan;
+
+	heapam_index_fetch_reset(scan);
+
+	pfree(hscan);
+}
+
+static bool
+heapam_index_fetch_tuple(struct IndexFetchTableData *scan,
+						 ItemPointer tid,
+						 Snapshot snapshot,
+						 TupleTableSlot *slot,
+						 bool *call_again, bool *all_dead)
+{
+	IndexFetchHeapData *hscan = (IndexFetchHeapData *) scan;
+	BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;
+	bool		got_heap_tuple;
+
+	Assert(TTS_IS_BUFFERTUPLE(slot));
+
+	/* We can skip the buffer-switching logic if we're in mid-HOT chain. */
+	if (!*call_again)
+	{
+		/* Switch to correct buffer if we don't have it already */
+		Buffer		prev_buf = hscan->xs_cbuf;
+
+		hscan->xs_cbuf = ReleaseAndReadBuffer(hscan->xs_cbuf,
+											  hscan->xs_base.rel,
+											  ItemPointerGetBlockNumber(tid));
+
+		/*
+		 * Prune page, but only if we weren't already on this page
+		 */
+		if (prev_buf != hscan->xs_cbuf)
+			heap_page_prune_opt(hscan->xs_base.rel, hscan->xs_cbuf);
+	}
+
+	/* Obtain share-lock on the buffer so we can examine visibility */
+	LockBuffer(hscan->xs_cbuf, BUFFER_LOCK_SHARE);
+	got_heap_tuple = heap_hot_search_buffer(tid,
+											hscan->xs_base.rel,
+											hscan->xs_cbuf,
+											snapshot,
+											&bslot->base.tupdata,
+											all_dead,
+											!*call_again);
+	bslot->base.tupdata.t_self = *tid;
+	LockBuffer(hscan->xs_cbuf, BUFFER_LOCK_UNLOCK);
+
+	if (got_heap_tuple)
+	{
+		/*
+		 * Only in a non-MVCC snapshot can more than one member of the HOT
+		 * chain be visible.
+		 */
+		*call_again = !IsMVCCSnapshot(snapshot);
+
+		slot->tts_tableOid = RelationGetRelid(scan->rel);
+		ExecStoreBufferHeapTuple(&bslot->base.tupdata, slot, hscan->xs_cbuf);
+	}
+	else
+	{
+		/* We've reached the end of the HOT chain. */
+		*call_again = false;
+	}
+
+	return got_heap_tuple;
+}
+
+
+/* ------------------------------------------------------------------------
+ * Callbacks for non-modifying operations on individual tuples for heap AM
+ * ------------------------------------------------------------------------
+ */
+
+static bool
+heapam_fetch_row_version(Relation relation,
+						 ItemPointer tid,
+						 Snapshot snapshot,
+						 TupleTableSlot *slot)
+{
+	BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;
+	Buffer		buffer;
+
+	Assert(TTS_IS_BUFFERTUPLE(slot));
+
+	bslot->base.tupdata.t_self = *tid;
+	if (heap_fetch(relation, snapshot, &bslot->base.tupdata, &buffer))
+	{
+		/* store in slot, transferring existing pin */
+		ExecStorePinnedBufferHeapTuple(&bslot->base.tupdata, slot, buffer);
+		slot->tts_tableOid = RelationGetRelid(relation);
+
+		return true;
+	}
+
+	return false;
+}
+
+static bool
+heapam_tuple_tid_valid(TableScanDesc scan, ItemPointer tid)
+{
+	HeapScanDesc hscan = (HeapScanDesc) scan;
+
+	return ItemPointerIsValid(tid) &&
+		ItemPointerGetBlockNumber(tid) < hscan->rs_nblocks;
+}
+
+static bool
+heapam_tuple_satisfies_snapshot(Relation rel, TupleTableSlot *slot,
+								Snapshot snapshot)
+{
+	BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;
+	bool		res;
+
+	Assert(TTS_IS_BUFFERTUPLE(slot));
+	Assert(BufferIsValid(bslot->buffer));
+
+	/*
+	 * We need buffer pin and lock to call HeapTupleSatisfiesVisibility.
+	 * Caller should be holding pin, but not lock.
+	 */
+	LockBuffer(bslot->buffer, BUFFER_LOCK_SHARE);
+	res = HeapTupleSatisfiesVisibility(bslot->base.tuple, snapshot,
+									   bslot->buffer);
+	LockBuffer(bslot->buffer, BUFFER_LOCK_UNLOCK);
+
+	return res;
+}
+
+
+/* ----------------------------------------------------------------------------
+ *  Functions for manipulations of physical tuples for heap AM.
+ * ----------------------------------------------------------------------------
+ */
+
+static void
+heapam_tuple_insert(Relation relation, TupleTableSlot *slot, CommandId cid,
+					int options, BulkInsertState bistate)
+{
+	bool		shouldFree = true;
+	HeapTuple	tuple = ExecFetchSlotHeapTuple(slot, true, &shouldFree);
+
+	/* Update the tuple with table oid */
+	slot->tts_tableOid = RelationGetRelid(relation);
+	tuple->t_tableOid = slot->tts_tableOid;
+
+	/* Perform the insertion, and copy the resulting ItemPointer */
+	heap_insert(relation, tuple, cid, options, bistate);
+	ItemPointerCopy(&tuple->t_self, &slot->tts_tid);
+
+	if (shouldFree)
+		pfree(tuple);
+}
+
+static void
+heapam_tuple_insert_speculative(Relation relation, TupleTableSlot *slot,
+								CommandId cid, int options,
+								BulkInsertState bistate, uint32 specToken)
+{
+	bool		shouldFree = true;
+	HeapTuple	tuple = ExecFetchSlotHeapTuple(slot, true, &shouldFree);
+
+	/* Update the tuple with table oid */
+	slot->tts_tableOid = RelationGetRelid(relation);
+	tuple->t_tableOid = slot->tts_tableOid;
+
+	HeapTupleHeaderSetSpeculativeToken(tuple->t_data, specToken);
+	options |= HEAP_INSERT_SPECULATIVE;
+
+	/* Perform the insertion, and copy the resulting ItemPointer */
+	heap_insert(relation, tuple, cid, options, bistate);
+	ItemPointerCopy(&tuple->t_self, &slot->tts_tid);
+
+	if (shouldFree)
+		pfree(tuple);
+}
+
+static void
+heapam_tuple_complete_speculative(Relation relation, TupleTableSlot *slot,
+								  uint32 specToken, bool succeeded)
+{
+	bool		shouldFree = true;
+	HeapTuple	tuple = ExecFetchSlotHeapTuple(slot, true, &shouldFree);
+
+	/* adjust the tuple's state accordingly */
+	if (succeeded)
+		heap_finish_speculative(relation, &slot->tts_tid);
+	else
+		heap_abort_speculative(relation, &slot->tts_tid);
+
+	if (shouldFree)
+		pfree(tuple);
+}
+
+static TM_Result
+heapam_tuple_delete(Relation relation, ItemPointer tid, CommandId cid,
+					Snapshot snapshot, Snapshot crosscheck, bool wait,
+					TM_FailureData *tmfd, bool changingPart)
+{
+	/*
+	 * Currently Deleting of index tuples are handled at vacuum, in case if
+	 * the storage itself is cleaning the dead tuples by itself, it is the
+	 * time to call the index tuple deletion also.
+	 */
+	return heap_delete(relation, tid, cid, crosscheck, wait, tmfd, changingPart);
+}
+
+
+static TM_Result
+heapam_tuple_update(Relation relation, ItemPointer otid, TupleTableSlot *slot,
+					CommandId cid, Snapshot snapshot, Snapshot crosscheck,
+					bool wait, TM_FailureData *tmfd,
+					LockTupleMode *lockmode, bool *update_indexes)
+{
+	bool		shouldFree = true;
+	HeapTuple	tuple = ExecFetchSlotHeapTuple(slot, true, &shouldFree);
+	TM_Result	result;
+
+	/* Update the tuple with table oid */
+	slot->tts_tableOid = RelationGetRelid(relation);
+	tuple->t_tableOid = slot->tts_tableOid;
+
+	result = heap_update(relation, otid, tuple, cid, crosscheck, wait,
+						 tmfd, lockmode);
+	ItemPointerCopy(&tuple->t_self, &slot->tts_tid);
+
+	/*
+	 * Decide whether new index entries are needed for the tuple
+	 *
+	 * Note: heap_update returns the tid (location) of the new tuple in the
+	 * t_self field.
+	 *
+	 * If it's a HOT update, we mustn't insert new index entries.
+	 */
+	*update_indexes = result == TM_Ok && !HeapTupleIsHeapOnly(tuple);
+
+	if (shouldFree)
+		pfree(tuple);
+
+	return result;
+}
+
+static TM_Result
+heapam_tuple_lock(Relation relation, ItemPointer tid, Snapshot snapshot,
+				  TupleTableSlot *slot, CommandId cid, LockTupleMode mode,
+				  LockWaitPolicy wait_policy, uint8 flags,
+				  TM_FailureData *tmfd)
+{
+	BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;
+	TM_Result	result;
+	Buffer		buffer;
+	HeapTuple	tuple = &bslot->base.tupdata;
+	bool		follow_updates;
+
+	follow_updates = (flags & TUPLE_LOCK_FLAG_LOCK_UPDATE_IN_PROGRESS) != 0;
+	tmfd->traversed = false;
+
+	Assert(TTS_IS_BUFFERTUPLE(slot));
+
+tuple_lock_retry:
+	tuple->t_self = *tid;
+	result = heap_lock_tuple(relation, tuple, cid, mode, wait_policy,
+							 follow_updates, &buffer, tmfd);
+
+	if (result == TM_Updated &&
+		(flags & TUPLE_LOCK_FLAG_FIND_LAST_VERSION))
+	{
+		/* Should not encounter speculative tuple on recheck */
+		Assert(!HeapTupleHeaderIsSpeculative(tuple->t_data));
+
+		ReleaseBuffer(buffer);
+
+		if (!ItemPointerEquals(&tmfd->ctid, &tuple->t_self))
+		{
+			SnapshotData SnapshotDirty;
+			TransactionId priorXmax;
+
+			/* it was updated, so look at the updated version */
+			*tid = tmfd->ctid;
+			/* updated row should have xmin matching this xmax */
+			priorXmax = tmfd->xmax;
+
+			/* signal that a tuple later in the chain is getting locked */
+			tmfd->traversed = true;
+
+			/*
+			 * fetch target tuple
+			 *
+			 * Loop here to deal with updated or busy tuples
+			 */
+			InitDirtySnapshot(SnapshotDirty);
+			for (;;)
+			{
+				if (ItemPointerIndicatesMovedPartitions(tid))
+					ereport(ERROR,
+							(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
+							 errmsg("tuple to be locked was already moved to another partition due to concurrent update")));
+
+				tuple->t_self = *tid;
+				if (heap_fetch_extended(relation, &SnapshotDirty, tuple,
+										&buffer, true))
+				{
+					/*
+					 * If xmin isn't what we're expecting, the slot must have
+					 * been recycled and reused for an unrelated tuple.  This
+					 * implies that the latest version of the row was deleted,
+					 * so we need do nothing.  (Should be safe to examine xmin
+					 * without getting buffer's content lock.  We assume
+					 * reading a TransactionId to be atomic, and Xmin never
+					 * changes in an existing tuple, except to invalid or
+					 * frozen, and neither of those can match priorXmax.)
+					 */
+					if (!TransactionIdEquals(HeapTupleHeaderGetXmin(tuple->t_data),
+											 priorXmax))
+					{
+						ReleaseBuffer(buffer);
+						return TM_Deleted;
+					}
+
+					/* otherwise xmin should not be dirty... */
+					if (TransactionIdIsValid(SnapshotDirty.xmin))
+						ereport(ERROR,
+								(errcode(ERRCODE_DATA_CORRUPTED),
+								 errmsg_internal("t_xmin %u is uncommitted in tuple (%u,%u) to be updated in table \"%s\"",
+												 SnapshotDirty.xmin,
+												 ItemPointerGetBlockNumber(&tuple->t_self),
+												 ItemPointerGetOffsetNumber(&tuple->t_self),
+												 RelationGetRelationName(relation))));
+
+					/*
+					 * If tuple is being updated by other transaction then we
+					 * have to wait for its commit/abort, or die trying.
+					 */
+					if (TransactionIdIsValid(SnapshotDirty.xmax))
+					{
+						ReleaseBuffer(buffer);
+						switch (wait_policy)
+						{
+							case LockWaitBlock:
+								XactLockTableWait(SnapshotDirty.xmax,
+												  relation, &tuple->t_self,
+												  XLTW_FetchUpdated);
+								break;
+							case LockWaitSkip:
+								if (!ConditionalXactLockTableWait(SnapshotDirty.xmax))
+									/* skip instead of waiting */
+									return TM_WouldBlock;
+								break;
+							case LockWaitError:
+								if (!ConditionalXactLockTableWait(SnapshotDirty.xmax))
+									ereport(ERROR,
+											(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
+											 errmsg("could not obtain lock on row in relation \"%s\"",
+													RelationGetRelationName(relation))));
+								break;
+						}
+						continue;	/* loop back to repeat heap_fetch */
+					}
+
+					/*
+					 * If tuple was inserted by our own transaction, we have
+					 * to check cmin against cid: cmin >= current CID means
+					 * our command cannot see the tuple, so we should ignore
+					 * it. Otherwise heap_lock_tuple() will throw an error,
+					 * and so would any later attempt to update or delete the
+					 * tuple.  (We need not check cmax because
+					 * HeapTupleSatisfiesDirty will consider a tuple deleted
+					 * by our transaction dead, regardless of cmax.)  We just
+					 * checked that priorXmax == xmin, so we can test that
+					 * variable instead of doing HeapTupleHeaderGetXmin again.
+					 */
+					if (TransactionIdIsCurrentTransactionId(priorXmax) &&
+						HeapTupleHeaderGetCmin(tuple->t_data) >= cid)
+					{
+						tmfd->xmax = priorXmax;
+
+						/*
+						 * Cmin is the problematic value, so store that. See
+						 * above.
+						 */
+						tmfd->cmax = HeapTupleHeaderGetCmin(tuple->t_data);
+						ReleaseBuffer(buffer);
+						return TM_SelfModified;
+					}
+
+					/*
+					 * This is a live tuple, so try to lock it again.
+					 */
+					ReleaseBuffer(buffer);
+					goto tuple_lock_retry;
+				}
+
+				/*
+				 * If the referenced slot was actually empty, the latest
+				 * version of the row must have been deleted, so we need do
+				 * nothing.
+				 */
+				if (tuple->t_data == NULL)
+				{
+					Assert(!BufferIsValid(buffer));
+					return TM_Deleted;
+				}
+
+				/*
+				 * As above, if xmin isn't what we're expecting, do nothing.
+				 */
+				if (!TransactionIdEquals(HeapTupleHeaderGetXmin(tuple->t_data),
+										 priorXmax))
+				{
+					ReleaseBuffer(buffer);
+					return TM_Deleted;
+				}
+
+				/*
+				 * If we get here, the tuple was found but failed
+				 * SnapshotDirty. Assuming the xmin is either a committed xact
+				 * or our own xact (as it certainly should be if we're trying
+				 * to modify the tuple), this must mean that the row was
+				 * updated or deleted by either a committed xact or our own
+				 * xact.  If it was deleted, we can ignore it; if it was
+				 * updated then chain up to the next version and repeat the
+				 * whole process.
+				 *
+				 * As above, it should be safe to examine xmax and t_ctid
+				 * without the buffer content lock, because they can't be
+				 * changing.  We'd better hold a buffer pin though.
+				 */
+				if (ItemPointerEquals(&tuple->t_self, &tuple->t_data->t_ctid))
+				{
+					/* deleted, so forget about it */
+					ReleaseBuffer(buffer);
+					return TM_Deleted;
+				}
+
+				/* updated, so look at the updated row */
+				*tid = tuple->t_data->t_ctid;
+				/* updated row should have xmin matching this xmax */
+				priorXmax = HeapTupleHeaderGetUpdateXid(tuple->t_data);
+				ReleaseBuffer(buffer);
+				/* loop back to fetch next in chain */
+			}
+		}
+		else
+		{
+			/* tuple was deleted, so give up */
+			return TM_Deleted;
+		}
+	}
+
+	slot->tts_tableOid = RelationGetRelid(relation);
+	tuple->t_tableOid = slot->tts_tableOid;
+
+	/* store in slot, transferring existing pin */
+	ExecStorePinnedBufferHeapTuple(tuple, slot, buffer);
+
+	return result;
+}
+
+
+/* ------------------------------------------------------------------------
+ * DDL related callbacks for heap AM.
+ * ------------------------------------------------------------------------
+ */
+
+static void
+heapam_relation_set_new_filenode(Relation rel,
+								 const RelFileNode *newrnode,
+								 char persistence,
+								 TransactionId *freezeXid,
+								 MultiXactId *minmulti)
+{
+	SMgrRelation srel;
+
+	/*
+	 * Initialize to the minimum XID that could put tuples in the table. We
+	 * know that no xacts older than RecentXmin are still running, so that
+	 * will do.
+	 */
+	*freezeXid = RecentXmin;
+
+	/*
+	 * Similarly, initialize the minimum Multixact to the first value that
+	 * could possibly be stored in tuples in the table.  Running transactions
+	 * could reuse values from their local cache, so we are careful to
+	 * consider all currently running multis.
+	 *
+	 * XXX this could be refined further, but is it worth the hassle?
+	 */
+	*minmulti = GetOldestMultiXactId();
+
+	srel = RelationCreateStorage(*newrnode, persistence);
+
+	/*
+	 * If required, set up an init fork for an unlogged table so that it can
+	 * be correctly reinitialized on restart.  An immediate sync is required
+	 * even if the page has been logged, because the write did not go through
+	 * shared_buffers and therefore a concurrent checkpoint may have moved the
+	 * redo pointer past our xlog record.  Recovery may as well remove it
+	 * while replaying, for example, XLOG_DBASE_CREATE or XLOG_TBLSPC_CREATE
+	 * record. Therefore, logging is necessary even if wal_level=minimal.
+	 */
+	if (persistence == RELPERSISTENCE_UNLOGGED)
+	{
+		Assert(rel->rd_rel->relkind == RELKIND_RELATION ||
+			   rel->rd_rel->relkind == RELKIND_MATVIEW ||
+			   rel->rd_rel->relkind == RELKIND_TOASTVALUE);
+		smgrcreate(srel, INIT_FORKNUM, false);
+		log_smgrcreate(newrnode, INIT_FORKNUM);
+		smgrimmedsync(srel, INIT_FORKNUM);
+	}
+
+	smgrclose(srel);
+}
+
+static void
+heapam_relation_nontransactional_truncate(Relation rel)
+{
+	RelationTruncate(rel, 0);
+}
+
+static void
+heapam_relation_copy_data(Relation rel, const RelFileNode *newrnode)
+{
+	SMgrRelation dstrel;
+
+	dstrel = smgropen(*newrnode, rel->rd_backend);
+	RelationOpenSmgr(rel);
+
+	/*
+	 * Since we copy the file directly without looking at the shared buffers,
+	 * we'd better first flush out any pages of the source relation that are
+	 * in shared buffers.  We assume no new changes will be made while we are
+	 * holding exclusive lock on the rel.
+	 */
+	FlushRelationBuffers(rel);
+
+	/*
+	 * Create and copy all forks of the relation, and schedule unlinking of
+	 * old physical files.
+	 *
+	 * NOTE: any conflict in relfilenode value will be caught in
+	 * RelationCreateStorage().
+	 */
+	RelationCreateStorage(*newrnode, rel->rd_rel->relpersistence);
+
+	/* copy main fork */
+	RelationCopyStorage(rel->rd_smgr, dstrel, MAIN_FORKNUM,
+						rel->rd_rel->relpersistence);
+
+	/* copy those extra forks that exist */
+	for (ForkNumber forkNum = MAIN_FORKNUM + 1;
+		 forkNum <= MAX_FORKNUM; forkNum++)
+	{
+		if (smgrexists(rel->rd_smgr, forkNum))
+		{
+			smgrcreate(dstrel, forkNum, false);
+
+			/*
+			 * WAL log creation if the relation is persistent, or this is the
+			 * init fork of an unlogged relation.
+			 */
+			if (RelationIsPermanent(rel) ||
+				(rel->rd_rel->relpersistence == RELPERSISTENCE_UNLOGGED &&
+				 forkNum == INIT_FORKNUM))
+				log_smgrcreate(newrnode, forkNum);
+			RelationCopyStorage(rel->rd_smgr, dstrel, forkNum,
+								rel->rd_rel->relpersistence);
+		}
+	}
+
+
+	/* drop old relation, and close new one */
+	RelationDropStorage(rel);
+	smgrclose(dstrel);
+}
+
+static void
+heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
+								 Relation OldIndex, bool use_sort,
+								 TransactionId OldestXmin,
+								 TransactionId *xid_cutoff,
+								 MultiXactId *multi_cutoff,
+								 double *num_tuples,
+								 double *tups_vacuumed,
+								 double *tups_recently_dead)
+{
+	RewriteState rwstate;
+	IndexScanDesc indexScan;
+	TableScanDesc tableScan;
+	HeapScanDesc heapScan;
+	bool		is_system_catalog;
+	Tuplesortstate *tuplesort;
+	TupleDesc	oldTupDesc = RelationGetDescr(OldHeap);
+	TupleDesc	newTupDesc = RelationGetDescr(NewHeap);
+	TupleTableSlot *slot;
+	int			natts;
+	Datum	   *values;
+	bool	   *isnull;
+	BufferHeapTupleTableSlot *hslot;
+	BlockNumber prev_cblock = InvalidBlockNumber;
+
+	/* Remember if it's a system catalog */
+	is_system_catalog = IsSystemRelation(OldHeap);
+
+	/*
+	 * Valid smgr_targblock implies something already wrote to the relation.
+	 * This may be harmless, but this function hasn't planned for it.
+	 */
+	Assert(RelationGetTargetBlock(NewHeap) == InvalidBlockNumber);
+
+	/* Preallocate values/isnull arrays */
+	natts = newTupDesc->natts;
+	values = (Datum *) palloc(natts * sizeof(Datum));
+	isnull = (bool *) palloc(natts * sizeof(bool));
+
+	/* Initialize the rewrite operation */
+	rwstate = begin_heap_rewrite(OldHeap, NewHeap, OldestXmin, *xid_cutoff,
+								 *multi_cutoff);
+
+
+	/* Set up sorting if wanted */
+	if (use_sort)
+		tuplesort = tuplesort_begin_cluster(oldTupDesc, OldIndex,
+											maintenance_work_mem,
+											NULL, false);
+	else
+		tuplesort = NULL;
+
+	/*
+	 * Prepare to scan the OldHeap.  To ensure we see recently-dead tuples
+	 * that still need to be copied, we scan with SnapshotAny and use
+	 * HeapTupleSatisfiesVacuum for the visibility test.
+	 */
+	if (OldIndex != NULL && !use_sort)
+	{
+		const int	ci_index[] = {
+			PROGRESS_CLUSTER_PHASE,
+			PROGRESS_CLUSTER_INDEX_RELID
+		};
+		int64		ci_val[2];
+
+		/* Set phase and OIDOldIndex to columns */
+		ci_val[0] = PROGRESS_CLUSTER_PHASE_INDEX_SCAN_HEAP;
+		ci_val[1] = RelationGetRelid(OldIndex);
+		pgstat_progress_update_multi_param(2, ci_index, ci_val);
+
+		tableScan = NULL;
+		heapScan = NULL;
+		indexScan = index_beginscan(OldHeap, OldIndex, SnapshotAny, 0, 0);
+		index_rescan(indexScan, NULL, 0, NULL, 0);
+	}
+	else
+	{
+		/* In scan-and-sort mode and also VACUUM FULL, set phase */
+		pgstat_progress_update_param(PROGRESS_CLUSTER_PHASE,
+									 PROGRESS_CLUSTER_PHASE_SEQ_SCAN_HEAP);
+
+		tableScan = table_beginscan(OldHeap, SnapshotAny, 0, (ScanKey) NULL);
+		heapScan = (HeapScanDesc) tableScan;
+		indexScan = NULL;
+
+		/* Set total heap blocks */
+		pgstat_progress_update_param(PROGRESS_CLUSTER_TOTAL_HEAP_BLKS,
+									 heapScan->rs_nblocks);
+	}
+
+	slot = table_slot_create(OldHeap, NULL);
+	hslot = (BufferHeapTupleTableSlot *) slot;
+
+	/*
+	 * Scan through the OldHeap, either in OldIndex order or sequentially;
+	 * copy each tuple into the NewHeap, or transiently to the tuplesort
+	 * module.  Note that we don't bother sorting dead tuples (they won't get
+	 * to the new table anyway).
+	 */
+	for (;;)
+	{
+		HeapTuple	tuple;
+		Buffer		buf;
+		bool		isdead;
+
+		CHECK_FOR_INTERRUPTS();
+
+		if (indexScan != NULL)
+		{
+			if (!index_getnext_slot(indexScan, ForwardScanDirection, slot))
+				break;
+
+			/* Since we used no scan keys, should never need to recheck */
+			if (indexScan->xs_recheck)
+				elog(ERROR, "CLUSTER does not support lossy index conditions");
+		}
+		else
+		{
+			if (!table_scan_getnextslot(tableScan, ForwardScanDirection, slot))
+			{
+				/*
+				 * If the last pages of the scan were empty, we would go to
+				 * the next phase while heap_blks_scanned != heap_blks_total.
+				 * Instead, to ensure that heap_blks_scanned is equivalent to
+				 * total_heap_blks after the table scan phase, this parameter
+				 * is manually updated to the correct value when the table
+				 * scan finishes.
+				 */
+				pgstat_progress_update_param(PROGRESS_CLUSTER_HEAP_BLKS_SCANNED,
+											 heapScan->rs_nblocks);
+				break;
+			}
+
+			/*
+			 * In scan-and-sort mode and also VACUUM FULL, set heap blocks
+			 * scanned
+			 *
+			 * Note that heapScan may start at an offset and wrap around, i.e.
+			 * rs_startblock may be >0, and rs_cblock may end with a number
+			 * below rs_startblock. To prevent showing this wraparound to the
+			 * user, we offset rs_cblock by rs_startblock (modulo rs_nblocks).
+			 */
+			if (prev_cblock != heapScan->rs_cblock)
+			{
+				pgstat_progress_update_param(PROGRESS_CLUSTER_HEAP_BLKS_SCANNED,
+											 (heapScan->rs_cblock +
+											  heapScan->rs_nblocks -
+											  heapScan->rs_startblock
+											  ) % heapScan->rs_nblocks + 1);
+				prev_cblock = heapScan->rs_cblock;
+			}
+		}
+
+		tuple = ExecFetchSlotHeapTuple(slot, false, NULL);
+		buf = hslot->buffer;
+
+		LockBuffer(buf, BUFFER_LOCK_SHARE);
+
+		switch (HeapTupleSatisfiesVacuum(tuple, OldestXmin, buf))
+		{
+			case HEAPTUPLE_DEAD:
+				/* Definitely dead */
+				isdead = true;
+				break;
+			case HEAPTUPLE_RECENTLY_DEAD:
+				*tups_recently_dead += 1;
+				/* fall through */
+			case HEAPTUPLE_LIVE:
+				/* Live or recently dead, must copy it */
+				isdead = false;
+				break;
+			case HEAPTUPLE_INSERT_IN_PROGRESS:
+
+				/*
+				 * Since we hold exclusive lock on the relation, normally the
+				 * only way to see this is if it was inserted earlier in our
+				 * own transaction.  However, it can happen in system
+				 * catalogs, since we tend to release write lock before commit
+				 * there.  Give a warning if neither case applies; but in any
+				 * case we had better copy it.
+				 */
+				if (!is_system_catalog &&
+					!TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmin(tuple->t_data)))
+					elog(WARNING, "concurrent insert in progress within table \"%s\"",
+						 RelationGetRelationName(OldHeap));
+				/* treat as live */
+				isdead = false;
+				break;
+			case HEAPTUPLE_DELETE_IN_PROGRESS:
+
+				/*
+				 * Similar situation to INSERT_IN_PROGRESS case.
+				 */
+				if (!is_system_catalog &&
+					!TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetUpdateXid(tuple->t_data)))
+					elog(WARNING, "concurrent delete in progress within table \"%s\"",
+						 RelationGetRelationName(OldHeap));
+				/* treat as recently dead */
+				*tups_recently_dead += 1;
+				isdead = false;
+				break;
+			default:
+				elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
+				isdead = false; /* keep compiler quiet */
+				break;
+		}
+
+		LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+
+		if (isdead)
+		{
+			*tups_vacuumed += 1;
+			/* heap rewrite module still needs to see it... */
+			if (rewrite_heap_dead_tuple(rwstate, tuple))
+			{
+				/* A previous recently-dead tuple is now known dead */
+				*tups_vacuumed += 1;
+				*tups_recently_dead -= 1;
+			}
+			continue;
+		}
+
+		*num_tuples += 1;
+		if (tuplesort != NULL)
+		{
+			tuplesort_putheaptuple(tuplesort, tuple);
+
+			/*
+			 * In scan-and-sort mode, report increase in number of tuples
+			 * scanned
+			 */
+			pgstat_progress_update_param(PROGRESS_CLUSTER_HEAP_TUPLES_SCANNED,
+										 *num_tuples);
+		}
+		else
+		{
+			const int	ct_index[] = {
+				PROGRESS_CLUSTER_HEAP_TUPLES_SCANNED,
+				PROGRESS_CLUSTER_HEAP_TUPLES_WRITTEN
+			};
+			int64		ct_val[2];
+
+			reform_and_rewrite_tuple(tuple, OldHeap, NewHeap,
+									 values, isnull, rwstate);
+
+			/*
+			 * In indexscan mode and also VACUUM FULL, report increase in
+			 * number of tuples scanned and written
+			 */
+			ct_val[0] = *num_tuples;
+			ct_val[1] = *num_tuples;
+			pgstat_progress_update_multi_param(2, ct_index, ct_val);
+		}
+	}
+
+	if (indexScan != NULL)
+		index_endscan(indexScan);
+	if (tableScan != NULL)
+		table_endscan(tableScan);
+	if (slot)
+		ExecDropSingleTupleTableSlot(slot);
+
+	/*
+	 * In scan-and-sort mode, complete the sort, then read out all live tuples
+	 * from the tuplestore and write them to the new relation.
+	 */
+	if (tuplesort != NULL)
+	{
+		double		n_tuples = 0;
+
+		/* Report that we are now sorting tuples */
+		pgstat_progress_update_param(PROGRESS_CLUSTER_PHASE,
+									 PROGRESS_CLUSTER_PHASE_SORT_TUPLES);
+
+		tuplesort_performsort(tuplesort);
+
+		/* Report that we are now writing new heap */
+		pgstat_progress_update_param(PROGRESS_CLUSTER_PHASE,
+									 PROGRESS_CLUSTER_PHASE_WRITE_NEW_HEAP);
+
+		for (;;)
+		{
+			HeapTuple	tuple;
+
+			CHECK_FOR_INTERRUPTS();
+
+			tuple = tuplesort_getheaptuple(tuplesort, true);
+			if (tuple == NULL)
+				break;
+
+			n_tuples += 1;
+			reform_and_rewrite_tuple(tuple,
+									 OldHeap, NewHeap,
+									 values, isnull,
+									 rwstate);
+			/* Report n_tuples */
+			pgstat_progress_update_param(PROGRESS_CLUSTER_HEAP_TUPLES_WRITTEN,
+										 n_tuples);
+		}
+
+		tuplesort_end(tuplesort);
+	}
+
+	/* Write out any remaining tuples, and fsync if needed */
+	end_heap_rewrite(rwstate);
+
+	/* Clean up */
+	pfree(values);
+	pfree(isnull);
+}
+
+static bool
+heapam_scan_analyze_next_block(TableScanDesc scan, BlockNumber blockno,
+							   BufferAccessStrategy bstrategy)
+{
+	HeapScanDesc hscan = (HeapScanDesc) scan;
+
+	/*
+	 * We must maintain a pin on the target page's buffer to ensure that
+	 * concurrent activity - e.g. HOT pruning - doesn't delete tuples out from
+	 * under us.  Hence, pin the page until we are done looking at it.  We
+	 * also choose to hold sharelock on the buffer throughout --- we could
+	 * release and re-acquire sharelock for each tuple, but since we aren't
+	 * doing much work per tuple, the extra lock traffic is probably better
+	 * avoided.
+	 */
+	hscan->rs_cblock = blockno;
+	hscan->rs_cindex = FirstOffsetNumber;
+	hscan->rs_cbuf = ReadBufferExtended(scan->rs_rd, MAIN_FORKNUM,
+										blockno, RBM_NORMAL, bstrategy);
+	LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_SHARE);
+
+	/* in heap all blocks can contain tuples, so always return true */
+	return true;
+}
+
+static bool
+heapam_scan_analyze_next_tuple(TableScanDesc scan, TransactionId OldestXmin,
+							   double *liverows, double *deadrows,
+							   TupleTableSlot *slot)
+{
+	HeapScanDesc hscan = (HeapScanDesc) scan;
+	Page		targpage;
+	OffsetNumber maxoffset;
+	BufferHeapTupleTableSlot *hslot;
+
+	Assert(TTS_IS_BUFFERTUPLE(slot));
+
+	hslot = (BufferHeapTupleTableSlot *) slot;
+	targpage = BufferGetPage(hscan->rs_cbuf);
+	maxoffset = PageGetMaxOffsetNumber(targpage);
+
+	/* Inner loop over all tuples on the selected page */
+	for (; hscan->rs_cindex <= maxoffset; hscan->rs_cindex++)
+	{
+		ItemId		itemid;
+		HeapTuple	targtuple = &hslot->base.tupdata;
+		bool		sample_it = false;
+
+		itemid = PageGetItemId(targpage, hscan->rs_cindex);
+
+		/*
+		 * We ignore unused and redirect line pointers.  DEAD line pointers
+		 * should be counted as dead, because we need vacuum to run to get rid
+		 * of them.  Note that this rule agrees with the way that
+		 * heap_page_prune() counts things.
+		 */
+		if (!ItemIdIsNormal(itemid))
+		{
+			if (ItemIdIsDead(itemid))
+				*deadrows += 1;
+			continue;
+		}
+
+		ItemPointerSet(&targtuple->t_self, hscan->rs_cblock, hscan->rs_cindex);
+
+		targtuple->t_tableOid = RelationGetRelid(scan->rs_rd);
+		targtuple->t_data = (HeapTupleHeader) PageGetItem(targpage, itemid);
+		targtuple->t_len = ItemIdGetLength(itemid);
+
+		switch (HeapTupleSatisfiesVacuum(targtuple, OldestXmin,
+										 hscan->rs_cbuf))
+		{
+			case HEAPTUPLE_LIVE:
+				sample_it = true;
+				*liverows += 1;
+				break;
+
+			case HEAPTUPLE_DEAD:
+			case HEAPTUPLE_RECENTLY_DEAD:
+				/* Count dead and recently-dead rows */
+				*deadrows += 1;
+				break;
+
+			case HEAPTUPLE_INSERT_IN_PROGRESS:
+
+				/*
+				 * Insert-in-progress rows are not counted.  We assume that
+				 * when the inserting transaction commits or aborts, it will
+				 * send a stats message to increment the proper count.  This
+				 * works right only if that transaction ends after we finish
+				 * analyzing the table; if things happen in the other order,
+				 * its stats update will be overwritten by ours.  However, the
+				 * error will be large only if the other transaction runs long
+				 * enough to insert many tuples, so assuming it will finish
+				 * after us is the safer option.
+				 *
+				 * A special case is that the inserting transaction might be
+				 * our own.  In this case we should count and sample the row,
+				 * to accommodate users who load a table and analyze it in one
+				 * transaction.  (pgstat_report_analyze has to adjust the
+				 * numbers we send to the stats collector to make this come
+				 * out right.)
+				 */
+				if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmin(targtuple->t_data)))
+				{
+					sample_it = true;
+					*liverows += 1;
+				}
+				break;
+
+			case HEAPTUPLE_DELETE_IN_PROGRESS:
+
+				/*
+				 * We count and sample delete-in-progress rows the same as
+				 * live ones, so that the stats counters come out right if the
+				 * deleting transaction commits after us, per the same
+				 * reasoning given above.
+				 *
+				 * If the delete was done by our own transaction, however, we
+				 * must count the row as dead to make pgstat_report_analyze's
+				 * stats adjustments come out right.  (Note: this works out
+				 * properly when the row was both inserted and deleted in our
+				 * xact.)
+				 *
+				 * The net effect of these choices is that we act as though an
+				 * IN_PROGRESS transaction hasn't happened yet, except if it
+				 * is our own transaction, which we assume has happened.
+				 *
+				 * This approach ensures that we behave sanely if we see both
+				 * the pre-image and post-image rows for a row being updated
+				 * by a concurrent transaction: we will sample the pre-image
+				 * but not the post-image.  We also get sane results if the
+				 * concurrent transaction never commits.
+				 */
+				if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetUpdateXid(targtuple->t_data)))
+					*deadrows += 1;
+				else
+				{
+					sample_it = true;
+					*liverows += 1;
+				}
+				break;
+
+			default:
+				elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
+				break;
+		}
+
+		if (sample_it)
+		{
+			ExecStoreBufferHeapTuple(targtuple, slot, hscan->rs_cbuf);
+			hscan->rs_cindex++;
+
+			/* note that we leave the buffer locked here! */
+			return true;
+		}
+	}
+
+	/* Now release the lock and pin on the page */
+	UnlockReleaseBuffer(hscan->rs_cbuf);
+	hscan->rs_cbuf = InvalidBuffer;
+
+	/* also prevent old slot contents from having pin on page */
+	ExecClearTuple(slot);
+
+	return false;
+}
+
+static double
+heapam_index_build_range_scan(Relation heapRelation,
+							  Relation indexRelation,
+							  IndexInfo *indexInfo,
+							  bool allow_sync,
+							  bool anyvisible,
+							  bool progress,
+							  BlockNumber start_blockno,
+							  BlockNumber numblocks,
+							  IndexBuildCallback callback,
+							  void *callback_state,
+							  TableScanDesc scan)
+{
+	HeapScanDesc hscan;
+	bool		is_system_catalog;
+	bool		checking_uniqueness;
+	HeapTuple	heapTuple;
+	Datum		values[INDEX_MAX_KEYS];
+	bool		isnull[INDEX_MAX_KEYS];
+	double		reltuples;
+	ExprState  *predicate;
+	TupleTableSlot *slot;
+	EState	   *estate;
+	ExprContext *econtext;
+	Snapshot	snapshot;
+	bool		need_unregister_snapshot = false;
+	TransactionId OldestXmin;
+	BlockNumber previous_blkno = InvalidBlockNumber;
+	BlockNumber root_blkno = InvalidBlockNumber;
+	OffsetNumber root_offsets[MaxHeapTuplesPerPage];
+
+	/*
+	 * sanity checks
+	 */
+	Assert(OidIsValid(indexRelation->rd_rel->relam));
+
+	/* Remember if it's a system catalog */
+	is_system_catalog = IsSystemRelation(heapRelation);
+
+	/* See whether we're verifying uniqueness/exclusion properties */
+	checking_uniqueness = (indexInfo->ii_Unique ||
+						   indexInfo->ii_ExclusionOps != NULL);
+
+	/*
+	 * "Any visible" mode is not compatible with uniqueness checks; make sure
+	 * only one of those is requested.
+	 */
+	Assert(!(anyvisible && checking_uniqueness));
+
+	/*
+	 * Need an EState for evaluation of index expressions and partial-index
+	 * predicates.  Also a slot to hold the current tuple.
+	 */
+	estate = CreateExecutorState();
+	econtext = GetPerTupleExprContext(estate);
+	slot = table_slot_create(heapRelation, NULL);
+
+	/* Arrange for econtext's scan tuple to be the tuple under test */
+	econtext->ecxt_scantuple = slot;
+
+	/* Set up execution state for predicate, if any. */
+	predicate = ExecPrepareQual(indexInfo->ii_Predicate, estate);
+
+	/*
+	 * Prepare for scan of the base relation.  In a normal index build, we use
+	 * SnapshotAny because we must retrieve all tuples and do our own time
+	 * qual checks (because we have to index RECENTLY_DEAD tuples). In a
+	 * concurrent build, or during bootstrap, we take a regular MVCC snapshot
+	 * and index whatever's live according to that.
+	 */
+	OldestXmin = InvalidTransactionId;
+
+	/* okay to ignore lazy VACUUMs here */
+	if (!IsBootstrapProcessingMode() && !indexInfo->ii_Concurrent)
+		OldestXmin = GetOldestNonRemovableTransactionId(heapRelation);
+
+	if (!scan)
+	{
+		/*
+		 * Serial index build.
+		 *
+		 * Must begin our own heap scan in this case.  We may also need to
+		 * register a snapshot whose lifetime is under our direct control.
+		 */
+		if (!TransactionIdIsValid(OldestXmin))
+		{
+			snapshot = RegisterSnapshot(GetTransactionSnapshot());
+			need_unregister_snapshot = true;
+		}
+		else
+			snapshot = SnapshotAny;
+
+		scan = table_beginscan_strat(heapRelation,	/* relation */
+									 snapshot,	/* snapshot */
+									 0, /* number of keys */
+									 NULL,	/* scan key */
+									 true,	/* buffer access strategy OK */
+									 allow_sync);	/* syncscan OK? */
+	}
+	else
+	{
+		/*
+		 * Parallel index build.
+		 *
+		 * Parallel case never registers/unregisters own snapshot.  Snapshot
+		 * is taken from parallel heap scan, and is SnapshotAny or an MVCC
+		 * snapshot, based on same criteria as serial case.
+		 */
+		Assert(!IsBootstrapProcessingMode());
+		Assert(allow_sync);
+		snapshot = scan->rs_snapshot;
+	}
+
+	hscan = (HeapScanDesc) scan;
+
+	/*
+	 * Must have called GetOldestNonRemovableTransactionId() if using
+	 * SnapshotAny.  Shouldn't have for an MVCC snapshot. (It's especially
+	 * worth checking this for parallel builds, since ambuild routines that
+	 * support parallel builds must work these details out for themselves.)
+	 */
+	Assert(snapshot == SnapshotAny || IsMVCCSnapshot(snapshot));
+	Assert(snapshot == SnapshotAny ? TransactionIdIsValid(OldestXmin) :
+		   !TransactionIdIsValid(OldestXmin));
+	Assert(snapshot == SnapshotAny || !anyvisible);
+
+	/* Publish number of blocks to scan */
+	if (progress)
+	{
+		BlockNumber nblocks;
+
+		if (hscan->rs_base.rs_parallel != NULL)
+		{
+			ParallelBlockTableScanDesc pbscan;
+
+			pbscan = (ParallelBlockTableScanDesc) hscan->rs_base.rs_parallel;
+			nblocks = pbscan->phs_nblocks;
+		}
+		else
+			nblocks = hscan->rs_nblocks;
+
+		pgstat_progress_update_param(PROGRESS_SCAN_BLOCKS_TOTAL,
+									 nblocks);
+	}
+
+	/* set our scan endpoints */
+	if (!allow_sync)
+		heap_setscanlimits(scan, start_blockno, numblocks);
+	else
+	{
+		/* syncscan can only be requested on whole relation */
+		Assert(start_blockno == 0);
+		Assert(numblocks == InvalidBlockNumber);
+	}
+
+	reltuples = 0;
+
+	/*
+	 * Scan all tuples in the base relation.
+	 */
+	while ((heapTuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
+	{
+		bool		tupleIsAlive;
+
+		CHECK_FOR_INTERRUPTS();
+
+		/* Report scan progress, if asked to. */
+		if (progress)
+		{
+			BlockNumber blocks_done = heapam_scan_get_blocks_done(hscan);
+
+			if (blocks_done != previous_blkno)
+			{
+				pgstat_progress_update_param(PROGRESS_SCAN_BLOCKS_DONE,
+											 blocks_done);
+				previous_blkno = blocks_done;
+			}
+		}
+
+		/*
+		 * When dealing with a HOT-chain of updated tuples, we want to index
+		 * the values of the live tuple (if any), but index it under the TID
+		 * of the chain's root tuple.  This approach is necessary to preserve
+		 * the HOT-chain structure in the heap. So we need to be able to find
+		 * the root item offset for every tuple that's in a HOT-chain.  When
+		 * first reaching a new page of the relation, call
+		 * heap_get_root_tuples() to build a map of root item offsets on the
+		 * page.
+		 *
+		 * It might look unsafe to use this information across buffer
+		 * lock/unlock.  However, we hold ShareLock on the table so no
+		 * ordinary insert/update/delete should occur; and we hold pin on the
+		 * buffer continuously while visiting the page, so no pruning
+		 * operation can occur either.
+		 *
+		 * In cases with only ShareUpdateExclusiveLock on the table, it's
+		 * possible for some HOT tuples to appear that we didn't know about
+		 * when we first read the page.  To handle that case, we re-obtain the
+		 * list of root offsets when a HOT tuple points to a root item that we
+		 * don't know about.
+		 *
+		 * Also, although our opinions about tuple liveness could change while
+		 * we scan the page (due to concurrent transaction commits/aborts),
+		 * the chain root locations won't, so this info doesn't need to be
+		 * rebuilt after waiting for another transaction.
+		 *
+		 * Note the implied assumption that there is no more than one live
+		 * tuple per HOT-chain --- else we could create more than one index
+		 * entry pointing to the same root tuple.
+		 */
+		if (hscan->rs_cblock != root_blkno)
+		{
+			Page		page = BufferGetPage(hscan->rs_cbuf);
+
+			LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_SHARE);
+			heap_get_root_tuples(page, root_offsets);
+			LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+
+			root_blkno = hscan->rs_cblock;
+		}
+
+		if (snapshot == SnapshotAny)
+		{
+			/* do our own time qual check */
+			bool		indexIt;
+			TransactionId xwait;
+
+	recheck:
+
+			/*
+			 * We could possibly get away with not locking the buffer here,
+			 * since caller should hold ShareLock on the relation, but let's
+			 * be conservative about it.  (This remark is still correct even
+			 * with HOT-pruning: our pin on the buffer prevents pruning.)
+			 */
+			LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_SHARE);
+
+			/*
+			 * The criteria for counting a tuple as live in this block need to
+			 * match what analyze.c's heapam_scan_analyze_next_tuple() does,
+			 * otherwise CREATE INDEX and ANALYZE may produce wildly different
+			 * reltuples values, e.g. when there are many recently-dead
+			 * tuples.
+			 */
+			switch (HeapTupleSatisfiesVacuum(heapTuple, OldestXmin,
+											 hscan->rs_cbuf))
+			{
+				case HEAPTUPLE_DEAD:
+					/* Definitely dead, we can ignore it */
+					indexIt = false;
+					tupleIsAlive = false;
+					break;
+				case HEAPTUPLE_LIVE:
+					/* Normal case, index and unique-check it */
+					indexIt = true;
+					tupleIsAlive = true;
+					/* Count it as live, too */
+					reltuples += 1;
+					break;
+				case HEAPTUPLE_RECENTLY_DEAD:
+
+					/*
+					 * If tuple is recently deleted then we must index it
+					 * anyway to preserve MVCC semantics.  (Pre-existing
+					 * transactions could try to use the index after we finish
+					 * building it, and may need to see such tuples.)
+					 *
+					 * However, if it was HOT-updated then we must only index
+					 * the live tuple at the end of the HOT-chain.  Since this
+					 * breaks semantics for pre-existing snapshots, mark the
+					 * index as unusable for them.
+					 *
+					 * We don't count recently-dead tuples in reltuples, even
+					 * if we index them; see heapam_scan_analyze_next_tuple().
+					 */
+					if (HeapTupleIsHotUpdated(heapTuple))
+					{
+						indexIt = false;
+						/* mark the index as unsafe for old snapshots */
+						indexInfo->ii_BrokenHotChain = true;
+					}
+					else
+						indexIt = true;
+					/* In any case, exclude the tuple from unique-checking */
+					tupleIsAlive = false;
+					break;
+				case HEAPTUPLE_INSERT_IN_PROGRESS:
+
+					/*
+					 * In "anyvisible" mode, this tuple is visible and we
+					 * don't need any further checks.
+					 */
+					if (anyvisible)
+					{
+						indexIt = true;
+						tupleIsAlive = true;
+						reltuples += 1;
+						break;
+					}
+
+					/*
+					 * Since caller should hold ShareLock or better, normally
+					 * the only way to see this is if it was inserted earlier
+					 * in our own transaction.  However, it can happen in
+					 * system catalogs, since we tend to release write lock
+					 * before commit there.  Give a warning if neither case
+					 * applies.
+					 */
+					xwait = HeapTupleHeaderGetXmin(heapTuple->t_data);
+					if (!TransactionIdIsCurrentTransactionId(xwait))
+					{
+						if (!is_system_catalog)
+							elog(WARNING, "concurrent insert in progress within table \"%s\"",
+								 RelationGetRelationName(heapRelation));
+
+						/*
+						 * If we are performing uniqueness checks, indexing
+						 * such a tuple could lead to a bogus uniqueness
+						 * failure.  In that case we wait for the inserting
+						 * transaction to finish and check again.
+						 */
+						if (checking_uniqueness)
+						{
+							/*
+							 * Must drop the lock on the buffer before we wait
+							 */
+							LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+							XactLockTableWait(xwait, heapRelation,
+											  &heapTuple->t_self,
+											  XLTW_InsertIndexUnique);
+							CHECK_FOR_INTERRUPTS();
+							goto recheck;
+						}
+					}
+					else
+					{
+						/*
+						 * For consistency with
+						 * heapam_scan_analyze_next_tuple(), count
+						 * HEAPTUPLE_INSERT_IN_PROGRESS tuples as live only
+						 * when inserted by our own transaction.
+						 */
+						reltuples += 1;
+					}
+
+					/*
+					 * We must index such tuples, since if the index build
+					 * commits then they're good.
+					 */
+					indexIt = true;
+					tupleIsAlive = true;
+					break;
+				case HEAPTUPLE_DELETE_IN_PROGRESS:
+
+					/*
+					 * As with INSERT_IN_PROGRESS case, this is unexpected
+					 * unless it's our own deletion or a system catalog; but
+					 * in anyvisible mode, this tuple is visible.
+					 */
+					if (anyvisible)
+					{
+						indexIt = true;
+						tupleIsAlive = false;
+						reltuples += 1;
+						break;
+					}
+
+					xwait = HeapTupleHeaderGetUpdateXid(heapTuple->t_data);
+					if (!TransactionIdIsCurrentTransactionId(xwait))
+					{
+						if (!is_system_catalog)
+							elog(WARNING, "concurrent delete in progress within table \"%s\"",
+								 RelationGetRelationName(heapRelation));
+
+						/*
+						 * If we are performing uniqueness checks, assuming
+						 * the tuple is dead could lead to missing a
+						 * uniqueness violation.  In that case we wait for the
+						 * deleting transaction to finish and check again.
+						 *
+						 * Also, if it's a HOT-updated tuple, we should not
+						 * index it but rather the live tuple at the end of
+						 * the HOT-chain.  However, the deleting transaction
+						 * could abort, possibly leaving this tuple as live
+						 * after all, in which case it has to be indexed. The
+						 * only way to know what to do is to wait for the
+						 * deleting transaction to finish and check again.
+						 */
+						if (checking_uniqueness ||
+							HeapTupleIsHotUpdated(heapTuple))
+						{
+							/*
+							 * Must drop the lock on the buffer before we wait
+							 */
+							LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+							XactLockTableWait(xwait, heapRelation,
+											  &heapTuple->t_self,
+											  XLTW_InsertIndexUnique);
+							CHECK_FOR_INTERRUPTS();
+							goto recheck;
+						}
+
+						/*
+						 * Otherwise index it but don't check for uniqueness,
+						 * the same as a RECENTLY_DEAD tuple.
+						 */
+						indexIt = true;
+
+						/*
+						 * Count HEAPTUPLE_DELETE_IN_PROGRESS tuples as live,
+						 * if they were not deleted by the current
+						 * transaction.  That's what
+						 * heapam_scan_analyze_next_tuple() does, and we want
+						 * the behavior to be consistent.
+						 */
+						reltuples += 1;
+					}
+					else if (HeapTupleIsHotUpdated(heapTuple))
+					{
+						/*
+						 * It's a HOT-updated tuple deleted by our own xact.
+						 * We can assume the deletion will commit (else the
+						 * index contents don't matter), so treat the same as
+						 * RECENTLY_DEAD HOT-updated tuples.
+						 */
+						indexIt = false;
+						/* mark the index as unsafe for old snapshots */
+						indexInfo->ii_BrokenHotChain = true;
+					}
+					else
+					{
+						/*
+						 * It's a regular tuple deleted by our own xact. Index
+						 * it, but don't check for uniqueness nor count in
+						 * reltuples, the same as a RECENTLY_DEAD tuple.
+						 */
+						indexIt = true;
+					}
+					/* In any case, exclude the tuple from unique-checking */
+					tupleIsAlive = false;
+					break;
+				default:
+					elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
+					indexIt = tupleIsAlive = false; /* keep compiler quiet */
+					break;
+			}
+
+			LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+
+			if (!indexIt)
+				continue;
+		}
+		else
+		{
+			/* heap_getnext did the time qual check */
+			tupleIsAlive = true;
+			reltuples += 1;
+		}
+
+		MemoryContextReset(econtext->ecxt_per_tuple_memory);
+
+		/* Set up for predicate or expression evaluation */
+		ExecStoreBufferHeapTuple(heapTuple, slot, hscan->rs_cbuf);
+
+		/*
+		 * In a partial index, discard tuples that don't satisfy the
+		 * predicate.
+		 */
+		if (predicate != NULL)
+		{
+			if (!ExecQual(predicate, econtext))
+				continue;
+		}
+
+		/*
+		 * For the current heap tuple, extract all the attributes we use in
+		 * this index, and note which are null.  This also performs evaluation
+		 * of any expressions needed.
+		 */
+		FormIndexDatum(indexInfo,
+					   slot,
+					   estate,
+					   values,
+					   isnull);
+
+		/*
+		 * You'd think we should go ahead and build the index tuple here, but
+		 * some index AMs want to do further processing on the data first.  So
+		 * pass the values[] and isnull[] arrays, instead.
+		 */
+
+		if (HeapTupleIsHeapOnly(heapTuple))
+		{
+			/*
+			 * For a heap-only tuple, pretend its TID is that of the root. See
+			 * src/backend/access/heap/README.HOT for discussion.
+			 */
+			ItemPointerData tid;
+			OffsetNumber offnum;
+
+			offnum = ItemPointerGetOffsetNumber(&heapTuple->t_self);
+
+			/*
+			 * If a HOT tuple points to a root that we don't know about,
+			 * obtain root items afresh.  If that still fails, report it as
+			 * corruption.
+			 */
+			if (root_offsets[offnum - 1] == InvalidOffsetNumber)
+			{
+				Page		page = BufferGetPage(hscan->rs_cbuf);
+
+				LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_SHARE);
+				heap_get_root_tuples(page, root_offsets);
+				LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+			}
+
+			if (!OffsetNumberIsValid(root_offsets[offnum - 1]))
+				ereport(ERROR,
+						(errcode(ERRCODE_DATA_CORRUPTED),
+						 errmsg_internal("failed to find parent tuple for heap-only tuple at (%u,%u) in table \"%s\"",
+										 ItemPointerGetBlockNumber(&heapTuple->t_self),
+										 offnum,
+										 RelationGetRelationName(heapRelation))));
+
+			ItemPointerSet(&tid, ItemPointerGetBlockNumber(&heapTuple->t_self),
+						   root_offsets[offnum - 1]);
+
+			/* Call the AM's callback routine to process the tuple */
+			callback(indexRelation, &tid, values, isnull, tupleIsAlive,
+					 callback_state);
+		}
+		else
+		{
+			/* Call the AM's callback routine to process the tuple */
+			callback(indexRelation, &heapTuple->t_self, values, isnull,
+					 tupleIsAlive, callback_state);
+		}
+	}
+
+	/* Report scan progress one last time. */
+	if (progress)
+	{
+		BlockNumber blks_done;
+
+		if (hscan->rs_base.rs_parallel != NULL)
+		{
+			ParallelBlockTableScanDesc pbscan;
+
+			pbscan = (ParallelBlockTableScanDesc) hscan->rs_base.rs_parallel;
+			blks_done = pbscan->phs_nblocks;
+		}
+		else
+			blks_done = hscan->rs_nblocks;
+
+		pgstat_progress_update_param(PROGRESS_SCAN_BLOCKS_DONE,
+									 blks_done);
+	}
+
+	table_endscan(scan);
+
+	/* we can now forget our snapshot, if set and registered by us */
+	if (need_unregister_snapshot)
+		UnregisterSnapshot(snapshot);
+
+	ExecDropSingleTupleTableSlot(slot);
+
+	FreeExecutorState(estate);
+
+	/* These may have been pointing to the now-gone estate */
+	indexInfo->ii_ExpressionsState = NIL;
+	indexInfo->ii_PredicateState = NULL;
+
+	return reltuples;
+}
+
+static void
+heapam_index_validate_scan(Relation heapRelation,
+						   Relation indexRelation,
+						   IndexInfo *indexInfo,
+						   Snapshot snapshot,
+						   ValidateIndexState *state)
+{
+	TableScanDesc scan;
+	HeapScanDesc hscan;
+	HeapTuple	heapTuple;
+	Datum		values[INDEX_MAX_KEYS];
+	bool		isnull[INDEX_MAX_KEYS];
+	ExprState  *predicate;
+	TupleTableSlot *slot;
+	EState	   *estate;
+	ExprContext *econtext;
+	BlockNumber root_blkno = InvalidBlockNumber;
+	OffsetNumber root_offsets[MaxHeapTuplesPerPage];
+	bool		in_index[MaxHeapTuplesPerPage];
+	BlockNumber previous_blkno = InvalidBlockNumber;
+
+	/* state variables for the merge */
+	ItemPointer indexcursor = NULL;
+	ItemPointerData decoded;
+	bool		tuplesort_empty = false;
+
+	/*
+	 * sanity checks
+	 */
+	Assert(OidIsValid(indexRelation->rd_rel->relam));
+
+	/*
+	 * Need an EState for evaluation of index expressions and partial-index
+	 * predicates.  Also a slot to hold the current tuple.
+	 */
+	estate = CreateExecutorState();
+	econtext = GetPerTupleExprContext(estate);
+	slot = MakeSingleTupleTableSlot(RelationGetDescr(heapRelation),
+									&TTSOpsHeapTuple);
+
+	/* Arrange for econtext's scan tuple to be the tuple under test */
+	econtext->ecxt_scantuple = slot;
+
+	/* Set up execution state for predicate, if any. */
+	predicate = ExecPrepareQual(indexInfo->ii_Predicate, estate);
+
+	/*
+	 * Prepare for scan of the base relation.  We need just those tuples
+	 * satisfying the passed-in reference snapshot.  We must disable syncscan
+	 * here, because it's critical that we read from block zero forward to
+	 * match the sorted TIDs.
+	 */
+	scan = table_beginscan_strat(heapRelation,	/* relation */
+								 snapshot,	/* snapshot */
+								 0, /* number of keys */
+								 NULL,	/* scan key */
+								 true,	/* buffer access strategy OK */
+								 false);	/* syncscan not OK */
+	hscan = (HeapScanDesc) scan;
+
+	pgstat_progress_update_param(PROGRESS_SCAN_BLOCKS_TOTAL,
+								 hscan->rs_nblocks);
+
+	/*
+	 * Scan all tuples matching the snapshot.
+	 */
+	while ((heapTuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
+	{
+		ItemPointer heapcursor = &heapTuple->t_self;
+		ItemPointerData rootTuple;
+		OffsetNumber root_offnum;
+
+		CHECK_FOR_INTERRUPTS();
+
+		state->htups += 1;
+
+		if ((previous_blkno == InvalidBlockNumber) ||
+			(hscan->rs_cblock != previous_blkno))
+		{
+			pgstat_progress_update_param(PROGRESS_SCAN_BLOCKS_DONE,
+										 hscan->rs_cblock);
+			previous_blkno = hscan->rs_cblock;
+		}
+
+		/*
+		 * As commented in table_index_build_scan, we should index heap-only
+		 * tuples under the TIDs of their root tuples; so when we advance onto
+		 * a new heap page, build a map of root item offsets on the page.
+		 *
+		 * This complicates merging against the tuplesort output: we will
+		 * visit the live tuples in order by their offsets, but the root
+		 * offsets that we need to compare against the index contents might be
+		 * ordered differently.  So we might have to "look back" within the
+		 * tuplesort output, but only within the current page.  We handle that
+		 * by keeping a bool array in_index[] showing all the
+		 * already-passed-over tuplesort output TIDs of the current page. We
+		 * clear that array here, when advancing onto a new heap page.
+		 */
+		if (hscan->rs_cblock != root_blkno)
+		{
+			Page		page = BufferGetPage(hscan->rs_cbuf);
+
+			LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_SHARE);
+			heap_get_root_tuples(page, root_offsets);
+			LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+
+			memset(in_index, 0, sizeof(in_index));
+
+			root_blkno = hscan->rs_cblock;
+		}
+
+		/* Convert actual tuple TID to root TID */
+		rootTuple = *heapcursor;
+		root_offnum = ItemPointerGetOffsetNumber(heapcursor);
+
+		if (HeapTupleIsHeapOnly(heapTuple))
+		{
+			root_offnum = root_offsets[root_offnum - 1];
+			if (!OffsetNumberIsValid(root_offnum))
+				ereport(ERROR,
+						(errcode(ERRCODE_DATA_CORRUPTED),
+						 errmsg_internal("failed to find parent tuple for heap-only tuple at (%u,%u) in table \"%s\"",
+										 ItemPointerGetBlockNumber(heapcursor),
+										 ItemPointerGetOffsetNumber(heapcursor),
+										 RelationGetRelationName(heapRelation))));
+			ItemPointerSetOffsetNumber(&rootTuple, root_offnum);
+		}
+
+		/*
+		 * "merge" by skipping through the index tuples until we find or pass
+		 * the current root tuple.
+		 */
+		while (!tuplesort_empty &&
+			   (!indexcursor ||
+				ItemPointerCompare(indexcursor, &rootTuple) < 0))
+		{
+			Datum		ts_val;
+			bool		ts_isnull;
+
+			if (indexcursor)
+			{
+				/*
+				 * Remember index items seen earlier on the current heap page
+				 */
+				if (ItemPointerGetBlockNumber(indexcursor) == root_blkno)
+					in_index[ItemPointerGetOffsetNumber(indexcursor) - 1] = true;
+			}
+
+			tuplesort_empty = !tuplesort_getdatum(state->tuplesort, true,
+												  &ts_val, &ts_isnull, NULL);
+			Assert(tuplesort_empty || !ts_isnull);
+			if (!tuplesort_empty)
+			{
+				itemptr_decode(&decoded, DatumGetInt64(ts_val));
+				indexcursor = &decoded;
+
+				/* If int8 is pass-by-ref, free (encoded) TID Datum memory */
+#ifndef USE_FLOAT8_BYVAL
+				pfree(DatumGetPointer(ts_val));
+#endif
+			}
+			else
+			{
+				/* Be tidy */
+				indexcursor = NULL;
+			}
+		}
+
+		/*
+		 * If the tuplesort has overshot *and* we didn't see a match earlier,
+		 * then this tuple is missing from the index, so insert it.
+		 */
+		if ((tuplesort_empty ||
+			 ItemPointerCompare(indexcursor, &rootTuple) > 0) &&
+			!in_index[root_offnum - 1])
+		{
+			MemoryContextReset(econtext->ecxt_per_tuple_memory);
+
+			/* Set up for predicate or expression evaluation */
+			ExecStoreHeapTuple(heapTuple, slot, false);
+
+			/*
+			 * In a partial index, discard tuples that don't satisfy the
+			 * predicate.
+			 */
+			if (predicate != NULL)
+			{
+				if (!ExecQual(predicate, econtext))
+					continue;
+			}
+
+			/*
+			 * For the current heap tuple, extract all the attributes we use
+			 * in this index, and note which are null.  This also performs
+			 * evaluation of any expressions needed.
+			 */
+			FormIndexDatum(indexInfo,
+						   slot,
+						   estate,
+						   values,
+						   isnull);
+
+			/*
+			 * You'd think we should go ahead and build the index tuple here,
+			 * but some index AMs want to do further processing on the data
+			 * first. So pass the values[] and isnull[] arrays, instead.
+			 */
+
+			/*
+			 * If the tuple is already committed dead, you might think we
+			 * could suppress uniqueness checking, but this is no longer true
+			 * in the presence of HOT, because the insert is actually a proxy
+			 * for a uniqueness check on the whole HOT-chain.  That is, the
+			 * tuple we have here could be dead because it was already
+			 * HOT-updated, and if so the updating transaction will not have
+			 * thought it should insert index entries.  The index AM will
+			 * check the whole HOT-chain and correctly detect a conflict if
+			 * there is one.
+			 */
+
+			index_insert(indexRelation,
+						 values,
+						 isnull,
+						 &rootTuple,
+						 heapRelation,
+						 indexInfo->ii_Unique ?
+						 UNIQUE_CHECK_YES : UNIQUE_CHECK_NO,
+						 false,
+						 indexInfo);
+
+			state->tups_inserted += 1;
+		}
+	}
+
+	table_endscan(scan);
+
+	ExecDropSingleTupleTableSlot(slot);
+
+	FreeExecutorState(estate);
+
+	/* These may have been pointing to the now-gone estate */
+	indexInfo->ii_ExpressionsState = NIL;
+	indexInfo->ii_PredicateState = NULL;
+}
+
+/*
+ * Return the number of blocks that have been read by this scan since
+ * starting.  This is meant for progress reporting rather than be fully
+ * accurate: in a parallel scan, workers can be concurrently reading blocks
+ * further ahead than what we report.
+ */
+static BlockNumber
+heapam_scan_get_blocks_done(HeapScanDesc hscan)
+{
+	ParallelBlockTableScanDesc bpscan = NULL;
+	BlockNumber startblock;
+	BlockNumber blocks_done;
+
+	if (hscan->rs_base.rs_parallel != NULL)
+	{
+		bpscan = (ParallelBlockTableScanDesc) hscan->rs_base.rs_parallel;
+		startblock = bpscan->phs_startblock;
+	}
+	else
+		startblock = hscan->rs_startblock;
+
+	/*
+	 * Might have wrapped around the end of the relation, if startblock was
+	 * not zero.
+	 */
+	if (hscan->rs_cblock > startblock)
+		blocks_done = hscan->rs_cblock - startblock;
+	else
+	{
+		BlockNumber nblocks;
+
+		nblocks = bpscan != NULL ? bpscan->phs_nblocks : hscan->rs_nblocks;
+		blocks_done = nblocks - startblock +
+			hscan->rs_cblock;
+	}
+
+	return blocks_done;
+}
+
+
+/* ------------------------------------------------------------------------
+ * Miscellaneous callbacks for the heap AM
+ * ------------------------------------------------------------------------
+ */
+
+/*
+ * Check to see whether the table needs a TOAST table.  It does only if
+ * (1) there are any toastable attributes, and (2) the maximum length
+ * of a tuple could exceed TOAST_TUPLE_THRESHOLD.  (We don't want to
+ * create a toast table for something like "f1 varchar(20)".)
+ */
+static bool
+heapam_relation_needs_toast_table(Relation rel)
+{
+	int32		data_length = 0;
+	bool		maxlength_unknown = false;
+	bool		has_toastable_attrs = false;
+	TupleDesc	tupdesc = rel->rd_att;
+	int32		tuple_length;
+	int			i;
+
+	for (i = 0; i < tupdesc->natts; i++)
+	{
+		Form_pg_attribute att = TupleDescAttr(tupdesc, i);
+
+		if (att->attisdropped)
+			continue;
+		data_length = att_align_nominal(data_length, att->attalign);
+		if (att->attlen > 0)
+		{
+			/* Fixed-length types are never toastable */
+			data_length += att->attlen;
+		}
+		else
+		{
+			int32		maxlen = type_maximum_size(att->atttypid,
+												   att->atttypmod);
+
+			if (maxlen < 0)
+				maxlength_unknown = true;
+			else
+				data_length += maxlen;
+			if (att->attstorage != TYPSTORAGE_PLAIN)
+				has_toastable_attrs = true;
+		}
+	}
+	if (!has_toastable_attrs)
+		return false;			/* nothing to toast? */
+	if (maxlength_unknown)
+		return true;			/* any unlimited-length attrs? */
+	tuple_length = MAXALIGN(SizeofHeapTupleHeader +
+							BITMAPLEN(tupdesc->natts)) +
+		MAXALIGN(data_length);
+	return (tuple_length > TOAST_TUPLE_THRESHOLD);
+}
+
+/*
+ * TOAST tables for heap relations are just heap relations.
+ */
+static Oid
+heapam_relation_toast_am(Relation rel)
+{
+	return rel->rd_rel->relam;
+}
+
+
+/* ------------------------------------------------------------------------
+ * Planner related callbacks for the heap AM
+ * ------------------------------------------------------------------------
+ */
+
+#define HEAP_OVERHEAD_BYTES_PER_TUPLE \
+	(MAXALIGN(SizeofHeapTupleHeader) + sizeof(ItemIdData))
+#define HEAP_USABLE_BYTES_PER_PAGE \
+	(BLCKSZ - SizeOfPageHeaderData)
+
+static void
+heapam_estimate_rel_size(Relation rel, int32 *attr_widths,
+						 BlockNumber *pages, double *tuples,
+						 double *allvisfrac)
+{
+	table_block_relation_estimate_size(rel, attr_widths, pages,
+									   tuples, allvisfrac,
+									   HEAP_OVERHEAD_BYTES_PER_TUPLE,
+									   HEAP_USABLE_BYTES_PER_PAGE);
+}
+
+
+/* ------------------------------------------------------------------------
+ * Executor related callbacks for the heap AM
+ * ------------------------------------------------------------------------
+ */
+
+static bool
+heapam_scan_bitmap_next_block(TableScanDesc scan,
+							  TBMIterateResult *tbmres)
+{
+	HeapScanDesc hscan = (HeapScanDesc) scan;
+	BlockNumber page = tbmres->blockno;
+	Buffer		buffer;
+	Snapshot	snapshot;
+	int			ntup;
+
+	hscan->rs_cindex = 0;
+	hscan->rs_ntuples = 0;
+
+	/*
+	 * Ignore any claimed entries past what we think is the end of the
+	 * relation. It may have been extended after the start of our scan (we
+	 * only hold an AccessShareLock, and it could be inserts from this
+	 * backend).
+	 */
+	if (page >= hscan->rs_nblocks)
+		return false;
+
+	/*
+	 * Acquire pin on the target heap page, trading in any pin we held before.
+	 */
+	hscan->rs_cbuf = ReleaseAndReadBuffer(hscan->rs_cbuf,
+										  scan->rs_rd,
+										  page);
+	hscan->rs_cblock = page;
+	buffer = hscan->rs_cbuf;
+	snapshot = scan->rs_snapshot;
+
+	ntup = 0;
+
+	/*
+	 * Prune and repair fragmentation for the whole page, if possible.
+	 */
+	heap_page_prune_opt(scan->rs_rd, buffer);
+
+	/*
+	 * We must hold share lock on the buffer content while examining tuple
+	 * visibility.  Afterwards, however, the tuples we have found to be
+	 * visible are guaranteed good as long as we hold the buffer pin.
+	 */
+	LockBuffer(buffer, BUFFER_LOCK_SHARE);
+
+	/*
+	 * We need two separate strategies for lossy and non-lossy cases.
+	 */
+	if (tbmres->ntuples >= 0)
+	{
+		/*
+		 * Bitmap is non-lossy, so we just look through the offsets listed in
+		 * tbmres; but we have to follow any HOT chain starting at each such
+		 * offset.
+		 */
+		int			curslot;
+
+		for (curslot = 0; curslot < tbmres->ntuples; curslot++)
+		{
+			OffsetNumber offnum = tbmres->offsets[curslot];
+			ItemPointerData tid;
+			HeapTupleData heapTuple;
+
+			ItemPointerSet(&tid, page, offnum);
+			if (heap_hot_search_buffer(&tid, scan->rs_rd, buffer, snapshot,
+									   &heapTuple, NULL, true))
+				hscan->rs_vistuples[ntup++] = ItemPointerGetOffsetNumber(&tid);
+		}
+	}
+	else
+	{
+		/*
+		 * Bitmap is lossy, so we must examine each line pointer on the page.
+		 * But we can ignore HOT chains, since we'll check each tuple anyway.
+		 */
+		Page		dp = (Page) BufferGetPage(buffer);
+		OffsetNumber maxoff = PageGetMaxOffsetNumber(dp);
+		OffsetNumber offnum;
+
+		for (offnum = FirstOffsetNumber; offnum <= maxoff; offnum = OffsetNumberNext(offnum))
+		{
+			ItemId		lp;
+			HeapTupleData loctup;
+			bool		valid;
+
+			lp = PageGetItemId(dp, offnum);
+			if (!ItemIdIsNormal(lp))
+				continue;
+			loctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lp);
+			loctup.t_len = ItemIdGetLength(lp);
+			loctup.t_tableOid = scan->rs_rd->rd_id;
+			ItemPointerSet(&loctup.t_self, page, offnum);
+			valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer);
+			if (valid)
+			{
+				hscan->rs_vistuples[ntup++] = offnum;
+				PredicateLockTID(scan->rs_rd, &loctup.t_self, snapshot,
+								 HeapTupleHeaderGetXmin(loctup.t_data));
+			}
+			HeapCheckForSerializableConflictOut(valid, scan->rs_rd, &loctup,
+												buffer, snapshot);
+		}
+	}
+
+	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+
+	Assert(ntup <= MaxHeapTuplesPerPage);
+	hscan->rs_ntuples = ntup;
+
+	return ntup > 0;
+}
+
+static bool
+heapam_scan_bitmap_next_tuple(TableScanDesc scan,
+							  TBMIterateResult *tbmres,
+							  TupleTableSlot *slot)
+{
+	HeapScanDesc hscan = (HeapScanDesc) scan;
+	OffsetNumber targoffset;
+	Page		dp;
+	ItemId		lp;
+
+	/*
+	 * Out of range?  If so, nothing more to look at on this page
+	 */
+	if (hscan->rs_cindex < 0 || hscan->rs_cindex >= hscan->rs_ntuples)
+		return false;
+
+	targoffset = hscan->rs_vistuples[hscan->rs_cindex];
+	dp = (Page) BufferGetPage(hscan->rs_cbuf);
+	lp = PageGetItemId(dp, targoffset);
+	Assert(ItemIdIsNormal(lp));
+
+	hscan->rs_ctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lp);
+	hscan->rs_ctup.t_len = ItemIdGetLength(lp);
+	hscan->rs_ctup.t_tableOid = scan->rs_rd->rd_id;
+	ItemPointerSet(&hscan->rs_ctup.t_self, hscan->rs_cblock, targoffset);
+
+	pgstat_count_heap_fetch(scan->rs_rd);
+
+	/*
+	 * Set up the result slot to point to this tuple.  Note that the slot
+	 * acquires a pin on the buffer.
+	 */
+	ExecStoreBufferHeapTuple(&hscan->rs_ctup,
+							 slot,
+							 hscan->rs_cbuf);
+
+	hscan->rs_cindex++;
+
+	return true;
+}
+
+static bool
+heapam_scan_sample_next_block(TableScanDesc scan, SampleScanState *scanstate)
+{
+	HeapScanDesc hscan = (HeapScanDesc) scan;
+	TsmRoutine *tsm = scanstate->tsmroutine;
+	BlockNumber blockno;
+
+	/* return false immediately if relation is empty */
+	if (hscan->rs_nblocks == 0)
+		return false;
+
+	if (tsm->NextSampleBlock)
+	{
+		blockno = tsm->NextSampleBlock(scanstate, hscan->rs_nblocks);
+		hscan->rs_cblock = blockno;
+	}
+	else
+	{
+		/* scanning table sequentially */
+
+		if (hscan->rs_cblock == InvalidBlockNumber)
+		{
+			Assert(!hscan->rs_inited);
+			blockno = hscan->rs_startblock;
+		}
+		else
+		{
+			Assert(hscan->rs_inited);
+
+			blockno = hscan->rs_cblock + 1;
+
+			if (blockno >= hscan->rs_nblocks)
+			{
+				/* wrap to beginning of rel, might not have started at 0 */
+				blockno = 0;
+			}
+
+			/*
+			 * Report our new scan position for synchronization purposes.
+			 *
+			 * Note: we do this before checking for end of scan so that the
+			 * final state of the position hint is back at the start of the
+			 * rel.  That's not strictly necessary, but otherwise when you run
+			 * the same query multiple times the starting position would shift
+			 * a little bit backwards on every invocation, which is confusing.
+			 * We don't guarantee any specific ordering in general, though.
+			 */
+			if (scan->rs_flags & SO_ALLOW_SYNC)
+				ss_report_location(scan->rs_rd, blockno);
+
+			if (blockno == hscan->rs_startblock)
+			{
+				blockno = InvalidBlockNumber;
+			}
+		}
+	}
+
+	if (!BlockNumberIsValid(blockno))
+	{
+		if (BufferIsValid(hscan->rs_cbuf))
+			ReleaseBuffer(hscan->rs_cbuf);
+		hscan->rs_cbuf = InvalidBuffer;
+		hscan->rs_cblock = InvalidBlockNumber;
+		hscan->rs_inited = false;
+
+		return false;
+	}
+
+	heapgetpage(scan, blockno);
+	hscan->rs_inited = true;
+
+	return true;
+}
+
+static bool
+heapam_scan_sample_next_tuple(TableScanDesc scan, SampleScanState *scanstate,
+							  TupleTableSlot *slot)
+{
+	HeapScanDesc hscan = (HeapScanDesc) scan;
+	TsmRoutine *tsm = scanstate->tsmroutine;
+	BlockNumber blockno = hscan->rs_cblock;
+	bool		pagemode = (scan->rs_flags & SO_ALLOW_PAGEMODE) != 0;
+
+	Page		page;
+	bool		all_visible;
+	OffsetNumber maxoffset;
+
+	/*
+	 * When not using pagemode, we must lock the buffer during tuple
+	 * visibility checks.
+	 */
+	if (!pagemode)
+		LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_SHARE);
+
+	page = (Page) BufferGetPage(hscan->rs_cbuf);
+	all_visible = PageIsAllVisible(page) &&
+		!scan->rs_snapshot->takenDuringRecovery;
+	maxoffset = PageGetMaxOffsetNumber(page);
+
+	for (;;)
+	{
+		OffsetNumber tupoffset;
+
+		CHECK_FOR_INTERRUPTS();
+
+		/* Ask the tablesample method which tuples to check on this page. */
+		tupoffset = tsm->NextSampleTuple(scanstate,
+										 blockno,
+										 maxoffset);
+
+		if (OffsetNumberIsValid(tupoffset))
+		{
+			ItemId		itemid;
+			bool		visible;
+			HeapTuple	tuple = &(hscan->rs_ctup);
+
+			/* Skip invalid tuple pointers. */
+			itemid = PageGetItemId(page, tupoffset);
+			if (!ItemIdIsNormal(itemid))
+				continue;
+
+			tuple->t_data = (HeapTupleHeader) PageGetItem(page, itemid);
+			tuple->t_len = ItemIdGetLength(itemid);
+			ItemPointerSet(&(tuple->t_self), blockno, tupoffset);
+
+
+			if (all_visible)
+				visible = true;
+			else
+				visible = SampleHeapTupleVisible(scan, hscan->rs_cbuf,
+												 tuple, tupoffset);
+
+			/* in pagemode, heapgetpage did this for us */
+			if (!pagemode)
+				HeapCheckForSerializableConflictOut(visible, scan->rs_rd, tuple,
+													hscan->rs_cbuf, scan->rs_snapshot);
+
+			/* Try next tuple from same page. */
+			if (!visible)
+				continue;
+
+			/* Found visible tuple, return it. */
+			if (!pagemode)
+				LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+
+			ExecStoreBufferHeapTuple(tuple, slot, hscan->rs_cbuf);
+
+			/* Count successfully-fetched tuples as heap fetches */
+			pgstat_count_heap_getnext(scan->rs_rd);
+
+			return true;
+		}
+		else
+		{
+			/*
+			 * If we get here, it means we've exhausted the items on this page
+			 * and it's time to move to the next.
+			 */
+			if (!pagemode)
+				LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+
+			ExecClearTuple(slot);
+			return false;
+		}
+	}
+
+	Assert(0);
+}
+
+
+/* ----------------------------------------------------------------------------
+ *  Helper functions for the above.
+ * ----------------------------------------------------------------------------
+ */
+
+/*
+ * Reconstruct and rewrite the given tuple
+ *
+ * We cannot simply copy the tuple as-is, for several reasons:
+ *
+ * 1. We'd like to squeeze out the values of any dropped columns, both
+ * to save space and to ensure we have no corner-case failures. (It's
+ * possible for example that the new table hasn't got a TOAST table
+ * and so is unable to store any large values of dropped cols.)
+ *
+ * 2. The tuple might not even be legal for the new table; this is
+ * currently only known to happen as an after-effect of ALTER TABLE
+ * SET WITHOUT OIDS.
+ *
+ * So, we must reconstruct the tuple from component Datums.
+ */
+static void
+reform_and_rewrite_tuple(HeapTuple tuple,
+						 Relation OldHeap, Relation NewHeap,
+						 Datum *values, bool *isnull, RewriteState rwstate)
+{
+	TupleDesc	oldTupDesc = RelationGetDescr(OldHeap);
+	TupleDesc	newTupDesc = RelationGetDescr(NewHeap);
+	HeapTuple	copiedTuple;
+	int			i;
+
+	heap_deform_tuple(tuple, oldTupDesc, values, isnull);
+
+	/* Be sure to null out any dropped columns */
+	for (i = 0; i < newTupDesc->natts; i++)
+	{
+		if (TupleDescAttr(newTupDesc, i)->attisdropped)
+			isnull[i] = true;
+	}
+
+	copiedTuple = heap_form_tuple(newTupDesc, values, isnull);
+
+	/* The heap rewrite module does the rest */
+	rewrite_heap_tuple(rwstate, tuple, copiedTuple);
+
+	heap_freetuple(copiedTuple);
+}
+
+/*
+ * Check visibility of the tuple.
+ */
+static bool
+SampleHeapTupleVisible(TableScanDesc scan, Buffer buffer,
+					   HeapTuple tuple,
+					   OffsetNumber tupoffset)
+{
+	HeapScanDesc hscan = (HeapScanDesc) scan;
+
+	if (scan->rs_flags & SO_ALLOW_PAGEMODE)
+	{
+		/*
+		 * In pageatatime mode, heapgetpage() already did visibility checks,
+		 * so just look at the info it left in rs_vistuples[].
+		 *
+		 * We use a binary search over the known-sorted array.  Note: we could
+		 * save some effort if we insisted that NextSampleTuple select tuples
+		 * in increasing order, but it's not clear that there would be enough
+		 * gain to justify the restriction.
+		 */
+		int			start = 0,
+					end = hscan->rs_ntuples - 1;
+
+		while (start <= end)
+		{
+			int			mid = (start + end) / 2;
+			OffsetNumber curoffset = hscan->rs_vistuples[mid];
+
+			if (tupoffset == curoffset)
+				return true;
+			else if (tupoffset < curoffset)
+				end = mid - 1;
+			else
+				start = mid + 1;
+		}
+
+		return false;
+	}
+	else
+	{
+		/* Otherwise, we have to check the tuple individually. */
+		return HeapTupleSatisfiesVisibility(tuple, scan->rs_snapshot,
+											buffer);
+	}
+}
+
+
+/* ------------------------------------------------------------------------
+ * Definition of the heap table access method.
+ * ------------------------------------------------------------------------
+ */
+
+static const TableAmRoutine heapam_methods = {
+	.type = T_TableAmRoutine,
+
+	.slot_callbacks = heapam_slot_callbacks,
+
+	.scan_begin = heap_beginscan,
+	.scan_end = heap_endscan,
+	.scan_rescan = heap_rescan,
+	.scan_getnextslot = heap_getnextslot,
+
+	.scan_set_tidrange = heap_set_tidrange,
+	.scan_getnextslot_tidrange = heap_getnextslot_tidrange,
+
+	.parallelscan_estimate = table_block_parallelscan_estimate,
+	.parallelscan_initialize = table_block_parallelscan_initialize,
+	.parallelscan_reinitialize = table_block_parallelscan_reinitialize,
+
+	.index_fetch_begin = heapam_index_fetch_begin,
+	.index_fetch_reset = heapam_index_fetch_reset,
+	.index_fetch_end = heapam_index_fetch_end,
+	.index_fetch_tuple = heapam_index_fetch_tuple,
+
+	.tuple_insert = heapam_tuple_insert,
+	.tuple_insert_speculative = heapam_tuple_insert_speculative,
+	.tuple_complete_speculative = heapam_tuple_complete_speculative,
+	.multi_insert = heap_multi_insert,
+	.tuple_delete = heapam_tuple_delete,
+	.tuple_update = heapam_tuple_update,
+	.tuple_lock = heapam_tuple_lock,
+
+	.tuple_fetch_row_version = heapam_fetch_row_version,
+	.tuple_get_latest_tid = heap_get_latest_tid,
+	.tuple_tid_valid = heapam_tuple_tid_valid,
+	.tuple_satisfies_snapshot = heapam_tuple_satisfies_snapshot,
+	.index_delete_tuples = heap_index_delete_tuples,
+
+	.relation_set_new_filenode = heapam_relation_set_new_filenode,
+	.relation_nontransactional_truncate = heapam_relation_nontransactional_truncate,
+	.relation_copy_data = heapam_relation_copy_data,
+	.relation_copy_for_cluster = heapam_relation_copy_for_cluster,
+	.relation_vacuum = heap_vacuum_rel,
+	.scan_analyze_next_block = heapam_scan_analyze_next_block,
+	.scan_analyze_next_tuple = heapam_scan_analyze_next_tuple,
+	.index_build_range_scan = heapam_index_build_range_scan,
+	.index_validate_scan = heapam_index_validate_scan,
+
+	.relation_size = table_block_relation_size,
+	.relation_needs_toast_table = heapam_relation_needs_toast_table,
+	.relation_toast_am = heapam_relation_toast_am,
+	.relation_fetch_toast_slice = heap_fetch_toast_slice,
+
+	.relation_estimate_size = heapam_estimate_rel_size,
+
+	.scan_bitmap_next_block = heapam_scan_bitmap_next_block,
+	.scan_bitmap_next_tuple = heapam_scan_bitmap_next_tuple,
+	.scan_sample_next_block = heapam_scan_sample_next_block,
+	.scan_sample_next_tuple = heapam_scan_sample_next_tuple
+};
+
+
+const TableAmRoutine *
+GetHeapamTableAmRoutine(void)
+{
+	return &heapam_methods;
+}
+
+Datum
+heap_tableam_handler(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_POINTER(&heapam_methods);
+}
diff --git a/src/backend/access/heap/heapam_visibility.c b/src/backend/access/heap/heapam_visibility.c
new file mode 100644
index 0000000..20d82ca
--- /dev/null
+++ b/src/backend/access/heap/heapam_visibility.c
@@ -0,0 +1,1794 @@
+/*-------------------------------------------------------------------------
+ *
+ * heapam_visibility.c
+ *	  Tuple visibility rules for tuples stored in heap.
+ *
+ * NOTE: all the HeapTupleSatisfies routines will update the tuple's
+ * "hint" status bits if we see that the inserting or deleting transaction
+ * has now committed or aborted (and it is safe to set the hint bits).
+ * If the hint bits are changed, MarkBufferDirtyHint is called on
+ * the passed-in buffer.  The caller must hold not only a pin, but at least
+ * shared buffer content lock on the buffer containing the tuple.
+ *
+ * NOTE: When using a non-MVCC snapshot, we must check
+ * TransactionIdIsInProgress (which looks in the PGPROC array)
+ * before TransactionIdDidCommit/TransactionIdDidAbort (which look in
+ * pg_xact).  Otherwise we have a race condition: we might decide that a
+ * just-committed transaction crashed, because none of the tests succeed.
+ * xact.c is careful to record commit/abort in pg_xact before it unsets
+ * MyProc->xid in the PGPROC array.  That fixes that problem, but it
+ * also means there is a window where TransactionIdIsInProgress and
+ * TransactionIdDidCommit will both return true.  If we check only
+ * TransactionIdDidCommit, we could consider a tuple committed when a
+ * later GetSnapshotData call will still think the originating transaction
+ * is in progress, which leads to application-level inconsistency.  The
+ * upshot is that we gotta check TransactionIdIsInProgress first in all
+ * code paths, except for a few cases where we are looking at
+ * subtransactions of our own main transaction and so there can't be any
+ * race condition.
+ *
+ * When using an MVCC snapshot, we rely on XidInMVCCSnapshot rather than
+ * TransactionIdIsInProgress, but the logic is otherwise the same: do not
+ * check pg_xact until after deciding that the xact is no longer in progress.
+ *
+ *
+ * Summary of visibility functions:
+ *
+ *	 HeapTupleSatisfiesMVCC()
+ *		  visible to supplied snapshot, excludes current command
+ *	 HeapTupleSatisfiesUpdate()
+ *		  visible to instant snapshot, with user-supplied command
+ *		  counter and more complex result
+ *	 HeapTupleSatisfiesSelf()
+ *		  visible to instant snapshot and current command
+ *	 HeapTupleSatisfiesDirty()
+ *		  like HeapTupleSatisfiesSelf(), but includes open transactions
+ *	 HeapTupleSatisfiesVacuum()
+ *		  visible to any running transaction, used by VACUUM
+ *	 HeapTupleSatisfiesNonVacuumable()
+ *		  Snapshot-style API for HeapTupleSatisfiesVacuum
+ *	 HeapTupleSatisfiesToast()
+ *		  visible unless part of interrupted vacuum, used for TOAST
+ *	 HeapTupleSatisfiesAny()
+ *		  all tuples are visible
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/heap/heapam_visibility.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/heapam.h"
+#include "access/htup_details.h"
+#include "access/multixact.h"
+#include "access/subtrans.h"
+#include "access/tableam.h"
+#include "access/transam.h"
+#include "access/xact.h"
+#include "access/xlog.h"
+#include "storage/bufmgr.h"
+#include "storage/procarray.h"
+#include "utils/builtins.h"
+#include "utils/combocid.h"
+#include "utils/snapmgr.h"
+
+
+/*
+ * SetHintBits()
+ *
+ * Set commit/abort hint bits on a tuple, if appropriate at this time.
+ *
+ * It is only safe to set a transaction-committed hint bit if we know the
+ * transaction's commit record is guaranteed to be flushed to disk before the
+ * buffer, or if the table is temporary or unlogged and will be obliterated by
+ * a crash anyway.  We cannot change the LSN of the page here, because we may
+ * hold only a share lock on the buffer, so we can only use the LSN to
+ * interlock this if the buffer's LSN already is newer than the commit LSN;
+ * otherwise we have to just refrain from setting the hint bit until some
+ * future re-examination of the tuple.
+ *
+ * We can always set hint bits when marking a transaction aborted.  (Some
+ * code in heapam.c relies on that!)
+ *
+ * Also, if we are cleaning up HEAP_MOVED_IN or HEAP_MOVED_OFF entries, then
+ * we can always set the hint bits, since pre-9.0 VACUUM FULL always used
+ * synchronous commits and didn't move tuples that weren't previously
+ * hinted.  (This is not known by this subroutine, but is applied by its
+ * callers.)  Note: old-style VACUUM FULL is gone, but we have to keep this
+ * module's support for MOVED_OFF/MOVED_IN flag bits for as long as we
+ * support in-place update from pre-9.0 databases.
+ *
+ * Normal commits may be asynchronous, so for those we need to get the LSN
+ * of the transaction and then check whether this is flushed.
+ *
+ * The caller should pass xid as the XID of the transaction to check, or
+ * InvalidTransactionId if no check is needed.
+ */
+static inline void
+SetHintBits(HeapTupleHeader tuple, Buffer buffer,
+			uint16 infomask, TransactionId xid)
+{
+	if (TransactionIdIsValid(xid))
+	{
+		/* NB: xid must be known committed here! */
+		XLogRecPtr	commitLSN = TransactionIdGetCommitLSN(xid);
+
+		if (BufferIsPermanent(buffer) && XLogNeedsFlush(commitLSN) &&
+			BufferGetLSNAtomic(buffer) < commitLSN)
+		{
+			/* not flushed and no LSN interlock, so don't set hint */
+			return;
+		}
+	}
+
+	tuple->t_infomask |= infomask;
+	MarkBufferDirtyHint(buffer, true);
+}
+
+/*
+ * HeapTupleSetHintBits --- exported version of SetHintBits()
+ *
+ * This must be separate because of C99's brain-dead notions about how to
+ * implement inline functions.
+ */
+void
+HeapTupleSetHintBits(HeapTupleHeader tuple, Buffer buffer,
+					 uint16 infomask, TransactionId xid)
+{
+	SetHintBits(tuple, buffer, infomask, xid);
+}
+
+
+/*
+ * HeapTupleSatisfiesSelf
+ *		True iff heap tuple is valid "for itself".
+ *
+ * See SNAPSHOT_MVCC's definition for the intended behaviour.
+ *
+ * Note:
+ *		Assumes heap tuple is valid.
+ *
+ * The satisfaction of "itself" requires the following:
+ *
+ * ((Xmin == my-transaction &&				the row was updated by the current transaction, and
+ *		(Xmax is null						it was not deleted
+ *		 [|| Xmax != my-transaction)])			[or it was deleted by another transaction]
+ * ||
+ *
+ * (Xmin is committed &&					the row was modified by a committed transaction, and
+ *		(Xmax is null ||					the row has not been deleted, or
+ *			(Xmax != my-transaction &&			the row was deleted by another transaction
+ *			 Xmax is not committed)))			that has not been committed
+ */
+static bool
+HeapTupleSatisfiesSelf(HeapTuple htup, Snapshot snapshot, Buffer buffer)
+{
+	HeapTupleHeader tuple = htup->t_data;
+
+	Assert(ItemPointerIsValid(&htup->t_self));
+	Assert(htup->t_tableOid != InvalidOid);
+
+	if (!HeapTupleHeaderXminCommitted(tuple))
+	{
+		if (HeapTupleHeaderXminInvalid(tuple))
+			return false;
+
+		/* Used by pre-9.0 binary upgrades */
+		if (tuple->t_infomask & HEAP_MOVED_OFF)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (TransactionIdIsCurrentTransactionId(xvac))
+				return false;
+			if (!TransactionIdIsInProgress(xvac))
+			{
+				if (TransactionIdDidCommit(xvac))
+				{
+					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+								InvalidTransactionId);
+					return false;
+				}
+				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+							InvalidTransactionId);
+			}
+		}
+		/* Used by pre-9.0 binary upgrades */
+		else if (tuple->t_infomask & HEAP_MOVED_IN)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (!TransactionIdIsCurrentTransactionId(xvac))
+			{
+				if (TransactionIdIsInProgress(xvac))
+					return false;
+				if (TransactionIdDidCommit(xvac))
+					SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+								InvalidTransactionId);
+				else
+				{
+					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+								InvalidTransactionId);
+					return false;
+				}
+			}
+		}
+		else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
+		{
+			if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid */
+				return true;
+
+			if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))	/* not deleter */
+				return true;
+
+			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+			{
+				TransactionId xmax;
+
+				xmax = HeapTupleGetUpdateXid(tuple);
+
+				/* not LOCKED_ONLY, so it has to have an xmax */
+				Assert(TransactionIdIsValid(xmax));
+
+				/* updating subtransaction must have aborted */
+				if (!TransactionIdIsCurrentTransactionId(xmax))
+					return true;
+				else
+					return false;
+			}
+
+			if (!TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
+			{
+				/* deleting subtransaction must have aborted */
+				SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+							InvalidTransactionId);
+				return true;
+			}
+
+			return false;
+		}
+		else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
+			return false;
+		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
+			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+						HeapTupleHeaderGetRawXmin(tuple));
+		else
+		{
+			/* it must have aborted or crashed */
+			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+						InvalidTransactionId);
+			return false;
+		}
+	}
+
+	/* by here, the inserting transaction has committed */
+
+	if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid or aborted */
+		return true;
+
+	if (tuple->t_infomask & HEAP_XMAX_COMMITTED)
+	{
+		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+			return true;
+		return false;			/* updated by other */
+	}
+
+	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+	{
+		TransactionId xmax;
+
+		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+			return true;
+
+		xmax = HeapTupleGetUpdateXid(tuple);
+
+		/* not LOCKED_ONLY, so it has to have an xmax */
+		Assert(TransactionIdIsValid(xmax));
+
+		if (TransactionIdIsCurrentTransactionId(xmax))
+			return false;
+		if (TransactionIdIsInProgress(xmax))
+			return true;
+		if (TransactionIdDidCommit(xmax))
+			return false;
+		/* it must have aborted or crashed */
+		return true;
+	}
+
+	if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
+	{
+		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+			return true;
+		return false;
+	}
+
+	if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
+		return true;
+
+	if (!TransactionIdDidCommit(HeapTupleHeaderGetRawXmax(tuple)))
+	{
+		/* it must have aborted or crashed */
+		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+					InvalidTransactionId);
+		return true;
+	}
+
+	/* xmax transaction committed */
+
+	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+	{
+		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+					InvalidTransactionId);
+		return true;
+	}
+
+	SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
+				HeapTupleHeaderGetRawXmax(tuple));
+	return false;
+}
+
+/*
+ * HeapTupleSatisfiesAny
+ *		Dummy "satisfies" routine: any tuple satisfies SnapshotAny.
+ */
+static bool
+HeapTupleSatisfiesAny(HeapTuple htup, Snapshot snapshot, Buffer buffer)
+{
+	return true;
+}
+
+/*
+ * HeapTupleSatisfiesToast
+ *		True iff heap tuple is valid as a TOAST row.
+ *
+ * See SNAPSHOT_TOAST's definition for the intended behaviour.
+ *
+ * This is a simplified version that only checks for VACUUM moving conditions.
+ * It's appropriate for TOAST usage because TOAST really doesn't want to do
+ * its own time qual checks; if you can see the main table row that contains
+ * a TOAST reference, you should be able to see the TOASTed value.  However,
+ * vacuuming a TOAST table is independent of the main table, and in case such
+ * a vacuum fails partway through, we'd better do this much checking.
+ *
+ * Among other things, this means you can't do UPDATEs of rows in a TOAST
+ * table.
+ */
+static bool
+HeapTupleSatisfiesToast(HeapTuple htup, Snapshot snapshot,
+						Buffer buffer)
+{
+	HeapTupleHeader tuple = htup->t_data;
+
+	Assert(ItemPointerIsValid(&htup->t_self));
+	Assert(htup->t_tableOid != InvalidOid);
+
+	if (!HeapTupleHeaderXminCommitted(tuple))
+	{
+		if (HeapTupleHeaderXminInvalid(tuple))
+			return false;
+
+		/* Used by pre-9.0 binary upgrades */
+		if (tuple->t_infomask & HEAP_MOVED_OFF)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (TransactionIdIsCurrentTransactionId(xvac))
+				return false;
+			if (!TransactionIdIsInProgress(xvac))
+			{
+				if (TransactionIdDidCommit(xvac))
+				{
+					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+								InvalidTransactionId);
+					return false;
+				}
+				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+							InvalidTransactionId);
+			}
+		}
+		/* Used by pre-9.0 binary upgrades */
+		else if (tuple->t_infomask & HEAP_MOVED_IN)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (!TransactionIdIsCurrentTransactionId(xvac))
+			{
+				if (TransactionIdIsInProgress(xvac))
+					return false;
+				if (TransactionIdDidCommit(xvac))
+					SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+								InvalidTransactionId);
+				else
+				{
+					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+								InvalidTransactionId);
+					return false;
+				}
+			}
+		}
+
+		/*
+		 * An invalid Xmin can be left behind by a speculative insertion that
+		 * is canceled by super-deleting the tuple.  This also applies to
+		 * TOAST tuples created during speculative insertion.
+		 */
+		else if (!TransactionIdIsValid(HeapTupleHeaderGetXmin(tuple)))
+			return false;
+	}
+
+	/* otherwise assume the tuple is valid for TOAST. */
+	return true;
+}
+
+/*
+ * HeapTupleSatisfiesUpdate
+ *
+ *	This function returns a more detailed result code than most of the
+ *	functions in this file, since UPDATE needs to know more than "is it
+ *	visible?".  It also allows for user-supplied CommandId rather than
+ *	relying on CurrentCommandId.
+ *
+ *	The possible return codes are:
+ *
+ *	TM_Invisible: the tuple didn't exist at all when the scan started, e.g. it
+ *	was created by a later CommandId.
+ *
+ *	TM_Ok: The tuple is valid and visible, so it may be updated.
+ *
+ *	TM_SelfModified: The tuple was updated by the current transaction, after
+ *	the current scan started.
+ *
+ *	TM_Updated: The tuple was updated by a committed transaction (including
+ *	the case where the tuple was moved into a different partition).
+ *
+ *	TM_Deleted: The tuple was deleted by a committed transaction.
+ *
+ *	TM_BeingModified: The tuple is being updated by an in-progress transaction
+ *	other than the current transaction.  (Note: this includes the case where
+ *	the tuple is share-locked by a MultiXact, even if the MultiXact includes
+ *	the current transaction.  Callers that want to distinguish that case must
+ *	test for it themselves.)
+ */
+TM_Result
+HeapTupleSatisfiesUpdate(HeapTuple htup, CommandId curcid,
+						 Buffer buffer)
+{
+	HeapTupleHeader tuple = htup->t_data;
+
+	Assert(ItemPointerIsValid(&htup->t_self));
+	Assert(htup->t_tableOid != InvalidOid);
+
+	if (!HeapTupleHeaderXminCommitted(tuple))
+	{
+		if (HeapTupleHeaderXminInvalid(tuple))
+			return TM_Invisible;
+
+		/* Used by pre-9.0 binary upgrades */
+		if (tuple->t_infomask & HEAP_MOVED_OFF)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (TransactionIdIsCurrentTransactionId(xvac))
+				return TM_Invisible;
+			if (!TransactionIdIsInProgress(xvac))
+			{
+				if (TransactionIdDidCommit(xvac))
+				{
+					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+								InvalidTransactionId);
+					return TM_Invisible;
+				}
+				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+							InvalidTransactionId);
+			}
+		}
+		/* Used by pre-9.0 binary upgrades */
+		else if (tuple->t_infomask & HEAP_MOVED_IN)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (!TransactionIdIsCurrentTransactionId(xvac))
+			{
+				if (TransactionIdIsInProgress(xvac))
+					return TM_Invisible;
+				if (TransactionIdDidCommit(xvac))
+					SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+								InvalidTransactionId);
+				else
+				{
+					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+								InvalidTransactionId);
+					return TM_Invisible;
+				}
+			}
+		}
+		else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
+		{
+			if (HeapTupleHeaderGetCmin(tuple) >= curcid)
+				return TM_Invisible;	/* inserted after scan started */
+
+			if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid */
+				return TM_Ok;
+
+			if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+			{
+				TransactionId xmax;
+
+				xmax = HeapTupleHeaderGetRawXmax(tuple);
+
+				/*
+				 * Careful here: even though this tuple was created by our own
+				 * transaction, it might be locked by other transactions, if
+				 * the original version was key-share locked when we updated
+				 * it.
+				 */
+
+				if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+				{
+					if (MultiXactIdIsRunning(xmax, true))
+						return TM_BeingModified;
+					else
+						return TM_Ok;
+				}
+
+				/*
+				 * If the locker is gone, then there is nothing of interest
+				 * left in this Xmax; otherwise, report the tuple as
+				 * locked/updated.
+				 */
+				if (!TransactionIdIsInProgress(xmax))
+					return TM_Ok;
+				return TM_BeingModified;
+			}
+
+			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+			{
+				TransactionId xmax;
+
+				xmax = HeapTupleGetUpdateXid(tuple);
+
+				/* not LOCKED_ONLY, so it has to have an xmax */
+				Assert(TransactionIdIsValid(xmax));
+
+				/* deleting subtransaction must have aborted */
+				if (!TransactionIdIsCurrentTransactionId(xmax))
+				{
+					if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple),
+											 false))
+						return TM_BeingModified;
+					return TM_Ok;
+				}
+				else
+				{
+					if (HeapTupleHeaderGetCmax(tuple) >= curcid)
+						return TM_SelfModified; /* updated after scan started */
+					else
+						return TM_Invisible;	/* updated before scan started */
+				}
+			}
+
+			if (!TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
+			{
+				/* deleting subtransaction must have aborted */
+				SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+							InvalidTransactionId);
+				return TM_Ok;
+			}
+
+			if (HeapTupleHeaderGetCmax(tuple) >= curcid)
+				return TM_SelfModified; /* updated after scan started */
+			else
+				return TM_Invisible;	/* updated before scan started */
+		}
+		else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
+			return TM_Invisible;
+		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
+			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+						HeapTupleHeaderGetRawXmin(tuple));
+		else
+		{
+			/* it must have aborted or crashed */
+			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+						InvalidTransactionId);
+			return TM_Invisible;
+		}
+	}
+
+	/* by here, the inserting transaction has committed */
+
+	if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid or aborted */
+		return TM_Ok;
+
+	if (tuple->t_infomask & HEAP_XMAX_COMMITTED)
+	{
+		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+			return TM_Ok;
+		if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid))
+			return TM_Updated;	/* updated by other */
+		else
+			return TM_Deleted;	/* deleted by other */
+	}
+
+	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+	{
+		TransactionId xmax;
+
+		if (HEAP_LOCKED_UPGRADED(tuple->t_infomask))
+			return TM_Ok;
+
+		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+		{
+			if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), true))
+				return TM_BeingModified;
+
+			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
+			return TM_Ok;
+		}
+
+		xmax = HeapTupleGetUpdateXid(tuple);
+		if (!TransactionIdIsValid(xmax))
+		{
+			if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), false))
+				return TM_BeingModified;
+		}
+
+		/* not LOCKED_ONLY, so it has to have an xmax */
+		Assert(TransactionIdIsValid(xmax));
+
+		if (TransactionIdIsCurrentTransactionId(xmax))
+		{
+			if (HeapTupleHeaderGetCmax(tuple) >= curcid)
+				return TM_SelfModified; /* updated after scan started */
+			else
+				return TM_Invisible;	/* updated before scan started */
+		}
+
+		if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), false))
+			return TM_BeingModified;
+
+		if (TransactionIdDidCommit(xmax))
+		{
+			if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid))
+				return TM_Updated;
+			else
+				return TM_Deleted;
+		}
+
+		/*
+		 * By here, the update in the Xmax is either aborted or crashed, but
+		 * what about the other members?
+		 */
+
+		if (!MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), false))
+		{
+			/*
+			 * There's no member, even just a locker, alive anymore, so we can
+			 * mark the Xmax as invalid.
+			 */
+			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+						InvalidTransactionId);
+			return TM_Ok;
+		}
+		else
+		{
+			/* There are lockers running */
+			return TM_BeingModified;
+		}
+	}
+
+	if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
+	{
+		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+			return TM_BeingModified;
+		if (HeapTupleHeaderGetCmax(tuple) >= curcid)
+			return TM_SelfModified; /* updated after scan started */
+		else
+			return TM_Invisible;	/* updated before scan started */
+	}
+
+	if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
+		return TM_BeingModified;
+
+	if (!TransactionIdDidCommit(HeapTupleHeaderGetRawXmax(tuple)))
+	{
+		/* it must have aborted or crashed */
+		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+					InvalidTransactionId);
+		return TM_Ok;
+	}
+
+	/* xmax transaction committed */
+
+	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+	{
+		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+					InvalidTransactionId);
+		return TM_Ok;
+	}
+
+	SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
+				HeapTupleHeaderGetRawXmax(tuple));
+	if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid))
+		return TM_Updated;		/* updated by other */
+	else
+		return TM_Deleted;		/* deleted by other */
+}
+
+/*
+ * HeapTupleSatisfiesDirty
+ *		True iff heap tuple is valid including effects of open transactions.
+ *
+ * See SNAPSHOT_DIRTY's definition for the intended behaviour.
+ *
+ * This is essentially like HeapTupleSatisfiesSelf as far as effects of
+ * the current transaction and committed/aborted xacts are concerned.
+ * However, we also include the effects of other xacts still in progress.
+ *
+ * A special hack is that the passed-in snapshot struct is used as an
+ * output argument to return the xids of concurrent xacts that affected the
+ * tuple.  snapshot->xmin is set to the tuple's xmin if that is another
+ * transaction that's still in progress; or to InvalidTransactionId if the
+ * tuple's xmin is committed good, committed dead, or my own xact.
+ * Similarly for snapshot->xmax and the tuple's xmax.  If the tuple was
+ * inserted speculatively, meaning that the inserter might still back down
+ * on the insertion without aborting the whole transaction, the associated
+ * token is also returned in snapshot->speculativeToken.
+ */
+static bool
+HeapTupleSatisfiesDirty(HeapTuple htup, Snapshot snapshot,
+						Buffer buffer)
+{
+	HeapTupleHeader tuple = htup->t_data;
+
+	Assert(ItemPointerIsValid(&htup->t_self));
+	Assert(htup->t_tableOid != InvalidOid);
+
+	snapshot->xmin = snapshot->xmax = InvalidTransactionId;
+	snapshot->speculativeToken = 0;
+
+	if (!HeapTupleHeaderXminCommitted(tuple))
+	{
+		if (HeapTupleHeaderXminInvalid(tuple))
+			return false;
+
+		/* Used by pre-9.0 binary upgrades */
+		if (tuple->t_infomask & HEAP_MOVED_OFF)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (TransactionIdIsCurrentTransactionId(xvac))
+				return false;
+			if (!TransactionIdIsInProgress(xvac))
+			{
+				if (TransactionIdDidCommit(xvac))
+				{
+					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+								InvalidTransactionId);
+					return false;
+				}
+				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+							InvalidTransactionId);
+			}
+		}
+		/* Used by pre-9.0 binary upgrades */
+		else if (tuple->t_infomask & HEAP_MOVED_IN)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (!TransactionIdIsCurrentTransactionId(xvac))
+			{
+				if (TransactionIdIsInProgress(xvac))
+					return false;
+				if (TransactionIdDidCommit(xvac))
+					SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+								InvalidTransactionId);
+				else
+				{
+					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+								InvalidTransactionId);
+					return false;
+				}
+			}
+		}
+		else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
+		{
+			if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid */
+				return true;
+
+			if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))	/* not deleter */
+				return true;
+
+			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+			{
+				TransactionId xmax;
+
+				xmax = HeapTupleGetUpdateXid(tuple);
+
+				/* not LOCKED_ONLY, so it has to have an xmax */
+				Assert(TransactionIdIsValid(xmax));
+
+				/* updating subtransaction must have aborted */
+				if (!TransactionIdIsCurrentTransactionId(xmax))
+					return true;
+				else
+					return false;
+			}
+
+			if (!TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
+			{
+				/* deleting subtransaction must have aborted */
+				SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+							InvalidTransactionId);
+				return true;
+			}
+
+			return false;
+		}
+		else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
+		{
+			/*
+			 * Return the speculative token to caller.  Caller can worry about
+			 * xmax, since it requires a conclusively locked row version, and
+			 * a concurrent update to this tuple is a conflict of its
+			 * purposes.
+			 */
+			if (HeapTupleHeaderIsSpeculative(tuple))
+			{
+				snapshot->speculativeToken =
+					HeapTupleHeaderGetSpeculativeToken(tuple);
+
+				Assert(snapshot->speculativeToken != 0);
+			}
+
+			snapshot->xmin = HeapTupleHeaderGetRawXmin(tuple);
+			/* XXX shouldn't we fall through to look at xmax? */
+			return true;		/* in insertion by other */
+		}
+		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
+			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+						HeapTupleHeaderGetRawXmin(tuple));
+		else
+		{
+			/* it must have aborted or crashed */
+			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+						InvalidTransactionId);
+			return false;
+		}
+	}
+
+	/* by here, the inserting transaction has committed */
+
+	if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid or aborted */
+		return true;
+
+	if (tuple->t_infomask & HEAP_XMAX_COMMITTED)
+	{
+		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+			return true;
+		return false;			/* updated by other */
+	}
+
+	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+	{
+		TransactionId xmax;
+
+		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+			return true;
+
+		xmax = HeapTupleGetUpdateXid(tuple);
+
+		/* not LOCKED_ONLY, so it has to have an xmax */
+		Assert(TransactionIdIsValid(xmax));
+
+		if (TransactionIdIsCurrentTransactionId(xmax))
+			return false;
+		if (TransactionIdIsInProgress(xmax))
+		{
+			snapshot->xmax = xmax;
+			return true;
+		}
+		if (TransactionIdDidCommit(xmax))
+			return false;
+		/* it must have aborted or crashed */
+		return true;
+	}
+
+	if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
+	{
+		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+			return true;
+		return false;
+	}
+
+	if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
+	{
+		if (!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+			snapshot->xmax = HeapTupleHeaderGetRawXmax(tuple);
+		return true;
+	}
+
+	if (!TransactionIdDidCommit(HeapTupleHeaderGetRawXmax(tuple)))
+	{
+		/* it must have aborted or crashed */
+		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+					InvalidTransactionId);
+		return true;
+	}
+
+	/* xmax transaction committed */
+
+	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+	{
+		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+					InvalidTransactionId);
+		return true;
+	}
+
+	SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
+				HeapTupleHeaderGetRawXmax(tuple));
+	return false;				/* updated by other */
+}
+
+/*
+ * HeapTupleSatisfiesMVCC
+ *		True iff heap tuple is valid for the given MVCC snapshot.
+ *
+ * See SNAPSHOT_MVCC's definition for the intended behaviour.
+ *
+ * Notice that here, we will not update the tuple status hint bits if the
+ * inserting/deleting transaction is still running according to our snapshot,
+ * even if in reality it's committed or aborted by now.  This is intentional.
+ * Checking the true transaction state would require access to high-traffic
+ * shared data structures, creating contention we'd rather do without, and it
+ * would not change the result of our visibility check anyway.  The hint bits
+ * will be updated by the first visitor that has a snapshot new enough to see
+ * the inserting/deleting transaction as done.  In the meantime, the cost of
+ * leaving the hint bits unset is basically that each HeapTupleSatisfiesMVCC
+ * call will need to run TransactionIdIsCurrentTransactionId in addition to
+ * XidInMVCCSnapshot (but it would have to do the latter anyway).  In the old
+ * coding where we tried to set the hint bits as soon as possible, we instead
+ * did TransactionIdIsInProgress in each call --- to no avail, as long as the
+ * inserting/deleting transaction was still running --- which was more cycles
+ * and more contention on ProcArrayLock.
+ */
+static bool
+HeapTupleSatisfiesMVCC(HeapTuple htup, Snapshot snapshot,
+					   Buffer buffer)
+{
+	HeapTupleHeader tuple = htup->t_data;
+
+	Assert(ItemPointerIsValid(&htup->t_self));
+	Assert(htup->t_tableOid != InvalidOid);
+
+	if (!HeapTupleHeaderXminCommitted(tuple))
+	{
+		if (HeapTupleHeaderXminInvalid(tuple))
+			return false;
+
+		/* Used by pre-9.0 binary upgrades */
+		if (tuple->t_infomask & HEAP_MOVED_OFF)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (TransactionIdIsCurrentTransactionId(xvac))
+				return false;
+			if (!XidInMVCCSnapshot(xvac, snapshot))
+			{
+				if (TransactionIdDidCommit(xvac))
+				{
+					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+								InvalidTransactionId);
+					return false;
+				}
+				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+							InvalidTransactionId);
+			}
+		}
+		/* Used by pre-9.0 binary upgrades */
+		else if (tuple->t_infomask & HEAP_MOVED_IN)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (!TransactionIdIsCurrentTransactionId(xvac))
+			{
+				if (XidInMVCCSnapshot(xvac, snapshot))
+					return false;
+				if (TransactionIdDidCommit(xvac))
+					SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+								InvalidTransactionId);
+				else
+				{
+					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+								InvalidTransactionId);
+					return false;
+				}
+			}
+		}
+		else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
+		{
+			if (HeapTupleHeaderGetCmin(tuple) >= snapshot->curcid)
+				return false;	/* inserted after scan started */
+
+			if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid */
+				return true;
+
+			if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))	/* not deleter */
+				return true;
+
+			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+			{
+				TransactionId xmax;
+
+				xmax = HeapTupleGetUpdateXid(tuple);
+
+				/* not LOCKED_ONLY, so it has to have an xmax */
+				Assert(TransactionIdIsValid(xmax));
+
+				/* updating subtransaction must have aborted */
+				if (!TransactionIdIsCurrentTransactionId(xmax))
+					return true;
+				else if (HeapTupleHeaderGetCmax(tuple) >= snapshot->curcid)
+					return true;	/* updated after scan started */
+				else
+					return false;	/* updated before scan started */
+			}
+
+			if (!TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
+			{
+				/* deleting subtransaction must have aborted */
+				SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+							InvalidTransactionId);
+				return true;
+			}
+
+			if (HeapTupleHeaderGetCmax(tuple) >= snapshot->curcid)
+				return true;	/* deleted after scan started */
+			else
+				return false;	/* deleted before scan started */
+		}
+		else if (XidInMVCCSnapshot(HeapTupleHeaderGetRawXmin(tuple), snapshot))
+			return false;
+		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
+			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+						HeapTupleHeaderGetRawXmin(tuple));
+		else
+		{
+			/* it must have aborted or crashed */
+			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+						InvalidTransactionId);
+			return false;
+		}
+	}
+	else
+	{
+		/* xmin is committed, but maybe not according to our snapshot */
+		if (!HeapTupleHeaderXminFrozen(tuple) &&
+			XidInMVCCSnapshot(HeapTupleHeaderGetRawXmin(tuple), snapshot))
+			return false;		/* treat as still in progress */
+	}
+
+	/* by here, the inserting transaction has committed */
+
+	if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid or aborted */
+		return true;
+
+	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+		return true;
+
+	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+	{
+		TransactionId xmax;
+
+		/* already checked above */
+		Assert(!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask));
+
+		xmax = HeapTupleGetUpdateXid(tuple);
+
+		/* not LOCKED_ONLY, so it has to have an xmax */
+		Assert(TransactionIdIsValid(xmax));
+
+		if (TransactionIdIsCurrentTransactionId(xmax))
+		{
+			if (HeapTupleHeaderGetCmax(tuple) >= snapshot->curcid)
+				return true;	/* deleted after scan started */
+			else
+				return false;	/* deleted before scan started */
+		}
+		if (XidInMVCCSnapshot(xmax, snapshot))
+			return true;
+		if (TransactionIdDidCommit(xmax))
+			return false;		/* updating transaction committed */
+		/* it must have aborted or crashed */
+		return true;
+	}
+
+	if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
+	{
+		if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
+		{
+			if (HeapTupleHeaderGetCmax(tuple) >= snapshot->curcid)
+				return true;	/* deleted after scan started */
+			else
+				return false;	/* deleted before scan started */
+		}
+
+		if (XidInMVCCSnapshot(HeapTupleHeaderGetRawXmax(tuple), snapshot))
+			return true;
+
+		if (!TransactionIdDidCommit(HeapTupleHeaderGetRawXmax(tuple)))
+		{
+			/* it must have aborted or crashed */
+			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+						InvalidTransactionId);
+			return true;
+		}
+
+		/* xmax transaction committed */
+		SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
+					HeapTupleHeaderGetRawXmax(tuple));
+	}
+	else
+	{
+		/* xmax is committed, but maybe not according to our snapshot */
+		if (XidInMVCCSnapshot(HeapTupleHeaderGetRawXmax(tuple), snapshot))
+			return true;		/* treat as still in progress */
+	}
+
+	/* xmax transaction committed */
+
+	return false;
+}
+
+
+/*
+ * HeapTupleSatisfiesVacuum
+ *
+ *	Determine the status of tuples for VACUUM purposes.  Here, what
+ *	we mainly want to know is if a tuple is potentially visible to *any*
+ *	running transaction.  If so, it can't be removed yet by VACUUM.
+ *
+ * OldestXmin is a cutoff XID (obtained from
+ * GetOldestNonRemovableTransactionId()).  Tuples deleted by XIDs >=
+ * OldestXmin are deemed "recently dead"; they might still be visible to some
+ * open transaction, so we can't remove them, even if we see that the deleting
+ * transaction has committed.
+ */
+HTSV_Result
+HeapTupleSatisfiesVacuum(HeapTuple htup, TransactionId OldestXmin,
+						 Buffer buffer)
+{
+	TransactionId dead_after = InvalidTransactionId;
+	HTSV_Result res;
+
+	res = HeapTupleSatisfiesVacuumHorizon(htup, buffer, &dead_after);
+
+	if (res == HEAPTUPLE_RECENTLY_DEAD)
+	{
+		Assert(TransactionIdIsValid(dead_after));
+
+		if (TransactionIdPrecedes(dead_after, OldestXmin))
+			res = HEAPTUPLE_DEAD;
+	}
+	else
+		Assert(!TransactionIdIsValid(dead_after));
+
+	return res;
+}
+
+/*
+ * Work horse for HeapTupleSatisfiesVacuum and similar routines.
+ *
+ * In contrast to HeapTupleSatisfiesVacuum this routine, when encountering a
+ * tuple that could still be visible to some backend, stores the xid that
+ * needs to be compared with the horizon in *dead_after, and returns
+ * HEAPTUPLE_RECENTLY_DEAD. The caller then can perform the comparison with
+ * the horizon.  This is e.g. useful when comparing with different horizons.
+ *
+ * Note: HEAPTUPLE_DEAD can still be returned here, e.g. if the inserting
+ * transaction aborted.
+ */
+HTSV_Result
+HeapTupleSatisfiesVacuumHorizon(HeapTuple htup, Buffer buffer, TransactionId *dead_after)
+{
+	HeapTupleHeader tuple = htup->t_data;
+
+	Assert(ItemPointerIsValid(&htup->t_self));
+	Assert(htup->t_tableOid != InvalidOid);
+	Assert(dead_after != NULL);
+
+	*dead_after = InvalidTransactionId;
+
+	/*
+	 * Has inserting transaction committed?
+	 *
+	 * If the inserting transaction aborted, then the tuple was never visible
+	 * to any other transaction, so we can delete it immediately.
+	 */
+	if (!HeapTupleHeaderXminCommitted(tuple))
+	{
+		if (HeapTupleHeaderXminInvalid(tuple))
+			return HEAPTUPLE_DEAD;
+		/* Used by pre-9.0 binary upgrades */
+		else if (tuple->t_infomask & HEAP_MOVED_OFF)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (TransactionIdIsCurrentTransactionId(xvac))
+				return HEAPTUPLE_DELETE_IN_PROGRESS;
+			if (TransactionIdIsInProgress(xvac))
+				return HEAPTUPLE_DELETE_IN_PROGRESS;
+			if (TransactionIdDidCommit(xvac))
+			{
+				SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+							InvalidTransactionId);
+				return HEAPTUPLE_DEAD;
+			}
+			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+						InvalidTransactionId);
+		}
+		/* Used by pre-9.0 binary upgrades */
+		else if (tuple->t_infomask & HEAP_MOVED_IN)
+		{
+			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
+
+			if (TransactionIdIsCurrentTransactionId(xvac))
+				return HEAPTUPLE_INSERT_IN_PROGRESS;
+			if (TransactionIdIsInProgress(xvac))
+				return HEAPTUPLE_INSERT_IN_PROGRESS;
+			if (TransactionIdDidCommit(xvac))
+				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+							InvalidTransactionId);
+			else
+			{
+				SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+							InvalidTransactionId);
+				return HEAPTUPLE_DEAD;
+			}
+		}
+		else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
+		{
+			if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid */
+				return HEAPTUPLE_INSERT_IN_PROGRESS;
+			/* only locked? run infomask-only check first, for performance */
+			if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask) ||
+				HeapTupleHeaderIsOnlyLocked(tuple))
+				return HEAPTUPLE_INSERT_IN_PROGRESS;
+			/* inserted and then deleted by same xact */
+			if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetUpdateXid(tuple)))
+				return HEAPTUPLE_DELETE_IN_PROGRESS;
+			/* deleting subtransaction must have aborted */
+			return HEAPTUPLE_INSERT_IN_PROGRESS;
+		}
+		else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
+		{
+			/*
+			 * It'd be possible to discern between INSERT/DELETE in progress
+			 * here by looking at xmax - but that doesn't seem beneficial for
+			 * the majority of callers and even detrimental for some. We'd
+			 * rather have callers look at/wait for xmin than xmax. It's
+			 * always correct to return INSERT_IN_PROGRESS because that's
+			 * what's happening from the view of other backends.
+			 */
+			return HEAPTUPLE_INSERT_IN_PROGRESS;
+		}
+		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
+			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
+						HeapTupleHeaderGetRawXmin(tuple));
+		else
+		{
+			/*
+			 * Not in Progress, Not Committed, so either Aborted or crashed
+			 */
+			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
+						InvalidTransactionId);
+			return HEAPTUPLE_DEAD;
+		}
+
+		/*
+		 * At this point the xmin is known committed, but we might not have
+		 * been able to set the hint bit yet; so we can no longer Assert that
+		 * it's set.
+		 */
+	}
+
+	/*
+	 * Okay, the inserter committed, so it was good at some point.  Now what
+	 * about the deleting transaction?
+	 */
+	if (tuple->t_infomask & HEAP_XMAX_INVALID)
+		return HEAPTUPLE_LIVE;
+
+	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+	{
+		/*
+		 * "Deleting" xact really only locked it, so the tuple is live in any
+		 * case.  However, we should make sure that either XMAX_COMMITTED or
+		 * XMAX_INVALID gets set once the xact is gone, to reduce the costs of
+		 * examining the tuple for future xacts.
+		 */
+		if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
+		{
+			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+			{
+				/*
+				 * If it's a pre-pg_upgrade tuple, the multixact cannot
+				 * possibly be running; otherwise have to check.
+				 */
+				if (!HEAP_LOCKED_UPGRADED(tuple->t_infomask) &&
+					MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple),
+										 true))
+					return HEAPTUPLE_LIVE;
+				SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
+			}
+			else
+			{
+				if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
+					return HEAPTUPLE_LIVE;
+				SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+							InvalidTransactionId);
+			}
+		}
+
+		/*
+		 * We don't really care whether xmax did commit, abort or crash. We
+		 * know that xmax did lock the tuple, but it did not and will never
+		 * actually update it.
+		 */
+
+		return HEAPTUPLE_LIVE;
+	}
+
+	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+	{
+		TransactionId xmax = HeapTupleGetUpdateXid(tuple);
+
+		/* already checked above */
+		Assert(!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask));
+
+		/* not LOCKED_ONLY, so it has to have an xmax */
+		Assert(TransactionIdIsValid(xmax));
+
+		if (TransactionIdIsInProgress(xmax))
+			return HEAPTUPLE_DELETE_IN_PROGRESS;
+		else if (TransactionIdDidCommit(xmax))
+		{
+			/*
+			 * The multixact might still be running due to lockers.  Need to
+			 * allow for pruning if below the xid horizon regardless --
+			 * otherwise we could end up with a tuple where the updater has to
+			 * be removed due to the horizon, but is not pruned away.  It's
+			 * not a problem to prune that tuple, because any remaining
+			 * lockers will also be present in newer tuple versions.
+			 */
+			*dead_after = xmax;
+			return HEAPTUPLE_RECENTLY_DEAD;
+		}
+		else if (!MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), false))
+		{
+			/*
+			 * Not in Progress, Not Committed, so either Aborted or crashed.
+			 * Mark the Xmax as invalid.
+			 */
+			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
+		}
+
+		return HEAPTUPLE_LIVE;
+	}
+
+	if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
+	{
+		if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
+			return HEAPTUPLE_DELETE_IN_PROGRESS;
+		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmax(tuple)))
+			SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
+						HeapTupleHeaderGetRawXmax(tuple));
+		else
+		{
+			/*
+			 * Not in Progress, Not Committed, so either Aborted or crashed
+			 */
+			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+						InvalidTransactionId);
+			return HEAPTUPLE_LIVE;
+		}
+
+		/*
+		 * At this point the xmax is known committed, but we might not have
+		 * been able to set the hint bit yet; so we can no longer Assert that
+		 * it's set.
+		 */
+	}
+
+	/*
+	 * Deleter committed, allow caller to check if it was recent enough that
+	 * some open transactions could still see the tuple.
+	 */
+	*dead_after = HeapTupleHeaderGetRawXmax(tuple);
+	return HEAPTUPLE_RECENTLY_DEAD;
+}
+
+
+/*
+ * HeapTupleSatisfiesNonVacuumable
+ *
+ *	True if tuple might be visible to some transaction; false if it's
+ *	surely dead to everyone, ie, vacuumable.
+ *
+ *	See SNAPSHOT_NON_VACUUMABLE's definition for the intended behaviour.
+ *
+ *	This is an interface to HeapTupleSatisfiesVacuum that's callable via
+ *	HeapTupleSatisfiesSnapshot, so it can be used through a Snapshot.
+ *	snapshot->vistest must have been set up with the horizon to use.
+ */
+static bool
+HeapTupleSatisfiesNonVacuumable(HeapTuple htup, Snapshot snapshot,
+								Buffer buffer)
+{
+	TransactionId dead_after = InvalidTransactionId;
+	HTSV_Result res;
+
+	res = HeapTupleSatisfiesVacuumHorizon(htup, buffer, &dead_after);
+
+	if (res == HEAPTUPLE_RECENTLY_DEAD)
+	{
+		Assert(TransactionIdIsValid(dead_after));
+
+		if (GlobalVisTestIsRemovableXid(snapshot->vistest, dead_after))
+			res = HEAPTUPLE_DEAD;
+	}
+	else
+		Assert(!TransactionIdIsValid(dead_after));
+
+	return res != HEAPTUPLE_DEAD;
+}
+
+
+/*
+ * HeapTupleIsSurelyDead
+ *
+ *	Cheaply determine whether a tuple is surely dead to all onlookers.
+ *	We sometimes use this in lieu of HeapTupleSatisfiesVacuum when the
+ *	tuple has just been tested by another visibility routine (usually
+ *	HeapTupleSatisfiesMVCC) and, therefore, any hint bits that can be set
+ *	should already be set.  We assume that if no hint bits are set, the xmin
+ *	or xmax transaction is still running.  This is therefore faster than
+ *	HeapTupleSatisfiesVacuum, because we consult neither procarray nor CLOG.
+ *	It's okay to return false when in doubt, but we must return true only
+ *	if the tuple is removable.
+ */
+bool
+HeapTupleIsSurelyDead(HeapTuple htup, GlobalVisState *vistest)
+{
+	HeapTupleHeader tuple = htup->t_data;
+
+	Assert(ItemPointerIsValid(&htup->t_self));
+	Assert(htup->t_tableOid != InvalidOid);
+
+	/*
+	 * If the inserting transaction is marked invalid, then it aborted, and
+	 * the tuple is definitely dead.  If it's marked neither committed nor
+	 * invalid, then we assume it's still alive (since the presumption is that
+	 * all relevant hint bits were just set moments ago).
+	 */
+	if (!HeapTupleHeaderXminCommitted(tuple))
+		return HeapTupleHeaderXminInvalid(tuple) ? true : false;
+
+	/*
+	 * If the inserting transaction committed, but any deleting transaction
+	 * aborted, the tuple is still alive.
+	 */
+	if (tuple->t_infomask & HEAP_XMAX_INVALID)
+		return false;
+
+	/*
+	 * If the XMAX is just a lock, the tuple is still alive.
+	 */
+	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+		return false;
+
+	/*
+	 * If the Xmax is a MultiXact, it might be dead or alive, but we cannot
+	 * know without checking pg_multixact.
+	 */
+	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+		return false;
+
+	/* If deleter isn't known to have committed, assume it's still running. */
+	if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
+		return false;
+
+	/* Deleter committed, so tuple is dead if the XID is old enough. */
+	return GlobalVisTestIsRemovableXid(vistest,
+									   HeapTupleHeaderGetRawXmax(tuple));
+}
+
+/*
+ * Is the tuple really only locked?  That is, is it not updated?
+ *
+ * It's easy to check just infomask bits if the locker is not a multi; but
+ * otherwise we need to verify that the updating transaction has not aborted.
+ *
+ * This function is here because it follows the same visibility rules laid out
+ * at the top of this file.
+ */
+bool
+HeapTupleHeaderIsOnlyLocked(HeapTupleHeader tuple)
+{
+	TransactionId xmax;
+
+	/* if there's no valid Xmax, then there's obviously no update either */
+	if (tuple->t_infomask & HEAP_XMAX_INVALID)
+		return true;
+
+	if (tuple->t_infomask & HEAP_XMAX_LOCK_ONLY)
+		return true;
+
+	/* invalid xmax means no update */
+	if (!TransactionIdIsValid(HeapTupleHeaderGetRawXmax(tuple)))
+		return true;
+
+	/*
+	 * if HEAP_XMAX_LOCK_ONLY is not set and not a multi, then this must
+	 * necessarily have been updated
+	 */
+	if (!(tuple->t_infomask & HEAP_XMAX_IS_MULTI))
+		return false;
+
+	/* ... but if it's a multi, then perhaps the updating Xid aborted. */
+	xmax = HeapTupleGetUpdateXid(tuple);
+
+	/* not LOCKED_ONLY, so it has to have an xmax */
+	Assert(TransactionIdIsValid(xmax));
+
+	if (TransactionIdIsCurrentTransactionId(xmax))
+		return false;
+	if (TransactionIdIsInProgress(xmax))
+		return false;
+	if (TransactionIdDidCommit(xmax))
+		return false;
+
+	/*
+	 * not current, not in progress, not committed -- must have aborted or
+	 * crashed
+	 */
+	return true;
+}
+
+/*
+ * check whether the transaction id 'xid' is in the pre-sorted array 'xip'.
+ */
+static bool
+TransactionIdInArray(TransactionId xid, TransactionId *xip, Size num)
+{
+	return num > 0 &&
+		bsearch(&xid, xip, num, sizeof(TransactionId), xidComparator) != NULL;
+}
+
+/*
+ * See the comments for HeapTupleSatisfiesMVCC for the semantics this function
+ * obeys.
+ *
+ * Only usable on tuples from catalog tables!
+ *
+ * We don't need to support HEAP_MOVED_(IN|OFF) for now because we only support
+ * reading catalog pages which couldn't have been created in an older version.
+ *
+ * We don't set any hint bits in here as it seems unlikely to be beneficial as
+ * those should already be set by normal access and it seems to be too
+ * dangerous to do so as the semantics of doing so during timetravel are more
+ * complicated than when dealing "only" with the present.
+ */
+static bool
+HeapTupleSatisfiesHistoricMVCC(HeapTuple htup, Snapshot snapshot,
+							   Buffer buffer)
+{
+	HeapTupleHeader tuple = htup->t_data;
+	TransactionId xmin = HeapTupleHeaderGetXmin(tuple);
+	TransactionId xmax = HeapTupleHeaderGetRawXmax(tuple);
+
+	Assert(ItemPointerIsValid(&htup->t_self));
+	Assert(htup->t_tableOid != InvalidOid);
+
+	/* inserting transaction aborted */
+	if (HeapTupleHeaderXminInvalid(tuple))
+	{
+		Assert(!TransactionIdDidCommit(xmin));
+		return false;
+	}
+	/* check if it's one of our txids, toplevel is also in there */
+	else if (TransactionIdInArray(xmin, snapshot->subxip, snapshot->subxcnt))
+	{
+		bool		resolved;
+		CommandId	cmin = HeapTupleHeaderGetRawCommandId(tuple);
+		CommandId	cmax = InvalidCommandId;
+
+		/*
+		 * another transaction might have (tried to) delete this tuple or
+		 * cmin/cmax was stored in a combo CID. So we need to lookup the
+		 * actual values externally.
+		 */
+		resolved = ResolveCminCmaxDuringDecoding(HistoricSnapshotGetTupleCids(), snapshot,
+												 htup, buffer,
+												 &cmin, &cmax);
+
+		/*
+		 * If we haven't resolved the combo CID to cmin/cmax, that means we
+		 * have not decoded the combo CID yet. That means the cmin is
+		 * definitely in the future, and we're not supposed to see the tuple
+		 * yet.
+		 *
+		 * XXX This only applies to decoding of in-progress transactions. In
+		 * regular logical decoding we only execute this code at commit time,
+		 * at which point we should have seen all relevant combo CIDs. So
+		 * ideally, we should error out in this case but in practice, this
+		 * won't happen. If we are too worried about this then we can add an
+		 * elog inside ResolveCminCmaxDuringDecoding.
+		 *
+		 * XXX For the streaming case, we can track the largest combo CID
+		 * assigned, and error out based on this (when unable to resolve combo
+		 * CID below that observed maximum value).
+		 */
+		if (!resolved)
+			return false;
+
+		Assert(cmin != InvalidCommandId);
+
+		if (cmin >= snapshot->curcid)
+			return false;		/* inserted after scan started */
+		/* fall through */
+	}
+	/* committed before our xmin horizon. Do a normal visibility check. */
+	else if (TransactionIdPrecedes(xmin, snapshot->xmin))
+	{
+		Assert(!(HeapTupleHeaderXminCommitted(tuple) &&
+				 !TransactionIdDidCommit(xmin)));
+
+		/* check for hint bit first, consult clog afterwards */
+		if (!HeapTupleHeaderXminCommitted(tuple) &&
+			!TransactionIdDidCommit(xmin))
+			return false;
+		/* fall through */
+	}
+	/* beyond our xmax horizon, i.e. invisible */
+	else if (TransactionIdFollowsOrEquals(xmin, snapshot->xmax))
+	{
+		return false;
+	}
+	/* check if it's a committed transaction in [xmin, xmax) */
+	else if (TransactionIdInArray(xmin, snapshot->xip, snapshot->xcnt))
+	{
+		/* fall through */
+	}
+
+	/*
+	 * none of the above, i.e. between [xmin, xmax) but hasn't committed. I.e.
+	 * invisible.
+	 */
+	else
+	{
+		return false;
+	}
+
+	/* at this point we know xmin is visible, go on to check xmax */
+
+	/* xid invalid or aborted */
+	if (tuple->t_infomask & HEAP_XMAX_INVALID)
+		return true;
+	/* locked tuples are always visible */
+	else if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
+		return true;
+
+	/*
+	 * We can see multis here if we're looking at user tables or if somebody
+	 * SELECT ... FOR SHARE/UPDATE a system table.
+	 */
+	else if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
+	{
+		xmax = HeapTupleGetUpdateXid(tuple);
+	}
+
+	/* check if it's one of our txids, toplevel is also in there */
+	if (TransactionIdInArray(xmax, snapshot->subxip, snapshot->subxcnt))
+	{
+		bool		resolved;
+		CommandId	cmin;
+		CommandId	cmax = HeapTupleHeaderGetRawCommandId(tuple);
+
+		/* Lookup actual cmin/cmax values */
+		resolved = ResolveCminCmaxDuringDecoding(HistoricSnapshotGetTupleCids(), snapshot,
+												 htup, buffer,
+												 &cmin, &cmax);
+
+		/*
+		 * If we haven't resolved the combo CID to cmin/cmax, that means we
+		 * have not decoded the combo CID yet. That means the cmax is
+		 * definitely in the future, and we're still supposed to see the
+		 * tuple.
+		 *
+		 * XXX This only applies to decoding of in-progress transactions. In
+		 * regular logical decoding we only execute this code at commit time,
+		 * at which point we should have seen all relevant combo CIDs. So
+		 * ideally, we should error out in this case but in practice, this
+		 * won't happen. If we are too worried about this then we can add an
+		 * elog inside ResolveCminCmaxDuringDecoding.
+		 *
+		 * XXX For the streaming case, we can track the largest combo CID
+		 * assigned, and error out based on this (when unable to resolve combo
+		 * CID below that observed maximum value).
+		 */
+		if (!resolved || cmax == InvalidCommandId)
+			return true;
+
+		if (cmax >= snapshot->curcid)
+			return true;		/* deleted after scan started */
+		else
+			return false;		/* deleted before scan started */
+	}
+	/* below xmin horizon, normal transaction state is valid */
+	else if (TransactionIdPrecedes(xmax, snapshot->xmin))
+	{
+		Assert(!(tuple->t_infomask & HEAP_XMAX_COMMITTED &&
+				 !TransactionIdDidCommit(xmax)));
+
+		/* check hint bit first */
+		if (tuple->t_infomask & HEAP_XMAX_COMMITTED)
+			return false;
+
+		/* check clog */
+		return !TransactionIdDidCommit(xmax);
+	}
+	/* above xmax horizon, we cannot possibly see the deleting transaction */
+	else if (TransactionIdFollowsOrEquals(xmax, snapshot->xmax))
+		return true;
+	/* xmax is between [xmin, xmax), check known committed array */
+	else if (TransactionIdInArray(xmax, snapshot->xip, snapshot->xcnt))
+		return false;
+	/* xmax is between [xmin, xmax), but known not to have committed yet */
+	else
+		return true;
+}
+
+/*
+ * HeapTupleSatisfiesVisibility
+ *		True iff heap tuple satisfies a time qual.
+ *
+ * Notes:
+ *	Assumes heap tuple is valid, and buffer at least share locked.
+ *
+ *	Hint bits in the HeapTuple's t_infomask may be updated as a side effect;
+ *	if so, the indicated buffer is marked dirty.
+ */
+bool
+HeapTupleSatisfiesVisibility(HeapTuple tup, Snapshot snapshot, Buffer buffer)
+{
+	switch (snapshot->snapshot_type)
+	{
+		case SNAPSHOT_MVCC:
+			return HeapTupleSatisfiesMVCC(tup, snapshot, buffer);
+			break;
+		case SNAPSHOT_SELF:
+			return HeapTupleSatisfiesSelf(tup, snapshot, buffer);
+			break;
+		case SNAPSHOT_ANY:
+			return HeapTupleSatisfiesAny(tup, snapshot, buffer);
+			break;
+		case SNAPSHOT_TOAST:
+			return HeapTupleSatisfiesToast(tup, snapshot, buffer);
+			break;
+		case SNAPSHOT_DIRTY:
+			return HeapTupleSatisfiesDirty(tup, snapshot, buffer);
+			break;
+		case SNAPSHOT_HISTORIC_MVCC:
+			return HeapTupleSatisfiesHistoricMVCC(tup, snapshot, buffer);
+			break;
+		case SNAPSHOT_NON_VACUUMABLE:
+			return HeapTupleSatisfiesNonVacuumable(tup, snapshot, buffer);
+			break;
+	}
+
+	return false;				/* keep compiler quiet */
+}
diff --git a/src/backend/access/heap/heaptoast.c b/src/backend/access/heap/heaptoast.c
new file mode 100644
index 0000000..55bbe1d
--- /dev/null
+++ b/src/backend/access/heap/heaptoast.c
@@ -0,0 +1,793 @@
+/*-------------------------------------------------------------------------
+ *
+ * heaptoast.c
+ *	  Heap-specific definitions for external and compressed storage
+ *	  of variable size attributes.
+ *
+ * Copyright (c) 2000-2021, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/heap/heaptoast.c
+ *
+ *
+ * INTERFACE ROUTINES
+ *		heap_toast_insert_or_update -
+ *			Try to make a given tuple fit into one page by compressing
+ *			or moving off attributes
+ *
+ *		heap_toast_delete -
+ *			Reclaim toast storage when a tuple is deleted
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/detoast.h"
+#include "access/genam.h"
+#include "access/heapam.h"
+#include "access/heaptoast.h"
+#include "access/toast_helper.h"
+#include "access/toast_internals.h"
+#include "utils/fmgroids.h"
+
+
+/* ----------
+ * heap_toast_delete -
+ *
+ *	Cascaded delete toast-entries on DELETE
+ * ----------
+ */
+void
+heap_toast_delete(Relation rel, HeapTuple oldtup, bool is_speculative)
+{
+	TupleDesc	tupleDesc;
+	Datum		toast_values[MaxHeapAttributeNumber];
+	bool		toast_isnull[MaxHeapAttributeNumber];
+
+	/*
+	 * We should only ever be called for tuples of plain relations or
+	 * materialized views --- recursing on a toast rel is bad news.
+	 */
+	Assert(rel->rd_rel->relkind == RELKIND_RELATION ||
+		   rel->rd_rel->relkind == RELKIND_MATVIEW);
+
+	/*
+	 * Get the tuple descriptor and break down the tuple into fields.
+	 *
+	 * NOTE: it's debatable whether to use heap_deform_tuple() here or just
+	 * heap_getattr() only the varlena columns.  The latter could win if there
+	 * are few varlena columns and many non-varlena ones. However,
+	 * heap_deform_tuple costs only O(N) while the heap_getattr way would cost
+	 * O(N^2) if there are many varlena columns, so it seems better to err on
+	 * the side of linear cost.  (We won't even be here unless there's at
+	 * least one varlena column, by the way.)
+	 */
+	tupleDesc = rel->rd_att;
+
+	Assert(tupleDesc->natts <= MaxHeapAttributeNumber);
+	heap_deform_tuple(oldtup, tupleDesc, toast_values, toast_isnull);
+
+	/* Do the real work. */
+	toast_delete_external(rel, toast_values, toast_isnull, is_speculative);
+}
+
+
+/* ----------
+ * heap_toast_insert_or_update -
+ *
+ *	Delete no-longer-used toast-entries and create new ones to
+ *	make the new tuple fit on INSERT or UPDATE
+ *
+ * Inputs:
+ *	newtup: the candidate new tuple to be inserted
+ *	oldtup: the old row version for UPDATE, or NULL for INSERT
+ *	options: options to be passed to heap_insert() for toast rows
+ * Result:
+ *	either newtup if no toasting is needed, or a palloc'd modified tuple
+ *	that is what should actually get stored
+ *
+ * NOTE: neither newtup nor oldtup will be modified.  This is a change
+ * from the pre-8.1 API of this routine.
+ * ----------
+ */
+HeapTuple
+heap_toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup,
+							int options)
+{
+	HeapTuple	result_tuple;
+	TupleDesc	tupleDesc;
+	int			numAttrs;
+
+	Size		maxDataLen;
+	Size		hoff;
+
+	bool		toast_isnull[MaxHeapAttributeNumber];
+	bool		toast_oldisnull[MaxHeapAttributeNumber];
+	Datum		toast_values[MaxHeapAttributeNumber];
+	Datum		toast_oldvalues[MaxHeapAttributeNumber];
+	ToastAttrInfo toast_attr[MaxHeapAttributeNumber];
+	ToastTupleContext ttc;
+
+	/*
+	 * Ignore the INSERT_SPECULATIVE option. Speculative insertions/super
+	 * deletions just normally insert/delete the toast values. It seems
+	 * easiest to deal with that here, instead on, potentially, multiple
+	 * callers.
+	 */
+	options &= ~HEAP_INSERT_SPECULATIVE;
+
+	/*
+	 * We should only ever be called for tuples of plain relations or
+	 * materialized views --- recursing on a toast rel is bad news.
+	 */
+	Assert(rel->rd_rel->relkind == RELKIND_RELATION ||
+		   rel->rd_rel->relkind == RELKIND_MATVIEW);
+
+	/*
+	 * Get the tuple descriptor and break down the tuple(s) into fields.
+	 */
+	tupleDesc = rel->rd_att;
+	numAttrs = tupleDesc->natts;
+
+	Assert(numAttrs <= MaxHeapAttributeNumber);
+	heap_deform_tuple(newtup, tupleDesc, toast_values, toast_isnull);
+	if (oldtup != NULL)
+		heap_deform_tuple(oldtup, tupleDesc, toast_oldvalues, toast_oldisnull);
+
+	/* ----------
+	 * Prepare for toasting
+	 * ----------
+	 */
+	ttc.ttc_rel = rel;
+	ttc.ttc_values = toast_values;
+	ttc.ttc_isnull = toast_isnull;
+	if (oldtup == NULL)
+	{
+		ttc.ttc_oldvalues = NULL;
+		ttc.ttc_oldisnull = NULL;
+	}
+	else
+	{
+		ttc.ttc_oldvalues = toast_oldvalues;
+		ttc.ttc_oldisnull = toast_oldisnull;
+	}
+	ttc.ttc_attr = toast_attr;
+	toast_tuple_init(&ttc);
+
+	/* ----------
+	 * Compress and/or save external until data fits into target length
+	 *
+	 *	1: Inline compress attributes with attstorage EXTENDED, and store very
+	 *	   large attributes with attstorage EXTENDED or EXTERNAL external
+	 *	   immediately
+	 *	2: Store attributes with attstorage EXTENDED or EXTERNAL external
+	 *	3: Inline compress attributes with attstorage MAIN
+	 *	4: Store attributes with attstorage MAIN external
+	 * ----------
+	 */
+
+	/* compute header overhead --- this should match heap_form_tuple() */
+	hoff = SizeofHeapTupleHeader;
+	if ((ttc.ttc_flags & TOAST_HAS_NULLS) != 0)
+		hoff += BITMAPLEN(numAttrs);
+	hoff = MAXALIGN(hoff);
+	/* now convert to a limit on the tuple data size */
+	maxDataLen = RelationGetToastTupleTarget(rel, TOAST_TUPLE_TARGET) - hoff;
+
+	/*
+	 * Look for attributes with attstorage EXTENDED to compress.  Also find
+	 * large attributes with attstorage EXTENDED or EXTERNAL, and store them
+	 * external.
+	 */
+	while (heap_compute_data_size(tupleDesc,
+								  toast_values, toast_isnull) > maxDataLen)
+	{
+		int			biggest_attno;
+
+		biggest_attno = toast_tuple_find_biggest_attribute(&ttc, true, false);
+		if (biggest_attno < 0)
+			break;
+
+		/*
+		 * Attempt to compress it inline, if it has attstorage EXTENDED
+		 */
+		if (TupleDescAttr(tupleDesc, biggest_attno)->attstorage == TYPSTORAGE_EXTENDED)
+			toast_tuple_try_compression(&ttc, biggest_attno);
+		else
+		{
+			/*
+			 * has attstorage EXTERNAL, ignore on subsequent compression
+			 * passes
+			 */
+			toast_attr[biggest_attno].tai_colflags |= TOASTCOL_INCOMPRESSIBLE;
+		}
+
+		/*
+		 * If this value is by itself more than maxDataLen (after compression
+		 * if any), push it out to the toast table immediately, if possible.
+		 * This avoids uselessly compressing other fields in the common case
+		 * where we have one long field and several short ones.
+		 *
+		 * XXX maybe the threshold should be less than maxDataLen?
+		 */
+		if (toast_attr[biggest_attno].tai_size > maxDataLen &&
+			rel->rd_rel->reltoastrelid != InvalidOid)
+			toast_tuple_externalize(&ttc, biggest_attno, options);
+	}
+
+	/*
+	 * Second we look for attributes of attstorage EXTENDED or EXTERNAL that
+	 * are still inline, and make them external.  But skip this if there's no
+	 * toast table to push them to.
+	 */
+	while (heap_compute_data_size(tupleDesc,
+								  toast_values, toast_isnull) > maxDataLen &&
+		   rel->rd_rel->reltoastrelid != InvalidOid)
+	{
+		int			biggest_attno;
+
+		biggest_attno = toast_tuple_find_biggest_attribute(&ttc, false, false);
+		if (biggest_attno < 0)
+			break;
+		toast_tuple_externalize(&ttc, biggest_attno, options);
+	}
+
+	/*
+	 * Round 3 - this time we take attributes with storage MAIN into
+	 * compression
+	 */
+	while (heap_compute_data_size(tupleDesc,
+								  toast_values, toast_isnull) > maxDataLen)
+	{
+		int			biggest_attno;
+
+		biggest_attno = toast_tuple_find_biggest_attribute(&ttc, true, true);
+		if (biggest_attno < 0)
+			break;
+
+		toast_tuple_try_compression(&ttc, biggest_attno);
+	}
+
+	/*
+	 * Finally we store attributes of type MAIN externally.  At this point we
+	 * increase the target tuple size, so that MAIN attributes aren't stored
+	 * externally unless really necessary.
+	 */
+	maxDataLen = TOAST_TUPLE_TARGET_MAIN - hoff;
+
+	while (heap_compute_data_size(tupleDesc,
+								  toast_values, toast_isnull) > maxDataLen &&
+		   rel->rd_rel->reltoastrelid != InvalidOid)
+	{
+		int			biggest_attno;
+
+		biggest_attno = toast_tuple_find_biggest_attribute(&ttc, false, true);
+		if (biggest_attno < 0)
+			break;
+
+		toast_tuple_externalize(&ttc, biggest_attno, options);
+	}
+
+	/*
+	 * In the case we toasted any values, we need to build a new heap tuple
+	 * with the changed values.
+	 */
+	if ((ttc.ttc_flags & TOAST_NEEDS_CHANGE) != 0)
+	{
+		HeapTupleHeader olddata = newtup->t_data;
+		HeapTupleHeader new_data;
+		int32		new_header_len;
+		int32		new_data_len;
+		int32		new_tuple_len;
+
+		/*
+		 * Calculate the new size of the tuple.
+		 *
+		 * Note: we used to assume here that the old tuple's t_hoff must equal
+		 * the new_header_len value, but that was incorrect.  The old tuple
+		 * might have a smaller-than-current natts, if there's been an ALTER
+		 * TABLE ADD COLUMN since it was stored; and that would lead to a
+		 * different conclusion about the size of the null bitmap, or even
+		 * whether there needs to be one at all.
+		 */
+		new_header_len = SizeofHeapTupleHeader;
+		if ((ttc.ttc_flags & TOAST_HAS_NULLS) != 0)
+			new_header_len += BITMAPLEN(numAttrs);
+		new_header_len = MAXALIGN(new_header_len);
+		new_data_len = heap_compute_data_size(tupleDesc,
+											  toast_values, toast_isnull);
+		new_tuple_len = new_header_len + new_data_len;
+
+		/*
+		 * Allocate and zero the space needed, and fill HeapTupleData fields.
+		 */
+		result_tuple = (HeapTuple) palloc0(HEAPTUPLESIZE + new_tuple_len);
+		result_tuple->t_len = new_tuple_len;
+		result_tuple->t_self = newtup->t_self;
+		result_tuple->t_tableOid = newtup->t_tableOid;
+		new_data = (HeapTupleHeader) ((char *) result_tuple + HEAPTUPLESIZE);
+		result_tuple->t_data = new_data;
+
+		/*
+		 * Copy the existing tuple header, but adjust natts and t_hoff.
+		 */
+		memcpy(new_data, olddata, SizeofHeapTupleHeader);
+		HeapTupleHeaderSetNatts(new_data, numAttrs);
+		new_data->t_hoff = new_header_len;
+
+		/* Copy over the data, and fill the null bitmap if needed */
+		heap_fill_tuple(tupleDesc,
+						toast_values,
+						toast_isnull,
+						(char *) new_data + new_header_len,
+						new_data_len,
+						&(new_data->t_infomask),
+						((ttc.ttc_flags & TOAST_HAS_NULLS) != 0) ?
+						new_data->t_bits : NULL);
+	}
+	else
+		result_tuple = newtup;
+
+	toast_tuple_cleanup(&ttc);
+
+	return result_tuple;
+}
+
+
+/* ----------
+ * toast_flatten_tuple -
+ *
+ *	"Flatten" a tuple to contain no out-of-line toasted fields.
+ *	(This does not eliminate compressed or short-header datums.)
+ *
+ *	Note: we expect the caller already checked HeapTupleHasExternal(tup),
+ *	so there is no need for a short-circuit path.
+ * ----------
+ */
+HeapTuple
+toast_flatten_tuple(HeapTuple tup, TupleDesc tupleDesc)
+{
+	HeapTuple	new_tuple;
+	int			numAttrs = tupleDesc->natts;
+	int			i;
+	Datum		toast_values[MaxTupleAttributeNumber];
+	bool		toast_isnull[MaxTupleAttributeNumber];
+	bool		toast_free[MaxTupleAttributeNumber];
+
+	/*
+	 * Break down the tuple into fields.
+	 */
+	Assert(numAttrs <= MaxTupleAttributeNumber);
+	heap_deform_tuple(tup, tupleDesc, toast_values, toast_isnull);
+
+	memset(toast_free, 0, numAttrs * sizeof(bool));
+
+	for (i = 0; i < numAttrs; i++)
+	{
+		/*
+		 * Look at non-null varlena attributes
+		 */
+		if (!toast_isnull[i] && TupleDescAttr(tupleDesc, i)->attlen == -1)
+		{
+			struct varlena *new_value;
+
+			new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
+			if (VARATT_IS_EXTERNAL(new_value))
+			{
+				new_value = detoast_external_attr(new_value);
+				toast_values[i] = PointerGetDatum(new_value);
+				toast_free[i] = true;
+			}
+		}
+	}
+
+	/*
+	 * Form the reconfigured tuple.
+	 */
+	new_tuple = heap_form_tuple(tupleDesc, toast_values, toast_isnull);
+
+	/*
+	 * Be sure to copy the tuple's identity fields.  We also make a point of
+	 * copying visibility info, just in case anybody looks at those fields in
+	 * a syscache entry.
+	 */
+	new_tuple->t_self = tup->t_self;
+	new_tuple->t_tableOid = tup->t_tableOid;
+
+	new_tuple->t_data->t_choice = tup->t_data->t_choice;
+	new_tuple->t_data->t_ctid = tup->t_data->t_ctid;
+	new_tuple->t_data->t_infomask &= ~HEAP_XACT_MASK;
+	new_tuple->t_data->t_infomask |=
+		tup->t_data->t_infomask & HEAP_XACT_MASK;
+	new_tuple->t_data->t_infomask2 &= ~HEAP2_XACT_MASK;
+	new_tuple->t_data->t_infomask2 |=
+		tup->t_data->t_infomask2 & HEAP2_XACT_MASK;
+
+	/*
+	 * Free allocated temp values
+	 */
+	for (i = 0; i < numAttrs; i++)
+		if (toast_free[i])
+			pfree(DatumGetPointer(toast_values[i]));
+
+	return new_tuple;
+}
+
+
+/* ----------
+ * toast_flatten_tuple_to_datum -
+ *
+ *	"Flatten" a tuple containing out-of-line toasted fields into a Datum.
+ *	The result is always palloc'd in the current memory context.
+ *
+ *	We have a general rule that Datums of container types (rows, arrays,
+ *	ranges, etc) must not contain any external TOAST pointers.  Without
+ *	this rule, we'd have to look inside each Datum when preparing a tuple
+ *	for storage, which would be expensive and would fail to extend cleanly
+ *	to new sorts of container types.
+ *
+ *	However, we don't want to say that tuples represented as HeapTuples
+ *	can't contain toasted fields, so instead this routine should be called
+ *	when such a HeapTuple is being converted into a Datum.
+ *
+ *	While we're at it, we decompress any compressed fields too.  This is not
+ *	necessary for correctness, but reflects an expectation that compression
+ *	will be more effective if applied to the whole tuple not individual
+ *	fields.  We are not so concerned about that that we want to deconstruct
+ *	and reconstruct tuples just to get rid of compressed fields, however.
+ *	So callers typically won't call this unless they see that the tuple has
+ *	at least one external field.
+ *
+ *	On the other hand, in-line short-header varlena fields are left alone.
+ *	If we "untoasted" them here, they'd just get changed back to short-header
+ *	format anyway within heap_fill_tuple.
+ * ----------
+ */
+Datum
+toast_flatten_tuple_to_datum(HeapTupleHeader tup,
+							 uint32 tup_len,
+							 TupleDesc tupleDesc)
+{
+	HeapTupleHeader new_data;
+	int32		new_header_len;
+	int32		new_data_len;
+	int32		new_tuple_len;
+	HeapTupleData tmptup;
+	int			numAttrs = tupleDesc->natts;
+	int			i;
+	bool		has_nulls = false;
+	Datum		toast_values[MaxTupleAttributeNumber];
+	bool		toast_isnull[MaxTupleAttributeNumber];
+	bool		toast_free[MaxTupleAttributeNumber];
+
+	/* Build a temporary HeapTuple control structure */
+	tmptup.t_len = tup_len;
+	ItemPointerSetInvalid(&(tmptup.t_self));
+	tmptup.t_tableOid = InvalidOid;
+	tmptup.t_data = tup;
+
+	/*
+	 * Break down the tuple into fields.
+	 */
+	Assert(numAttrs <= MaxTupleAttributeNumber);
+	heap_deform_tuple(&tmptup, tupleDesc, toast_values, toast_isnull);
+
+	memset(toast_free, 0, numAttrs * sizeof(bool));
+
+	for (i = 0; i < numAttrs; i++)
+	{
+		/*
+		 * Look at non-null varlena attributes
+		 */
+		if (toast_isnull[i])
+			has_nulls = true;
+		else if (TupleDescAttr(tupleDesc, i)->attlen == -1)
+		{
+			struct varlena *new_value;
+
+			new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
+			if (VARATT_IS_EXTERNAL(new_value) ||
+				VARATT_IS_COMPRESSED(new_value))
+			{
+				new_value = detoast_attr(new_value);
+				toast_values[i] = PointerGetDatum(new_value);
+				toast_free[i] = true;
+			}
+		}
+	}
+
+	/*
+	 * Calculate the new size of the tuple.
+	 *
+	 * This should match the reconstruction code in
+	 * heap_toast_insert_or_update.
+	 */
+	new_header_len = SizeofHeapTupleHeader;
+	if (has_nulls)
+		new_header_len += BITMAPLEN(numAttrs);
+	new_header_len = MAXALIGN(new_header_len);
+	new_data_len = heap_compute_data_size(tupleDesc,
+										  toast_values, toast_isnull);
+	new_tuple_len = new_header_len + new_data_len;
+
+	new_data = (HeapTupleHeader) palloc0(new_tuple_len);
+
+	/*
+	 * Copy the existing tuple header, but adjust natts and t_hoff.
+	 */
+	memcpy(new_data, tup, SizeofHeapTupleHeader);
+	HeapTupleHeaderSetNatts(new_data, numAttrs);
+	new_data->t_hoff = new_header_len;
+
+	/* Set the composite-Datum header fields correctly */
+	HeapTupleHeaderSetDatumLength(new_data, new_tuple_len);
+	HeapTupleHeaderSetTypeId(new_data, tupleDesc->tdtypeid);
+	HeapTupleHeaderSetTypMod(new_data, tupleDesc->tdtypmod);
+
+	/* Copy over the data, and fill the null bitmap if needed */
+	heap_fill_tuple(tupleDesc,
+					toast_values,
+					toast_isnull,
+					(char *) new_data + new_header_len,
+					new_data_len,
+					&(new_data->t_infomask),
+					has_nulls ? new_data->t_bits : NULL);
+
+	/*
+	 * Free allocated temp values
+	 */
+	for (i = 0; i < numAttrs; i++)
+		if (toast_free[i])
+			pfree(DatumGetPointer(toast_values[i]));
+
+	return PointerGetDatum(new_data);
+}
+
+
+/* ----------
+ * toast_build_flattened_tuple -
+ *
+ *	Build a tuple containing no out-of-line toasted fields.
+ *	(This does not eliminate compressed or short-header datums.)
+ *
+ *	This is essentially just like heap_form_tuple, except that it will
+ *	expand any external-data pointers beforehand.
+ *
+ *	It's not very clear whether it would be preferable to decompress
+ *	in-line compressed datums while at it.  For now, we don't.
+ * ----------
+ */
+HeapTuple
+toast_build_flattened_tuple(TupleDesc tupleDesc,
+							Datum *values,
+							bool *isnull)
+{
+	HeapTuple	new_tuple;
+	int			numAttrs = tupleDesc->natts;
+	int			num_to_free;
+	int			i;
+	Datum		new_values[MaxTupleAttributeNumber];
+	Pointer		freeable_values[MaxTupleAttributeNumber];
+
+	/*
+	 * We can pass the caller's isnull array directly to heap_form_tuple, but
+	 * we potentially need to modify the values array.
+	 */
+	Assert(numAttrs <= MaxTupleAttributeNumber);
+	memcpy(new_values, values, numAttrs * sizeof(Datum));
+
+	num_to_free = 0;
+	for (i = 0; i < numAttrs; i++)
+	{
+		/*
+		 * Look at non-null varlena attributes
+		 */
+		if (!isnull[i] && TupleDescAttr(tupleDesc, i)->attlen == -1)
+		{
+			struct varlena *new_value;
+
+			new_value = (struct varlena *) DatumGetPointer(new_values[i]);
+			if (VARATT_IS_EXTERNAL(new_value))
+			{
+				new_value = detoast_external_attr(new_value);
+				new_values[i] = PointerGetDatum(new_value);
+				freeable_values[num_to_free++] = (Pointer) new_value;
+			}
+		}
+	}
+
+	/*
+	 * Form the reconfigured tuple.
+	 */
+	new_tuple = heap_form_tuple(tupleDesc, new_values, isnull);
+
+	/*
+	 * Free allocated temp values
+	 */
+	for (i = 0; i < num_to_free; i++)
+		pfree(freeable_values[i]);
+
+	return new_tuple;
+}
+
+/*
+ * Fetch a TOAST slice from a heap table.
+ *
+ * toastrel is the relation from which chunks are to be fetched.
+ * valueid identifies the TOAST value from which chunks are being fetched.
+ * attrsize is the total size of the TOAST value.
+ * sliceoffset is the byte offset within the TOAST value from which to fetch.
+ * slicelength is the number of bytes to be fetched from the TOAST value.
+ * result is the varlena into which the results should be written.
+ */
+void
+heap_fetch_toast_slice(Relation toastrel, Oid valueid, int32 attrsize,
+					   int32 sliceoffset, int32 slicelength,
+					   struct varlena *result)
+{
+	Relation   *toastidxs;
+	ScanKeyData toastkey[3];
+	TupleDesc	toasttupDesc = toastrel->rd_att;
+	int			nscankeys;
+	SysScanDesc toastscan;
+	HeapTuple	ttup;
+	int32		expectedchunk;
+	int32		totalchunks = ((attrsize - 1) / TOAST_MAX_CHUNK_SIZE) + 1;
+	int			startchunk;
+	int			endchunk;
+	int			num_indexes;
+	int			validIndex;
+	SnapshotData SnapshotToast;
+
+	/* Look for the valid index of toast relation */
+	validIndex = toast_open_indexes(toastrel,
+									AccessShareLock,
+									&toastidxs,
+									&num_indexes);
+
+	startchunk = sliceoffset / TOAST_MAX_CHUNK_SIZE;
+	endchunk = (sliceoffset + slicelength - 1) / TOAST_MAX_CHUNK_SIZE;
+	Assert(endchunk <= totalchunks);
+
+	/* Set up a scan key to fetch from the index. */
+	ScanKeyInit(&toastkey[0],
+				(AttrNumber) 1,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(valueid));
+
+	/*
+	 * No additional condition if fetching all chunks. Otherwise, use an
+	 * equality condition for one chunk, and a range condition otherwise.
+	 */
+	if (startchunk == 0 && endchunk == totalchunks - 1)
+		nscankeys = 1;
+	else if (startchunk == endchunk)
+	{
+		ScanKeyInit(&toastkey[1],
+					(AttrNumber) 2,
+					BTEqualStrategyNumber, F_INT4EQ,
+					Int32GetDatum(startchunk));
+		nscankeys = 2;
+	}
+	else
+	{
+		ScanKeyInit(&toastkey[1],
+					(AttrNumber) 2,
+					BTGreaterEqualStrategyNumber, F_INT4GE,
+					Int32GetDatum(startchunk));
+		ScanKeyInit(&toastkey[2],
+					(AttrNumber) 2,
+					BTLessEqualStrategyNumber, F_INT4LE,
+					Int32GetDatum(endchunk));
+		nscankeys = 3;
+	}
+
+	/* Prepare for scan */
+	init_toast_snapshot(&SnapshotToast);
+	toastscan = systable_beginscan_ordered(toastrel, toastidxs[validIndex],
+										   &SnapshotToast, nscankeys, toastkey);
+
+	/*
+	 * Read the chunks by index
+	 *
+	 * The index is on (valueid, chunkidx) so they will come in order
+	 */
+	expectedchunk = startchunk;
+	while ((ttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
+	{
+		int32		curchunk;
+		Pointer		chunk;
+		bool		isnull;
+		char	   *chunkdata;
+		int32		chunksize;
+		int32		expected_size;
+		int32		chcpystrt;
+		int32		chcpyend;
+
+		/*
+		 * Have a chunk, extract the sequence number and the data
+		 */
+		curchunk = DatumGetInt32(fastgetattr(ttup, 2, toasttupDesc, &isnull));
+		Assert(!isnull);
+		chunk = DatumGetPointer(fastgetattr(ttup, 3, toasttupDesc, &isnull));
+		Assert(!isnull);
+		if (!VARATT_IS_EXTENDED(chunk))
+		{
+			chunksize = VARSIZE(chunk) - VARHDRSZ;
+			chunkdata = VARDATA(chunk);
+		}
+		else if (VARATT_IS_SHORT(chunk))
+		{
+			/* could happen due to heap_form_tuple doing its thing */
+			chunksize = VARSIZE_SHORT(chunk) - VARHDRSZ_SHORT;
+			chunkdata = VARDATA_SHORT(chunk);
+		}
+		else
+		{
+			/* should never happen */
+			elog(ERROR, "found toasted toast chunk for toast value %u in %s",
+				 valueid, RelationGetRelationName(toastrel));
+			chunksize = 0;		/* keep compiler quiet */
+			chunkdata = NULL;
+		}
+
+		/*
+		 * Some checks on the data we've found
+		 */
+		if (curchunk != expectedchunk)
+			ereport(ERROR,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg_internal("unexpected chunk number %d (expected %d) for toast value %u in %s",
+									 curchunk, expectedchunk, valueid,
+									 RelationGetRelationName(toastrel))));
+		if (curchunk > endchunk)
+			ereport(ERROR,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg_internal("unexpected chunk number %d (out of range %d..%d) for toast value %u in %s",
+									 curchunk,
+									 startchunk, endchunk, valueid,
+									 RelationGetRelationName(toastrel))));
+		expected_size = curchunk < totalchunks - 1 ? TOAST_MAX_CHUNK_SIZE
+			: attrsize - ((totalchunks - 1) * TOAST_MAX_CHUNK_SIZE);
+		if (chunksize != expected_size)
+			ereport(ERROR,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg_internal("unexpected chunk size %d (expected %d) in chunk %d of %d for toast value %u in %s",
+									 chunksize, expected_size,
+									 curchunk, totalchunks, valueid,
+									 RelationGetRelationName(toastrel))));
+
+		/*
+		 * Copy the data into proper place in our result
+		 */
+		chcpystrt = 0;
+		chcpyend = chunksize - 1;
+		if (curchunk == startchunk)
+			chcpystrt = sliceoffset % TOAST_MAX_CHUNK_SIZE;
+		if (curchunk == endchunk)
+			chcpyend = (sliceoffset + slicelength - 1) % TOAST_MAX_CHUNK_SIZE;
+
+		memcpy(VARDATA(result) +
+			   (curchunk * TOAST_MAX_CHUNK_SIZE - sliceoffset) + chcpystrt,
+			   chunkdata + chcpystrt,
+			   (chcpyend - chcpystrt) + 1);
+
+		expectedchunk++;
+	}
+
+	/*
+	 * Final checks that we successfully fetched the datum
+	 */
+	if (expectedchunk != (endchunk + 1))
+		ereport(ERROR,
+				(errcode(ERRCODE_DATA_CORRUPTED),
+				 errmsg_internal("missing chunk number %d for toast value %u in %s",
+								 expectedchunk, valueid,
+								 RelationGetRelationName(toastrel))));
+
+	/* End scan and close indexes. */
+	systable_endscan_ordered(toastscan);
+	toast_close_indexes(toastidxs, num_indexes, AccessShareLock);
+}
diff --git a/src/backend/access/heap/hio.c b/src/backend/access/heap/hio.c
new file mode 100644
index 0000000..d34edb4
--- /dev/null
+++ b/src/backend/access/heap/hio.c
@@ -0,0 +1,721 @@
+/*-------------------------------------------------------------------------
+ *
+ * hio.c
+ *	  POSTGRES heap access method input/output code.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/heap/hio.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/heapam.h"
+#include "access/hio.h"
+#include "access/htup_details.h"
+#include "access/visibilitymap.h"
+#include "storage/bufmgr.h"
+#include "storage/freespace.h"
+#include "storage/lmgr.h"
+#include "storage/smgr.h"
+
+
+/*
+ * RelationPutHeapTuple - place tuple at specified page
+ *
+ * !!! EREPORT(ERROR) IS DISALLOWED HERE !!!  Must PANIC on failure!!!
+ *
+ * Note - caller must hold BUFFER_LOCK_EXCLUSIVE on the buffer.
+ */
+void
+RelationPutHeapTuple(Relation relation,
+					 Buffer buffer,
+					 HeapTuple tuple,
+					 bool token)
+{
+	Page		pageHeader;
+	OffsetNumber offnum;
+
+	/*
+	 * A tuple that's being inserted speculatively should already have its
+	 * token set.
+	 */
+	Assert(!token || HeapTupleHeaderIsSpeculative(tuple->t_data));
+
+	/*
+	 * Do not allow tuples with invalid combinations of hint bits to be placed
+	 * on a page.  This combination is detected as corruption by the
+	 * contrib/amcheck logic, so if you disable this assertion, make
+	 * corresponding changes there.
+	 */
+	Assert(!((tuple->t_data->t_infomask & HEAP_XMAX_COMMITTED) &&
+			 (tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI)));
+
+	/* Add the tuple to the page */
+	pageHeader = BufferGetPage(buffer);
+
+	offnum = PageAddItem(pageHeader, (Item) tuple->t_data,
+						 tuple->t_len, InvalidOffsetNumber, false, true);
+
+	if (offnum == InvalidOffsetNumber)
+		elog(PANIC, "failed to add tuple to page");
+
+	/* Update tuple->t_self to the actual position where it was stored */
+	ItemPointerSet(&(tuple->t_self), BufferGetBlockNumber(buffer), offnum);
+
+	/*
+	 * Insert the correct position into CTID of the stored tuple, too (unless
+	 * this is a speculative insertion, in which case the token is held in
+	 * CTID field instead)
+	 */
+	if (!token)
+	{
+		ItemId		itemId = PageGetItemId(pageHeader, offnum);
+		HeapTupleHeader item = (HeapTupleHeader) PageGetItem(pageHeader, itemId);
+
+		item->t_ctid = tuple->t_self;
+	}
+}
+
+/*
+ * Read in a buffer in mode, using bulk-insert strategy if bistate isn't NULL.
+ */
+static Buffer
+ReadBufferBI(Relation relation, BlockNumber targetBlock,
+			 ReadBufferMode mode, BulkInsertState bistate)
+{
+	Buffer		buffer;
+
+	/* If not bulk-insert, exactly like ReadBuffer */
+	if (!bistate)
+		return ReadBufferExtended(relation, MAIN_FORKNUM, targetBlock,
+								  mode, NULL);
+
+	/* If we have the desired block already pinned, re-pin and return it */
+	if (bistate->current_buf != InvalidBuffer)
+	{
+		if (BufferGetBlockNumber(bistate->current_buf) == targetBlock)
+		{
+			/*
+			 * Currently the LOCK variants are only used for extending
+			 * relation, which should never reach this branch.
+			 */
+			Assert(mode != RBM_ZERO_AND_LOCK &&
+				   mode != RBM_ZERO_AND_CLEANUP_LOCK);
+
+			IncrBufferRefCount(bistate->current_buf);
+			return bistate->current_buf;
+		}
+		/* ... else drop the old buffer */
+		ReleaseBuffer(bistate->current_buf);
+		bistate->current_buf = InvalidBuffer;
+	}
+
+	/* Perform a read using the buffer strategy */
+	buffer = ReadBufferExtended(relation, MAIN_FORKNUM, targetBlock,
+								mode, bistate->strategy);
+
+	/* Save the selected block as target for future inserts */
+	IncrBufferRefCount(buffer);
+	bistate->current_buf = buffer;
+
+	return buffer;
+}
+
+/*
+ * For each heap page which is all-visible, acquire a pin on the appropriate
+ * visibility map page, if we haven't already got one.
+ *
+ * buffer2 may be InvalidBuffer, if only one buffer is involved.  buffer1
+ * must not be InvalidBuffer.  If both buffers are specified, block1 must
+ * be less than block2.
+ */
+static void
+GetVisibilityMapPins(Relation relation, Buffer buffer1, Buffer buffer2,
+					 BlockNumber block1, BlockNumber block2,
+					 Buffer *vmbuffer1, Buffer *vmbuffer2)
+{
+	bool		need_to_pin_buffer1;
+	bool		need_to_pin_buffer2;
+
+	Assert(BufferIsValid(buffer1));
+	Assert(buffer2 == InvalidBuffer || block1 <= block2);
+
+	while (1)
+	{
+		/* Figure out which pins we need but don't have. */
+		need_to_pin_buffer1 = PageIsAllVisible(BufferGetPage(buffer1))
+			&& !visibilitymap_pin_ok(block1, *vmbuffer1);
+		need_to_pin_buffer2 = buffer2 != InvalidBuffer
+			&& PageIsAllVisible(BufferGetPage(buffer2))
+			&& !visibilitymap_pin_ok(block2, *vmbuffer2);
+		if (!need_to_pin_buffer1 && !need_to_pin_buffer2)
+			return;
+
+		/* We must unlock both buffers before doing any I/O. */
+		LockBuffer(buffer1, BUFFER_LOCK_UNLOCK);
+		if (buffer2 != InvalidBuffer && buffer2 != buffer1)
+			LockBuffer(buffer2, BUFFER_LOCK_UNLOCK);
+
+		/* Get pins. */
+		if (need_to_pin_buffer1)
+			visibilitymap_pin(relation, block1, vmbuffer1);
+		if (need_to_pin_buffer2)
+			visibilitymap_pin(relation, block2, vmbuffer2);
+
+		/* Relock buffers. */
+		LockBuffer(buffer1, BUFFER_LOCK_EXCLUSIVE);
+		if (buffer2 != InvalidBuffer && buffer2 != buffer1)
+			LockBuffer(buffer2, BUFFER_LOCK_EXCLUSIVE);
+
+		/*
+		 * If there are two buffers involved and we pinned just one of them,
+		 * it's possible that the second one became all-visible while we were
+		 * busy pinning the first one.  If it looks like that's a possible
+		 * scenario, we'll need to make a second pass through this loop.
+		 */
+		if (buffer2 == InvalidBuffer || buffer1 == buffer2
+			|| (need_to_pin_buffer1 && need_to_pin_buffer2))
+			break;
+	}
+}
+
+/*
+ * Extend a relation by multiple blocks to avoid future contention on the
+ * relation extension lock.  Our goal is to pre-extend the relation by an
+ * amount which ramps up as the degree of contention ramps up, but limiting
+ * the result to some sane overall value.
+ */
+static void
+RelationAddExtraBlocks(Relation relation, BulkInsertState bistate)
+{
+	BlockNumber blockNum,
+				firstBlock = InvalidBlockNumber;
+	int			extraBlocks;
+	int			lockWaiters;
+
+	/* Use the length of the lock wait queue to judge how much to extend. */
+	lockWaiters = RelationExtensionLockWaiterCount(relation);
+	if (lockWaiters <= 0)
+		return;
+
+	/*
+	 * It might seem like multiplying the number of lock waiters by as much as
+	 * 20 is too aggressive, but benchmarking revealed that smaller numbers
+	 * were insufficient.  512 is just an arbitrary cap to prevent
+	 * pathological results.
+	 */
+	extraBlocks = Min(512, lockWaiters * 20);
+
+	do
+	{
+		Buffer		buffer;
+		Page		page;
+		Size		freespace;
+
+		/*
+		 * Extend by one page.  This should generally match the main-line
+		 * extension code in RelationGetBufferForTuple, except that we hold
+		 * the relation extension lock throughout, and we don't immediately
+		 * initialize the page (see below).
+		 */
+		buffer = ReadBufferBI(relation, P_NEW, RBM_ZERO_AND_LOCK, bistate);
+		page = BufferGetPage(buffer);
+
+		if (!PageIsNew(page))
+			elog(ERROR, "page %u of relation \"%s\" should be empty but is not",
+				 BufferGetBlockNumber(buffer),
+				 RelationGetRelationName(relation));
+
+		/*
+		 * Add the page to the FSM without initializing. If we were to
+		 * initialize here, the page would potentially get flushed out to disk
+		 * before we add any useful content. There's no guarantee that that'd
+		 * happen before a potential crash, so we need to deal with
+		 * uninitialized pages anyway, thus avoid the potential for
+		 * unnecessary writes.
+		 */
+
+		/* we'll need this info below */
+		blockNum = BufferGetBlockNumber(buffer);
+		freespace = BufferGetPageSize(buffer) - SizeOfPageHeaderData;
+
+		UnlockReleaseBuffer(buffer);
+
+		/* Remember first block number thus added. */
+		if (firstBlock == InvalidBlockNumber)
+			firstBlock = blockNum;
+
+		/*
+		 * Immediately update the bottom level of the FSM.  This has a good
+		 * chance of making this page visible to other concurrently inserting
+		 * backends, and we want that to happen without delay.
+		 */
+		RecordPageWithFreeSpace(relation, blockNum, freespace);
+	}
+	while (--extraBlocks > 0);
+
+	/*
+	 * Updating the upper levels of the free space map is too expensive to do
+	 * for every block, but it's worth doing once at the end to make sure that
+	 * subsequent insertion activity sees all of those nifty free pages we
+	 * just inserted.
+	 */
+	FreeSpaceMapVacuumRange(relation, firstBlock, blockNum + 1);
+}
+
+/*
+ * RelationGetBufferForTuple
+ *
+ *	Returns pinned and exclusive-locked buffer of a page in given relation
+ *	with free space >= given len.
+ *
+ *	If otherBuffer is not InvalidBuffer, then it references a previously
+ *	pinned buffer of another page in the same relation; on return, this
+ *	buffer will also be exclusive-locked.  (This case is used by heap_update;
+ *	the otherBuffer contains the tuple being updated.)
+ *
+ *	The reason for passing otherBuffer is that if two backends are doing
+ *	concurrent heap_update operations, a deadlock could occur if they try
+ *	to lock the same two buffers in opposite orders.  To ensure that this
+ *	can't happen, we impose the rule that buffers of a relation must be
+ *	locked in increasing page number order.  This is most conveniently done
+ *	by having RelationGetBufferForTuple lock them both, with suitable care
+ *	for ordering.
+ *
+ *	NOTE: it is unlikely, but not quite impossible, for otherBuffer to be the
+ *	same buffer we select for insertion of the new tuple (this could only
+ *	happen if space is freed in that page after heap_update finds there's not
+ *	enough there).  In that case, the page will be pinned and locked only once.
+ *
+ *	We also handle the possibility that the all-visible flag will need to be
+ *	cleared on one or both pages.  If so, pin on the associated visibility map
+ *	page must be acquired before acquiring buffer lock(s), to avoid possibly
+ *	doing I/O while holding buffer locks.  The pins are passed back to the
+ *	caller using the input-output arguments vmbuffer and vmbuffer_other.
+ *	Note that in some cases the caller might have already acquired such pins,
+ *	which is indicated by these arguments not being InvalidBuffer on entry.
+ *
+ *	We normally use FSM to help us find free space.  However,
+ *	if HEAP_INSERT_SKIP_FSM is specified, we just append a new empty page to
+ *	the end of the relation if the tuple won't fit on the current target page.
+ *	This can save some cycles when we know the relation is new and doesn't
+ *	contain useful amounts of free space.
+ *
+ *	HEAP_INSERT_SKIP_FSM is also useful for non-WAL-logged additions to a
+ *	relation, if the caller holds exclusive lock and is careful to invalidate
+ *	relation's smgr_targblock before the first insertion --- that ensures that
+ *	all insertions will occur into newly added pages and not be intermixed
+ *	with tuples from other transactions.  That way, a crash can't risk losing
+ *	any committed data of other transactions.  (See heap_insert's comments
+ *	for additional constraints needed for safe usage of this behavior.)
+ *
+ *	The caller can also provide a BulkInsertState object to optimize many
+ *	insertions into the same relation.  This keeps a pin on the current
+ *	insertion target page (to save pin/unpin cycles) and also passes a
+ *	BULKWRITE buffer selection strategy object to the buffer manager.
+ *	Passing NULL for bistate selects the default behavior.
+ *
+ *	We don't fill existing pages further than the fillfactor, except for large
+ *	tuples in nearly-empty pages.  This is OK since this routine is not
+ *	consulted when updating a tuple and keeping it on the same page, which is
+ *	the scenario fillfactor is meant to reserve space for.
+ *
+ *	ereport(ERROR) is allowed here, so this routine *must* be called
+ *	before any (unlogged) changes are made in buffer pool.
+ */
+Buffer
+RelationGetBufferForTuple(Relation relation, Size len,
+						  Buffer otherBuffer, int options,
+						  BulkInsertState bistate,
+						  Buffer *vmbuffer, Buffer *vmbuffer_other)
+{
+	bool		use_fsm = !(options & HEAP_INSERT_SKIP_FSM);
+	Buffer		buffer = InvalidBuffer;
+	Page		page;
+	Size		nearlyEmptyFreeSpace,
+				pageFreeSpace = 0,
+				saveFreeSpace = 0,
+				targetFreeSpace = 0;
+	BlockNumber targetBlock,
+				otherBlock;
+	bool		needLock;
+
+	len = MAXALIGN(len);		/* be conservative */
+
+	/* Bulk insert is not supported for updates, only inserts. */
+	Assert(otherBuffer == InvalidBuffer || !bistate);
+
+	/*
+	 * If we're gonna fail for oversize tuple, do it right away
+	 */
+	if (len > MaxHeapTupleSize)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("row is too big: size %zu, maximum size %zu",
+						len, MaxHeapTupleSize)));
+
+	/* Compute desired extra freespace due to fillfactor option */
+	saveFreeSpace = RelationGetTargetPageFreeSpace(relation,
+												   HEAP_DEFAULT_FILLFACTOR);
+
+	/*
+	 * Since pages without tuples can still have line pointers, we consider
+	 * pages "empty" when the unavailable space is slight.  This threshold is
+	 * somewhat arbitrary, but it should prevent most unnecessary relation
+	 * extensions while inserting large tuples into low-fillfactor tables.
+	 */
+	nearlyEmptyFreeSpace = MaxHeapTupleSize -
+		(MaxHeapTuplesPerPage / 8 * sizeof(ItemIdData));
+	if (len + saveFreeSpace > nearlyEmptyFreeSpace)
+		targetFreeSpace = Max(len, nearlyEmptyFreeSpace);
+	else
+		targetFreeSpace = len + saveFreeSpace;
+
+	if (otherBuffer != InvalidBuffer)
+		otherBlock = BufferGetBlockNumber(otherBuffer);
+	else
+		otherBlock = InvalidBlockNumber;	/* just to keep compiler quiet */
+
+	/*
+	 * We first try to put the tuple on the same page we last inserted a tuple
+	 * on, as cached in the BulkInsertState or relcache entry.  If that
+	 * doesn't work, we ask the Free Space Map to locate a suitable page.
+	 * Since the FSM's info might be out of date, we have to be prepared to
+	 * loop around and retry multiple times. (To insure this isn't an infinite
+	 * loop, we must update the FSM with the correct amount of free space on
+	 * each page that proves not to be suitable.)  If the FSM has no record of
+	 * a page with enough free space, we give up and extend the relation.
+	 *
+	 * When use_fsm is false, we either put the tuple onto the existing target
+	 * page or extend the relation.
+	 */
+	if (bistate && bistate->current_buf != InvalidBuffer)
+		targetBlock = BufferGetBlockNumber(bistate->current_buf);
+	else
+		targetBlock = RelationGetTargetBlock(relation);
+
+	if (targetBlock == InvalidBlockNumber && use_fsm)
+	{
+		/*
+		 * We have no cached target page, so ask the FSM for an initial
+		 * target.
+		 */
+		targetBlock = GetPageWithFreeSpace(relation, targetFreeSpace);
+	}
+
+	/*
+	 * If the FSM knows nothing of the rel, try the last page before we give
+	 * up and extend.  This avoids one-tuple-per-page syndrome during
+	 * bootstrapping or in a recently-started system.
+	 */
+	if (targetBlock == InvalidBlockNumber)
+	{
+		BlockNumber nblocks = RelationGetNumberOfBlocks(relation);
+
+		if (nblocks > 0)
+			targetBlock = nblocks - 1;
+	}
+
+loop:
+	while (targetBlock != InvalidBlockNumber)
+	{
+		/*
+		 * Read and exclusive-lock the target block, as well as the other
+		 * block if one was given, taking suitable care with lock ordering and
+		 * the possibility they are the same block.
+		 *
+		 * If the page-level all-visible flag is set, caller will need to
+		 * clear both that and the corresponding visibility map bit.  However,
+		 * by the time we return, we'll have x-locked the buffer, and we don't
+		 * want to do any I/O while in that state.  So we check the bit here
+		 * before taking the lock, and pin the page if it appears necessary.
+		 * Checking without the lock creates a risk of getting the wrong
+		 * answer, so we'll have to recheck after acquiring the lock.
+		 */
+		if (otherBuffer == InvalidBuffer)
+		{
+			/* easy case */
+			buffer = ReadBufferBI(relation, targetBlock, RBM_NORMAL, bistate);
+			if (PageIsAllVisible(BufferGetPage(buffer)))
+				visibilitymap_pin(relation, targetBlock, vmbuffer);
+
+			/*
+			 * If the page is empty, pin vmbuffer to set all_frozen bit later.
+			 */
+			if ((options & HEAP_INSERT_FROZEN) &&
+				(PageGetMaxOffsetNumber(BufferGetPage(buffer)) == 0))
+				visibilitymap_pin(relation, targetBlock, vmbuffer);
+
+			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+		}
+		else if (otherBlock == targetBlock)
+		{
+			/* also easy case */
+			buffer = otherBuffer;
+			if (PageIsAllVisible(BufferGetPage(buffer)))
+				visibilitymap_pin(relation, targetBlock, vmbuffer);
+			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+		}
+		else if (otherBlock < targetBlock)
+		{
+			/* lock other buffer first */
+			buffer = ReadBuffer(relation, targetBlock);
+			if (PageIsAllVisible(BufferGetPage(buffer)))
+				visibilitymap_pin(relation, targetBlock, vmbuffer);
+			LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE);
+			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+		}
+		else
+		{
+			/* lock target buffer first */
+			buffer = ReadBuffer(relation, targetBlock);
+			if (PageIsAllVisible(BufferGetPage(buffer)))
+				visibilitymap_pin(relation, targetBlock, vmbuffer);
+			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+			LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE);
+		}
+
+		/*
+		 * We now have the target page (and the other buffer, if any) pinned
+		 * and locked.  However, since our initial PageIsAllVisible checks
+		 * were performed before acquiring the lock, the results might now be
+		 * out of date, either for the selected victim buffer, or for the
+		 * other buffer passed by the caller.  In that case, we'll need to
+		 * give up our locks, go get the pin(s) we failed to get earlier, and
+		 * re-lock.  That's pretty painful, but hopefully shouldn't happen
+		 * often.
+		 *
+		 * Note that there's a small possibility that we didn't pin the page
+		 * above but still have the correct page pinned anyway, either because
+		 * we've already made a previous pass through this loop, or because
+		 * caller passed us the right page anyway.
+		 *
+		 * Note also that it's possible that by the time we get the pin and
+		 * retake the buffer locks, the visibility map bit will have been
+		 * cleared by some other backend anyway.  In that case, we'll have
+		 * done a bit of extra work for no gain, but there's no real harm
+		 * done.
+		 */
+		if (otherBuffer == InvalidBuffer || targetBlock <= otherBlock)
+			GetVisibilityMapPins(relation, buffer, otherBuffer,
+								 targetBlock, otherBlock, vmbuffer,
+								 vmbuffer_other);
+		else
+			GetVisibilityMapPins(relation, otherBuffer, buffer,
+								 otherBlock, targetBlock, vmbuffer_other,
+								 vmbuffer);
+
+		/*
+		 * Now we can check to see if there's enough free space here. If so,
+		 * we're done.
+		 */
+		page = BufferGetPage(buffer);
+
+		/*
+		 * If necessary initialize page, it'll be used soon.  We could avoid
+		 * dirtying the buffer here, and rely on the caller to do so whenever
+		 * it puts a tuple onto the page, but there seems not much benefit in
+		 * doing so.
+		 */
+		if (PageIsNew(page))
+		{
+			PageInit(page, BufferGetPageSize(buffer), 0);
+			MarkBufferDirty(buffer);
+		}
+
+		pageFreeSpace = PageGetHeapFreeSpace(page);
+		if (targetFreeSpace <= pageFreeSpace)
+		{
+			/* use this page as future insert target, too */
+			RelationSetTargetBlock(relation, targetBlock);
+			return buffer;
+		}
+
+		/*
+		 * Not enough space, so we must give up our page locks and pin (if
+		 * any) and prepare to look elsewhere.  We don't care which order we
+		 * unlock the two buffers in, so this can be slightly simpler than the
+		 * code above.
+		 */
+		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+		if (otherBuffer == InvalidBuffer)
+			ReleaseBuffer(buffer);
+		else if (otherBlock != targetBlock)
+		{
+			LockBuffer(otherBuffer, BUFFER_LOCK_UNLOCK);
+			ReleaseBuffer(buffer);
+		}
+
+		/* Without FSM, always fall out of the loop and extend */
+		if (!use_fsm)
+			break;
+
+		/*
+		 * Update FSM as to condition of this page, and ask for another page
+		 * to try.
+		 */
+		targetBlock = RecordAndGetPageWithFreeSpace(relation,
+													targetBlock,
+													pageFreeSpace,
+													targetFreeSpace);
+	}
+
+	/*
+	 * Have to extend the relation.
+	 *
+	 * We have to use a lock to ensure no one else is extending the rel at the
+	 * same time, else we will both try to initialize the same new page.  We
+	 * can skip locking for new or temp relations, however, since no one else
+	 * could be accessing them.
+	 */
+	needLock = !RELATION_IS_LOCAL(relation);
+
+	/*
+	 * If we need the lock but are not able to acquire it immediately, we'll
+	 * consider extending the relation by multiple blocks at a time to manage
+	 * contention on the relation extension lock.  However, this only makes
+	 * sense if we're using the FSM; otherwise, there's no point.
+	 */
+	if (needLock)
+	{
+		if (!use_fsm)
+			LockRelationForExtension(relation, ExclusiveLock);
+		else if (!ConditionalLockRelationForExtension(relation, ExclusiveLock))
+		{
+			/* Couldn't get the lock immediately; wait for it. */
+			LockRelationForExtension(relation, ExclusiveLock);
+
+			/*
+			 * Check if some other backend has extended a block for us while
+			 * we were waiting on the lock.
+			 */
+			targetBlock = GetPageWithFreeSpace(relation, targetFreeSpace);
+
+			/*
+			 * If some other waiter has already extended the relation, we
+			 * don't need to do so; just use the existing freespace.
+			 */
+			if (targetBlock != InvalidBlockNumber)
+			{
+				UnlockRelationForExtension(relation, ExclusiveLock);
+				goto loop;
+			}
+
+			/* Time to bulk-extend. */
+			RelationAddExtraBlocks(relation, bistate);
+		}
+	}
+
+	/*
+	 * In addition to whatever extension we performed above, we always add at
+	 * least one block to satisfy our own request.
+	 *
+	 * XXX This does an lseek - rather expensive - but at the moment it is the
+	 * only way to accurately determine how many blocks are in a relation.  Is
+	 * it worth keeping an accurate file length in shared memory someplace,
+	 * rather than relying on the kernel to do it for us?
+	 */
+	buffer = ReadBufferBI(relation, P_NEW, RBM_ZERO_AND_LOCK, bistate);
+
+	/*
+	 * We need to initialize the empty new page.  Double-check that it really
+	 * is empty (this should never happen, but if it does we don't want to
+	 * risk wiping out valid data).
+	 */
+	page = BufferGetPage(buffer);
+
+	if (!PageIsNew(page))
+		elog(ERROR, "page %u of relation \"%s\" should be empty but is not",
+			 BufferGetBlockNumber(buffer),
+			 RelationGetRelationName(relation));
+
+	PageInit(page, BufferGetPageSize(buffer), 0);
+	MarkBufferDirty(buffer);
+
+	/*
+	 * The page is empty, pin vmbuffer to set all_frozen bit.
+	 */
+	if (options & HEAP_INSERT_FROZEN)
+	{
+		Assert(PageGetMaxOffsetNumber(BufferGetPage(buffer)) == 0);
+		visibilitymap_pin(relation, BufferGetBlockNumber(buffer), vmbuffer);
+	}
+
+	/*
+	 * Release the file-extension lock; it's now OK for someone else to extend
+	 * the relation some more.
+	 */
+	if (needLock)
+		UnlockRelationForExtension(relation, ExclusiveLock);
+
+	/*
+	 * Lock the other buffer. It's guaranteed to be of a lower page number
+	 * than the new page. To conform with the deadlock prevent rules, we ought
+	 * to lock otherBuffer first, but that would give other backends a chance
+	 * to put tuples on our page. To reduce the likelihood of that, attempt to
+	 * lock the other buffer conditionally, that's very likely to work.
+	 * Otherwise we need to lock buffers in the correct order, and retry if
+	 * the space has been used in the mean time.
+	 *
+	 * Alternatively, we could acquire the lock on otherBuffer before
+	 * extending the relation, but that'd require holding the lock while
+	 * performing IO, which seems worse than an unlikely retry.
+	 */
+	if (otherBuffer != InvalidBuffer)
+	{
+		Assert(otherBuffer != buffer);
+		targetBlock = BufferGetBlockNumber(buffer);
+		Assert(targetBlock > otherBlock);
+
+		if (unlikely(!ConditionalLockBuffer(otherBuffer)))
+		{
+			LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+			LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE);
+			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
+			/*
+			 * Because the buffers were unlocked for a while, it's possible,
+			 * although unlikely, that an all-visible flag became set or that
+			 * somebody used up the available space in the new page.  We can
+			 * use GetVisibilityMapPins to deal with the first case.  In the
+			 * second case, just retry from start.
+			 */
+			GetVisibilityMapPins(relation, otherBuffer, buffer,
+								 otherBlock, targetBlock, vmbuffer_other,
+								 vmbuffer);
+
+			if (len > PageGetHeapFreeSpace(page))
+			{
+				LockBuffer(otherBuffer, BUFFER_LOCK_UNLOCK);
+				UnlockReleaseBuffer(buffer);
+
+				goto loop;
+			}
+		}
+	}
+
+	if (len > PageGetHeapFreeSpace(page))
+	{
+		/* We should not get here given the test at the top */
+		elog(PANIC, "tuple is too big: size %zu", len);
+	}
+
+	/*
+	 * Remember the new page as our target for future insertions.
+	 *
+	 * XXX should we enter the new page into the free space map immediately,
+	 * or just keep it for this backend's exclusive use in the short run
+	 * (until VACUUM sees it)?	Seems to depend on whether you expect the
+	 * current backend to make more insertions or not, which is probably a
+	 * good bet most of the time.  So for now, don't add it to FSM yet.
+	 */
+	RelationSetTargetBlock(relation, BufferGetBlockNumber(buffer));
+
+	return buffer;
+}
diff --git a/src/backend/access/heap/pruneheap.c b/src/backend/access/heap/pruneheap.c
new file mode 100644
index 0000000..f7f8056
--- /dev/null
+++ b/src/backend/access/heap/pruneheap.c
@@ -0,0 +1,1052 @@
+/*-------------------------------------------------------------------------
+ *
+ * pruneheap.c
+ *	  heap page pruning and HOT-chain management code
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/heap/pruneheap.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/heapam.h"
+#include "access/heapam_xlog.h"
+#include "access/htup_details.h"
+#include "access/transam.h"
+#include "access/xlog.h"
+#include "catalog/catalog.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "storage/bufmgr.h"
+#include "utils/snapmgr.h"
+#include "utils/rel.h"
+#include "utils/snapmgr.h"
+
+/* Working data for heap_page_prune and subroutines */
+typedef struct
+{
+	Relation	rel;
+
+	/* tuple visibility test, initialized for the relation */
+	GlobalVisState *vistest;
+
+	/*
+	 * Thresholds set by TransactionIdLimitedForOldSnapshots() if they have
+	 * been computed (done on demand, and only if
+	 * OldSnapshotThresholdActive()). The first time a tuple is about to be
+	 * removed based on the limited horizon, old_snap_used is set to true, and
+	 * SetOldSnapshotThresholdTimestamp() is called. See
+	 * heap_prune_satisfies_vacuum().
+	 */
+	TimestampTz old_snap_ts;
+	TransactionId old_snap_xmin;
+	bool		old_snap_used;
+
+	TransactionId new_prune_xid;	/* new prune hint value for page */
+	TransactionId latestRemovedXid; /* latest xid to be removed by this prune */
+	int			nredirected;	/* numbers of entries in arrays below */
+	int			ndead;
+	int			nunused;
+	/* arrays that accumulate indexes of items to be changed */
+	OffsetNumber redirected[MaxHeapTuplesPerPage * 2];
+	OffsetNumber nowdead[MaxHeapTuplesPerPage];
+	OffsetNumber nowunused[MaxHeapTuplesPerPage];
+
+	/*
+	 * marked[i] is true if item i is entered in one of the above arrays.
+	 *
+	 * This needs to be MaxHeapTuplesPerPage + 1 long as FirstOffsetNumber is
+	 * 1. Otherwise every access would need to subtract 1.
+	 */
+	bool		marked[MaxHeapTuplesPerPage + 1];
+
+	/*
+	 * Tuple visibility is only computed once for each tuple, for correctness
+	 * and efficiency reasons; see comment in heap_page_prune() for
+	 * details. This is of type int8[,] intead of HTSV_Result[], so we can use
+	 * -1 to indicate no visibility has been computed, e.g. for LP_DEAD items.
+	 *
+	 * Same indexing as ->marked.
+	 */
+	int8		htsv[MaxHeapTuplesPerPage + 1];
+} PruneState;
+
+/* Local functions */
+static HTSV_Result heap_prune_satisfies_vacuum(PruneState *prstate,
+											   HeapTuple tup,
+											   Buffer buffer);
+static int	heap_prune_chain(Buffer buffer,
+							 OffsetNumber rootoffnum,
+							 PruneState *prstate);
+static void heap_prune_record_prunable(PruneState *prstate, TransactionId xid);
+static void heap_prune_record_redirect(PruneState *prstate,
+									   OffsetNumber offnum, OffsetNumber rdoffnum);
+static void heap_prune_record_dead(PruneState *prstate, OffsetNumber offnum);
+static void heap_prune_record_unused(PruneState *prstate, OffsetNumber offnum);
+
+
+/*
+ * Optionally prune and repair fragmentation in the specified page.
+ *
+ * This is an opportunistic function.  It will perform housekeeping
+ * only if the page heuristically looks like a candidate for pruning and we
+ * can acquire buffer cleanup lock without blocking.
+ *
+ * Note: this is called quite often.  It's important that it fall out quickly
+ * if there's not any use in pruning.
+ *
+ * Caller must have pin on the buffer, and must *not* have a lock on it.
+ */
+void
+heap_page_prune_opt(Relation relation, Buffer buffer)
+{
+	Page		page = BufferGetPage(buffer);
+	TransactionId prune_xid;
+	GlobalVisState *vistest;
+	TransactionId limited_xmin = InvalidTransactionId;
+	TimestampTz limited_ts = 0;
+	Size		minfree;
+
+	/*
+	 * We can't write WAL in recovery mode, so there's no point trying to
+	 * clean the page. The primary will likely issue a cleaning WAL record
+	 * soon anyway, so this is no particular loss.
+	 */
+	if (RecoveryInProgress())
+		return;
+
+	/*
+	 * XXX: Magic to keep old_snapshot_threshold tests appear "working". They
+	 * currently are broken, and discussion of what to do about them is
+	 * ongoing. See
+	 * https://www.postgresql.org/message-id/20200403001235.e6jfdll3gh2ygbuc%40alap3.anarazel.de
+	 */
+	if (old_snapshot_threshold == 0)
+		SnapshotTooOldMagicForTest();
+
+	/*
+	 * First check whether there's any chance there's something to prune,
+	 * determining the appropriate horizon is a waste if there's no prune_xid
+	 * (i.e. no updates/deletes left potentially dead tuples around).
+	 */
+	prune_xid = ((PageHeader) page)->pd_prune_xid;
+	if (!TransactionIdIsValid(prune_xid))
+		return;
+
+	/*
+	 * Check whether prune_xid indicates that there may be dead rows that can
+	 * be cleaned up.
+	 *
+	 * It is OK to check the old snapshot limit before acquiring the cleanup
+	 * lock because the worst that can happen is that we are not quite as
+	 * aggressive about the cleanup (by however many transaction IDs are
+	 * consumed between this point and acquiring the lock).  This allows us to
+	 * save significant overhead in the case where the page is found not to be
+	 * prunable.
+	 *
+	 * Even if old_snapshot_threshold is set, we first check whether the page
+	 * can be pruned without. Both because
+	 * TransactionIdLimitedForOldSnapshots() is not cheap, and because not
+	 * unnecessarily relying on old_snapshot_threshold avoids causing
+	 * conflicts.
+	 */
+	vistest = GlobalVisTestFor(relation);
+
+	if (!GlobalVisTestIsRemovableXid(vistest, prune_xid))
+	{
+		if (!OldSnapshotThresholdActive())
+			return;
+
+		if (!TransactionIdLimitedForOldSnapshots(GlobalVisTestNonRemovableHorizon(vistest),
+												 relation,
+												 &limited_xmin, &limited_ts))
+			return;
+
+		if (!TransactionIdPrecedes(prune_xid, limited_xmin))
+			return;
+	}
+
+	/*
+	 * We prune when a previous UPDATE failed to find enough space on the page
+	 * for a new tuple version, or when free space falls below the relation's
+	 * fill-factor target (but not less than 10%).
+	 *
+	 * Checking free space here is questionable since we aren't holding any
+	 * lock on the buffer; in the worst case we could get a bogus answer. It's
+	 * unlikely to be *seriously* wrong, though, since reading either pd_lower
+	 * or pd_upper is probably atomic.  Avoiding taking a lock seems more
+	 * important than sometimes getting a wrong answer in what is after all
+	 * just a heuristic estimate.
+	 */
+	minfree = RelationGetTargetPageFreeSpace(relation,
+											 HEAP_DEFAULT_FILLFACTOR);
+	minfree = Max(minfree, BLCKSZ / 10);
+
+	if (PageIsFull(page) || PageGetHeapFreeSpace(page) < minfree)
+	{
+		/* OK, try to get exclusive buffer lock */
+		if (!ConditionalLockBufferForCleanup(buffer))
+			return;
+
+		/*
+		 * Now that we have buffer lock, get accurate information about the
+		 * page's free space, and recheck the heuristic about whether to
+		 * prune. (We needn't recheck PageIsPrunable, since no one else could
+		 * have pruned while we hold pin.)
+		 */
+		if (PageIsFull(page) || PageGetHeapFreeSpace(page) < minfree)
+		{
+			/* OK to prune */
+			(void) heap_page_prune(relation, buffer, vistest,
+								   limited_xmin, limited_ts,
+								   true, NULL);
+		}
+
+		/* And release buffer lock */
+		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+	}
+}
+
+
+/*
+ * Prune and repair fragmentation in the specified page.
+ *
+ * Caller must have pin and buffer cleanup lock on the page.
+ *
+ * vistest is used to distinguish whether tuples are DEAD or RECENTLY_DEAD
+ * (see heap_prune_satisfies_vacuum and
+ * HeapTupleSatisfiesVacuum). old_snap_xmin / old_snap_ts need to
+ * either have been set by TransactionIdLimitedForOldSnapshots, or
+ * InvalidTransactionId/0 respectively.
+ *
+ * If report_stats is true then we send the number of reclaimed heap-only
+ * tuples to pgstats.  (This must be false during vacuum, since vacuum will
+ * send its own new total to pgstats, and we don't want this delta applied
+ * on top of that.)
+ *
+ * off_loc is the offset location required by the caller to use in error
+ * callback.
+ *
+ * Returns the number of tuples deleted from the page during this call.
+ */
+int
+heap_page_prune(Relation relation, Buffer buffer,
+				GlobalVisState *vistest,
+				TransactionId old_snap_xmin,
+				TimestampTz old_snap_ts,
+				bool report_stats,
+				OffsetNumber *off_loc)
+{
+	int			ndeleted = 0;
+	Page		page = BufferGetPage(buffer);
+	OffsetNumber offnum,
+				maxoff;
+	PruneState	prstate;
+	HeapTupleData tup;
+
+	/*
+	 * Our strategy is to scan the page and make lists of items to change,
+	 * then apply the changes within a critical section.  This keeps as much
+	 * logic as possible out of the critical section, and also ensures that
+	 * WAL replay will work the same as the normal case.
+	 *
+	 * First, initialize the new pd_prune_xid value to zero (indicating no
+	 * prunable tuples).  If we find any tuples which may soon become
+	 * prunable, we will save the lowest relevant XID in new_prune_xid. Also
+	 * initialize the rest of our working state.
+	 */
+	prstate.new_prune_xid = InvalidTransactionId;
+	prstate.rel = relation;
+	prstate.vistest = vistest;
+	prstate.old_snap_xmin = old_snap_xmin;
+	prstate.old_snap_ts = old_snap_ts;
+	prstate.old_snap_used = false;
+	prstate.latestRemovedXid = InvalidTransactionId;
+	prstate.nredirected = prstate.ndead = prstate.nunused = 0;
+	memset(prstate.marked, 0, sizeof(prstate.marked));
+
+	maxoff = PageGetMaxOffsetNumber(page);
+	tup.t_tableOid = RelationGetRelid(prstate.rel);
+
+	/*
+	 * Determine HTSV for all tuples.
+	 *
+	 * This is required for correctness to deal with cases where running HTSV
+	 * twice could result in different results (e.g. RECENTLY_DEAD can turn to
+	 * DEAD if another checked item causes GlobalVisTestIsRemovableFullXid()
+	 * to update the horizon, INSERT_IN_PROGRESS can change to DEAD if the
+	 * inserting transaction aborts, ...). That in turn could cause
+	 * heap_prune_chain() to behave incorrectly if a tuple is reached twice,
+	 * once directly via a heap_prune_chain() and once following a HOT chain.
+	 *
+	 * It's also good for performance. Most commonly tuples within a page are
+	 * stored at decreasing offsets (while the items are stored at increasing
+	 * offsets). When processing all tuples on a page this leads to reading
+	 * memory at decreasing offsets within a page, with a variable stride.
+	 * That's hard for CPU prefetchers to deal with. Processing the items in
+	 * reverse order (and thus the tuples in increasing order) increases
+	 * prefetching efficiency significantly / decreases the number of cache
+	 * misses.
+	 */
+	for (offnum = maxoff;
+		 offnum >= FirstOffsetNumber;
+		 offnum = OffsetNumberPrev(offnum))
+	{
+		ItemId		itemid = PageGetItemId(page, offnum);
+		HeapTupleHeader htup;
+
+		/* Nothing to do if slot doesn't contain a tuple */
+		if (!ItemIdIsNormal(itemid))
+		{
+			prstate.htsv[offnum] = -1;
+			continue;
+		}
+
+		htup = (HeapTupleHeader) PageGetItem(page, itemid);
+		tup.t_data = htup;
+		tup.t_len = ItemIdGetLength(itemid);
+		ItemPointerSet(&(tup.t_self), BufferGetBlockNumber(buffer), offnum);
+
+		/*
+		 * Set the offset number so that we can display it along with any
+		 * error that occurred while processing this tuple.
+		 */
+		if (off_loc)
+			*off_loc = offnum;
+
+		prstate.htsv[offnum] = heap_prune_satisfies_vacuum(&prstate, &tup,
+														   buffer);
+	}
+
+	/* Scan the page */
+	for (offnum = FirstOffsetNumber;
+		 offnum <= maxoff;
+		 offnum = OffsetNumberNext(offnum))
+	{
+		ItemId		itemid;
+
+		/* Ignore items already processed as part of an earlier chain */
+		if (prstate.marked[offnum])
+			continue;
+
+		/* see preceding loop */
+		if (off_loc)
+			*off_loc = offnum;
+
+		/* Nothing to do if slot is empty or already dead */
+		itemid = PageGetItemId(page, offnum);
+		if (!ItemIdIsUsed(itemid) || ItemIdIsDead(itemid))
+			continue;
+
+		/* Process this item or chain of items */
+		ndeleted += heap_prune_chain(buffer, offnum, &prstate);
+	}
+
+	/* Clear the offset information once we have processed the given page. */
+	if (off_loc)
+		*off_loc = InvalidOffsetNumber;
+
+	/* Any error while applying the changes is critical */
+	START_CRIT_SECTION();
+
+	/* Have we found any prunable items? */
+	if (prstate.nredirected > 0 || prstate.ndead > 0 || prstate.nunused > 0)
+	{
+		/*
+		 * Apply the planned item changes, then repair page fragmentation, and
+		 * update the page's hint bit about whether it has free line pointers.
+		 */
+		heap_page_prune_execute(buffer,
+								prstate.redirected, prstate.nredirected,
+								prstate.nowdead, prstate.ndead,
+								prstate.nowunused, prstate.nunused);
+
+		/*
+		 * Update the page's pd_prune_xid field to either zero, or the lowest
+		 * XID of any soon-prunable tuple.
+		 */
+		((PageHeader) page)->pd_prune_xid = prstate.new_prune_xid;
+
+		/*
+		 * Also clear the "page is full" flag, since there's no point in
+		 * repeating the prune/defrag process until something else happens to
+		 * the page.
+		 */
+		PageClearFull(page);
+
+		MarkBufferDirty(buffer);
+
+		/*
+		 * Emit a WAL XLOG_HEAP2_PRUNE record showing what we did
+		 */
+		if (RelationNeedsWAL(relation))
+		{
+			xl_heap_prune xlrec;
+			XLogRecPtr	recptr;
+
+			xlrec.latestRemovedXid = prstate.latestRemovedXid;
+			xlrec.nredirected = prstate.nredirected;
+			xlrec.ndead = prstate.ndead;
+
+			XLogBeginInsert();
+			XLogRegisterData((char *) &xlrec, SizeOfHeapPrune);
+
+			XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
+
+			/*
+			 * The OffsetNumber arrays are not actually in the buffer, but we
+			 * pretend that they are.  When XLogInsert stores the whole
+			 * buffer, the offset arrays need not be stored too.
+			 */
+			if (prstate.nredirected > 0)
+				XLogRegisterBufData(0, (char *) prstate.redirected,
+									prstate.nredirected *
+									sizeof(OffsetNumber) * 2);
+
+			if (prstate.ndead > 0)
+				XLogRegisterBufData(0, (char *) prstate.nowdead,
+									prstate.ndead * sizeof(OffsetNumber));
+
+			if (prstate.nunused > 0)
+				XLogRegisterBufData(0, (char *) prstate.nowunused,
+									prstate.nunused * sizeof(OffsetNumber));
+
+			recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_PRUNE);
+
+			PageSetLSN(BufferGetPage(buffer), recptr);
+		}
+	}
+	else
+	{
+		/*
+		 * If we didn't prune anything, but have found a new value for the
+		 * pd_prune_xid field, update it and mark the buffer dirty. This is
+		 * treated as a non-WAL-logged hint.
+		 *
+		 * Also clear the "page is full" flag if it is set, since there's no
+		 * point in repeating the prune/defrag process until something else
+		 * happens to the page.
+		 */
+		if (((PageHeader) page)->pd_prune_xid != prstate.new_prune_xid ||
+			PageIsFull(page))
+		{
+			((PageHeader) page)->pd_prune_xid = prstate.new_prune_xid;
+			PageClearFull(page);
+			MarkBufferDirtyHint(buffer, true);
+		}
+	}
+
+	END_CRIT_SECTION();
+
+	/*
+	 * If requested, report the number of tuples reclaimed to pgstats. This is
+	 * ndeleted minus ndead, because we don't want to count a now-DEAD root
+	 * item as a deletion for this purpose.
+	 */
+	if (report_stats && ndeleted > prstate.ndead)
+		pgstat_update_heap_dead_tuples(relation, ndeleted - prstate.ndead);
+
+	/*
+	 * XXX Should we update the FSM information of this page ?
+	 *
+	 * There are two schools of thought here. We may not want to update FSM
+	 * information so that the page is not used for unrelated UPDATEs/INSERTs
+	 * and any free space in this page will remain available for further
+	 * UPDATEs in *this* page, thus improving chances for doing HOT updates.
+	 *
+	 * But for a large table and where a page does not receive further UPDATEs
+	 * for a long time, we might waste this space by not updating the FSM
+	 * information. The relation may get extended and fragmented further.
+	 *
+	 * One possibility is to leave "fillfactor" worth of space in this page
+	 * and update FSM with the remaining space.
+	 */
+
+	return ndeleted;
+}
+
+
+/*
+ * Perform visibility checks for heap pruning.
+ *
+ * This is more complicated than just using GlobalVisTestIsRemovableXid()
+ * because of old_snapshot_threshold. We only want to increase the threshold
+ * that triggers errors for old snapshots when we actually decide to remove a
+ * row based on the limited horizon.
+ *
+ * Due to its cost we also only want to call
+ * TransactionIdLimitedForOldSnapshots() if necessary, i.e. we might not have
+ * done so in heap_hot_prune_opt() if pd_prune_xid was old enough. But we
+ * still want to be able to remove rows that are too new to be removed
+ * according to prstate->vistest, but that can be removed based on
+ * old_snapshot_threshold. So we call TransactionIdLimitedForOldSnapshots() on
+ * demand in here, if appropriate.
+ */
+static HTSV_Result
+heap_prune_satisfies_vacuum(PruneState *prstate, HeapTuple tup, Buffer buffer)
+{
+	HTSV_Result res;
+	TransactionId dead_after;
+
+	res = HeapTupleSatisfiesVacuumHorizon(tup, buffer, &dead_after);
+
+	if (res != HEAPTUPLE_RECENTLY_DEAD)
+		return res;
+
+	/*
+	 * If we are already relying on the limited xmin, there is no need to
+	 * delay doing so anymore.
+	 */
+	if (prstate->old_snap_used)
+	{
+		Assert(TransactionIdIsValid(prstate->old_snap_xmin));
+
+		if (TransactionIdPrecedes(dead_after, prstate->old_snap_xmin))
+			res = HEAPTUPLE_DEAD;
+		return res;
+	}
+
+	/*
+	 * First check if GlobalVisTestIsRemovableXid() is sufficient to find the
+	 * row dead. If not, and old_snapshot_threshold is enabled, try to use the
+	 * lowered horizon.
+	 */
+	if (GlobalVisTestIsRemovableXid(prstate->vistest, dead_after))
+		res = HEAPTUPLE_DEAD;
+	else if (OldSnapshotThresholdActive())
+	{
+		/* haven't determined limited horizon yet, requests */
+		if (!TransactionIdIsValid(prstate->old_snap_xmin))
+		{
+			TransactionId horizon =
+			GlobalVisTestNonRemovableHorizon(prstate->vistest);
+
+			TransactionIdLimitedForOldSnapshots(horizon, prstate->rel,
+												&prstate->old_snap_xmin,
+												&prstate->old_snap_ts);
+		}
+
+		if (TransactionIdIsValid(prstate->old_snap_xmin) &&
+			TransactionIdPrecedes(dead_after, prstate->old_snap_xmin))
+		{
+			/*
+			 * About to remove row based on snapshot_too_old. Need to raise
+			 * the threshold so problematic accesses would error.
+			 */
+			Assert(!prstate->old_snap_used);
+			SetOldSnapshotThresholdTimestamp(prstate->old_snap_ts,
+											 prstate->old_snap_xmin);
+			prstate->old_snap_used = true;
+			res = HEAPTUPLE_DEAD;
+		}
+	}
+
+	return res;
+}
+
+
+/*
+ * Prune specified line pointer or a HOT chain originating at line pointer.
+ *
+ * If the item is an index-referenced tuple (i.e. not a heap-only tuple),
+ * the HOT chain is pruned by removing all DEAD tuples at the start of the HOT
+ * chain.  We also prune any RECENTLY_DEAD tuples preceding a DEAD tuple.
+ * This is OK because a RECENTLY_DEAD tuple preceding a DEAD tuple is really
+ * DEAD, our visibility test is just too coarse to detect it.
+ *
+ * The root line pointer is redirected to the tuple immediately after the
+ * latest DEAD tuple.  If all tuples in the chain are DEAD, the root line
+ * pointer is marked LP_DEAD.  (This includes the case of a DEAD simple
+ * tuple, which we treat as a chain of length 1.)
+ *
+ * We don't actually change the page here. We just add entries to the arrays in
+ * prstate showing the changes to be made.  Items to be redirected are added
+ * to the redirected[] array (two entries per redirection); items to be set to
+ * LP_DEAD state are added to nowdead[]; and items to be set to LP_UNUSED
+ * state are added to nowunused[].
+ *
+ * Returns the number of tuples (to be) deleted from the page.
+ */
+static int
+heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum, PruneState *prstate)
+{
+	int			ndeleted = 0;
+	Page		dp = (Page) BufferGetPage(buffer);
+	TransactionId priorXmax = InvalidTransactionId;
+	ItemId		rootlp;
+	HeapTupleHeader htup;
+	OffsetNumber latestdead = InvalidOffsetNumber,
+				maxoff = PageGetMaxOffsetNumber(dp),
+				offnum;
+	OffsetNumber chainitems[MaxHeapTuplesPerPage];
+	int			nchain = 0,
+				i;
+
+	rootlp = PageGetItemId(dp, rootoffnum);
+
+	/*
+	 * If it's a heap-only tuple, then it is not the start of a HOT chain.
+	 */
+	if (ItemIdIsNormal(rootlp))
+	{
+		Assert(prstate->htsv[rootoffnum] != -1);
+		htup = (HeapTupleHeader) PageGetItem(dp, rootlp);
+
+		if (HeapTupleHeaderIsHeapOnly(htup))
+		{
+			/*
+			 * If the tuple is DEAD and doesn't chain to anything else, mark
+			 * it unused immediately.  (If it does chain, we can only remove
+			 * it as part of pruning its chain.)
+			 *
+			 * We need this primarily to handle aborted HOT updates, that is,
+			 * XMIN_INVALID heap-only tuples.  Those might not be linked to by
+			 * any chain, since the parent tuple might be re-updated before
+			 * any pruning occurs.  So we have to be able to reap them
+			 * separately from chain-pruning.  (Note that
+			 * HeapTupleHeaderIsHotUpdated will never return true for an
+			 * XMIN_INVALID tuple, so this code will work even when there were
+			 * sequential updates within the aborted transaction.)
+			 *
+			 * Note that we might first arrive at a dead heap-only tuple
+			 * either here or while following a chain below.  Whichever path
+			 * gets there first will mark the tuple unused.
+			 */
+			if (prstate->htsv[rootoffnum] == HEAPTUPLE_DEAD &&
+				!HeapTupleHeaderIsHotUpdated(htup))
+			{
+				heap_prune_record_unused(prstate, rootoffnum);
+				HeapTupleHeaderAdvanceLatestRemovedXid(htup,
+													   &prstate->latestRemovedXid);
+				ndeleted++;
+			}
+
+			/* Nothing more to do */
+			return ndeleted;
+		}
+	}
+
+	/* Start from the root tuple */
+	offnum = rootoffnum;
+
+	/* while not end of the chain */
+	for (;;)
+	{
+		ItemId		lp;
+		bool		tupdead,
+					recent_dead;
+
+		/* Some sanity checks */
+		if (offnum < FirstOffsetNumber || offnum > maxoff)
+			break;
+
+		/* If item is already processed, stop --- it must not be same chain */
+		if (prstate->marked[offnum])
+			break;
+
+		lp = PageGetItemId(dp, offnum);
+
+		/* Unused item obviously isn't part of the chain */
+		if (!ItemIdIsUsed(lp))
+			break;
+
+		/*
+		 * If we are looking at the redirected root line pointer, jump to the
+		 * first normal tuple in the chain.  If we find a redirect somewhere
+		 * else, stop --- it must not be same chain.
+		 */
+		if (ItemIdIsRedirected(lp))
+		{
+			if (nchain > 0)
+				break;			/* not at start of chain */
+			chainitems[nchain++] = offnum;
+			offnum = ItemIdGetRedirect(rootlp);
+			continue;
+		}
+
+		/*
+		 * Likewise, a dead line pointer can't be part of the chain. (We
+		 * already eliminated the case of dead root tuple outside this
+		 * function.)
+		 */
+		if (ItemIdIsDead(lp))
+			break;
+
+		Assert(ItemIdIsNormal(lp));
+		Assert(prstate->htsv[offnum] != -1);
+		htup = (HeapTupleHeader) PageGetItem(dp, lp);
+
+		/*
+		 * Check the tuple XMIN against prior XMAX, if any
+		 */
+		if (TransactionIdIsValid(priorXmax) &&
+			!TransactionIdEquals(HeapTupleHeaderGetXmin(htup), priorXmax))
+			break;
+
+		/*
+		 * OK, this tuple is indeed a member of the chain.
+		 */
+		chainitems[nchain++] = offnum;
+
+		/*
+		 * Check tuple's visibility status.
+		 */
+		tupdead = recent_dead = false;
+
+		switch ((HTSV_Result) prstate->htsv[offnum])
+		{
+			case HEAPTUPLE_DEAD:
+				tupdead = true;
+				break;
+
+			case HEAPTUPLE_RECENTLY_DEAD:
+				recent_dead = true;
+
+				/*
+				 * This tuple may soon become DEAD.  Update the hint field so
+				 * that the page is reconsidered for pruning in future.
+				 */
+				heap_prune_record_prunable(prstate,
+										   HeapTupleHeaderGetUpdateXid(htup));
+				break;
+
+			case HEAPTUPLE_DELETE_IN_PROGRESS:
+
+				/*
+				 * This tuple may soon become DEAD.  Update the hint field so
+				 * that the page is reconsidered for pruning in future.
+				 */
+				heap_prune_record_prunable(prstate,
+										   HeapTupleHeaderGetUpdateXid(htup));
+				break;
+
+			case HEAPTUPLE_LIVE:
+			case HEAPTUPLE_INSERT_IN_PROGRESS:
+
+				/*
+				 * If we wanted to optimize for aborts, we might consider
+				 * marking the page prunable when we see INSERT_IN_PROGRESS.
+				 * But we don't.  See related decisions about when to mark the
+				 * page prunable in heapam.c.
+				 */
+				break;
+
+			default:
+				elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
+				break;
+		}
+
+		/*
+		 * Remember the last DEAD tuple seen.  We will advance past
+		 * RECENTLY_DEAD tuples just in case there's a DEAD one after them;
+		 * but we can't advance past anything else.  (XXX is it really worth
+		 * continuing to scan beyond RECENTLY_DEAD?  The case where we will
+		 * find another DEAD tuple is a fairly unusual corner case.)
+		 */
+		if (tupdead)
+		{
+			latestdead = offnum;
+			HeapTupleHeaderAdvanceLatestRemovedXid(htup,
+												   &prstate->latestRemovedXid);
+		}
+		else if (!recent_dead)
+			break;
+
+		/*
+		 * If the tuple is not HOT-updated, then we are at the end of this
+		 * HOT-update chain.
+		 */
+		if (!HeapTupleHeaderIsHotUpdated(htup))
+			break;
+
+		/* HOT implies it can't have moved to different partition */
+		Assert(!HeapTupleHeaderIndicatesMovedPartitions(htup));
+
+		/*
+		 * Advance to next chain member.
+		 */
+		Assert(ItemPointerGetBlockNumber(&htup->t_ctid) ==
+			   BufferGetBlockNumber(buffer));
+		offnum = ItemPointerGetOffsetNumber(&htup->t_ctid);
+		priorXmax = HeapTupleHeaderGetUpdateXid(htup);
+	}
+
+	/*
+	 * If we found a DEAD tuple in the chain, adjust the HOT chain so that all
+	 * the DEAD tuples at the start of the chain are removed and the root line
+	 * pointer is appropriately redirected.
+	 */
+	if (OffsetNumberIsValid(latestdead))
+	{
+		/*
+		 * Mark as unused each intermediate item that we are able to remove
+		 * from the chain.
+		 *
+		 * When the previous item is the last dead tuple seen, we are at the
+		 * right candidate for redirection.
+		 */
+		for (i = 1; (i < nchain) && (chainitems[i - 1] != latestdead); i++)
+		{
+			heap_prune_record_unused(prstate, chainitems[i]);
+			ndeleted++;
+		}
+
+		/*
+		 * If the root entry had been a normal tuple, we are deleting it, so
+		 * count it in the result.  But changing a redirect (even to DEAD
+		 * state) doesn't count.
+		 */
+		if (ItemIdIsNormal(rootlp))
+			ndeleted++;
+
+		/*
+		 * If the DEAD tuple is at the end of the chain, the entire chain is
+		 * dead and the root line pointer can be marked dead.  Otherwise just
+		 * redirect the root to the correct chain member.
+		 */
+		if (i >= nchain)
+			heap_prune_record_dead(prstate, rootoffnum);
+		else
+			heap_prune_record_redirect(prstate, rootoffnum, chainitems[i]);
+	}
+	else if (nchain < 2 && ItemIdIsRedirected(rootlp))
+	{
+		/*
+		 * We found a redirect item that doesn't point to a valid follow-on
+		 * item.  This can happen if the loop in heap_page_prune caused us to
+		 * visit the dead successor of a redirect item before visiting the
+		 * redirect item.  We can clean up by setting the redirect item to
+		 * DEAD state.
+		 */
+		heap_prune_record_dead(prstate, rootoffnum);
+	}
+
+	return ndeleted;
+}
+
+/* Record lowest soon-prunable XID */
+static void
+heap_prune_record_prunable(PruneState *prstate, TransactionId xid)
+{
+	/*
+	 * This should exactly match the PageSetPrunable macro.  We can't store
+	 * directly into the page header yet, so we update working state.
+	 */
+	Assert(TransactionIdIsNormal(xid));
+	if (!TransactionIdIsValid(prstate->new_prune_xid) ||
+		TransactionIdPrecedes(xid, prstate->new_prune_xid))
+		prstate->new_prune_xid = xid;
+}
+
+/* Record line pointer to be redirected */
+static void
+heap_prune_record_redirect(PruneState *prstate,
+						   OffsetNumber offnum, OffsetNumber rdoffnum)
+{
+	Assert(prstate->nredirected < MaxHeapTuplesPerPage);
+	prstate->redirected[prstate->nredirected * 2] = offnum;
+	prstate->redirected[prstate->nredirected * 2 + 1] = rdoffnum;
+	prstate->nredirected++;
+	Assert(!prstate->marked[offnum]);
+	prstate->marked[offnum] = true;
+	Assert(!prstate->marked[rdoffnum]);
+	prstate->marked[rdoffnum] = true;
+}
+
+/* Record line pointer to be marked dead */
+static void
+heap_prune_record_dead(PruneState *prstate, OffsetNumber offnum)
+{
+	Assert(prstate->ndead < MaxHeapTuplesPerPage);
+	prstate->nowdead[prstate->ndead] = offnum;
+	prstate->ndead++;
+	Assert(!prstate->marked[offnum]);
+	prstate->marked[offnum] = true;
+}
+
+/* Record line pointer to be marked unused */
+static void
+heap_prune_record_unused(PruneState *prstate, OffsetNumber offnum)
+{
+	Assert(prstate->nunused < MaxHeapTuplesPerPage);
+	prstate->nowunused[prstate->nunused] = offnum;
+	prstate->nunused++;
+	Assert(!prstate->marked[offnum]);
+	prstate->marked[offnum] = true;
+}
+
+
+/*
+ * Perform the actual page changes needed by heap_page_prune.
+ * It is expected that the caller has a super-exclusive lock on the
+ * buffer.
+ */
+void
+heap_page_prune_execute(Buffer buffer,
+						OffsetNumber *redirected, int nredirected,
+						OffsetNumber *nowdead, int ndead,
+						OffsetNumber *nowunused, int nunused)
+{
+	Page		page = (Page) BufferGetPage(buffer);
+	OffsetNumber *offnum;
+	int			i;
+
+	/* Shouldn't be called unless there's something to do */
+	Assert(nredirected > 0 || ndead > 0 || nunused > 0);
+
+	/* Update all redirected line pointers */
+	offnum = redirected;
+	for (i = 0; i < nredirected; i++)
+	{
+		OffsetNumber fromoff = *offnum++;
+		OffsetNumber tooff = *offnum++;
+		ItemId		fromlp = PageGetItemId(page, fromoff);
+
+		ItemIdSetRedirect(fromlp, tooff);
+	}
+
+	/* Update all now-dead line pointers */
+	offnum = nowdead;
+	for (i = 0; i < ndead; i++)
+	{
+		OffsetNumber off = *offnum++;
+		ItemId		lp = PageGetItemId(page, off);
+
+		ItemIdSetDead(lp);
+	}
+
+	/* Update all now-unused line pointers */
+	offnum = nowunused;
+	for (i = 0; i < nunused; i++)
+	{
+		OffsetNumber off = *offnum++;
+		ItemId		lp = PageGetItemId(page, off);
+
+		ItemIdSetUnused(lp);
+	}
+
+	/*
+	 * Finally, repair any fragmentation, and update the page's hint bit about
+	 * whether it has free pointers.
+	 */
+	PageRepairFragmentation(page);
+}
+
+
+/*
+ * For all items in this page, find their respective root line pointers.
+ * If item k is part of a HOT-chain with root at item j, then we set
+ * root_offsets[k - 1] = j.
+ *
+ * The passed-in root_offsets array must have MaxHeapTuplesPerPage entries.
+ * Unused entries are filled with InvalidOffsetNumber (zero).
+ *
+ * The function must be called with at least share lock on the buffer, to
+ * prevent concurrent prune operations.
+ *
+ * Note: The information collected here is valid only as long as the caller
+ * holds a pin on the buffer. Once pin is released, a tuple might be pruned
+ * and reused by a completely unrelated tuple.
+ */
+void
+heap_get_root_tuples(Page page, OffsetNumber *root_offsets)
+{
+	OffsetNumber offnum,
+				maxoff;
+
+	MemSet(root_offsets, InvalidOffsetNumber,
+		   MaxHeapTuplesPerPage * sizeof(OffsetNumber));
+
+	maxoff = PageGetMaxOffsetNumber(page);
+	for (offnum = FirstOffsetNumber; offnum <= maxoff; offnum = OffsetNumberNext(offnum))
+	{
+		ItemId		lp = PageGetItemId(page, offnum);
+		HeapTupleHeader htup;
+		OffsetNumber nextoffnum;
+		TransactionId priorXmax;
+
+		/* skip unused and dead items */
+		if (!ItemIdIsUsed(lp) || ItemIdIsDead(lp))
+			continue;
+
+		if (ItemIdIsNormal(lp))
+		{
+			htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+			/*
+			 * Check if this tuple is part of a HOT-chain rooted at some other
+			 * tuple. If so, skip it for now; we'll process it when we find
+			 * its root.
+			 */
+			if (HeapTupleHeaderIsHeapOnly(htup))
+				continue;
+
+			/*
+			 * This is either a plain tuple or the root of a HOT-chain.
+			 * Remember it in the mapping.
+			 */
+			root_offsets[offnum - 1] = offnum;
+
+			/* If it's not the start of a HOT-chain, we're done with it */
+			if (!HeapTupleHeaderIsHotUpdated(htup))
+				continue;
+
+			/* Set up to scan the HOT-chain */
+			nextoffnum = ItemPointerGetOffsetNumber(&htup->t_ctid);
+			priorXmax = HeapTupleHeaderGetUpdateXid(htup);
+		}
+		else
+		{
+			/* Must be a redirect item. We do not set its root_offsets entry */
+			Assert(ItemIdIsRedirected(lp));
+			/* Set up to scan the HOT-chain */
+			nextoffnum = ItemIdGetRedirect(lp);
+			priorXmax = InvalidTransactionId;
+		}
+
+		/*
+		 * Now follow the HOT-chain and collect other tuples in the chain.
+		 *
+		 * Note: Even though this is a nested loop, the complexity of the
+		 * function is O(N) because a tuple in the page should be visited not
+		 * more than twice, once in the outer loop and once in HOT-chain
+		 * chases.
+		 */
+		for (;;)
+		{
+			/* Sanity check */
+			if (nextoffnum < FirstOffsetNumber || nextoffnum > maxoff)
+				break;
+
+			lp = PageGetItemId(page, nextoffnum);
+
+			/* Check for broken chains */
+			if (!ItemIdIsNormal(lp))
+				break;
+
+			htup = (HeapTupleHeader) PageGetItem(page, lp);
+
+			if (TransactionIdIsValid(priorXmax) &&
+				!TransactionIdEquals(priorXmax, HeapTupleHeaderGetXmin(htup)))
+				break;
+
+			/* Remember the root line pointer for this item */
+			root_offsets[nextoffnum - 1] = offnum;
+
+			/* Advance to next chain member, if any */
+			if (!HeapTupleHeaderIsHotUpdated(htup))
+				break;
+
+			/* HOT implies it can't have moved to different partition */
+			Assert(!HeapTupleHeaderIndicatesMovedPartitions(htup));
+
+			nextoffnum = ItemPointerGetOffsetNumber(&htup->t_ctid);
+			priorXmax = HeapTupleHeaderGetUpdateXid(htup);
+		}
+	}
+}
diff --git a/src/backend/access/heap/rewriteheap.c b/src/backend/access/heap/rewriteheap.c
new file mode 100644
index 0000000..15bef9f
--- /dev/null
+++ b/src/backend/access/heap/rewriteheap.c
@@ -0,0 +1,1295 @@
+/*-------------------------------------------------------------------------
+ *
+ * rewriteheap.c
+ *	  Support functions to rewrite tables.
+ *
+ * These functions provide a facility to completely rewrite a heap, while
+ * preserving visibility information and update chains.
+ *
+ * INTERFACE
+ *
+ * The caller is responsible for creating the new heap, all catalog
+ * changes, supplying the tuples to be written to the new heap, and
+ * rebuilding indexes.  The caller must hold AccessExclusiveLock on the
+ * target table, because we assume no one else is writing into it.
+ *
+ * To use the facility:
+ *
+ * begin_heap_rewrite
+ * while (fetch next tuple)
+ * {
+ *	   if (tuple is dead)
+ *		   rewrite_heap_dead_tuple
+ *	   else
+ *	   {
+ *		   // do any transformations here if required
+ *		   rewrite_heap_tuple
+ *	   }
+ * }
+ * end_heap_rewrite
+ *
+ * The contents of the new relation shouldn't be relied on until after
+ * end_heap_rewrite is called.
+ *
+ *
+ * IMPLEMENTATION
+ *
+ * This would be a fairly trivial affair, except that we need to maintain
+ * the ctid chains that link versions of an updated tuple together.
+ * Since the newly stored tuples will have tids different from the original
+ * ones, if we just copied t_ctid fields to the new table the links would
+ * be wrong.  When we are required to copy a (presumably recently-dead or
+ * delete-in-progress) tuple whose ctid doesn't point to itself, we have
+ * to substitute the correct ctid instead.
+ *
+ * For each ctid reference from A -> B, we might encounter either A first
+ * or B first.  (Note that a tuple in the middle of a chain is both A and B
+ * of different pairs.)
+ *
+ * If we encounter A first, we'll store the tuple in the unresolved_tups
+ * hash table. When we later encounter B, we remove A from the hash table,
+ * fix the ctid to point to the new location of B, and insert both A and B
+ * to the new heap.
+ *
+ * If we encounter B first, we can insert B to the new heap right away.
+ * We then add an entry to the old_new_tid_map hash table showing B's
+ * original tid (in the old heap) and new tid (in the new heap).
+ * When we later encounter A, we get the new location of B from the table,
+ * and can write A immediately with the correct ctid.
+ *
+ * Entries in the hash tables can be removed as soon as the later tuple
+ * is encountered.  That helps to keep the memory usage down.  At the end,
+ * both tables are usually empty; we should have encountered both A and B
+ * of each pair.  However, it's possible for A to be RECENTLY_DEAD and B
+ * entirely DEAD according to HeapTupleSatisfiesVacuum, because the test
+ * for deadness using OldestXmin is not exact.  In such a case we might
+ * encounter B first, and skip it, and find A later.  Then A would be added
+ * to unresolved_tups, and stay there until end of the rewrite.  Since
+ * this case is very unusual, we don't worry about the memory usage.
+ *
+ * Using in-memory hash tables means that we use some memory for each live
+ * update chain in the table, from the time we find one end of the
+ * reference until we find the other end.  That shouldn't be a problem in
+ * practice, but if you do something like an UPDATE without a where-clause
+ * on a large table, and then run CLUSTER in the same transaction, you
+ * could run out of memory.  It doesn't seem worthwhile to add support for
+ * spill-to-disk, as there shouldn't be that many RECENTLY_DEAD tuples in a
+ * table under normal circumstances.  Furthermore, in the typical scenario
+ * of CLUSTERing on an unchanging key column, we'll see all the versions
+ * of a given tuple together anyway, and so the peak memory usage is only
+ * proportional to the number of RECENTLY_DEAD versions of a single row, not
+ * in the whole table.  Note that if we do fail halfway through a CLUSTER,
+ * the old table is still valid, so failure is not catastrophic.
+ *
+ * We can't use the normal heap_insert function to insert into the new
+ * heap, because heap_insert overwrites the visibility information.
+ * We use a special-purpose raw_heap_insert function instead, which
+ * is optimized for bulk inserting a lot of tuples, knowing that we have
+ * exclusive access to the heap.  raw_heap_insert builds new pages in
+ * local storage.  When a page is full, or at the end of the process,
+ * we insert it to WAL as a single record and then write it to disk
+ * directly through smgr.  Note, however, that any data sent to the new
+ * heap's TOAST table will go through the normal bufmgr.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994-5, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/heap/rewriteheap.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "access/heapam.h"
+#include "access/heapam_xlog.h"
+#include "access/heaptoast.h"
+#include "access/rewriteheap.h"
+#include "access/transam.h"
+#include "access/xact.h"
+#include "access/xloginsert.h"
+#include "catalog/catalog.h"
+#include "lib/ilist.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "replication/logical.h"
+#include "replication/slot.h"
+#include "storage/bufmgr.h"
+#include "storage/fd.h"
+#include "storage/procarray.h"
+#include "storage/smgr.h"
+#include "utils/memutils.h"
+#include "utils/rel.h"
+
+/*
+ * State associated with a rewrite operation. This is opaque to the user
+ * of the rewrite facility.
+ */
+typedef struct RewriteStateData
+{
+	Relation	rs_old_rel;		/* source heap */
+	Relation	rs_new_rel;		/* destination heap */
+	Page		rs_buffer;		/* page currently being built */
+	BlockNumber rs_blockno;		/* block where page will go */
+	bool		rs_buffer_valid;	/* T if any tuples in buffer */
+	bool		rs_logical_rewrite; /* do we need to do logical rewriting */
+	TransactionId rs_oldest_xmin;	/* oldest xmin used by caller to determine
+									 * tuple visibility */
+	TransactionId rs_freeze_xid;	/* Xid that will be used as freeze cutoff
+									 * point */
+	TransactionId rs_logical_xmin;	/* Xid that will be used as cutoff point
+									 * for logical rewrites */
+	MultiXactId rs_cutoff_multi;	/* MultiXactId that will be used as cutoff
+									 * point for multixacts */
+	MemoryContext rs_cxt;		/* for hash tables and entries and tuples in
+								 * them */
+	XLogRecPtr	rs_begin_lsn;	/* XLogInsertLsn when starting the rewrite */
+	HTAB	   *rs_unresolved_tups; /* unmatched A tuples */
+	HTAB	   *rs_old_new_tid_map; /* unmatched B tuples */
+	HTAB	   *rs_logical_mappings;	/* logical remapping files */
+	uint32		rs_num_rewrite_mappings;	/* # in memory mappings */
+}			RewriteStateData;
+
+/*
+ * The lookup keys for the hash tables are tuple TID and xmin (we must check
+ * both to avoid false matches from dead tuples).  Beware that there is
+ * probably some padding space in this struct; it must be zeroed out for
+ * correct hashtable operation.
+ */
+typedef struct
+{
+	TransactionId xmin;			/* tuple xmin */
+	ItemPointerData tid;		/* tuple location in old heap */
+} TidHashKey;
+
+/*
+ * Entry structures for the hash tables
+ */
+typedef struct
+{
+	TidHashKey	key;			/* expected xmin/old location of B tuple */
+	ItemPointerData old_tid;	/* A's location in the old heap */
+	HeapTuple	tuple;			/* A's tuple contents */
+} UnresolvedTupData;
+
+typedef UnresolvedTupData *UnresolvedTup;
+
+typedef struct
+{
+	TidHashKey	key;			/* actual xmin/old location of B tuple */
+	ItemPointerData new_tid;	/* where we put it in the new heap */
+} OldToNewMappingData;
+
+typedef OldToNewMappingData *OldToNewMapping;
+
+/*
+ * In-Memory data for an xid that might need logical remapping entries
+ * to be logged.
+ */
+typedef struct RewriteMappingFile
+{
+	TransactionId xid;			/* xid that might need to see the row */
+	int			vfd;			/* fd of mappings file */
+	off_t		off;			/* how far have we written yet */
+	uint32		num_mappings;	/* number of in-memory mappings */
+	dlist_head	mappings;		/* list of in-memory mappings */
+	char		path[MAXPGPATH];	/* path, for error messages */
+} RewriteMappingFile;
+
+/*
+ * A single In-Memory logical rewrite mapping, hanging off
+ * RewriteMappingFile->mappings.
+ */
+typedef struct RewriteMappingDataEntry
+{
+	LogicalRewriteMappingData map;	/* map between old and new location of the
+									 * tuple */
+	dlist_node	node;
+} RewriteMappingDataEntry;
+
+
+/* prototypes for internal functions */
+static void raw_heap_insert(RewriteState state, HeapTuple tup);
+
+/* internal logical remapping prototypes */
+static void logical_begin_heap_rewrite(RewriteState state);
+static void logical_rewrite_heap_tuple(RewriteState state, ItemPointerData old_tid, HeapTuple new_tuple);
+static void logical_end_heap_rewrite(RewriteState state);
+
+
+/*
+ * Begin a rewrite of a table
+ *
+ * old_heap		old, locked heap relation tuples will be read from
+ * new_heap		new, locked heap relation to insert tuples to
+ * oldest_xmin	xid used by the caller to determine which tuples are dead
+ * freeze_xid	xid before which tuples will be frozen
+ * cutoff_multi	multixact before which multis will be removed
+ *
+ * Returns an opaque RewriteState, allocated in current memory context,
+ * to be used in subsequent calls to the other functions.
+ */
+RewriteState
+begin_heap_rewrite(Relation old_heap, Relation new_heap, TransactionId oldest_xmin,
+				   TransactionId freeze_xid, MultiXactId cutoff_multi)
+{
+	RewriteState state;
+	MemoryContext rw_cxt;
+	MemoryContext old_cxt;
+	HASHCTL		hash_ctl;
+
+	/*
+	 * To ease cleanup, make a separate context that will contain the
+	 * RewriteState struct itself plus all subsidiary data.
+	 */
+	rw_cxt = AllocSetContextCreate(CurrentMemoryContext,
+								   "Table rewrite",
+								   ALLOCSET_DEFAULT_SIZES);
+	old_cxt = MemoryContextSwitchTo(rw_cxt);
+
+	/* Create and fill in the state struct */
+	state = palloc0(sizeof(RewriteStateData));
+
+	state->rs_old_rel = old_heap;
+	state->rs_new_rel = new_heap;
+	state->rs_buffer = (Page) palloc(BLCKSZ);
+	/* new_heap needn't be empty, just locked */
+	state->rs_blockno = RelationGetNumberOfBlocks(new_heap);
+	state->rs_buffer_valid = false;
+	state->rs_oldest_xmin = oldest_xmin;
+	state->rs_freeze_xid = freeze_xid;
+	state->rs_cutoff_multi = cutoff_multi;
+	state->rs_cxt = rw_cxt;
+
+	/* Initialize hash tables used to track update chains */
+	hash_ctl.keysize = sizeof(TidHashKey);
+	hash_ctl.entrysize = sizeof(UnresolvedTupData);
+	hash_ctl.hcxt = state->rs_cxt;
+
+	state->rs_unresolved_tups =
+		hash_create("Rewrite / Unresolved ctids",
+					128,		/* arbitrary initial size */
+					&hash_ctl,
+					HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	hash_ctl.entrysize = sizeof(OldToNewMappingData);
+
+	state->rs_old_new_tid_map =
+		hash_create("Rewrite / Old to new tid map",
+					128,		/* arbitrary initial size */
+					&hash_ctl,
+					HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	MemoryContextSwitchTo(old_cxt);
+
+	logical_begin_heap_rewrite(state);
+
+	return state;
+}
+
+/*
+ * End a rewrite.
+ *
+ * state and any other resources are freed.
+ */
+void
+end_heap_rewrite(RewriteState state)
+{
+	HASH_SEQ_STATUS seq_status;
+	UnresolvedTup unresolved;
+
+	/*
+	 * Write any remaining tuples in the UnresolvedTups table. If we have any
+	 * left, they should in fact be dead, but let's err on the safe side.
+	 */
+	hash_seq_init(&seq_status, state->rs_unresolved_tups);
+
+	while ((unresolved = hash_seq_search(&seq_status)) != NULL)
+	{
+		ItemPointerSetInvalid(&unresolved->tuple->t_data->t_ctid);
+		raw_heap_insert(state, unresolved->tuple);
+	}
+
+	/* Write the last page, if any */
+	if (state->rs_buffer_valid)
+	{
+		if (RelationNeedsWAL(state->rs_new_rel))
+			log_newpage(&state->rs_new_rel->rd_node,
+						MAIN_FORKNUM,
+						state->rs_blockno,
+						state->rs_buffer,
+						true);
+
+		PageSetChecksumInplace(state->rs_buffer, state->rs_blockno);
+
+		RelationOpenSmgr(state->rs_new_rel);
+		smgrextend(state->rs_new_rel->rd_smgr, MAIN_FORKNUM, state->rs_blockno,
+				   (char *) state->rs_buffer, true);
+	}
+
+	/*
+	 * When we WAL-logged rel pages, we must nonetheless fsync them.  The
+	 * reason is the same as in storage.c's RelationCopyStorage(): we're
+	 * writing data that's not in shared buffers, and so a CHECKPOINT
+	 * occurring during the rewriteheap operation won't have fsync'd data we
+	 * wrote before the checkpoint.
+	 */
+	if (RelationNeedsWAL(state->rs_new_rel))
+	{
+		/* for an empty table, this could be first smgr access */
+		RelationOpenSmgr(state->rs_new_rel);
+		smgrimmedsync(state->rs_new_rel->rd_smgr, MAIN_FORKNUM);
+	}
+
+	logical_end_heap_rewrite(state);
+
+	/* Deleting the context frees everything */
+	MemoryContextDelete(state->rs_cxt);
+}
+
+/*
+ * Add a tuple to the new heap.
+ *
+ * Visibility information is copied from the original tuple, except that
+ * we "freeze" very-old tuples.  Note that since we scribble on new_tuple,
+ * it had better be temp storage not a pointer to the original tuple.
+ *
+ * state		opaque state as returned by begin_heap_rewrite
+ * old_tuple	original tuple in the old heap
+ * new_tuple	new, rewritten tuple to be inserted to new heap
+ */
+void
+rewrite_heap_tuple(RewriteState state,
+				   HeapTuple old_tuple, HeapTuple new_tuple)
+{
+	MemoryContext old_cxt;
+	ItemPointerData old_tid;
+	TidHashKey	hashkey;
+	bool		found;
+	bool		free_new;
+
+	old_cxt = MemoryContextSwitchTo(state->rs_cxt);
+
+	/*
+	 * Copy the original tuple's visibility information into new_tuple.
+	 *
+	 * XXX we might later need to copy some t_infomask2 bits, too? Right now,
+	 * we intentionally clear the HOT status bits.
+	 */
+	memcpy(&new_tuple->t_data->t_choice.t_heap,
+		   &old_tuple->t_data->t_choice.t_heap,
+		   sizeof(HeapTupleFields));
+
+	new_tuple->t_data->t_infomask &= ~HEAP_XACT_MASK;
+	new_tuple->t_data->t_infomask2 &= ~HEAP2_XACT_MASK;
+	new_tuple->t_data->t_infomask |=
+		old_tuple->t_data->t_infomask & HEAP_XACT_MASK;
+
+	/*
+	 * While we have our hands on the tuple, we may as well freeze any
+	 * eligible xmin or xmax, so that future VACUUM effort can be saved.
+	 */
+	heap_freeze_tuple(new_tuple->t_data,
+					  state->rs_old_rel->rd_rel->relfrozenxid,
+					  state->rs_old_rel->rd_rel->relminmxid,
+					  state->rs_freeze_xid,
+					  state->rs_cutoff_multi);
+
+	/*
+	 * Invalid ctid means that ctid should point to the tuple itself. We'll
+	 * override it later if the tuple is part of an update chain.
+	 */
+	ItemPointerSetInvalid(&new_tuple->t_data->t_ctid);
+
+	/*
+	 * If the tuple has been updated, check the old-to-new mapping hash table.
+	 */
+	if (!((old_tuple->t_data->t_infomask & HEAP_XMAX_INVALID) ||
+		  HeapTupleHeaderIsOnlyLocked(old_tuple->t_data)) &&
+		!HeapTupleHeaderIndicatesMovedPartitions(old_tuple->t_data) &&
+		!(ItemPointerEquals(&(old_tuple->t_self),
+							&(old_tuple->t_data->t_ctid))))
+	{
+		OldToNewMapping mapping;
+
+		memset(&hashkey, 0, sizeof(hashkey));
+		hashkey.xmin = HeapTupleHeaderGetUpdateXid(old_tuple->t_data);
+		hashkey.tid = old_tuple->t_data->t_ctid;
+
+		mapping = (OldToNewMapping)
+			hash_search(state->rs_old_new_tid_map, &hashkey,
+						HASH_FIND, NULL);
+
+		if (mapping != NULL)
+		{
+			/*
+			 * We've already copied the tuple that t_ctid points to, so we can
+			 * set the ctid of this tuple to point to the new location, and
+			 * insert it right away.
+			 */
+			new_tuple->t_data->t_ctid = mapping->new_tid;
+
+			/* We don't need the mapping entry anymore */
+			hash_search(state->rs_old_new_tid_map, &hashkey,
+						HASH_REMOVE, &found);
+			Assert(found);
+		}
+		else
+		{
+			/*
+			 * We haven't seen the tuple t_ctid points to yet. Stash this
+			 * tuple into unresolved_tups to be written later.
+			 */
+			UnresolvedTup unresolved;
+
+			unresolved = hash_search(state->rs_unresolved_tups, &hashkey,
+									 HASH_ENTER, &found);
+			Assert(!found);
+
+			unresolved->old_tid = old_tuple->t_self;
+			unresolved->tuple = heap_copytuple(new_tuple);
+
+			/*
+			 * We can't do anything more now, since we don't know where the
+			 * tuple will be written.
+			 */
+			MemoryContextSwitchTo(old_cxt);
+			return;
+		}
+	}
+
+	/*
+	 * Now we will write the tuple, and then check to see if it is the B tuple
+	 * in any new or known pair.  When we resolve a known pair, we will be
+	 * able to write that pair's A tuple, and then we have to check if it
+	 * resolves some other pair.  Hence, we need a loop here.
+	 */
+	old_tid = old_tuple->t_self;
+	free_new = false;
+
+	for (;;)
+	{
+		ItemPointerData new_tid;
+
+		/* Insert the tuple and find out where it's put in new_heap */
+		raw_heap_insert(state, new_tuple);
+		new_tid = new_tuple->t_self;
+
+		logical_rewrite_heap_tuple(state, old_tid, new_tuple);
+
+		/*
+		 * If the tuple is the updated version of a row, and the prior version
+		 * wouldn't be DEAD yet, then we need to either resolve the prior
+		 * version (if it's waiting in rs_unresolved_tups), or make an entry
+		 * in rs_old_new_tid_map (so we can resolve it when we do see it). The
+		 * previous tuple's xmax would equal this one's xmin, so it's
+		 * RECENTLY_DEAD if and only if the xmin is not before OldestXmin.
+		 */
+		if ((new_tuple->t_data->t_infomask & HEAP_UPDATED) &&
+			!TransactionIdPrecedes(HeapTupleHeaderGetXmin(new_tuple->t_data),
+								   state->rs_oldest_xmin))
+		{
+			/*
+			 * Okay, this is B in an update pair.  See if we've seen A.
+			 */
+			UnresolvedTup unresolved;
+
+			memset(&hashkey, 0, sizeof(hashkey));
+			hashkey.xmin = HeapTupleHeaderGetXmin(new_tuple->t_data);
+			hashkey.tid = old_tid;
+
+			unresolved = hash_search(state->rs_unresolved_tups, &hashkey,
+									 HASH_FIND, NULL);
+
+			if (unresolved != NULL)
+			{
+				/*
+				 * We have seen and memorized the previous tuple already. Now
+				 * that we know where we inserted the tuple its t_ctid points
+				 * to, fix its t_ctid and insert it to the new heap.
+				 */
+				if (free_new)
+					heap_freetuple(new_tuple);
+				new_tuple = unresolved->tuple;
+				free_new = true;
+				old_tid = unresolved->old_tid;
+				new_tuple->t_data->t_ctid = new_tid;
+
+				/*
+				 * We don't need the hash entry anymore, but don't free its
+				 * tuple just yet.
+				 */
+				hash_search(state->rs_unresolved_tups, &hashkey,
+							HASH_REMOVE, &found);
+				Assert(found);
+
+				/* loop back to insert the previous tuple in the chain */
+				continue;
+			}
+			else
+			{
+				/*
+				 * Remember the new tid of this tuple. We'll use it to set the
+				 * ctid when we find the previous tuple in the chain.
+				 */
+				OldToNewMapping mapping;
+
+				mapping = hash_search(state->rs_old_new_tid_map, &hashkey,
+									  HASH_ENTER, &found);
+				Assert(!found);
+
+				mapping->new_tid = new_tid;
+			}
+		}
+
+		/* Done with this (chain of) tuples, for now */
+		if (free_new)
+			heap_freetuple(new_tuple);
+		break;
+	}
+
+	MemoryContextSwitchTo(old_cxt);
+}
+
+/*
+ * Register a dead tuple with an ongoing rewrite. Dead tuples are not
+ * copied to the new table, but we still make note of them so that we
+ * can release some resources earlier.
+ *
+ * Returns true if a tuple was removed from the unresolved_tups table.
+ * This indicates that that tuple, previously thought to be "recently dead",
+ * is now known really dead and won't be written to the output.
+ */
+bool
+rewrite_heap_dead_tuple(RewriteState state, HeapTuple old_tuple)
+{
+	/*
+	 * If we have already seen an earlier tuple in the update chain that
+	 * points to this tuple, let's forget about that earlier tuple. It's in
+	 * fact dead as well, our simple xmax < OldestXmin test in
+	 * HeapTupleSatisfiesVacuum just wasn't enough to detect it. It happens
+	 * when xmin of a tuple is greater than xmax, which sounds
+	 * counter-intuitive but is perfectly valid.
+	 *
+	 * We don't bother to try to detect the situation the other way round,
+	 * when we encounter the dead tuple first and then the recently dead one
+	 * that points to it. If that happens, we'll have some unmatched entries
+	 * in the UnresolvedTups hash table at the end. That can happen anyway,
+	 * because a vacuum might have removed the dead tuple in the chain before
+	 * us.
+	 */
+	UnresolvedTup unresolved;
+	TidHashKey	hashkey;
+	bool		found;
+
+	memset(&hashkey, 0, sizeof(hashkey));
+	hashkey.xmin = HeapTupleHeaderGetXmin(old_tuple->t_data);
+	hashkey.tid = old_tuple->t_self;
+
+	unresolved = hash_search(state->rs_unresolved_tups, &hashkey,
+							 HASH_FIND, NULL);
+
+	if (unresolved != NULL)
+	{
+		/* Need to free the contained tuple as well as the hashtable entry */
+		heap_freetuple(unresolved->tuple);
+		hash_search(state->rs_unresolved_tups, &hashkey,
+					HASH_REMOVE, &found);
+		Assert(found);
+		return true;
+	}
+
+	return false;
+}
+
+/*
+ * Insert a tuple to the new relation.  This has to track heap_insert
+ * and its subsidiary functions!
+ *
+ * t_self of the tuple is set to the new TID of the tuple. If t_ctid of the
+ * tuple is invalid on entry, it's replaced with the new TID as well (in
+ * the inserted data only, not in the caller's copy).
+ */
+static void
+raw_heap_insert(RewriteState state, HeapTuple tup)
+{
+	Page		page = state->rs_buffer;
+	Size		pageFreeSpace,
+				saveFreeSpace;
+	Size		len;
+	OffsetNumber newoff;
+	HeapTuple	heaptup;
+
+	/*
+	 * If the new tuple is too big for storage or contains already toasted
+	 * out-of-line attributes from some other relation, invoke the toaster.
+	 *
+	 * Note: below this point, heaptup is the data we actually intend to store
+	 * into the relation; tup is the caller's original untoasted data.
+	 */
+	if (state->rs_new_rel->rd_rel->relkind == RELKIND_TOASTVALUE)
+	{
+		/* toast table entries should never be recursively toasted */
+		Assert(!HeapTupleHasExternal(tup));
+		heaptup = tup;
+	}
+	else if (HeapTupleHasExternal(tup) || tup->t_len > TOAST_TUPLE_THRESHOLD)
+	{
+		int			options = HEAP_INSERT_SKIP_FSM;
+
+		/*
+		 * While rewriting the heap for VACUUM FULL / CLUSTER, make sure data
+		 * for the TOAST table are not logically decoded.  The main heap is
+		 * WAL-logged as XLOG FPI records, which are not logically decoded.
+		 */
+		options |= HEAP_INSERT_NO_LOGICAL;
+
+		heaptup = heap_toast_insert_or_update(state->rs_new_rel, tup, NULL,
+											  options);
+	}
+	else
+		heaptup = tup;
+
+	len = MAXALIGN(heaptup->t_len); /* be conservative */
+
+	/*
+	 * If we're gonna fail for oversize tuple, do it right away
+	 */
+	if (len > MaxHeapTupleSize)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("row is too big: size %zu, maximum size %zu",
+						len, MaxHeapTupleSize)));
+
+	/* Compute desired extra freespace due to fillfactor option */
+	saveFreeSpace = RelationGetTargetPageFreeSpace(state->rs_new_rel,
+												   HEAP_DEFAULT_FILLFACTOR);
+
+	/* Now we can check to see if there's enough free space already. */
+	if (state->rs_buffer_valid)
+	{
+		pageFreeSpace = PageGetHeapFreeSpace(page);
+
+		if (len + saveFreeSpace > pageFreeSpace)
+		{
+			/*
+			 * Doesn't fit, so write out the existing page.  It always
+			 * contains a tuple.  Hence, unlike RelationGetBufferForTuple(),
+			 * enforce saveFreeSpace unconditionally.
+			 */
+
+			/* XLOG stuff */
+			if (RelationNeedsWAL(state->rs_new_rel))
+				log_newpage(&state->rs_new_rel->rd_node,
+							MAIN_FORKNUM,
+							state->rs_blockno,
+							page,
+							true);
+
+			/*
+			 * Now write the page. We say skipFsync = true because there's no
+			 * need for smgr to schedule an fsync for this write; we'll do it
+			 * ourselves in end_heap_rewrite.
+			 */
+			RelationOpenSmgr(state->rs_new_rel);
+
+			PageSetChecksumInplace(page, state->rs_blockno);
+
+			smgrextend(state->rs_new_rel->rd_smgr, MAIN_FORKNUM,
+					   state->rs_blockno, (char *) page, true);
+
+			state->rs_blockno++;
+			state->rs_buffer_valid = false;
+		}
+	}
+
+	if (!state->rs_buffer_valid)
+	{
+		/* Initialize a new empty page */
+		PageInit(page, BLCKSZ, 0);
+		state->rs_buffer_valid = true;
+	}
+
+	/* And now we can insert the tuple into the page */
+	newoff = PageAddItem(page, (Item) heaptup->t_data, heaptup->t_len,
+						 InvalidOffsetNumber, false, true);
+	if (newoff == InvalidOffsetNumber)
+		elog(ERROR, "failed to add tuple");
+
+	/* Update caller's t_self to the actual position where it was stored */
+	ItemPointerSet(&(tup->t_self), state->rs_blockno, newoff);
+
+	/*
+	 * Insert the correct position into CTID of the stored tuple, too, if the
+	 * caller didn't supply a valid CTID.
+	 */
+	if (!ItemPointerIsValid(&tup->t_data->t_ctid))
+	{
+		ItemId		newitemid;
+		HeapTupleHeader onpage_tup;
+
+		newitemid = PageGetItemId(page, newoff);
+		onpage_tup = (HeapTupleHeader) PageGetItem(page, newitemid);
+
+		onpage_tup->t_ctid = tup->t_self;
+	}
+
+	/* If heaptup is a private copy, release it. */
+	if (heaptup != tup)
+		heap_freetuple(heaptup);
+}
+
+/* ------------------------------------------------------------------------
+ * Logical rewrite support
+ *
+ * When doing logical decoding - which relies on using cmin/cmax of catalog
+ * tuples, via xl_heap_new_cid records - heap rewrites have to log enough
+ * information to allow the decoding backend to updates its internal mapping
+ * of (relfilenode,ctid) => (cmin, cmax) to be correct for the rewritten heap.
+ *
+ * For that, every time we find a tuple that's been modified in a catalog
+ * relation within the xmin horizon of any decoding slot, we log a mapping
+ * from the old to the new location.
+ *
+ * To deal with rewrites that abort the filename of a mapping file contains
+ * the xid of the transaction performing the rewrite, which then can be
+ * checked before being read in.
+ *
+ * For efficiency we don't immediately spill every single map mapping for a
+ * row to disk but only do so in batches when we've collected several of them
+ * in memory or when end_heap_rewrite() has been called.
+ *
+ * Crash-Safety: This module diverts from the usual patterns of doing WAL
+ * since it cannot rely on checkpoint flushing out all buffers and thus
+ * waiting for exclusive locks on buffers. Usually the XLogInsert() covering
+ * buffer modifications is performed while the buffer(s) that are being
+ * modified are exclusively locked guaranteeing that both the WAL record and
+ * the modified heap are on either side of the checkpoint. But since the
+ * mapping files we log aren't in shared_buffers that interlock doesn't work.
+ *
+ * Instead we simply write the mapping files out to disk, *before* the
+ * XLogInsert() is performed. That guarantees that either the XLogInsert() is
+ * inserted after the checkpoint's redo pointer or that the checkpoint (via
+ * CheckPointLogicalRewriteHeap()) has flushed the (partial) mapping file to
+ * disk. That leaves the tail end that has not yet been flushed open to
+ * corruption, which is solved by including the current offset in the
+ * xl_heap_rewrite_mapping records and truncating the mapping file to it
+ * during replay. Every time a rewrite is finished all generated mapping files
+ * are synced to disk.
+ *
+ * Note that if we were only concerned about crash safety we wouldn't have to
+ * deal with WAL logging at all - an fsync() at the end of a rewrite would be
+ * sufficient for crash safety. Any mapping that hasn't been safely flushed to
+ * disk has to be by an aborted (explicitly or via a crash) transaction and is
+ * ignored by virtue of the xid in its name being subject to a
+ * TransactionDidCommit() check. But we want to support having standbys via
+ * physical replication, both for availability and to do logical decoding
+ * there.
+ * ------------------------------------------------------------------------
+ */
+
+/*
+ * Do preparations for logging logical mappings during a rewrite if
+ * necessary. If we detect that we don't need to log anything we'll prevent
+ * any further action by the various logical rewrite functions.
+ */
+static void
+logical_begin_heap_rewrite(RewriteState state)
+{
+	HASHCTL		hash_ctl;
+	TransactionId logical_xmin;
+
+	/*
+	 * We only need to persist these mappings if the rewritten table can be
+	 * accessed during logical decoding, if not, we can skip doing any
+	 * additional work.
+	 */
+	state->rs_logical_rewrite =
+		RelationIsAccessibleInLogicalDecoding(state->rs_old_rel);
+
+	if (!state->rs_logical_rewrite)
+		return;
+
+	ProcArrayGetReplicationSlotXmin(NULL, &logical_xmin);
+
+	/*
+	 * If there are no logical slots in progress we don't need to do anything,
+	 * there cannot be any remappings for relevant rows yet. The relation's
+	 * lock protects us against races.
+	 */
+	if (logical_xmin == InvalidTransactionId)
+	{
+		state->rs_logical_rewrite = false;
+		return;
+	}
+
+	state->rs_logical_xmin = logical_xmin;
+	state->rs_begin_lsn = GetXLogInsertRecPtr();
+	state->rs_num_rewrite_mappings = 0;
+
+	hash_ctl.keysize = sizeof(TransactionId);
+	hash_ctl.entrysize = sizeof(RewriteMappingFile);
+	hash_ctl.hcxt = state->rs_cxt;
+
+	state->rs_logical_mappings =
+		hash_create("Logical rewrite mapping",
+					128,		/* arbitrary initial size */
+					&hash_ctl,
+					HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+}
+
+/*
+ * Flush all logical in-memory mappings to disk, but don't fsync them yet.
+ */
+static void
+logical_heap_rewrite_flush_mappings(RewriteState state)
+{
+	HASH_SEQ_STATUS seq_status;
+	RewriteMappingFile *src;
+	dlist_mutable_iter iter;
+
+	Assert(state->rs_logical_rewrite);
+
+	/* no logical rewrite in progress, no need to iterate over mappings */
+	if (state->rs_num_rewrite_mappings == 0)
+		return;
+
+	elog(DEBUG1, "flushing %u logical rewrite mapping entries",
+		 state->rs_num_rewrite_mappings);
+
+	hash_seq_init(&seq_status, state->rs_logical_mappings);
+	while ((src = (RewriteMappingFile *) hash_seq_search(&seq_status)) != NULL)
+	{
+		char	   *waldata;
+		char	   *waldata_start;
+		xl_heap_rewrite_mapping xlrec;
+		Oid			dboid;
+		uint32		len;
+		int			written;
+
+		/* this file hasn't got any new mappings */
+		if (src->num_mappings == 0)
+			continue;
+
+		if (state->rs_old_rel->rd_rel->relisshared)
+			dboid = InvalidOid;
+		else
+			dboid = MyDatabaseId;
+
+		xlrec.num_mappings = src->num_mappings;
+		xlrec.mapped_rel = RelationGetRelid(state->rs_old_rel);
+		xlrec.mapped_xid = src->xid;
+		xlrec.mapped_db = dboid;
+		xlrec.offset = src->off;
+		xlrec.start_lsn = state->rs_begin_lsn;
+
+		/* write all mappings consecutively */
+		len = src->num_mappings * sizeof(LogicalRewriteMappingData);
+		waldata_start = waldata = palloc(len);
+
+		/*
+		 * collect data we need to write out, but don't modify ondisk data yet
+		 */
+		dlist_foreach_modify(iter, &src->mappings)
+		{
+			RewriteMappingDataEntry *pmap;
+
+			pmap = dlist_container(RewriteMappingDataEntry, node, iter.cur);
+
+			memcpy(waldata, &pmap->map, sizeof(pmap->map));
+			waldata += sizeof(pmap->map);
+
+			/* remove from the list and free */
+			dlist_delete(&pmap->node);
+			pfree(pmap);
+
+			/* update bookkeeping */
+			state->rs_num_rewrite_mappings--;
+			src->num_mappings--;
+		}
+
+		Assert(src->num_mappings == 0);
+		Assert(waldata == waldata_start + len);
+
+		/*
+		 * Note that we deviate from the usual WAL coding practices here,
+		 * check the above "Logical rewrite support" comment for reasoning.
+		 */
+		written = FileWrite(src->vfd, waldata_start, len, src->off,
+							WAIT_EVENT_LOGICAL_REWRITE_WRITE);
+		if (written != len)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not write to file \"%s\", wrote %d of %d: %m", src->path,
+							written, len)));
+		src->off += len;
+
+		XLogBeginInsert();
+		XLogRegisterData((char *) (&xlrec), sizeof(xlrec));
+		XLogRegisterData(waldata_start, len);
+
+		/* write xlog record */
+		XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_REWRITE);
+
+		pfree(waldata_start);
+	}
+	Assert(state->rs_num_rewrite_mappings == 0);
+}
+
+/*
+ * Logical remapping part of end_heap_rewrite().
+ */
+static void
+logical_end_heap_rewrite(RewriteState state)
+{
+	HASH_SEQ_STATUS seq_status;
+	RewriteMappingFile *src;
+
+	/* done, no logical rewrite in progress */
+	if (!state->rs_logical_rewrite)
+		return;
+
+	/* writeout remaining in-memory entries */
+	if (state->rs_num_rewrite_mappings > 0)
+		logical_heap_rewrite_flush_mappings(state);
+
+	/* Iterate over all mappings we have written and fsync the files. */
+	hash_seq_init(&seq_status, state->rs_logical_mappings);
+	while ((src = (RewriteMappingFile *) hash_seq_search(&seq_status)) != NULL)
+	{
+		if (FileSync(src->vfd, WAIT_EVENT_LOGICAL_REWRITE_SYNC) != 0)
+			ereport(data_sync_elevel(ERROR),
+					(errcode_for_file_access(),
+					 errmsg("could not fsync file \"%s\": %m", src->path)));
+		FileClose(src->vfd);
+	}
+	/* memory context cleanup will deal with the rest */
+}
+
+/*
+ * Log a single (old->new) mapping for 'xid'.
+ */
+static void
+logical_rewrite_log_mapping(RewriteState state, TransactionId xid,
+							LogicalRewriteMappingData *map)
+{
+	RewriteMappingFile *src;
+	RewriteMappingDataEntry *pmap;
+	Oid			relid;
+	bool		found;
+
+	relid = RelationGetRelid(state->rs_old_rel);
+
+	/* look for existing mappings for this 'mapped' xid */
+	src = hash_search(state->rs_logical_mappings, &xid,
+					  HASH_ENTER, &found);
+
+	/*
+	 * We haven't yet had the need to map anything for this xid, create
+	 * per-xid data structures.
+	 */
+	if (!found)
+	{
+		char		path[MAXPGPATH];
+		Oid			dboid;
+
+		if (state->rs_old_rel->rd_rel->relisshared)
+			dboid = InvalidOid;
+		else
+			dboid = MyDatabaseId;
+
+		snprintf(path, MAXPGPATH,
+				 "pg_logical/mappings/" LOGICAL_REWRITE_FORMAT,
+				 dboid, relid,
+				 LSN_FORMAT_ARGS(state->rs_begin_lsn),
+				 xid, GetCurrentTransactionId());
+
+		dlist_init(&src->mappings);
+		src->num_mappings = 0;
+		src->off = 0;
+		memcpy(src->path, path, sizeof(path));
+		src->vfd = PathNameOpenFile(path,
+									O_CREAT | O_EXCL | O_WRONLY | PG_BINARY);
+		if (src->vfd < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not create file \"%s\": %m", path)));
+	}
+
+	pmap = MemoryContextAlloc(state->rs_cxt,
+							  sizeof(RewriteMappingDataEntry));
+	memcpy(&pmap->map, map, sizeof(LogicalRewriteMappingData));
+	dlist_push_tail(&src->mappings, &pmap->node);
+	src->num_mappings++;
+	state->rs_num_rewrite_mappings++;
+
+	/*
+	 * Write out buffer every time we've too many in-memory entries across all
+	 * mapping files.
+	 */
+	if (state->rs_num_rewrite_mappings >= 1000 /* arbitrary number */ )
+		logical_heap_rewrite_flush_mappings(state);
+}
+
+/*
+ * Perform logical remapping for a tuple that's mapped from old_tid to
+ * new_tuple->t_self by rewrite_heap_tuple() if necessary for the tuple.
+ */
+static void
+logical_rewrite_heap_tuple(RewriteState state, ItemPointerData old_tid,
+						   HeapTuple new_tuple)
+{
+	ItemPointerData new_tid = new_tuple->t_self;
+	TransactionId cutoff = state->rs_logical_xmin;
+	TransactionId xmin;
+	TransactionId xmax;
+	bool		do_log_xmin = false;
+	bool		do_log_xmax = false;
+	LogicalRewriteMappingData map;
+
+	/* no logical rewrite in progress, we don't need to log anything */
+	if (!state->rs_logical_rewrite)
+		return;
+
+	xmin = HeapTupleHeaderGetXmin(new_tuple->t_data);
+	/* use *GetUpdateXid to correctly deal with multixacts */
+	xmax = HeapTupleHeaderGetUpdateXid(new_tuple->t_data);
+
+	/*
+	 * Log the mapping iff the tuple has been created recently.
+	 */
+	if (TransactionIdIsNormal(xmin) && !TransactionIdPrecedes(xmin, cutoff))
+		do_log_xmin = true;
+
+	if (!TransactionIdIsNormal(xmax))
+	{
+		/*
+		 * no xmax is set, can't have any permanent ones, so this check is
+		 * sufficient
+		 */
+	}
+	else if (HEAP_XMAX_IS_LOCKED_ONLY(new_tuple->t_data->t_infomask))
+	{
+		/* only locked, we don't care */
+	}
+	else if (!TransactionIdPrecedes(xmax, cutoff))
+	{
+		/* tuple has been deleted recently, log */
+		do_log_xmax = true;
+	}
+
+	/* if neither needs to be logged, we're done */
+	if (!do_log_xmin && !do_log_xmax)
+		return;
+
+	/* fill out mapping information */
+	map.old_node = state->rs_old_rel->rd_node;
+	map.old_tid = old_tid;
+	map.new_node = state->rs_new_rel->rd_node;
+	map.new_tid = new_tid;
+
+	/* ---
+	 * Now persist the mapping for the individual xids that are affected. We
+	 * need to log for both xmin and xmax if they aren't the same transaction
+	 * since the mapping files are per "affected" xid.
+	 * We don't muster all that much effort detecting whether xmin and xmax
+	 * are actually the same transaction, we just check whether the xid is the
+	 * same disregarding subtransactions. Logging too much is relatively
+	 * harmless and we could never do the check fully since subtransaction
+	 * data is thrown away during restarts.
+	 * ---
+	 */
+	if (do_log_xmin)
+		logical_rewrite_log_mapping(state, xmin, &map);
+	/* separately log mapping for xmax unless it'd be redundant */
+	if (do_log_xmax && !TransactionIdEquals(xmin, xmax))
+		logical_rewrite_log_mapping(state, xmax, &map);
+}
+
+/*
+ * Replay XLOG_HEAP2_REWRITE records
+ */
+void
+heap_xlog_logical_rewrite(XLogReaderState *r)
+{
+	char		path[MAXPGPATH];
+	int			fd;
+	xl_heap_rewrite_mapping *xlrec;
+	uint32		len;
+	char	   *data;
+
+	xlrec = (xl_heap_rewrite_mapping *) XLogRecGetData(r);
+
+	snprintf(path, MAXPGPATH,
+			 "pg_logical/mappings/" LOGICAL_REWRITE_FORMAT,
+			 xlrec->mapped_db, xlrec->mapped_rel,
+			 LSN_FORMAT_ARGS(xlrec->start_lsn),
+			 xlrec->mapped_xid, XLogRecGetXid(r));
+
+	fd = OpenTransientFile(path,
+						   O_CREAT | O_WRONLY | PG_BINARY);
+	if (fd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not create file \"%s\": %m", path)));
+
+	/*
+	 * Truncate all data that's not guaranteed to have been safely fsynced (by
+	 * previous record or by the last checkpoint).
+	 */
+	pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_TRUNCATE);
+	if (ftruncate(fd, xlrec->offset) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not truncate file \"%s\" to %u: %m",
+						path, (uint32) xlrec->offset)));
+	pgstat_report_wait_end();
+
+	data = XLogRecGetData(r) + sizeof(*xlrec);
+
+	len = xlrec->num_mappings * sizeof(LogicalRewriteMappingData);
+
+	/* write out tail end of mapping file (again) */
+	errno = 0;
+	pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_MAPPING_WRITE);
+	if (pg_pwrite(fd, data, len, xlrec->offset) != len)
+	{
+		/* if write didn't set errno, assume problem is no disk space */
+		if (errno == 0)
+			errno = ENOSPC;
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write to file \"%s\": %m", path)));
+	}
+	pgstat_report_wait_end();
+
+	/*
+	 * Now fsync all previously written data. We could improve things and only
+	 * do this for the last write to a file, but the required bookkeeping
+	 * doesn't seem worth the trouble.
+	 */
+	pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_MAPPING_SYNC);
+	if (pg_fsync(fd) != 0)
+		ereport(data_sync_elevel(ERROR),
+				(errcode_for_file_access(),
+				 errmsg("could not fsync file \"%s\": %m", path)));
+	pgstat_report_wait_end();
+
+	if (CloseTransientFile(fd) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", path)));
+}
+
+/* ---
+ * Perform a checkpoint for logical rewrite mappings
+ *
+ * This serves two tasks:
+ * 1) Remove all mappings not needed anymore based on the logical restart LSN
+ * 2) Flush all remaining mappings to disk, so that replay after a checkpoint
+ *	  only has to deal with the parts of a mapping that have been written out
+ *	  after the checkpoint started.
+ * ---
+ */
+void
+CheckPointLogicalRewriteHeap(void)
+{
+	XLogRecPtr	cutoff;
+	XLogRecPtr	redo;
+	DIR		   *mappings_dir;
+	struct dirent *mapping_de;
+	char		path[MAXPGPATH + 20];
+
+	/*
+	 * We start of with a minimum of the last redo pointer. No new decoding
+	 * slot will start before that, so that's a safe upper bound for removal.
+	 */
+	redo = GetRedoRecPtr();
+
+	/* now check for the restart ptrs from existing slots */
+	cutoff = ReplicationSlotsComputeLogicalRestartLSN();
+
+	/* don't start earlier than the restart lsn */
+	if (cutoff != InvalidXLogRecPtr && redo < cutoff)
+		cutoff = redo;
+
+	mappings_dir = AllocateDir("pg_logical/mappings");
+	while ((mapping_de = ReadDir(mappings_dir, "pg_logical/mappings")) != NULL)
+	{
+		struct stat statbuf;
+		Oid			dboid;
+		Oid			relid;
+		XLogRecPtr	lsn;
+		TransactionId rewrite_xid;
+		TransactionId create_xid;
+		uint32		hi,
+					lo;
+
+		if (strcmp(mapping_de->d_name, ".") == 0 ||
+			strcmp(mapping_de->d_name, "..") == 0)
+			continue;
+
+		snprintf(path, sizeof(path), "pg_logical/mappings/%s", mapping_de->d_name);
+		if (lstat(path, &statbuf) == 0 && !S_ISREG(statbuf.st_mode))
+			continue;
+
+		/* Skip over files that cannot be ours. */
+		if (strncmp(mapping_de->d_name, "map-", 4) != 0)
+			continue;
+
+		if (sscanf(mapping_de->d_name, LOGICAL_REWRITE_FORMAT,
+				   &dboid, &relid, &hi, &lo, &rewrite_xid, &create_xid) != 6)
+			elog(ERROR, "could not parse filename \"%s\"", mapping_de->d_name);
+
+		lsn = ((uint64) hi) << 32 | lo;
+
+		if (lsn < cutoff || cutoff == InvalidXLogRecPtr)
+		{
+			elog(DEBUG1, "removing logical rewrite file \"%s\"", path);
+			if (unlink(path) < 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not remove file \"%s\": %m", path)));
+		}
+		else
+		{
+			/* on some operating systems fsyncing a file requires O_RDWR */
+			int			fd = OpenTransientFile(path, O_RDWR | PG_BINARY);
+
+			/*
+			 * The file cannot vanish due to concurrency since this function
+			 * is the only one removing logical mappings and only one
+			 * checkpoint can be in progress at a time.
+			 */
+			if (fd < 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not open file \"%s\": %m", path)));
+
+			/*
+			 * We could try to avoid fsyncing files that either haven't
+			 * changed or have only been created since the checkpoint's start,
+			 * but it's currently not deemed worth the effort.
+			 */
+			pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_CHECKPOINT_SYNC);
+			if (pg_fsync(fd) != 0)
+				ereport(data_sync_elevel(ERROR),
+						(errcode_for_file_access(),
+						 errmsg("could not fsync file \"%s\": %m", path)));
+			pgstat_report_wait_end();
+
+			if (CloseTransientFile(fd) != 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not close file \"%s\": %m", path)));
+		}
+	}
+	FreeDir(mappings_dir);
+
+	/* persist directory entries to disk */
+	fsync_fname("pg_logical/mappings", true);
+}
diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
new file mode 100644
index 0000000..8aab6e3
--- /dev/null
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -0,0 +1,4353 @@
+/*-------------------------------------------------------------------------
+ *
+ * vacuumlazy.c
+ *	  Concurrent ("lazy") vacuuming.
+ *
+ *
+ * The major space usage for LAZY VACUUM is storage for the array of dead tuple
+ * TIDs.  We want to ensure we can vacuum even the very largest relations with
+ * finite memory space usage.  To do that, we set upper bounds on the number of
+ * tuples we will keep track of at once.
+ *
+ * We are willing to use at most maintenance_work_mem (or perhaps
+ * autovacuum_work_mem) memory space to keep track of dead tuples.  We
+ * initially allocate an array of TIDs of that size, with an upper limit that
+ * depends on table size (this limit ensures we don't allocate a huge area
+ * uselessly for vacuuming small tables).  If the array threatens to overflow,
+ * we suspend the heap scan phase and perform a pass of index cleanup and page
+ * compaction, then resume the heap scan with an empty TID array.
+ *
+ * If we're processing a table with no indexes, we can just vacuum each page
+ * as we go; there's no need to save up multiple tuples to minimize the number
+ * of index scans performed.  So we don't use maintenance_work_mem memory for
+ * the TID array, just enough to hold as many heap tuples as fit on one page.
+ *
+ * Lazy vacuum supports parallel execution with parallel worker processes.  In
+ * a parallel vacuum, we perform both index vacuum and index cleanup with
+ * parallel worker processes.  Individual indexes are processed by one vacuum
+ * process.  At the beginning of a lazy vacuum (at lazy_scan_heap) we prepare
+ * the parallel context and initialize the DSM segment that contains shared
+ * information as well as the memory space for storing dead tuples.  When
+ * starting either index vacuum or index cleanup, we launch parallel worker
+ * processes.  Once all indexes are processed the parallel worker processes
+ * exit.  After that, the leader process re-initializes the parallel context
+ * so that it can use the same DSM for multiple passes of index vacuum and
+ * for performing index cleanup.  For updating the index statistics, we need
+ * to update the system table and since updates are not allowed during
+ * parallel mode we update the index statistics after exiting from the
+ * parallel mode.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/heap/vacuumlazy.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <math.h>
+
+#include "access/amapi.h"
+#include "access/genam.h"
+#include "access/heapam.h"
+#include "access/heapam_xlog.h"
+#include "access/htup_details.h"
+#include "access/multixact.h"
+#include "access/parallel.h"
+#include "access/transam.h"
+#include "access/visibilitymap.h"
+#include "access/xact.h"
+#include "access/xlog.h"
+#include "catalog/index.h"
+#include "catalog/storage.h"
+#include "commands/dbcommands.h"
+#include "commands/progress.h"
+#include "commands/vacuum.h"
+#include "executor/instrument.h"
+#include "miscadmin.h"
+#include "optimizer/paths.h"
+#include "pgstat.h"
+#include "portability/instr_time.h"
+#include "postmaster/autovacuum.h"
+#include "storage/bufmgr.h"
+#include "storage/freespace.h"
+#include "storage/lmgr.h"
+#include "tcop/tcopprot.h"
+#include "utils/lsyscache.h"
+#include "utils/memutils.h"
+#include "utils/pg_rusage.h"
+#include "utils/timestamp.h"
+
+
+/*
+ * Space/time tradeoff parameters: do these need to be user-tunable?
+ *
+ * To consider truncating the relation, we want there to be at least
+ * REL_TRUNCATE_MINIMUM or (relsize / REL_TRUNCATE_FRACTION) (whichever
+ * is less) potentially-freeable pages.
+ */
+#define REL_TRUNCATE_MINIMUM	1000
+#define REL_TRUNCATE_FRACTION	16
+
+/*
+ * Timing parameters for truncate locking heuristics.
+ *
+ * These were not exposed as user tunable GUC values because it didn't seem
+ * that the potential for improvement was great enough to merit the cost of
+ * supporting them.
+ */
+#define VACUUM_TRUNCATE_LOCK_CHECK_INTERVAL		20	/* ms */
+#define VACUUM_TRUNCATE_LOCK_WAIT_INTERVAL		50	/* ms */
+#define VACUUM_TRUNCATE_LOCK_TIMEOUT			5000	/* ms */
+
+/*
+ * Threshold that controls whether we bypass index vacuuming and heap
+ * vacuuming as an optimization
+ */
+#define BYPASS_THRESHOLD_PAGES	0.02	/* i.e. 2% of rel_pages */
+
+/*
+ * Perform a failsafe check every 4GB during the heap scan, approximately
+ */
+#define FAILSAFE_EVERY_PAGES \
+	((BlockNumber) (((uint64) 4 * 1024 * 1024 * 1024) / BLCKSZ))
+
+/*
+ * When a table has no indexes, vacuum the FSM after every 8GB, approximately
+ * (it won't be exact because we only vacuum FSM after processing a heap page
+ * that has some removable tuples).  When there are indexes, this is ignored,
+ * and we vacuum FSM after each index/heap cleaning pass.
+ */
+#define VACUUM_FSM_EVERY_PAGES \
+	((BlockNumber) (((uint64) 8 * 1024 * 1024 * 1024) / BLCKSZ))
+
+/*
+ * Guesstimation of number of dead tuples per page.  This is used to
+ * provide an upper limit to memory allocated when vacuuming small
+ * tables.
+ */
+#define LAZY_ALLOC_TUPLES		MaxHeapTuplesPerPage
+
+/*
+ * Before we consider skipping a page that's marked as clean in
+ * visibility map, we must've seen at least this many clean pages.
+ */
+#define SKIP_PAGES_THRESHOLD	((BlockNumber) 32)
+
+/*
+ * Size of the prefetch window for lazy vacuum backwards truncation scan.
+ * Needs to be a power of 2.
+ */
+#define PREFETCH_SIZE			((BlockNumber) 32)
+
+/*
+ * DSM keys for parallel vacuum.  Unlike other parallel execution code, since
+ * we don't need to worry about DSM keys conflicting with plan_node_id we can
+ * use small integers.
+ */
+#define PARALLEL_VACUUM_KEY_SHARED			1
+#define PARALLEL_VACUUM_KEY_DEAD_TUPLES		2
+#define PARALLEL_VACUUM_KEY_QUERY_TEXT		3
+#define PARALLEL_VACUUM_KEY_BUFFER_USAGE	4
+#define PARALLEL_VACUUM_KEY_WAL_USAGE		5
+
+/*
+ * Macro to check if we are in a parallel vacuum.  If true, we are in the
+ * parallel mode and the DSM segment is initialized.
+ */
+#define ParallelVacuumIsActive(vacrel) ((vacrel)->lps != NULL)
+
+/* Phases of vacuum during which we report error context. */
+typedef enum
+{
+	VACUUM_ERRCB_PHASE_UNKNOWN,
+	VACUUM_ERRCB_PHASE_SCAN_HEAP,
+	VACUUM_ERRCB_PHASE_VACUUM_INDEX,
+	VACUUM_ERRCB_PHASE_VACUUM_HEAP,
+	VACUUM_ERRCB_PHASE_INDEX_CLEANUP,
+	VACUUM_ERRCB_PHASE_TRUNCATE
+} VacErrPhase;
+
+/*
+ * LVDeadTuples stores the dead tuple TIDs collected during the heap scan.
+ * This is allocated in the DSM segment in parallel mode and in local memory
+ * in non-parallel mode.
+ */
+typedef struct LVDeadTuples
+{
+	int			max_tuples;		/* # slots allocated in array */
+	int			num_tuples;		/* current # of entries */
+	/* List of TIDs of tuples we intend to delete */
+	/* NB: this list is ordered by TID address */
+	ItemPointerData itemptrs[FLEXIBLE_ARRAY_MEMBER];	/* array of
+														 * ItemPointerData */
+} LVDeadTuples;
+
+/* The dead tuple space consists of LVDeadTuples and dead tuple TIDs */
+#define SizeOfDeadTuples(cnt) \
+	add_size(offsetof(LVDeadTuples, itemptrs), \
+			 mul_size(sizeof(ItemPointerData), cnt))
+#define MAXDEADTUPLES(max_size) \
+		(((max_size) - offsetof(LVDeadTuples, itemptrs)) / sizeof(ItemPointerData))
+
+/*
+ * Shared information among parallel workers.  So this is allocated in the DSM
+ * segment.
+ */
+typedef struct LVShared
+{
+	/*
+	 * Target table relid and log level.  These fields are not modified during
+	 * the lazy vacuum.
+	 */
+	Oid			relid;
+	int			elevel;
+
+	/*
+	 * An indication for vacuum workers to perform either index vacuum or
+	 * index cleanup.  first_time is true only if for_cleanup is true and
+	 * bulk-deletion is not performed yet.
+	 */
+	bool		for_cleanup;
+	bool		first_time;
+
+	/*
+	 * Fields for both index vacuum and cleanup.
+	 *
+	 * reltuples is the total number of input heap tuples.  We set either old
+	 * live tuples in the index vacuum case or the new live tuples in the
+	 * index cleanup case.
+	 *
+	 * estimated_count is true if reltuples is an estimated value.  (Note that
+	 * reltuples could be -1 in this case, indicating we have no idea.)
+	 */
+	double		reltuples;
+	bool		estimated_count;
+
+	/*
+	 * In single process lazy vacuum we could consume more memory during index
+	 * vacuuming or cleanup apart from the memory for heap scanning.  In
+	 * parallel vacuum, since individual vacuum workers can consume memory
+	 * equal to maintenance_work_mem, the new maintenance_work_mem for each
+	 * worker is set such that the parallel operation doesn't consume more
+	 * memory than single process lazy vacuum.
+	 */
+	int			maintenance_work_mem_worker;
+
+	/*
+	 * Shared vacuum cost balance.  During parallel vacuum,
+	 * VacuumSharedCostBalance points to this value and it accumulates the
+	 * balance of each parallel vacuum worker.
+	 */
+	pg_atomic_uint32 cost_balance;
+
+	/*
+	 * Number of active parallel workers.  This is used for computing the
+	 * minimum threshold of the vacuum cost balance before a worker sleeps for
+	 * cost-based delay.
+	 */
+	pg_atomic_uint32 active_nworkers;
+
+	/*
+	 * Variables to control parallel vacuum.  We have a bitmap to indicate
+	 * which index has stats in shared memory.  The set bit in the map
+	 * indicates that the particular index supports a parallel vacuum.
+	 */
+	pg_atomic_uint32 idx;		/* counter for vacuuming and clean up */
+	uint32		offset;			/* sizeof header incl. bitmap */
+	bits8		bitmap[FLEXIBLE_ARRAY_MEMBER];	/* bit map of NULLs */
+
+	/* Shared index statistics data follows at end of struct */
+} LVShared;
+
+#define SizeOfLVShared (offsetof(LVShared, bitmap) + sizeof(bits8))
+#define GetSharedIndStats(s) \
+	((LVSharedIndStats *)((char *)(s) + ((LVShared *)(s))->offset))
+#define IndStatsIsNull(s, i) \
+	(!(((LVShared *)(s))->bitmap[(i) >> 3] & (1 << ((i) & 0x07))))
+
+/*
+ * Struct for an index bulk-deletion statistic used for parallel vacuum.  This
+ * is allocated in the DSM segment.
+ */
+typedef struct LVSharedIndStats
+{
+	bool		updated;		/* are the stats updated? */
+	IndexBulkDeleteResult istat;
+} LVSharedIndStats;
+
+/* Struct for maintaining a parallel vacuum state. */
+typedef struct LVParallelState
+{
+	ParallelContext *pcxt;
+
+	/* Shared information among parallel vacuum workers */
+	LVShared   *lvshared;
+
+	/* Points to buffer usage area in DSM */
+	BufferUsage *buffer_usage;
+
+	/* Points to WAL usage area in DSM */
+	WalUsage   *wal_usage;
+
+	/*
+	 * The number of indexes that support parallel index bulk-deletion and
+	 * parallel index cleanup respectively.
+	 */
+	int			nindexes_parallel_bulkdel;
+	int			nindexes_parallel_cleanup;
+	int			nindexes_parallel_condcleanup;
+} LVParallelState;
+
+typedef struct LVRelState
+{
+	/* Target heap relation and its indexes */
+	Relation	rel;
+	Relation   *indrels;
+	int			nindexes;
+
+	/* Wraparound failsafe has been triggered? */
+	bool		failsafe_active;
+	/* Consider index vacuuming bypass optimization? */
+	bool		consider_bypass_optimization;
+
+	/* Doing index vacuuming, index cleanup, rel truncation? */
+	bool		do_index_vacuuming;
+	bool		do_index_cleanup;
+	bool		do_rel_truncate;
+
+	/* Buffer access strategy and parallel state */
+	BufferAccessStrategy bstrategy;
+	LVParallelState *lps;
+
+	/* Statistics from pg_class when we start out */
+	BlockNumber old_rel_pages;	/* previous value of pg_class.relpages */
+	double		old_live_tuples;	/* previous value of pg_class.reltuples */
+	/* rel's initial relfrozenxid and relminmxid */
+	TransactionId relfrozenxid;
+	MultiXactId relminmxid;
+
+	/* VACUUM operation's cutoff for pruning */
+	TransactionId OldestXmin;
+	/* VACUUM operation's cutoff for freezing XIDs and MultiXactIds */
+	TransactionId FreezeLimit;
+	MultiXactId MultiXactCutoff;
+
+	/* Error reporting state */
+	char	   *relnamespace;
+	char	   *relname;
+	char	   *indname;
+	BlockNumber blkno;			/* used only for heap operations */
+	OffsetNumber offnum;		/* used only for heap operations */
+	VacErrPhase phase;
+
+	/*
+	 * State managed by lazy_scan_heap() follows
+	 */
+	LVDeadTuples *dead_tuples;	/* items to vacuum from indexes */
+	BlockNumber rel_pages;		/* total number of pages */
+	BlockNumber scanned_pages;	/* number of pages we examined */
+	BlockNumber pinskipped_pages;	/* # of pages skipped due to a pin */
+	BlockNumber frozenskipped_pages;	/* # of frozen pages we skipped */
+	BlockNumber tupcount_pages; /* pages whose tuples we counted */
+	BlockNumber pages_removed;	/* pages remove by truncation */
+	BlockNumber lpdead_item_pages;	/* # pages with LP_DEAD items */
+	BlockNumber nonempty_pages; /* actually, last nonempty page + 1 */
+
+	/* Statistics output by us, for table */
+	double		new_rel_tuples; /* new estimated total # of tuples */
+	double		new_live_tuples;	/* new estimated total # of live tuples */
+	/* Statistics output by index AMs */
+	IndexBulkDeleteResult **indstats;
+
+	/* Instrumentation counters */
+	int			num_index_scans;
+	int64		tuples_deleted; /* # deleted from table */
+	int64		lpdead_items;	/* # deleted from indexes */
+	int64		new_dead_tuples;	/* new estimated total # of dead items in
+									 * table */
+	int64		num_tuples;		/* total number of nonremovable tuples */
+	int64		live_tuples;	/* live tuples (reltuples estimate) */
+} LVRelState;
+
+/*
+ * State returned by lazy_scan_prune()
+ */
+typedef struct LVPagePruneState
+{
+	bool		hastup;			/* Page is truncatable? */
+	bool		has_lpdead_items;	/* includes existing LP_DEAD items */
+
+	/*
+	 * State describes the proper VM bit states to set for the page following
+	 * pruning and freezing.  all_visible implies !has_lpdead_items, but don't
+	 * trust all_frozen result unless all_visible is also set to true.
+	 */
+	bool		all_visible;	/* Every item visible to all? */
+	bool		all_frozen;		/* provided all_visible is also true */
+	TransactionId visibility_cutoff_xid;	/* For recovery conflicts */
+} LVPagePruneState;
+
+/* Struct for saving and restoring vacuum error information. */
+typedef struct LVSavedErrInfo
+{
+	BlockNumber blkno;
+	OffsetNumber offnum;
+	VacErrPhase phase;
+} LVSavedErrInfo;
+
+/* elevel controls whole VACUUM's verbosity */
+static int	elevel = -1;
+
+
+/* non-export function prototypes */
+static void lazy_scan_heap(LVRelState *vacrel, VacuumParams *params,
+						   bool aggressive);
+static void lazy_scan_prune(LVRelState *vacrel, Buffer buf,
+							BlockNumber blkno, Page page,
+							GlobalVisState *vistest,
+							LVPagePruneState *prunestate);
+static void lazy_vacuum(LVRelState *vacrel);
+static bool lazy_vacuum_all_indexes(LVRelState *vacrel);
+static void lazy_vacuum_heap_rel(LVRelState *vacrel);
+static int	lazy_vacuum_heap_page(LVRelState *vacrel, BlockNumber blkno,
+								  Buffer buffer, int tupindex, Buffer *vmbuffer);
+static bool lazy_check_needs_freeze(Buffer buf, bool *hastup,
+									LVRelState *vacrel);
+static bool lazy_check_wraparound_failsafe(LVRelState *vacrel);
+static void do_parallel_lazy_vacuum_all_indexes(LVRelState *vacrel);
+static void do_parallel_lazy_cleanup_all_indexes(LVRelState *vacrel);
+static void do_parallel_vacuum_or_cleanup(LVRelState *vacrel, int nworkers);
+static void do_parallel_processing(LVRelState *vacrel,
+								   LVShared *lvshared);
+static void do_serial_processing_for_unsafe_indexes(LVRelState *vacrel,
+													LVShared *lvshared);
+static IndexBulkDeleteResult *parallel_process_one_index(Relation indrel,
+														 IndexBulkDeleteResult *istat,
+														 LVShared *lvshared,
+														 LVSharedIndStats *shared_indstats,
+														 LVRelState *vacrel);
+static void lazy_cleanup_all_indexes(LVRelState *vacrel);
+static IndexBulkDeleteResult *lazy_vacuum_one_index(Relation indrel,
+													IndexBulkDeleteResult *istat,
+													double reltuples,
+													LVRelState *vacrel);
+static IndexBulkDeleteResult *lazy_cleanup_one_index(Relation indrel,
+													 IndexBulkDeleteResult *istat,
+													 double reltuples,
+													 bool estimated_count,
+													 LVRelState *vacrel);
+static bool should_attempt_truncation(LVRelState *vacrel);
+static void lazy_truncate_heap(LVRelState *vacrel);
+static BlockNumber count_nondeletable_pages(LVRelState *vacrel,
+											bool *lock_waiter_detected);
+static long compute_max_dead_tuples(BlockNumber relblocks, bool hasindex);
+static void lazy_space_alloc(LVRelState *vacrel, int nworkers,
+							 BlockNumber relblocks);
+static void lazy_space_free(LVRelState *vacrel);
+static bool lazy_tid_reaped(ItemPointer itemptr, void *state);
+static int	vac_cmp_itemptr(const void *left, const void *right);
+static bool heap_page_is_all_visible(LVRelState *vacrel, Buffer buf,
+									 TransactionId *visibility_cutoff_xid, bool *all_frozen);
+static int	compute_parallel_vacuum_workers(LVRelState *vacrel,
+											int nrequested,
+											bool *will_parallel_vacuum);
+static void update_index_statistics(LVRelState *vacrel);
+static LVParallelState *begin_parallel_vacuum(LVRelState *vacrel,
+											  BlockNumber nblocks,
+											  int nrequested);
+static void end_parallel_vacuum(LVRelState *vacrel);
+static LVSharedIndStats *parallel_stats_for_idx(LVShared *lvshared, int getidx);
+static bool parallel_processing_is_safe(Relation indrel, LVShared *lvshared);
+static void vacuum_error_callback(void *arg);
+static void update_vacuum_error_info(LVRelState *vacrel,
+									 LVSavedErrInfo *saved_vacrel,
+									 int phase, BlockNumber blkno,
+									 OffsetNumber offnum);
+static void restore_vacuum_error_info(LVRelState *vacrel,
+									  const LVSavedErrInfo *saved_vacrel);
+
+
+/*
+ *	heap_vacuum_rel() -- perform VACUUM for one heap relation
+ *
+ *		This routine vacuums a single heap, cleans out its indexes, and
+ *		updates its relpages and reltuples statistics.
+ *
+ *		At entry, we have already established a transaction and opened
+ *		and locked the relation.
+ */
+void
+heap_vacuum_rel(Relation rel, VacuumParams *params,
+				BufferAccessStrategy bstrategy)
+{
+	LVRelState *vacrel;
+	PGRUsage	ru0;
+	TimestampTz starttime = 0;
+	WalUsage	walusage_start = pgWalUsage;
+	WalUsage	walusage = {0, 0, 0};
+	long		secs;
+	int			usecs;
+	double		read_rate,
+				write_rate;
+	bool		aggressive;		/* should we scan all unfrozen pages? */
+	bool		scanned_all_unfrozen;	/* actually scanned all such pages? */
+	char	  **indnames = NULL;
+	TransactionId xidFullScanLimit;
+	MultiXactId mxactFullScanLimit;
+	BlockNumber new_rel_pages;
+	BlockNumber new_rel_allvisible;
+	double		new_live_tuples;
+	TransactionId new_frozen_xid;
+	MultiXactId new_min_multi;
+	ErrorContextCallback errcallback;
+	PgStat_Counter startreadtime = 0;
+	PgStat_Counter startwritetime = 0;
+	TransactionId OldestXmin;
+	TransactionId FreezeLimit;
+	MultiXactId MultiXactCutoff;
+
+	/* measure elapsed time iff autovacuum logging requires it */
+	if (IsAutoVacuumWorkerProcess() && params->log_min_duration >= 0)
+	{
+		pg_rusage_init(&ru0);
+		starttime = GetCurrentTimestamp();
+		if (track_io_timing)
+		{
+			startreadtime = pgStatBlockReadTime;
+			startwritetime = pgStatBlockWriteTime;
+		}
+	}
+
+	if (params->options & VACOPT_VERBOSE)
+		elevel = INFO;
+	else
+		elevel = DEBUG2;
+
+	pgstat_progress_start_command(PROGRESS_COMMAND_VACUUM,
+								  RelationGetRelid(rel));
+
+	vacuum_set_xid_limits(rel,
+						  params->freeze_min_age,
+						  params->freeze_table_age,
+						  params->multixact_freeze_min_age,
+						  params->multixact_freeze_table_age,
+						  &OldestXmin, &FreezeLimit, &xidFullScanLimit,
+						  &MultiXactCutoff, &mxactFullScanLimit);
+
+	/*
+	 * We request an aggressive scan if the table's frozen Xid is now older
+	 * than or equal to the requested Xid full-table scan limit; or if the
+	 * table's minimum MultiXactId is older than or equal to the requested
+	 * mxid full-table scan limit; or if DISABLE_PAGE_SKIPPING was specified.
+	 */
+	aggressive = TransactionIdPrecedesOrEquals(rel->rd_rel->relfrozenxid,
+											   xidFullScanLimit);
+	aggressive |= MultiXactIdPrecedesOrEquals(rel->rd_rel->relminmxid,
+											  mxactFullScanLimit);
+	if (params->options & VACOPT_DISABLE_PAGE_SKIPPING)
+		aggressive = true;
+
+	vacrel = (LVRelState *) palloc0(sizeof(LVRelState));
+
+	/* Set up high level stuff about rel */
+	vacrel->rel = rel;
+	vac_open_indexes(vacrel->rel, RowExclusiveLock, &vacrel->nindexes,
+					 &vacrel->indrels);
+	vacrel->failsafe_active = false;
+	vacrel->consider_bypass_optimization = true;
+
+	/*
+	 * The index_cleanup param either disables index vacuuming and cleanup or
+	 * forces it to go ahead when we would otherwise apply the index bypass
+	 * optimization.  The default is 'auto', which leaves the final decision
+	 * up to lazy_vacuum().
+	 *
+	 * The truncate param allows user to avoid attempting relation truncation,
+	 * though it can't force truncation to happen.
+	 */
+	Assert(params->index_cleanup != VACOPTVALUE_UNSPECIFIED);
+	Assert(params->truncate != VACOPTVALUE_UNSPECIFIED &&
+		   params->truncate != VACOPTVALUE_AUTO);
+	vacrel->do_index_vacuuming = true;
+	vacrel->do_index_cleanup = true;
+	vacrel->do_rel_truncate = (params->truncate != VACOPTVALUE_DISABLED);
+	if (params->index_cleanup == VACOPTVALUE_DISABLED)
+	{
+		/* Force disable index vacuuming up-front */
+		vacrel->do_index_vacuuming = false;
+		vacrel->do_index_cleanup = false;
+	}
+	else if (params->index_cleanup == VACOPTVALUE_ENABLED)
+	{
+		/* Force index vacuuming.  Note that failsafe can still bypass. */
+		vacrel->consider_bypass_optimization = false;
+	}
+	else
+	{
+		/* Default/auto, make all decisions dynamically */
+		Assert(params->index_cleanup == VACOPTVALUE_AUTO);
+	}
+
+	vacrel->bstrategy = bstrategy;
+	vacrel->old_rel_pages = rel->rd_rel->relpages;
+	vacrel->old_live_tuples = rel->rd_rel->reltuples;
+	vacrel->relfrozenxid = rel->rd_rel->relfrozenxid;
+	vacrel->relminmxid = rel->rd_rel->relminmxid;
+
+	/* Set cutoffs for entire VACUUM */
+	vacrel->OldestXmin = OldestXmin;
+	vacrel->FreezeLimit = FreezeLimit;
+	vacrel->MultiXactCutoff = MultiXactCutoff;
+
+	vacrel->relnamespace = get_namespace_name(RelationGetNamespace(rel));
+	vacrel->relname = pstrdup(RelationGetRelationName(rel));
+	vacrel->indname = NULL;
+	vacrel->phase = VACUUM_ERRCB_PHASE_UNKNOWN;
+
+	/* Save index names iff autovacuum logging requires it */
+	if (IsAutoVacuumWorkerProcess() && params->log_min_duration >= 0 &&
+		vacrel->nindexes > 0)
+	{
+		indnames = palloc(sizeof(char *) * vacrel->nindexes);
+		for (int i = 0; i < vacrel->nindexes; i++)
+			indnames[i] =
+				pstrdup(RelationGetRelationName(vacrel->indrels[i]));
+	}
+
+	/*
+	 * Setup error traceback support for ereport().  The idea is to set up an
+	 * error context callback to display additional information on any error
+	 * during a vacuum.  During different phases of vacuum (heap scan, heap
+	 * vacuum, index vacuum, index clean up, heap truncate), we update the
+	 * error context callback to display appropriate information.
+	 *
+	 * Note that the index vacuum and heap vacuum phases may be called
+	 * multiple times in the middle of the heap scan phase.  So the old phase
+	 * information is restored at the end of those phases.
+	 */
+	errcallback.callback = vacuum_error_callback;
+	errcallback.arg = vacrel;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* Do the vacuuming */
+	lazy_scan_heap(vacrel, params, aggressive);
+
+	/* Done with indexes */
+	vac_close_indexes(vacrel->nindexes, vacrel->indrels, NoLock);
+
+	/*
+	 * Compute whether we actually scanned the all unfrozen pages. If we did,
+	 * we can adjust relfrozenxid and relminmxid.
+	 *
+	 * NB: We need to check this before truncating the relation, because that
+	 * will change ->rel_pages.
+	 */
+	if ((vacrel->scanned_pages + vacrel->frozenskipped_pages)
+		< vacrel->rel_pages)
+	{
+		Assert(!aggressive);
+		scanned_all_unfrozen = false;
+	}
+	else
+		scanned_all_unfrozen = true;
+
+	/*
+	 * Optionally truncate the relation.
+	 */
+	if (should_attempt_truncation(vacrel))
+	{
+		/*
+		 * Update error traceback information.  This is the last phase during
+		 * which we add context information to errors, so we don't need to
+		 * revert to the previous phase.
+		 */
+		update_vacuum_error_info(vacrel, NULL, VACUUM_ERRCB_PHASE_TRUNCATE,
+								 vacrel->nonempty_pages,
+								 InvalidOffsetNumber);
+		lazy_truncate_heap(vacrel);
+	}
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+
+	/* Report that we are now doing final cleanup */
+	pgstat_progress_update_param(PROGRESS_VACUUM_PHASE,
+								 PROGRESS_VACUUM_PHASE_FINAL_CLEANUP);
+
+	/*
+	 * Update statistics in pg_class.
+	 *
+	 * In principle new_live_tuples could be -1 indicating that we (still)
+	 * don't know the tuple count.  In practice that probably can't happen,
+	 * since we'd surely have scanned some pages if the table is new and
+	 * nonempty.
+	 *
+	 * For safety, clamp relallvisible to be not more than what we're setting
+	 * relpages to.
+	 *
+	 * Also, don't change relfrozenxid/relminmxid if we skipped any pages,
+	 * since then we don't know for certain that all tuples have a newer xmin.
+	 */
+	new_rel_pages = vacrel->rel_pages;
+	new_live_tuples = vacrel->new_live_tuples;
+
+	visibilitymap_count(rel, &new_rel_allvisible, NULL);
+	if (new_rel_allvisible > new_rel_pages)
+		new_rel_allvisible = new_rel_pages;
+
+	new_frozen_xid = scanned_all_unfrozen ? FreezeLimit : InvalidTransactionId;
+	new_min_multi = scanned_all_unfrozen ? MultiXactCutoff : InvalidMultiXactId;
+
+	vac_update_relstats(rel,
+						new_rel_pages,
+						new_live_tuples,
+						new_rel_allvisible,
+						vacrel->nindexes > 0,
+						new_frozen_xid,
+						new_min_multi,
+						false);
+
+	/*
+	 * Report results to the stats collector, too.
+	 *
+	 * Deliberately avoid telling the stats collector about LP_DEAD items that
+	 * remain in the table due to VACUUM bypassing index and heap vacuuming.
+	 * ANALYZE will consider the remaining LP_DEAD items to be dead tuples. It
+	 * seems like a good idea to err on the side of not vacuuming again too
+	 * soon in cases where the failsafe prevented significant amounts of heap
+	 * vacuuming.
+	 */
+	pgstat_report_vacuum(RelationGetRelid(rel),
+						 rel->rd_rel->relisshared,
+						 Max(new_live_tuples, 0),
+						 vacrel->new_dead_tuples);
+	pgstat_progress_end_command();
+
+	/* and log the action if appropriate */
+	if (IsAutoVacuumWorkerProcess() && params->log_min_duration >= 0)
+	{
+		TimestampTz endtime = GetCurrentTimestamp();
+
+		if (params->log_min_duration == 0 ||
+			TimestampDifferenceExceeds(starttime, endtime,
+									   params->log_min_duration))
+		{
+			StringInfoData buf;
+			char	   *msgfmt;
+			BlockNumber orig_rel_pages;
+
+			TimestampDifference(starttime, endtime, &secs, &usecs);
+
+			memset(&walusage, 0, sizeof(WalUsage));
+			WalUsageAccumDiff(&walusage, &pgWalUsage, &walusage_start);
+
+			read_rate = 0;
+			write_rate = 0;
+			if ((secs > 0) || (usecs > 0))
+			{
+				read_rate = (double) BLCKSZ * VacuumPageMiss / (1024 * 1024) /
+					(secs + usecs / 1000000.0);
+				write_rate = (double) BLCKSZ * VacuumPageDirty / (1024 * 1024) /
+					(secs + usecs / 1000000.0);
+			}
+
+			/*
+			 * This is pretty messy, but we split it up so that we can skip
+			 * emitting individual parts of the message when not applicable.
+			 */
+			initStringInfo(&buf);
+			if (params->is_wraparound)
+			{
+				/*
+				 * While it's possible for a VACUUM to be both is_wraparound
+				 * and !aggressive, that's just a corner-case -- is_wraparound
+				 * implies aggressive.  Produce distinct output for the corner
+				 * case all the same, just in case.
+				 */
+				if (aggressive)
+					msgfmt = _("automatic aggressive vacuum to prevent wraparound of table \"%s.%s.%s\": index scans: %d\n");
+				else
+					msgfmt = _("automatic vacuum to prevent wraparound of table \"%s.%s.%s\": index scans: %d\n");
+			}
+			else
+			{
+				if (aggressive)
+					msgfmt = _("automatic aggressive vacuum of table \"%s.%s.%s\": index scans: %d\n");
+				else
+					msgfmt = _("automatic vacuum of table \"%s.%s.%s\": index scans: %d\n");
+			}
+			appendStringInfo(&buf, msgfmt,
+							 get_database_name(MyDatabaseId),
+							 vacrel->relnamespace,
+							 vacrel->relname,
+							 vacrel->num_index_scans);
+			appendStringInfo(&buf, _("pages: %u removed, %u remain, %u skipped due to pins, %u skipped frozen\n"),
+							 vacrel->pages_removed,
+							 vacrel->rel_pages,
+							 vacrel->pinskipped_pages,
+							 vacrel->frozenskipped_pages);
+			appendStringInfo(&buf,
+							 _("tuples: %lld removed, %lld remain, %lld are dead but not yet removable, oldest xmin: %u\n"),
+							 (long long) vacrel->tuples_deleted,
+							 (long long) vacrel->new_rel_tuples,
+							 (long long) vacrel->new_dead_tuples,
+							 OldestXmin);
+			orig_rel_pages = vacrel->rel_pages + vacrel->pages_removed;
+			if (orig_rel_pages > 0)
+			{
+				if (vacrel->do_index_vacuuming)
+				{
+					if (vacrel->nindexes == 0 || vacrel->num_index_scans == 0)
+						appendStringInfoString(&buf, _("index scan not needed: "));
+					else
+						appendStringInfoString(&buf, _("index scan needed: "));
+
+					msgfmt = _("%u pages from table (%.2f%% of total) had %lld dead item identifiers removed\n");
+				}
+				else
+				{
+					if (!vacrel->failsafe_active)
+						appendStringInfoString(&buf, _("index scan bypassed: "));
+					else
+						appendStringInfoString(&buf, _("index scan bypassed by failsafe: "));
+
+					msgfmt = _("%u pages from table (%.2f%% of total) have %lld dead item identifiers\n");
+				}
+				appendStringInfo(&buf, msgfmt,
+								 vacrel->lpdead_item_pages,
+								 100.0 * vacrel->lpdead_item_pages / orig_rel_pages,
+								 (long long) vacrel->lpdead_items);
+			}
+			for (int i = 0; i < vacrel->nindexes; i++)
+			{
+				IndexBulkDeleteResult *istat = vacrel->indstats[i];
+
+				if (!istat)
+					continue;
+
+				appendStringInfo(&buf,
+								 _("index \"%s\": pages: %u in total, %u newly deleted, %u currently deleted, %u reusable\n"),
+								 indnames[i],
+								 istat->num_pages,
+								 istat->pages_newly_deleted,
+								 istat->pages_deleted,
+								 istat->pages_free);
+			}
+			if (track_io_timing)
+			{
+				double		read_ms = (double) (pgStatBlockReadTime - startreadtime) / 1000;
+				double		write_ms = (double) (pgStatBlockWriteTime - startwritetime) / 1000;
+
+				appendStringInfo(&buf, _("I/O timings: read: %.3f ms, write: %.3f ms\n"),
+								 read_ms, write_ms);
+			}
+			appendStringInfo(&buf, _("avg read rate: %.3f MB/s, avg write rate: %.3f MB/s\n"),
+							 read_rate, write_rate);
+			appendStringInfo(&buf,
+							 _("buffer usage: %lld hits, %lld misses, %lld dirtied\n"),
+							 (long long) VacuumPageHit,
+							 (long long) VacuumPageMiss,
+							 (long long) VacuumPageDirty);
+			appendStringInfo(&buf,
+							 _("WAL usage: %lld records, %lld full page images, %llu bytes\n"),
+							 (long long) walusage.wal_records,
+							 (long long) walusage.wal_fpi,
+							 (unsigned long long) walusage.wal_bytes);
+			appendStringInfo(&buf, _("system usage: %s"), pg_rusage_show(&ru0));
+
+			ereport(LOG,
+					(errmsg_internal("%s", buf.data)));
+			pfree(buf.data);
+		}
+	}
+
+	/* Cleanup index statistics and index names */
+	for (int i = 0; i < vacrel->nindexes; i++)
+	{
+		if (vacrel->indstats[i])
+			pfree(vacrel->indstats[i]);
+
+		if (indnames && indnames[i])
+			pfree(indnames[i]);
+	}
+}
+
+/*
+ *	lazy_scan_heap() -- scan an open heap relation
+ *
+ *		This routine prunes each page in the heap, which will among other
+ *		things truncate dead tuples to dead line pointers, defragment the
+ *		page, and set commit status bits (see heap_page_prune).  It also builds
+ *		lists of dead tuples and pages with free space, calculates statistics
+ *		on the number of live tuples in the heap, and marks pages as
+ *		all-visible if appropriate.  When done, or when we run low on space
+ *		for dead-tuple TIDs, invoke lazy_vacuum to vacuum indexes and vacuum
+ *		heap relation during its own second pass over the heap.
+ *
+ *		If the table has at least two indexes, we execute both index vacuum
+ *		and index cleanup with parallel workers unless parallel vacuum is
+ *		disabled.  In a parallel vacuum, we enter parallel mode and then
+ *		create both the parallel context and the DSM segment before starting
+ *		heap scan so that we can record dead tuples to the DSM segment.  All
+ *		parallel workers are launched at beginning of index vacuuming and
+ *		index cleanup and they exit once done with all indexes.  At the end of
+ *		this function we exit from parallel mode.  Index bulk-deletion results
+ *		are stored in the DSM segment and we update index statistics for all
+ *		the indexes after exiting from parallel mode since writes are not
+ *		allowed during parallel mode.
+ *
+ *		If there are no indexes then we can reclaim line pointers on the fly;
+ *		dead line pointers need only be retained until all index pointers that
+ *		reference them have been killed.
+ */
+static void
+lazy_scan_heap(LVRelState *vacrel, VacuumParams *params, bool aggressive)
+{
+	LVDeadTuples *dead_tuples;
+	BlockNumber nblocks,
+				blkno,
+				next_unskippable_block,
+				next_failsafe_block,
+				next_fsm_block_to_vacuum;
+	PGRUsage	ru0;
+	Buffer		vmbuffer = InvalidBuffer;
+	bool		skipping_blocks;
+	StringInfoData buf;
+	const int	initprog_index[] = {
+		PROGRESS_VACUUM_PHASE,
+		PROGRESS_VACUUM_TOTAL_HEAP_BLKS,
+		PROGRESS_VACUUM_MAX_DEAD_TUPLES
+	};
+	int64		initprog_val[3];
+	GlobalVisState *vistest;
+
+	pg_rusage_init(&ru0);
+
+	if (aggressive)
+		ereport(elevel,
+				(errmsg("aggressively vacuuming \"%s.%s\"",
+						vacrel->relnamespace,
+						vacrel->relname)));
+	else
+		ereport(elevel,
+				(errmsg("vacuuming \"%s.%s\"",
+						vacrel->relnamespace,
+						vacrel->relname)));
+
+	nblocks = RelationGetNumberOfBlocks(vacrel->rel);
+	next_unskippable_block = 0;
+	next_failsafe_block = 0;
+	next_fsm_block_to_vacuum = 0;
+	vacrel->rel_pages = nblocks;
+	vacrel->scanned_pages = 0;
+	vacrel->pinskipped_pages = 0;
+	vacrel->frozenskipped_pages = 0;
+	vacrel->tupcount_pages = 0;
+	vacrel->pages_removed = 0;
+	vacrel->lpdead_item_pages = 0;
+	vacrel->nonempty_pages = 0;
+
+	/* Initialize instrumentation counters */
+	vacrel->num_index_scans = 0;
+	vacrel->tuples_deleted = 0;
+	vacrel->lpdead_items = 0;
+	vacrel->new_dead_tuples = 0;
+	vacrel->num_tuples = 0;
+	vacrel->live_tuples = 0;
+
+	vistest = GlobalVisTestFor(vacrel->rel);
+
+	vacrel->indstats = (IndexBulkDeleteResult **)
+		palloc0(vacrel->nindexes * sizeof(IndexBulkDeleteResult *));
+
+	/*
+	 * Before beginning scan, check if it's already necessary to apply
+	 * failsafe
+	 */
+	lazy_check_wraparound_failsafe(vacrel);
+
+	/*
+	 * Allocate the space for dead tuples.  Note that this handles parallel
+	 * VACUUM initialization as part of allocating shared memory space used
+	 * for dead_tuples.
+	 */
+	lazy_space_alloc(vacrel, params->nworkers, nblocks);
+	dead_tuples = vacrel->dead_tuples;
+
+	/* Report that we're scanning the heap, advertising total # of blocks */
+	initprog_val[0] = PROGRESS_VACUUM_PHASE_SCAN_HEAP;
+	initprog_val[1] = nblocks;
+	initprog_val[2] = dead_tuples->max_tuples;
+	pgstat_progress_update_multi_param(3, initprog_index, initprog_val);
+
+	/*
+	 * Except when aggressive is set, we want to skip pages that are
+	 * all-visible according to the visibility map, but only when we can skip
+	 * at least SKIP_PAGES_THRESHOLD consecutive pages.  Since we're reading
+	 * sequentially, the OS should be doing readahead for us, so there's no
+	 * gain in skipping a page now and then; that's likely to disable
+	 * readahead and so be counterproductive. Also, skipping even a single
+	 * page means that we can't update relfrozenxid, so we only want to do it
+	 * if we can skip a goodly number of pages.
+	 *
+	 * When aggressive is set, we can't skip pages just because they are
+	 * all-visible, but we can still skip pages that are all-frozen, since
+	 * such pages do not need freezing and do not affect the value that we can
+	 * safely set for relfrozenxid or relminmxid.
+	 *
+	 * Before entering the main loop, establish the invariant that
+	 * next_unskippable_block is the next block number >= blkno that we can't
+	 * skip based on the visibility map, either all-visible for a regular scan
+	 * or all-frozen for an aggressive scan.  We set it to nblocks if there's
+	 * no such block.  We also set up the skipping_blocks flag correctly at
+	 * this stage.
+	 *
+	 * Note: The value returned by visibilitymap_get_status could be slightly
+	 * out-of-date, since we make this test before reading the corresponding
+	 * heap page or locking the buffer.  This is OK.  If we mistakenly think
+	 * that the page is all-visible or all-frozen when in fact the flag's just
+	 * been cleared, we might fail to vacuum the page.  It's easy to see that
+	 * skipping a page when aggressive is not set is not a very big deal; we
+	 * might leave some dead tuples lying around, but the next vacuum will
+	 * find them.  But even when aggressive *is* set, it's still OK if we miss
+	 * a page whose all-frozen marking has just been cleared.  Any new XIDs
+	 * just added to that page are necessarily newer than the GlobalXmin we
+	 * computed, so they'll have no effect on the value to which we can safely
+	 * set relfrozenxid.  A similar argument applies for MXIDs and relminmxid.
+	 *
+	 * We will scan the table's last page, at least to the extent of
+	 * determining whether it has tuples or not, even if it should be skipped
+	 * according to the above rules; except when we've already determined that
+	 * it's not worth trying to truncate the table.  This avoids having
+	 * lazy_truncate_heap() take access-exclusive lock on the table to attempt
+	 * a truncation that just fails immediately because there are tuples in
+	 * the last page.  This is worth avoiding mainly because such a lock must
+	 * be replayed on any hot standby, where it can be disruptive.
+	 */
+	if ((params->options & VACOPT_DISABLE_PAGE_SKIPPING) == 0)
+	{
+		while (next_unskippable_block < nblocks)
+		{
+			uint8		vmstatus;
+
+			vmstatus = visibilitymap_get_status(vacrel->rel,
+												next_unskippable_block,
+												&vmbuffer);
+			if (aggressive)
+			{
+				if ((vmstatus & VISIBILITYMAP_ALL_FROZEN) == 0)
+					break;
+			}
+			else
+			{
+				if ((vmstatus & VISIBILITYMAP_ALL_VISIBLE) == 0)
+					break;
+			}
+			vacuum_delay_point();
+			next_unskippable_block++;
+		}
+	}
+
+	if (next_unskippable_block >= SKIP_PAGES_THRESHOLD)
+		skipping_blocks = true;
+	else
+		skipping_blocks = false;
+
+	for (blkno = 0; blkno < nblocks; blkno++)
+	{
+		Buffer		buf;
+		Page		page;
+		bool		all_visible_according_to_vm = false;
+		LVPagePruneState prunestate;
+
+		/*
+		 * Consider need to skip blocks.  See note above about forcing
+		 * scanning of last page.
+		 */
+#define FORCE_CHECK_PAGE() \
+		(blkno == nblocks - 1 && should_attempt_truncation(vacrel))
+
+		pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_SCANNED, blkno);
+
+		update_vacuum_error_info(vacrel, NULL, VACUUM_ERRCB_PHASE_SCAN_HEAP,
+								 blkno, InvalidOffsetNumber);
+
+		if (blkno == next_unskippable_block)
+		{
+			/* Time to advance next_unskippable_block */
+			next_unskippable_block++;
+			if ((params->options & VACOPT_DISABLE_PAGE_SKIPPING) == 0)
+			{
+				while (next_unskippable_block < nblocks)
+				{
+					uint8		vmskipflags;
+
+					vmskipflags = visibilitymap_get_status(vacrel->rel,
+														   next_unskippable_block,
+														   &vmbuffer);
+					if (aggressive)
+					{
+						if ((vmskipflags & VISIBILITYMAP_ALL_FROZEN) == 0)
+							break;
+					}
+					else
+					{
+						if ((vmskipflags & VISIBILITYMAP_ALL_VISIBLE) == 0)
+							break;
+					}
+					vacuum_delay_point();
+					next_unskippable_block++;
+				}
+			}
+
+			/*
+			 * We know we can't skip the current block.  But set up
+			 * skipping_blocks to do the right thing at the following blocks.
+			 */
+			if (next_unskippable_block - blkno > SKIP_PAGES_THRESHOLD)
+				skipping_blocks = true;
+			else
+				skipping_blocks = false;
+
+			/*
+			 * Normally, the fact that we can't skip this block must mean that
+			 * it's not all-visible.  But in an aggressive vacuum we know only
+			 * that it's not all-frozen, so it might still be all-visible.
+			 */
+			if (aggressive && VM_ALL_VISIBLE(vacrel->rel, blkno, &vmbuffer))
+				all_visible_according_to_vm = true;
+		}
+		else
+		{
+			/*
+			 * The current block is potentially skippable; if we've seen a
+			 * long enough run of skippable blocks to justify skipping it, and
+			 * we're not forced to check it, then go ahead and skip.
+			 * Otherwise, the page must be at least all-visible if not
+			 * all-frozen, so we can set all_visible_according_to_vm = true.
+			 */
+			if (skipping_blocks && !FORCE_CHECK_PAGE())
+			{
+				/*
+				 * Tricky, tricky.  If this is in aggressive vacuum, the page
+				 * must have been all-frozen at the time we checked whether it
+				 * was skippable, but it might not be any more.  We must be
+				 * careful to count it as a skipped all-frozen page in that
+				 * case, or else we'll think we can't update relfrozenxid and
+				 * relminmxid.  If it's not an aggressive vacuum, we don't
+				 * know whether it was all-frozen, so we have to recheck; but
+				 * in this case an approximate answer is OK.
+				 */
+				if (aggressive || VM_ALL_FROZEN(vacrel->rel, blkno, &vmbuffer))
+					vacrel->frozenskipped_pages++;
+				continue;
+			}
+			all_visible_according_to_vm = true;
+		}
+
+		vacuum_delay_point();
+
+		/*
+		 * Regularly check if wraparound failsafe should trigger.
+		 *
+		 * There is a similar check inside lazy_vacuum_all_indexes(), but
+		 * relfrozenxid might start to look dangerously old before we reach
+		 * that point.  This check also provides failsafe coverage for the
+		 * one-pass strategy, and the two-pass strategy with the index_cleanup
+		 * param set to 'off'.
+		 */
+		if (blkno - next_failsafe_block >= FAILSAFE_EVERY_PAGES)
+		{
+			lazy_check_wraparound_failsafe(vacrel);
+			next_failsafe_block = blkno;
+		}
+
+		/*
+		 * Consider if we definitely have enough space to process TIDs on page
+		 * already.  If we are close to overrunning the available space for
+		 * dead-tuple TIDs, pause and do a cycle of vacuuming before we tackle
+		 * this page.
+		 */
+		if ((dead_tuples->max_tuples - dead_tuples->num_tuples) < MaxHeapTuplesPerPage &&
+			dead_tuples->num_tuples > 0)
+		{
+			/*
+			 * Before beginning index vacuuming, we release any pin we may
+			 * hold on the visibility map page.  This isn't necessary for
+			 * correctness, but we do it anyway to avoid holding the pin
+			 * across a lengthy, unrelated operation.
+			 */
+			if (BufferIsValid(vmbuffer))
+			{
+				ReleaseBuffer(vmbuffer);
+				vmbuffer = InvalidBuffer;
+			}
+
+			/* Remove the collected garbage tuples from table and indexes */
+			vacrel->consider_bypass_optimization = false;
+			lazy_vacuum(vacrel);
+
+			/*
+			 * Vacuum the Free Space Map to make newly-freed space visible on
+			 * upper-level FSM pages.  Note we have not yet processed blkno.
+			 */
+			FreeSpaceMapVacuumRange(vacrel->rel, next_fsm_block_to_vacuum,
+									blkno);
+			next_fsm_block_to_vacuum = blkno;
+
+			/* Report that we are once again scanning the heap */
+			pgstat_progress_update_param(PROGRESS_VACUUM_PHASE,
+										 PROGRESS_VACUUM_PHASE_SCAN_HEAP);
+		}
+
+		/*
+		 * Set up visibility map page as needed.
+		 *
+		 * Pin the visibility map page in case we need to mark the page
+		 * all-visible.  In most cases this will be very cheap, because we'll
+		 * already have the correct page pinned anyway.  However, it's
+		 * possible that (a) next_unskippable_block is covered by a different
+		 * VM page than the current block or (b) we released our pin and did a
+		 * cycle of index vacuuming.
+		 */
+		visibilitymap_pin(vacrel->rel, blkno, &vmbuffer);
+
+		buf = ReadBufferExtended(vacrel->rel, MAIN_FORKNUM, blkno,
+								 RBM_NORMAL, vacrel->bstrategy);
+
+		/*
+		 * We need buffer cleanup lock so that we can prune HOT chains and
+		 * defragment the page.
+		 */
+		if (!ConditionalLockBufferForCleanup(buf))
+		{
+			bool		hastup;
+
+			/*
+			 * If we're not performing an aggressive scan to guard against XID
+			 * wraparound, and we don't want to forcibly check the page, then
+			 * it's OK to skip vacuuming pages we get a lock conflict on. They
+			 * will be dealt with in some future vacuum.
+			 */
+			if (!aggressive && !FORCE_CHECK_PAGE())
+			{
+				ReleaseBuffer(buf);
+				vacrel->pinskipped_pages++;
+				continue;
+			}
+
+			/*
+			 * Read the page with share lock to see if any xids on it need to
+			 * be frozen.  If not we just skip the page, after updating our
+			 * scan statistics.  If there are some, we wait for cleanup lock.
+			 *
+			 * We could defer the lock request further by remembering the page
+			 * and coming back to it later, or we could even register
+			 * ourselves for multiple buffers and then service whichever one
+			 * is received first.  For now, this seems good enough.
+			 *
+			 * If we get here with aggressive false, then we're just forcibly
+			 * checking the page, and so we don't want to insist on getting
+			 * the lock; we only need to know if the page contains tuples, so
+			 * that we can update nonempty_pages correctly.  It's convenient
+			 * to use lazy_check_needs_freeze() for both situations, though.
+			 */
+			LockBuffer(buf, BUFFER_LOCK_SHARE);
+			if (!lazy_check_needs_freeze(buf, &hastup, vacrel))
+			{
+				UnlockReleaseBuffer(buf);
+				vacrel->scanned_pages++;
+				vacrel->pinskipped_pages++;
+				if (hastup)
+					vacrel->nonempty_pages = blkno + 1;
+				continue;
+			}
+			if (!aggressive)
+			{
+				/*
+				 * Here, we must not advance scanned_pages; that would amount
+				 * to claiming that the page contains no freezable tuples.
+				 */
+				UnlockReleaseBuffer(buf);
+				vacrel->pinskipped_pages++;
+				if (hastup)
+					vacrel->nonempty_pages = blkno + 1;
+				continue;
+			}
+			LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+			LockBufferForCleanup(buf);
+			/* drop through to normal processing */
+		}
+
+		/*
+		 * By here we definitely have enough dead_tuples space for whatever
+		 * LP_DEAD tids are on this page, we have the visibility map page set
+		 * up in case we need to set this page's all_visible/all_frozen bit,
+		 * and we have a super-exclusive lock.  Any tuples on this page are
+		 * now sure to be "counted" by this VACUUM.
+		 *
+		 * One last piece of preamble needs to take place before we can prune:
+		 * we need to consider new and empty pages.
+		 */
+		vacrel->scanned_pages++;
+		vacrel->tupcount_pages++;
+
+		page = BufferGetPage(buf);
+
+		if (PageIsNew(page))
+		{
+			/*
+			 * All-zeroes pages can be left over if either a backend extends
+			 * the relation by a single page, but crashes before the newly
+			 * initialized page has been written out, or when bulk-extending
+			 * the relation (which creates a number of empty pages at the tail
+			 * end of the relation, but enters them into the FSM).
+			 *
+			 * Note we do not enter the page into the visibilitymap. That has
+			 * the downside that we repeatedly visit this page in subsequent
+			 * vacuums, but otherwise we'll never not discover the space on a
+			 * promoted standby. The harm of repeated checking ought to
+			 * normally not be too bad - the space usually should be used at
+			 * some point, otherwise there wouldn't be any regular vacuums.
+			 *
+			 * Make sure these pages are in the FSM, to ensure they can be
+			 * reused. Do that by testing if there's any space recorded for
+			 * the page. If not, enter it. We do so after releasing the lock
+			 * on the heap page, the FSM is approximate, after all.
+			 */
+			UnlockReleaseBuffer(buf);
+
+			if (GetRecordedFreeSpace(vacrel->rel, blkno) == 0)
+			{
+				Size		freespace = BLCKSZ - SizeOfPageHeaderData;
+
+				RecordPageWithFreeSpace(vacrel->rel, blkno, freespace);
+			}
+			continue;
+		}
+
+		if (PageIsEmpty(page))
+		{
+			Size		freespace = PageGetHeapFreeSpace(page);
+
+			/*
+			 * Empty pages are always all-visible and all-frozen (note that
+			 * the same is currently not true for new pages, see above).
+			 */
+			if (!PageIsAllVisible(page))
+			{
+				START_CRIT_SECTION();
+
+				/* mark buffer dirty before writing a WAL record */
+				MarkBufferDirty(buf);
+
+				/*
+				 * It's possible that another backend has extended the heap,
+				 * initialized the page, and then failed to WAL-log the page
+				 * due to an ERROR.  Since heap extension is not WAL-logged,
+				 * recovery might try to replay our record setting the page
+				 * all-visible and find that the page isn't initialized, which
+				 * will cause a PANIC.  To prevent that, check whether the
+				 * page has been previously WAL-logged, and if not, do that
+				 * now.
+				 */
+				if (RelationNeedsWAL(vacrel->rel) &&
+					PageGetLSN(page) == InvalidXLogRecPtr)
+					log_newpage_buffer(buf, true);
+
+				PageSetAllVisible(page);
+				visibilitymap_set(vacrel->rel, blkno, buf, InvalidXLogRecPtr,
+								  vmbuffer, InvalidTransactionId,
+								  VISIBILITYMAP_ALL_VISIBLE | VISIBILITYMAP_ALL_FROZEN);
+				END_CRIT_SECTION();
+			}
+
+			UnlockReleaseBuffer(buf);
+			RecordPageWithFreeSpace(vacrel->rel, blkno, freespace);
+			continue;
+		}
+
+		/*
+		 * Prune and freeze tuples.
+		 *
+		 * Accumulates details of remaining LP_DEAD line pointers on page in
+		 * dead tuple list.  This includes LP_DEAD line pointers that we
+		 * pruned ourselves, as well as existing LP_DEAD line pointers that
+		 * were pruned some time earlier.  Also considers freezing XIDs in the
+		 * tuple headers of remaining items with storage.
+		 */
+		lazy_scan_prune(vacrel, buf, blkno, page, vistest, &prunestate);
+
+		Assert(!prunestate.all_visible || !prunestate.has_lpdead_items);
+
+		/* Remember the location of the last page with nonremovable tuples */
+		if (prunestate.hastup)
+			vacrel->nonempty_pages = blkno + 1;
+
+		if (vacrel->nindexes == 0)
+		{
+			/*
+			 * Consider the need to do page-at-a-time heap vacuuming when
+			 * using the one-pass strategy now.
+			 *
+			 * The one-pass strategy will never call lazy_vacuum().  The steps
+			 * performed here can be thought of as the one-pass equivalent of
+			 * a call to lazy_vacuum().
+			 */
+			if (prunestate.has_lpdead_items)
+			{
+				Size		freespace;
+
+				lazy_vacuum_heap_page(vacrel, blkno, buf, 0, &vmbuffer);
+
+				/* Forget the now-vacuumed tuples */
+				dead_tuples->num_tuples = 0;
+
+				/*
+				 * Periodically perform FSM vacuuming to make newly-freed
+				 * space visible on upper FSM pages.  Note we have not yet
+				 * performed FSM processing for blkno.
+				 */
+				if (blkno - next_fsm_block_to_vacuum >= VACUUM_FSM_EVERY_PAGES)
+				{
+					FreeSpaceMapVacuumRange(vacrel->rel, next_fsm_block_to_vacuum,
+											blkno);
+					next_fsm_block_to_vacuum = blkno;
+				}
+
+				/*
+				 * Now perform FSM processing for blkno, and move on to next
+				 * page.
+				 *
+				 * Our call to lazy_vacuum_heap_page() will have considered if
+				 * it's possible to set all_visible/all_frozen independently
+				 * of lazy_scan_prune().  Note that prunestate was invalidated
+				 * by lazy_vacuum_heap_page() call.
+				 */
+				freespace = PageGetHeapFreeSpace(page);
+
+				UnlockReleaseBuffer(buf);
+				RecordPageWithFreeSpace(vacrel->rel, blkno, freespace);
+				continue;
+			}
+
+			/*
+			 * There was no call to lazy_vacuum_heap_page() because pruning
+			 * didn't encounter/create any LP_DEAD items that needed to be
+			 * vacuumed.  Prune state has not been invalidated, so proceed
+			 * with prunestate-driven visibility map and FSM steps (just like
+			 * the two-pass strategy).
+			 */
+			Assert(dead_tuples->num_tuples == 0);
+		}
+
+		/*
+		 * Handle setting visibility map bit based on what the VM said about
+		 * the page before pruning started, and using prunestate
+		 */
+		if (!all_visible_according_to_vm && prunestate.all_visible)
+		{
+			uint8		flags = VISIBILITYMAP_ALL_VISIBLE;
+
+			if (prunestate.all_frozen)
+				flags |= VISIBILITYMAP_ALL_FROZEN;
+
+			/*
+			 * It should never be the case that the visibility map page is set
+			 * while the page-level bit is clear, but the reverse is allowed
+			 * (if checksums are not enabled).  Regardless, set both bits so
+			 * that we get back in sync.
+			 *
+			 * NB: If the heap page is all-visible but the VM bit is not set,
+			 * we don't need to dirty the heap page.  However, if checksums
+			 * are enabled, we do need to make sure that the heap page is
+			 * dirtied before passing it to visibilitymap_set(), because it
+			 * may be logged.  Given that this situation should only happen in
+			 * rare cases after a crash, it is not worth optimizing.
+			 */
+			PageSetAllVisible(page);
+			MarkBufferDirty(buf);
+			visibilitymap_set(vacrel->rel, blkno, buf, InvalidXLogRecPtr,
+							  vmbuffer, prunestate.visibility_cutoff_xid,
+							  flags);
+		}
+
+		/*
+		 * As of PostgreSQL 9.2, the visibility map bit should never be set if
+		 * the page-level bit is clear.  However, it's possible that the bit
+		 * got cleared after we checked it and before we took the buffer
+		 * content lock, so we must recheck before jumping to the conclusion
+		 * that something bad has happened.
+		 */
+		else if (all_visible_according_to_vm && !PageIsAllVisible(page)
+				 && VM_ALL_VISIBLE(vacrel->rel, blkno, &vmbuffer))
+		{
+			elog(WARNING, "page is not marked all-visible but visibility map bit is set in relation \"%s\" page %u",
+				 vacrel->relname, blkno);
+			visibilitymap_clear(vacrel->rel, blkno, vmbuffer,
+								VISIBILITYMAP_VALID_BITS);
+		}
+
+		/*
+		 * It's possible for the value returned by
+		 * GetOldestNonRemovableTransactionId() to move backwards, so it's not
+		 * wrong for us to see tuples that appear to not be visible to
+		 * everyone yet, while PD_ALL_VISIBLE is already set. The real safe
+		 * xmin value never moves backwards, but
+		 * GetOldestNonRemovableTransactionId() is conservative and sometimes
+		 * returns a value that's unnecessarily small, so if we see that
+		 * contradiction it just means that the tuples that we think are not
+		 * visible to everyone yet actually are, and the PD_ALL_VISIBLE flag
+		 * is correct.
+		 *
+		 * There should never be dead tuples on a page with PD_ALL_VISIBLE
+		 * set, however.
+		 */
+		else if (prunestate.has_lpdead_items && PageIsAllVisible(page))
+		{
+			elog(WARNING, "page containing dead tuples is marked as all-visible in relation \"%s\" page %u",
+				 vacrel->relname, blkno);
+			PageClearAllVisible(page);
+			MarkBufferDirty(buf);
+			visibilitymap_clear(vacrel->rel, blkno, vmbuffer,
+								VISIBILITYMAP_VALID_BITS);
+		}
+
+		/*
+		 * If the all-visible page is all-frozen but not marked as such yet,
+		 * mark it as all-frozen.  Note that all_frozen is only valid if
+		 * all_visible is true, so we must check both.
+		 */
+		else if (all_visible_according_to_vm && prunestate.all_visible &&
+				 prunestate.all_frozen &&
+				 !VM_ALL_FROZEN(vacrel->rel, blkno, &vmbuffer))
+		{
+			/*
+			 * We can pass InvalidTransactionId as the cutoff XID here,
+			 * because setting the all-frozen bit doesn't cause recovery
+			 * conflicts.
+			 */
+			visibilitymap_set(vacrel->rel, blkno, buf, InvalidXLogRecPtr,
+							  vmbuffer, InvalidTransactionId,
+							  VISIBILITYMAP_ALL_FROZEN);
+		}
+
+		/*
+		 * Final steps for block: drop super-exclusive lock, record free space
+		 * in the FSM
+		 */
+		if (prunestate.has_lpdead_items && vacrel->do_index_vacuuming)
+		{
+			/*
+			 * Wait until lazy_vacuum_heap_rel() to save free space.  This
+			 * doesn't just save us some cycles; it also allows us to record
+			 * any additional free space that lazy_vacuum_heap_page() will
+			 * make available in cases where it's possible to truncate the
+			 * page's line pointer array.
+			 *
+			 * Note: It's not in fact 100% certain that we really will call
+			 * lazy_vacuum_heap_rel() -- lazy_vacuum() might yet opt to skip
+			 * index vacuuming (and so must skip heap vacuuming).  This is
+			 * deemed okay because it only happens in emergencies, or when
+			 * there is very little free space anyway. (Besides, we start
+			 * recording free space in the FSM once index vacuuming has been
+			 * abandoned.)
+			 *
+			 * Note: The one-pass (no indexes) case is only supposed to make
+			 * it this far when there were no LP_DEAD items during pruning.
+			 */
+			Assert(vacrel->nindexes > 0);
+			UnlockReleaseBuffer(buf);
+		}
+		else
+		{
+			Size		freespace = PageGetHeapFreeSpace(page);
+
+			UnlockReleaseBuffer(buf);
+			RecordPageWithFreeSpace(vacrel->rel, blkno, freespace);
+		}
+	}
+
+	/* report that everything is now scanned */
+	pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_SCANNED, blkno);
+
+	/* Clear the block number information */
+	vacrel->blkno = InvalidBlockNumber;
+
+	/* now we can compute the new value for pg_class.reltuples */
+	vacrel->new_live_tuples = vac_estimate_reltuples(vacrel->rel, nblocks,
+													 vacrel->tupcount_pages,
+													 vacrel->live_tuples);
+
+	/*
+	 * Also compute the total number of surviving heap entries.  In the
+	 * (unlikely) scenario that new_live_tuples is -1, take it as zero.
+	 */
+	vacrel->new_rel_tuples =
+		Max(vacrel->new_live_tuples, 0) + vacrel->new_dead_tuples;
+
+	/*
+	 * Release any remaining pin on visibility map page.
+	 */
+	if (BufferIsValid(vmbuffer))
+	{
+		ReleaseBuffer(vmbuffer);
+		vmbuffer = InvalidBuffer;
+	}
+
+	/* If any tuples need to be deleted, perform final vacuum cycle */
+	if (dead_tuples->num_tuples > 0)
+		lazy_vacuum(vacrel);
+
+	/*
+	 * Vacuum the remainder of the Free Space Map.  We must do this whether or
+	 * not there were indexes, and whether or not we bypassed index vacuuming.
+	 */
+	if (blkno > next_fsm_block_to_vacuum)
+		FreeSpaceMapVacuumRange(vacrel->rel, next_fsm_block_to_vacuum, blkno);
+
+	/* report all blocks vacuumed */
+	pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_VACUUMED, blkno);
+
+	/* Do post-vacuum cleanup */
+	if (vacrel->nindexes > 0 && vacrel->do_index_cleanup)
+		lazy_cleanup_all_indexes(vacrel);
+
+	/*
+	 * Free resources managed by lazy_space_alloc().  (We must end parallel
+	 * mode/free shared memory before updating index statistics.  We cannot
+	 * write while in parallel mode.)
+	 */
+	lazy_space_free(vacrel);
+
+	/* Update index statistics */
+	if (vacrel->nindexes > 0 && vacrel->do_index_cleanup)
+		update_index_statistics(vacrel);
+
+	/*
+	 * When the table has no indexes (i.e. in the one-pass strategy case),
+	 * make log report that lazy_vacuum_heap_rel would've made had there been
+	 * indexes.  (As in the two-pass strategy case, only make this report when
+	 * there were LP_DEAD line pointers vacuumed in lazy_vacuum_heap_page.)
+	 */
+	if (vacrel->nindexes == 0 && vacrel->lpdead_item_pages > 0)
+		ereport(elevel,
+				(errmsg("table \"%s\": removed %lld dead item identifiers in %u pages",
+						vacrel->relname, (long long) vacrel->lpdead_items,
+						vacrel->lpdead_item_pages)));
+
+	/*
+	 * Make a log report summarizing pruning and freezing.
+	 *
+	 * The autovacuum specific logging in heap_vacuum_rel summarizes an entire
+	 * VACUUM operation, whereas each VACUUM VERBOSE log report generally
+	 * summarizes a single round of index/heap vacuuming (or rel truncation).
+	 * It wouldn't make sense to report on pruning or freezing while following
+	 * that convention, though.  You can think of this log report as a summary
+	 * of our first pass over the heap.
+	 */
+	initStringInfo(&buf);
+	appendStringInfo(&buf,
+					 _("%lld dead row versions cannot be removed yet, oldest xmin: %u\n"),
+					 (long long) vacrel->new_dead_tuples, vacrel->OldestXmin);
+	appendStringInfo(&buf, ngettext("Skipped %u page due to buffer pins, ",
+									"Skipped %u pages due to buffer pins, ",
+									vacrel->pinskipped_pages),
+					 vacrel->pinskipped_pages);
+	appendStringInfo(&buf, ngettext("%u frozen page.\n",
+									"%u frozen pages.\n",
+									vacrel->frozenskipped_pages),
+					 vacrel->frozenskipped_pages);
+	appendStringInfo(&buf, _("%s."), pg_rusage_show(&ru0));
+
+	ereport(elevel,
+			(errmsg("table \"%s\": found %lld removable, %lld nonremovable row versions in %u out of %u pages",
+					vacrel->relname,
+					(long long) vacrel->tuples_deleted,
+					(long long) vacrel->num_tuples, vacrel->scanned_pages,
+					nblocks),
+			 errdetail_internal("%s", buf.data)));
+	pfree(buf.data);
+}
+
+/*
+ *	lazy_scan_prune() -- lazy_scan_heap() pruning and freezing.
+ *
+ * Caller must hold pin and buffer cleanup lock on the buffer.
+ *
+ * Prior to PostgreSQL 14 there were very rare cases where heap_page_prune()
+ * was allowed to disagree with our HeapTupleSatisfiesVacuum() call about
+ * whether or not a tuple should be considered DEAD.  This happened when an
+ * inserting transaction concurrently aborted (after our heap_page_prune()
+ * call, before our HeapTupleSatisfiesVacuum() call).  There was rather a lot
+ * of complexity just so we could deal with tuples that were DEAD to VACUUM,
+ * but nevertheless were left with storage after pruning.
+ *
+ * The approach we take now is to restart pruning when the race condition is
+ * detected.  This allows heap_page_prune() to prune the tuples inserted by
+ * the now-aborted transaction.  This is a little crude, but it guarantees
+ * that any items that make it into the dead_tuples array are simple LP_DEAD
+ * line pointers, and that every remaining item with tuple storage is
+ * considered as a candidate for freezing.
+ */
+static void
+lazy_scan_prune(LVRelState *vacrel,
+				Buffer buf,
+				BlockNumber blkno,
+				Page page,
+				GlobalVisState *vistest,
+				LVPagePruneState *prunestate)
+{
+	Relation	rel = vacrel->rel;
+	OffsetNumber offnum,
+				maxoff;
+	ItemId		itemid;
+	HeapTupleData tuple;
+	HTSV_Result res;
+	int			tuples_deleted,
+				lpdead_items,
+				new_dead_tuples,
+				num_tuples,
+				live_tuples;
+	int			nfrozen;
+	OffsetNumber deadoffsets[MaxHeapTuplesPerPage];
+	xl_heap_freeze_tuple frozen[MaxHeapTuplesPerPage];
+
+	maxoff = PageGetMaxOffsetNumber(page);
+
+retry:
+
+	/* Initialize (or reset) page-level counters */
+	tuples_deleted = 0;
+	lpdead_items = 0;
+	new_dead_tuples = 0;
+	num_tuples = 0;
+	live_tuples = 0;
+
+	/*
+	 * Prune all HOT-update chains in this page.
+	 *
+	 * We count tuples removed by the pruning step as tuples_deleted.  Its
+	 * final value can be thought of as the number of tuples that have been
+	 * deleted from the table.  It should not be confused with lpdead_items;
+	 * lpdead_items's final value can be thought of as the number of tuples
+	 * that were deleted from indexes.
+	 */
+	tuples_deleted = heap_page_prune(rel, buf, vistest,
+									 InvalidTransactionId, 0, false,
+									 &vacrel->offnum);
+
+	/*
+	 * Now scan the page to collect LP_DEAD items and check for tuples
+	 * requiring freezing among remaining tuples with storage
+	 */
+	prunestate->hastup = false;
+	prunestate->has_lpdead_items = false;
+	prunestate->all_visible = true;
+	prunestate->all_frozen = true;
+	prunestate->visibility_cutoff_xid = InvalidTransactionId;
+	nfrozen = 0;
+
+	for (offnum = FirstOffsetNumber;
+		 offnum <= maxoff;
+		 offnum = OffsetNumberNext(offnum))
+	{
+		bool		tuple_totally_frozen;
+
+		/*
+		 * Set the offset number so that we can display it along with any
+		 * error that occurred while processing this tuple.
+		 */
+		vacrel->offnum = offnum;
+		itemid = PageGetItemId(page, offnum);
+
+		if (!ItemIdIsUsed(itemid))
+			continue;
+
+		/* Redirect items mustn't be touched */
+		if (ItemIdIsRedirected(itemid))
+		{
+			prunestate->hastup = true;	/* page won't be truncatable */
+			continue;
+		}
+
+		/*
+		 * LP_DEAD items are processed outside of the loop.
+		 *
+		 * Note that we deliberately don't set hastup=true in the case of an
+		 * LP_DEAD item here, which is not how lazy_check_needs_freeze() or
+		 * count_nondeletable_pages() do it -- they only consider pages empty
+		 * when they only have LP_UNUSED items, which is important for
+		 * correctness.
+		 *
+		 * Our assumption is that any LP_DEAD items we encounter here will
+		 * become LP_UNUSED inside lazy_vacuum_heap_page() before we actually
+		 * call count_nondeletable_pages().  In any case our opinion of
+		 * whether or not a page 'hastup' (which is how our caller sets its
+		 * vacrel->nonempty_pages value) is inherently race-prone.  It must be
+		 * treated as advisory/unreliable, so we might as well be slightly
+		 * optimistic.
+		 */
+		if (ItemIdIsDead(itemid))
+		{
+			deadoffsets[lpdead_items++] = offnum;
+			prunestate->all_visible = false;
+			prunestate->has_lpdead_items = true;
+			continue;
+		}
+
+		Assert(ItemIdIsNormal(itemid));
+
+		ItemPointerSet(&(tuple.t_self), blkno, offnum);
+		tuple.t_data = (HeapTupleHeader) PageGetItem(page, itemid);
+		tuple.t_len = ItemIdGetLength(itemid);
+		tuple.t_tableOid = RelationGetRelid(rel);
+
+		/*
+		 * DEAD tuples are almost always pruned into LP_DEAD line pointers by
+		 * heap_page_prune(), but it's possible that the tuple state changed
+		 * since heap_page_prune() looked.  Handle that here by restarting.
+		 * (See comments at the top of function for a full explanation.)
+		 */
+		res = HeapTupleSatisfiesVacuum(&tuple, vacrel->OldestXmin, buf);
+
+		if (unlikely(res == HEAPTUPLE_DEAD))
+			goto retry;
+
+		/*
+		 * The criteria for counting a tuple as live in this block need to
+		 * match what analyze.c's acquire_sample_rows() does, otherwise VACUUM
+		 * and ANALYZE may produce wildly different reltuples values, e.g.
+		 * when there are many recently-dead tuples.
+		 *
+		 * The logic here is a bit simpler than acquire_sample_rows(), as
+		 * VACUUM can't run inside a transaction block, which makes some cases
+		 * impossible (e.g. in-progress insert from the same transaction).
+		 *
+		 * We treat LP_DEAD items a little differently, too -- we don't count
+		 * them as dead_tuples at all (we only consider new_dead_tuples).  The
+		 * outcome is no different because we assume that any LP_DEAD items we
+		 * encounter here will become LP_UNUSED inside lazy_vacuum_heap_page()
+		 * before we report anything to the stats collector. (Cases where we
+		 * bypass index vacuuming will violate our assumption, but the overall
+		 * impact of that should be negligible.)
+		 */
+		switch (res)
+		{
+			case HEAPTUPLE_LIVE:
+
+				/*
+				 * Count it as live.  Not only is this natural, but it's also
+				 * what acquire_sample_rows() does.
+				 */
+				live_tuples++;
+
+				/*
+				 * Is the tuple definitely visible to all transactions?
+				 *
+				 * NB: Like with per-tuple hint bits, we can't set the
+				 * PD_ALL_VISIBLE flag if the inserter committed
+				 * asynchronously. See SetHintBits for more info. Check that
+				 * the tuple is hinted xmin-committed because of that.
+				 */
+				if (prunestate->all_visible)
+				{
+					TransactionId xmin;
+
+					if (!HeapTupleHeaderXminCommitted(tuple.t_data))
+					{
+						prunestate->all_visible = false;
+						break;
+					}
+
+					/*
+					 * The inserter definitely committed. But is it old enough
+					 * that everyone sees it as committed?
+					 */
+					xmin = HeapTupleHeaderGetXmin(tuple.t_data);
+					if (!TransactionIdPrecedes(xmin, vacrel->OldestXmin))
+					{
+						prunestate->all_visible = false;
+						break;
+					}
+
+					/* Track newest xmin on page. */
+					if (TransactionIdFollows(xmin, prunestate->visibility_cutoff_xid))
+						prunestate->visibility_cutoff_xid = xmin;
+				}
+				break;
+			case HEAPTUPLE_RECENTLY_DEAD:
+
+				/*
+				 * If tuple is recently deleted then we must not remove it
+				 * from relation.  (We only remove items that are LP_DEAD from
+				 * pruning.)
+				 */
+				new_dead_tuples++;
+				prunestate->all_visible = false;
+				break;
+			case HEAPTUPLE_INSERT_IN_PROGRESS:
+
+				/*
+				 * We do not count these rows as live, because we expect the
+				 * inserting transaction to update the counters at commit, and
+				 * we assume that will happen only after we report our
+				 * results.  This assumption is a bit shaky, but it is what
+				 * acquire_sample_rows() does, so be consistent.
+				 */
+				prunestate->all_visible = false;
+				break;
+			case HEAPTUPLE_DELETE_IN_PROGRESS:
+				/* This is an expected case during concurrent vacuum */
+				prunestate->all_visible = false;
+
+				/*
+				 * Count such rows as live.  As above, we assume the deleting
+				 * transaction will commit and update the counters after we
+				 * report.
+				 */
+				live_tuples++;
+				break;
+			default:
+				elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
+				break;
+		}
+
+		/*
+		 * Non-removable tuple (i.e. tuple with storage).
+		 *
+		 * Check tuple left behind after pruning to see if needs to be frozen
+		 * now.
+		 */
+		num_tuples++;
+		prunestate->hastup = true;
+		if (heap_prepare_freeze_tuple(tuple.t_data,
+									  vacrel->relfrozenxid,
+									  vacrel->relminmxid,
+									  vacrel->FreezeLimit,
+									  vacrel->MultiXactCutoff,
+									  &frozen[nfrozen],
+									  &tuple_totally_frozen))
+		{
+			/* Will execute freeze below */
+			frozen[nfrozen++].offset = offnum;
+		}
+
+		/*
+		 * If tuple is not frozen (and not about to become frozen) then caller
+		 * had better not go on to set this page's VM bit
+		 */
+		if (!tuple_totally_frozen)
+			prunestate->all_frozen = false;
+	}
+
+	/*
+	 * We have now divided every item on the page into either an LP_DEAD item
+	 * that will need to be vacuumed in indexes later, or a LP_NORMAL tuple
+	 * that remains and needs to be considered for freezing now (LP_UNUSED and
+	 * LP_REDIRECT items also remain, but are of no further interest to us).
+	 */
+	vacrel->offnum = InvalidOffsetNumber;
+
+	/*
+	 * Consider the need to freeze any items with tuple storage from the page
+	 * first (arbitrary)
+	 */
+	if (nfrozen > 0)
+	{
+		Assert(prunestate->hastup);
+
+		/*
+		 * At least one tuple with storage needs to be frozen -- execute that
+		 * now.
+		 *
+		 * If we need to freeze any tuples we'll mark the buffer dirty, and
+		 * write a WAL record recording the changes.  We must log the changes
+		 * to be crash-safe against future truncation of CLOG.
+		 */
+		START_CRIT_SECTION();
+
+		MarkBufferDirty(buf);
+
+		/* execute collected freezes */
+		for (int i = 0; i < nfrozen; i++)
+		{
+			HeapTupleHeader htup;
+
+			itemid = PageGetItemId(page, frozen[i].offset);
+			htup = (HeapTupleHeader) PageGetItem(page, itemid);
+
+			heap_execute_freeze_tuple(htup, &frozen[i]);
+		}
+
+		/* Now WAL-log freezing if necessary */
+		if (RelationNeedsWAL(vacrel->rel))
+		{
+			XLogRecPtr	recptr;
+
+			recptr = log_heap_freeze(vacrel->rel, buf, vacrel->FreezeLimit,
+									 frozen, nfrozen);
+			PageSetLSN(page, recptr);
+		}
+
+		END_CRIT_SECTION();
+	}
+
+	/*
+	 * The second pass over the heap can also set visibility map bits, using
+	 * the same approach.  This is important when the table frequently has a
+	 * few old LP_DEAD items on each page by the time we get to it (typically
+	 * because past opportunistic pruning operations freed some non-HOT
+	 * tuples).
+	 *
+	 * VACUUM will call heap_page_is_all_visible() during the second pass over
+	 * the heap to determine all_visible and all_frozen for the page -- this
+	 * is a specialized version of the logic from this function.  Now that
+	 * we've finished pruning and freezing, make sure that we're in total
+	 * agreement with heap_page_is_all_visible() using an assertion.
+	 */
+#ifdef USE_ASSERT_CHECKING
+	/* Note that all_frozen value does not matter when !all_visible */
+	if (prunestate->all_visible)
+	{
+		TransactionId cutoff;
+		bool		all_frozen;
+
+		if (!heap_page_is_all_visible(vacrel, buf, &cutoff, &all_frozen))
+			Assert(false);
+
+		Assert(lpdead_items == 0);
+		Assert(prunestate->all_frozen == all_frozen);
+
+		/*
+		 * It's possible that we froze tuples and made the page's XID cutoff
+		 * (for recovery conflict purposes) FrozenTransactionId.  This is okay
+		 * because visibility_cutoff_xid will be logged by our caller in a
+		 * moment.
+		 */
+		Assert(cutoff == FrozenTransactionId ||
+			   cutoff == prunestate->visibility_cutoff_xid);
+	}
+#endif
+
+	/*
+	 * Now save details of the LP_DEAD items from the page in the dead_tuples
+	 * array.  Also record that page has dead items in per-page prunestate.
+	 */
+	if (lpdead_items > 0)
+	{
+		LVDeadTuples *dead_tuples = vacrel->dead_tuples;
+		ItemPointerData tmp;
+
+		Assert(!prunestate->all_visible);
+		Assert(prunestate->has_lpdead_items);
+
+		vacrel->lpdead_item_pages++;
+
+		ItemPointerSetBlockNumber(&tmp, blkno);
+
+		for (int i = 0; i < lpdead_items; i++)
+		{
+			ItemPointerSetOffsetNumber(&tmp, deadoffsets[i]);
+			dead_tuples->itemptrs[dead_tuples->num_tuples++] = tmp;
+		}
+
+		Assert(dead_tuples->num_tuples <= dead_tuples->max_tuples);
+		pgstat_progress_update_param(PROGRESS_VACUUM_NUM_DEAD_TUPLES,
+									 dead_tuples->num_tuples);
+	}
+
+	/* Finally, add page-local counts to whole-VACUUM counts */
+	vacrel->tuples_deleted += tuples_deleted;
+	vacrel->lpdead_items += lpdead_items;
+	vacrel->new_dead_tuples += new_dead_tuples;
+	vacrel->num_tuples += num_tuples;
+	vacrel->live_tuples += live_tuples;
+}
+
+/*
+ * Remove the collected garbage tuples from the table and its indexes.
+ *
+ * We may choose to bypass index vacuuming at this point, though only when the
+ * ongoing VACUUM operation will definitely only have one index scan/round of
+ * index vacuuming.  Caller indicates whether or not this is such a VACUUM
+ * operation using 'onecall' argument.
+ *
+ * In rare emergencies, the ongoing VACUUM operation can be made to skip both
+ * index vacuuming and index cleanup at the point we're called.  This avoids
+ * having the whole system refuse to allocate further XIDs/MultiXactIds due to
+ * wraparound.
+ */
+static void
+lazy_vacuum(LVRelState *vacrel)
+{
+	bool		bypass;
+
+	/* Should not end up here with no indexes */
+	Assert(vacrel->nindexes > 0);
+	Assert(!IsParallelWorker());
+	Assert(vacrel->lpdead_item_pages > 0);
+
+	if (!vacrel->do_index_vacuuming)
+	{
+		Assert(!vacrel->do_index_cleanup);
+		vacrel->dead_tuples->num_tuples = 0;
+		return;
+	}
+
+	/*
+	 * Consider bypassing index vacuuming (and heap vacuuming) entirely.
+	 *
+	 * We currently only do this in cases where the number of LP_DEAD items
+	 * for the entire VACUUM operation is close to zero.  This avoids sharp
+	 * discontinuities in the duration and overhead of successive VACUUM
+	 * operations that run against the same table with a fixed workload.
+	 * Ideally, successive VACUUM operations will behave as if there are
+	 * exactly zero LP_DEAD items in cases where there are close to zero.
+	 *
+	 * This is likely to be helpful with a table that is continually affected
+	 * by UPDATEs that can mostly apply the HOT optimization, but occasionally
+	 * have small aberrations that lead to just a few heap pages retaining
+	 * only one or two LP_DEAD items.  This is pretty common; even when the
+	 * DBA goes out of their way to make UPDATEs use HOT, it is practically
+	 * impossible to predict whether HOT will be applied in 100% of cases.
+	 * It's far easier to ensure that 99%+ of all UPDATEs against a table use
+	 * HOT through careful tuning.
+	 */
+	bypass = false;
+	if (vacrel->consider_bypass_optimization && vacrel->rel_pages > 0)
+	{
+		BlockNumber threshold;
+
+		Assert(vacrel->num_index_scans == 0);
+		Assert(vacrel->lpdead_items == vacrel->dead_tuples->num_tuples);
+		Assert(vacrel->do_index_vacuuming);
+		Assert(vacrel->do_index_cleanup);
+
+		/*
+		 * This crossover point at which we'll start to do index vacuuming is
+		 * expressed as a percentage of the total number of heap pages in the
+		 * table that are known to have at least one LP_DEAD item.  This is
+		 * much more important than the total number of LP_DEAD items, since
+		 * it's a proxy for the number of heap pages whose visibility map bits
+		 * cannot be set on account of bypassing index and heap vacuuming.
+		 *
+		 * We apply one further precautionary test: the space currently used
+		 * to store the TIDs (TIDs that now all point to LP_DEAD items) must
+		 * not exceed 32MB.  This limits the risk that we will bypass index
+		 * vacuuming again and again until eventually there is a VACUUM whose
+		 * dead_tuples space is not CPU cache resident.
+		 *
+		 * We don't take any special steps to remember the LP_DEAD items (such
+		 * as counting them in new_dead_tuples report to the stats collector)
+		 * when the optimization is applied.  Though the accounting used in
+		 * analyze.c's acquire_sample_rows() will recognize the same LP_DEAD
+		 * items as dead rows in its own stats collector report, that's okay.
+		 * The discrepancy should be negligible.  If this optimization is ever
+		 * expanded to cover more cases then this may need to be reconsidered.
+		 */
+		threshold = (double) vacrel->rel_pages * BYPASS_THRESHOLD_PAGES;
+		bypass = (vacrel->lpdead_item_pages < threshold &&
+				  vacrel->lpdead_items < MAXDEADTUPLES(32L * 1024L * 1024L));
+	}
+
+	if (bypass)
+	{
+		/*
+		 * There are almost zero TIDs.  Behave as if there were precisely
+		 * zero: bypass index vacuuming, but do index cleanup.
+		 *
+		 * We expect that the ongoing VACUUM operation will finish very
+		 * quickly, so there is no point in considering speeding up as a
+		 * failsafe against wraparound failure. (Index cleanup is expected to
+		 * finish very quickly in cases where there were no ambulkdelete()
+		 * calls.)
+		 */
+		vacrel->do_index_vacuuming = false;
+		ereport(elevel,
+				(errmsg("table \"%s\": index scan bypassed: %u pages from table (%.2f%% of total) have %lld dead item identifiers",
+						vacrel->relname, vacrel->lpdead_item_pages,
+						100.0 * vacrel->lpdead_item_pages / vacrel->rel_pages,
+						(long long) vacrel->lpdead_items)));
+	}
+	else if (lazy_vacuum_all_indexes(vacrel))
+	{
+		/*
+		 * We successfully completed a round of index vacuuming.  Do related
+		 * heap vacuuming now.
+		 */
+		lazy_vacuum_heap_rel(vacrel);
+	}
+	else
+	{
+		/*
+		 * Failsafe case.
+		 *
+		 * we attempted index vacuuming, but didn't finish a full round/full
+		 * index scan.  This happens when relfrozenxid or relminmxid is too
+		 * far in the past.
+		 *
+		 * From this point on the VACUUM operation will do no further index
+		 * vacuuming or heap vacuuming.  This VACUUM operation won't end up
+		 * back here again.
+		 */
+		Assert(vacrel->failsafe_active);
+	}
+
+	/*
+	 * Forget the LP_DEAD items that we just vacuumed (or just decided to not
+	 * vacuum)
+	 */
+	vacrel->dead_tuples->num_tuples = 0;
+}
+
+/*
+ *	lazy_vacuum_all_indexes() -- Main entry for index vacuuming
+ *
+ * Returns true in the common case when all indexes were successfully
+ * vacuumed.  Returns false in rare cases where we determined that the ongoing
+ * VACUUM operation is at risk of taking too long to finish, leading to
+ * wraparound failure.
+ */
+static bool
+lazy_vacuum_all_indexes(LVRelState *vacrel)
+{
+	bool		allindexes = true;
+
+	Assert(!IsParallelWorker());
+	Assert(vacrel->nindexes > 0);
+	Assert(vacrel->do_index_vacuuming);
+	Assert(vacrel->do_index_cleanup);
+	Assert(TransactionIdIsNormal(vacrel->relfrozenxid));
+	Assert(MultiXactIdIsValid(vacrel->relminmxid));
+
+	/* Precheck for XID wraparound emergencies */
+	if (lazy_check_wraparound_failsafe(vacrel))
+	{
+		/* Wraparound emergency -- don't even start an index scan */
+		return false;
+	}
+
+	/* Report that we are now vacuuming indexes */
+	pgstat_progress_update_param(PROGRESS_VACUUM_PHASE,
+								 PROGRESS_VACUUM_PHASE_VACUUM_INDEX);
+
+	if (!ParallelVacuumIsActive(vacrel))
+	{
+		for (int idx = 0; idx < vacrel->nindexes; idx++)
+		{
+			Relation	indrel = vacrel->indrels[idx];
+			IndexBulkDeleteResult *istat = vacrel->indstats[idx];
+
+			vacrel->indstats[idx] =
+				lazy_vacuum_one_index(indrel, istat, vacrel->old_live_tuples,
+									  vacrel);
+
+			if (lazy_check_wraparound_failsafe(vacrel))
+			{
+				/* Wraparound emergency -- end current index scan */
+				allindexes = false;
+				break;
+			}
+		}
+	}
+	else
+	{
+		/* Outsource everything to parallel variant */
+		do_parallel_lazy_vacuum_all_indexes(vacrel);
+
+		/*
+		 * Do a postcheck to consider applying wraparound failsafe now.  Note
+		 * that parallel VACUUM only gets the precheck and this postcheck.
+		 */
+		if (lazy_check_wraparound_failsafe(vacrel))
+			allindexes = false;
+	}
+
+	/*
+	 * We delete all LP_DEAD items from the first heap pass in all indexes on
+	 * each call here (except calls where we choose to do the failsafe). This
+	 * makes the next call to lazy_vacuum_heap_rel() safe (except in the event
+	 * of the failsafe triggering, which prevents the next call from taking
+	 * place).
+	 */
+	Assert(vacrel->num_index_scans > 0 ||
+		   vacrel->dead_tuples->num_tuples == vacrel->lpdead_items);
+	Assert(allindexes || vacrel->failsafe_active);
+
+	/*
+	 * Increase and report the number of index scans.
+	 *
+	 * We deliberately include the case where we started a round of bulk
+	 * deletes that we weren't able to finish due to the failsafe triggering.
+	 */
+	vacrel->num_index_scans++;
+	pgstat_progress_update_param(PROGRESS_VACUUM_NUM_INDEX_VACUUMS,
+								 vacrel->num_index_scans);
+
+	return allindexes;
+}
+
+/*
+ *	lazy_vacuum_heap_rel() -- second pass over the heap for two pass strategy
+ *
+ * This routine marks LP_DEAD items in vacrel->dead_tuples array as LP_UNUSED.
+ * Pages that never had lazy_scan_prune record LP_DEAD items are not visited
+ * at all.
+ *
+ * We may also be able to truncate the line pointer array of the heap pages we
+ * visit.  If there is a contiguous group of LP_UNUSED items at the end of the
+ * array, it can be reclaimed as free space.  These LP_UNUSED items usually
+ * start out as LP_DEAD items recorded by lazy_scan_prune (we set items from
+ * each page to LP_UNUSED, and then consider if it's possible to truncate the
+ * page's line pointer array).
+ *
+ * Note: the reason for doing this as a second pass is we cannot remove the
+ * tuples until we've removed their index entries, and we want to process
+ * index entry removal in batches as large as possible.
+ */
+static void
+lazy_vacuum_heap_rel(LVRelState *vacrel)
+{
+	int			tupindex;
+	BlockNumber vacuumed_pages;
+	PGRUsage	ru0;
+	Buffer		vmbuffer = InvalidBuffer;
+	LVSavedErrInfo saved_err_info;
+
+	Assert(vacrel->do_index_vacuuming);
+	Assert(vacrel->do_index_cleanup);
+	Assert(vacrel->num_index_scans > 0);
+
+	/* Report that we are now vacuuming the heap */
+	pgstat_progress_update_param(PROGRESS_VACUUM_PHASE,
+								 PROGRESS_VACUUM_PHASE_VACUUM_HEAP);
+
+	/* Update error traceback information */
+	update_vacuum_error_info(vacrel, &saved_err_info,
+							 VACUUM_ERRCB_PHASE_VACUUM_HEAP,
+							 InvalidBlockNumber, InvalidOffsetNumber);
+
+	pg_rusage_init(&ru0);
+	vacuumed_pages = 0;
+
+	tupindex = 0;
+	while (tupindex < vacrel->dead_tuples->num_tuples)
+	{
+		BlockNumber tblk;
+		Buffer		buf;
+		Page		page;
+		Size		freespace;
+
+		vacuum_delay_point();
+
+		tblk = ItemPointerGetBlockNumber(&vacrel->dead_tuples->itemptrs[tupindex]);
+		vacrel->blkno = tblk;
+		buf = ReadBufferExtended(vacrel->rel, MAIN_FORKNUM, tblk, RBM_NORMAL,
+								 vacrel->bstrategy);
+		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
+		tupindex = lazy_vacuum_heap_page(vacrel, tblk, buf, tupindex,
+										 &vmbuffer);
+
+		/* Now that we've vacuumed the page, record its available space */
+		page = BufferGetPage(buf);
+		freespace = PageGetHeapFreeSpace(page);
+
+		UnlockReleaseBuffer(buf);
+		RecordPageWithFreeSpace(vacrel->rel, tblk, freespace);
+		vacuumed_pages++;
+	}
+
+	/* Clear the block number information */
+	vacrel->blkno = InvalidBlockNumber;
+
+	if (BufferIsValid(vmbuffer))
+	{
+		ReleaseBuffer(vmbuffer);
+		vmbuffer = InvalidBuffer;
+	}
+
+	/*
+	 * We set all LP_DEAD items from the first heap pass to LP_UNUSED during
+	 * the second heap pass.  No more, no less.
+	 */
+	Assert(tupindex > 0);
+	Assert(vacrel->num_index_scans > 1 ||
+		   (tupindex == vacrel->lpdead_items &&
+			vacuumed_pages == vacrel->lpdead_item_pages));
+
+	ereport(elevel,
+			(errmsg("table \"%s\": removed %lld dead item identifiers in %u pages",
+					vacrel->relname, (long long ) tupindex, vacuumed_pages),
+			 errdetail_internal("%s", pg_rusage_show(&ru0))));
+
+	/* Revert to the previous phase information for error traceback */
+	restore_vacuum_error_info(vacrel, &saved_err_info);
+}
+
+/*
+ *	lazy_vacuum_heap_page() -- free page's LP_DEAD items listed in the
+ *						  vacrel->dead_tuples array.
+ *
+ * Caller must have an exclusive buffer lock on the buffer (though a
+ * super-exclusive lock is also acceptable).
+ *
+ * tupindex is the index in vacrel->dead_tuples of the first dead tuple for
+ * this page.  We assume the rest follow sequentially.  The return value is
+ * the first tupindex after the tuples of this page.
+ *
+ * Prior to PostgreSQL 14 there were rare cases where this routine had to set
+ * tuples with storage to unused.  These days it is strictly responsible for
+ * marking LP_DEAD stub line pointers as unused.  This only happens for those
+ * LP_DEAD items on the page that were determined to be LP_DEAD items back
+ * when the same page was visited by lazy_scan_prune() (i.e. those whose TID
+ * was recorded in the dead_tuples array).
+ */
+static int
+lazy_vacuum_heap_page(LVRelState *vacrel, BlockNumber blkno, Buffer buffer,
+					  int tupindex, Buffer *vmbuffer)
+{
+	LVDeadTuples *dead_tuples = vacrel->dead_tuples;
+	Page		page = BufferGetPage(buffer);
+	OffsetNumber unused[MaxHeapTuplesPerPage];
+	int			uncnt = 0;
+	TransactionId visibility_cutoff_xid;
+	bool		all_frozen;
+	LVSavedErrInfo saved_err_info;
+
+	Assert(vacrel->nindexes == 0 || vacrel->do_index_vacuuming);
+
+	pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_VACUUMED, blkno);
+
+	/* Update error traceback information */
+	update_vacuum_error_info(vacrel, &saved_err_info,
+							 VACUUM_ERRCB_PHASE_VACUUM_HEAP, blkno,
+							 InvalidOffsetNumber);
+
+	START_CRIT_SECTION();
+
+	for (; tupindex < dead_tuples->num_tuples; tupindex++)
+	{
+		BlockNumber tblk;
+		OffsetNumber toff;
+		ItemId		itemid;
+
+		tblk = ItemPointerGetBlockNumber(&dead_tuples->itemptrs[tupindex]);
+		if (tblk != blkno)
+			break;				/* past end of tuples for this block */
+		toff = ItemPointerGetOffsetNumber(&dead_tuples->itemptrs[tupindex]);
+		itemid = PageGetItemId(page, toff);
+
+		Assert(ItemIdIsDead(itemid) && !ItemIdHasStorage(itemid));
+		ItemIdSetUnused(itemid);
+		unused[uncnt++] = toff;
+	}
+
+	Assert(uncnt > 0);
+
+	/* Attempt to truncate line pointer array now */
+	PageTruncateLinePointerArray(page);
+
+	/*
+	 * Mark buffer dirty before we write WAL.
+	 */
+	MarkBufferDirty(buffer);
+
+	/* XLOG stuff */
+	if (RelationNeedsWAL(vacrel->rel))
+	{
+		xl_heap_vacuum xlrec;
+		XLogRecPtr	recptr;
+
+		xlrec.nunused = uncnt;
+
+		XLogBeginInsert();
+		XLogRegisterData((char *) &xlrec, SizeOfHeapVacuum);
+
+		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
+		XLogRegisterBufData(0, (char *) unused, uncnt * sizeof(OffsetNumber));
+
+		recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_VACUUM);
+
+		PageSetLSN(page, recptr);
+	}
+
+	/*
+	 * End critical section, so we safely can do visibility tests (which
+	 * possibly need to perform IO and allocate memory!). If we crash now the
+	 * page (including the corresponding vm bit) might not be marked all
+	 * visible, but that's fine. A later vacuum will fix that.
+	 */
+	END_CRIT_SECTION();
+
+	/*
+	 * Now that we have removed the LD_DEAD items from the page, once again
+	 * check if the page has become all-visible.  The page is already marked
+	 * dirty, exclusively locked, and, if needed, a full page image has been
+	 * emitted.
+	 */
+	if (heap_page_is_all_visible(vacrel, buffer, &visibility_cutoff_xid,
+								 &all_frozen))
+		PageSetAllVisible(page);
+
+	/*
+	 * All the changes to the heap page have been done. If the all-visible
+	 * flag is now set, also set the VM all-visible bit (and, if possible, the
+	 * all-frozen bit) unless this has already been done previously.
+	 */
+	if (PageIsAllVisible(page))
+	{
+		uint8		flags = 0;
+		uint8		vm_status = visibilitymap_get_status(vacrel->rel,
+														 blkno, vmbuffer);
+
+		/* Set the VM all-frozen bit to flag, if needed */
+		if ((vm_status & VISIBILITYMAP_ALL_VISIBLE) == 0)
+			flags |= VISIBILITYMAP_ALL_VISIBLE;
+		if ((vm_status & VISIBILITYMAP_ALL_FROZEN) == 0 && all_frozen)
+			flags |= VISIBILITYMAP_ALL_FROZEN;
+
+		Assert(BufferIsValid(*vmbuffer));
+		if (flags != 0)
+			visibilitymap_set(vacrel->rel, blkno, buffer, InvalidXLogRecPtr,
+							  *vmbuffer, visibility_cutoff_xid, flags);
+	}
+
+	/* Revert to the previous phase information for error traceback */
+	restore_vacuum_error_info(vacrel, &saved_err_info);
+	return tupindex;
+}
+
+/*
+ *	lazy_check_needs_freeze() -- scan page to see if any tuples
+ *					 need to be cleaned to avoid wraparound
+ *
+ * Returns true if the page needs to be vacuumed using cleanup lock.
+ * Also returns a flag indicating whether page contains any tuples at all.
+ */
+static bool
+lazy_check_needs_freeze(Buffer buf, bool *hastup, LVRelState *vacrel)
+{
+	Page		page = BufferGetPage(buf);
+	OffsetNumber offnum,
+				maxoff;
+	HeapTupleHeader tupleheader;
+
+	*hastup = false;
+
+	/*
+	 * New and empty pages, obviously, don't contain tuples. We could make
+	 * sure that the page is registered in the FSM, but it doesn't seem worth
+	 * waiting for a cleanup lock just for that, especially because it's
+	 * likely that the pin holder will do so.
+	 */
+	if (PageIsNew(page) || PageIsEmpty(page))
+		return false;
+
+	maxoff = PageGetMaxOffsetNumber(page);
+	for (offnum = FirstOffsetNumber;
+		 offnum <= maxoff;
+		 offnum = OffsetNumberNext(offnum))
+	{
+		ItemId		itemid;
+
+		/*
+		 * Set the offset number so that we can display it along with any
+		 * error that occurred while processing this tuple.
+		 */
+		vacrel->offnum = offnum;
+		itemid = PageGetItemId(page, offnum);
+
+		/* this should match hastup test in count_nondeletable_pages() */
+		if (ItemIdIsUsed(itemid))
+			*hastup = true;
+
+		/* dead and redirect items never need freezing */
+		if (!ItemIdIsNormal(itemid))
+			continue;
+
+		tupleheader = (HeapTupleHeader) PageGetItem(page, itemid);
+
+		if (heap_tuple_needs_freeze(tupleheader, vacrel->FreezeLimit,
+									vacrel->MultiXactCutoff, buf))
+			break;
+	}							/* scan along page */
+
+	/* Clear the offset information once we have processed the given page. */
+	vacrel->offnum = InvalidOffsetNumber;
+
+	return (offnum <= maxoff);
+}
+
+/*
+ * Trigger the failsafe to avoid wraparound failure when vacrel table has a
+ * relfrozenxid and/or relminmxid that is dangerously far in the past.
+ * Triggering the failsafe makes the ongoing VACUUM bypass any further index
+ * vacuuming and heap vacuuming.  Truncating the heap is also bypassed.
+ *
+ * Any remaining work (work that VACUUM cannot just bypass) is typically sped
+ * up when the failsafe triggers.  VACUUM stops applying any cost-based delay
+ * that it started out with.
+ *
+ * Returns true when failsafe has been triggered.
+ */
+static bool
+lazy_check_wraparound_failsafe(LVRelState *vacrel)
+{
+	/* Don't warn more than once per VACUUM */
+	if (vacrel->failsafe_active)
+		return true;
+
+	if (unlikely(vacuum_xid_failsafe_check(vacrel->relfrozenxid,
+										   vacrel->relminmxid)))
+	{
+		vacrel->failsafe_active = true;
+
+		/* Disable index vacuuming, index cleanup, and heap rel truncation */
+		vacrel->do_index_vacuuming = false;
+		vacrel->do_index_cleanup = false;
+		vacrel->do_rel_truncate = false;
+
+		ereport(WARNING,
+				(errmsg("bypassing nonessential maintenance of table \"%s.%s.%s\" as a failsafe after %d index scans",
+						get_database_name(MyDatabaseId),
+						vacrel->relnamespace,
+						vacrel->relname,
+						vacrel->num_index_scans),
+				 errdetail("The table's relfrozenxid or relminmxid is too far in the past."),
+				 errhint("Consider increasing configuration parameter \"maintenance_work_mem\" or \"autovacuum_work_mem\".\n"
+						 "You might also need to consider other ways for VACUUM to keep up with the allocation of transaction IDs.")));
+
+		/* Stop applying cost limits from this point on */
+		VacuumCostActive = false;
+		VacuumCostBalance = 0;
+
+		return true;
+	}
+
+	return false;
+}
+
+/*
+ * Perform lazy_vacuum_all_indexes() steps in parallel
+ */
+static void
+do_parallel_lazy_vacuum_all_indexes(LVRelState *vacrel)
+{
+	/* Tell parallel workers to do index vacuuming */
+	vacrel->lps->lvshared->for_cleanup = false;
+	vacrel->lps->lvshared->first_time = false;
+
+	/*
+	 * We can only provide an approximate value of num_heap_tuples, at least
+	 * for now.  Matches serial VACUUM case.
+	 */
+	vacrel->lps->lvshared->reltuples = vacrel->old_live_tuples;
+	vacrel->lps->lvshared->estimated_count = true;
+
+	do_parallel_vacuum_or_cleanup(vacrel,
+								  vacrel->lps->nindexes_parallel_bulkdel);
+}
+
+/*
+ * Perform lazy_cleanup_all_indexes() steps in parallel
+ */
+static void
+do_parallel_lazy_cleanup_all_indexes(LVRelState *vacrel)
+{
+	int			nworkers;
+
+	/*
+	 * If parallel vacuum is active we perform index cleanup with parallel
+	 * workers.
+	 *
+	 * Tell parallel workers to do index cleanup.
+	 */
+	vacrel->lps->lvshared->for_cleanup = true;
+	vacrel->lps->lvshared->first_time = (vacrel->num_index_scans == 0);
+
+	/*
+	 * Now we can provide a better estimate of total number of surviving
+	 * tuples (we assume indexes are more interested in that than in the
+	 * number of nominally live tuples).
+	 */
+	vacrel->lps->lvshared->reltuples = vacrel->new_rel_tuples;
+	vacrel->lps->lvshared->estimated_count =
+		(vacrel->tupcount_pages < vacrel->rel_pages);
+
+	/* Determine the number of parallel workers to launch */
+	if (vacrel->lps->lvshared->first_time)
+		nworkers = vacrel->lps->nindexes_parallel_cleanup +
+			vacrel->lps->nindexes_parallel_condcleanup;
+	else
+		nworkers = vacrel->lps->nindexes_parallel_cleanup;
+
+	do_parallel_vacuum_or_cleanup(vacrel, nworkers);
+}
+
+/*
+ * Perform index vacuum or index cleanup with parallel workers.  This function
+ * must be used by the parallel vacuum leader process.  The caller must set
+ * lps->lvshared->for_cleanup to indicate whether to perform vacuum or
+ * cleanup.
+ */
+static void
+do_parallel_vacuum_or_cleanup(LVRelState *vacrel, int nworkers)
+{
+	LVParallelState *lps = vacrel->lps;
+
+	Assert(!IsParallelWorker());
+	Assert(ParallelVacuumIsActive(vacrel));
+	Assert(vacrel->nindexes > 0);
+
+	/* The leader process will participate */
+	nworkers--;
+
+	/*
+	 * It is possible that parallel context is initialized with fewer workers
+	 * than the number of indexes that need a separate worker in the current
+	 * phase, so we need to consider it.  See compute_parallel_vacuum_workers.
+	 */
+	nworkers = Min(nworkers, lps->pcxt->nworkers);
+
+	/* Setup the shared cost-based vacuum delay and launch workers */
+	if (nworkers > 0)
+	{
+		if (vacrel->num_index_scans > 0)
+		{
+			/* Reset the parallel index processing counter */
+			pg_atomic_write_u32(&(lps->lvshared->idx), 0);
+
+			/* Reinitialize the parallel context to relaunch parallel workers */
+			ReinitializeParallelDSM(lps->pcxt);
+		}
+
+		/*
+		 * Set up shared cost balance and the number of active workers for
+		 * vacuum delay.  We need to do this before launching workers as
+		 * otherwise, they might not see the updated values for these
+		 * parameters.
+		 */
+		pg_atomic_write_u32(&(lps->lvshared->cost_balance), VacuumCostBalance);
+		pg_atomic_write_u32(&(lps->lvshared->active_nworkers), 0);
+
+		/*
+		 * The number of workers can vary between bulkdelete and cleanup
+		 * phase.
+		 */
+		ReinitializeParallelWorkers(lps->pcxt, nworkers);
+
+		LaunchParallelWorkers(lps->pcxt);
+
+		if (lps->pcxt->nworkers_launched > 0)
+		{
+			/*
+			 * Reset the local cost values for leader backend as we have
+			 * already accumulated the remaining balance of heap.
+			 */
+			VacuumCostBalance = 0;
+			VacuumCostBalanceLocal = 0;
+
+			/* Enable shared cost balance for leader backend */
+			VacuumSharedCostBalance = &(lps->lvshared->cost_balance);
+			VacuumActiveNWorkers = &(lps->lvshared->active_nworkers);
+		}
+
+		if (lps->lvshared->for_cleanup)
+			ereport(elevel,
+					(errmsg(ngettext("launched %d parallel vacuum worker for index cleanup (planned: %d)",
+									 "launched %d parallel vacuum workers for index cleanup (planned: %d)",
+									 lps->pcxt->nworkers_launched),
+							lps->pcxt->nworkers_launched, nworkers)));
+		else
+			ereport(elevel,
+					(errmsg(ngettext("launched %d parallel vacuum worker for index vacuuming (planned: %d)",
+									 "launched %d parallel vacuum workers for index vacuuming (planned: %d)",
+									 lps->pcxt->nworkers_launched),
+							lps->pcxt->nworkers_launched, nworkers)));
+	}
+
+	/* Process the indexes that can be processed by only leader process */
+	do_serial_processing_for_unsafe_indexes(vacrel, lps->lvshared);
+
+	/*
+	 * Join as a parallel worker.  The leader process alone processes all the
+	 * indexes in the case where no workers are launched.
+	 */
+	do_parallel_processing(vacrel, lps->lvshared);
+
+	/*
+	 * Next, accumulate buffer and WAL usage.  (This must wait for the workers
+	 * to finish, or we might get incomplete data.)
+	 */
+	if (nworkers > 0)
+	{
+		/* Wait for all vacuum workers to finish */
+		WaitForParallelWorkersToFinish(lps->pcxt);
+
+		for (int i = 0; i < lps->pcxt->nworkers_launched; i++)
+			InstrAccumParallelQuery(&lps->buffer_usage[i], &lps->wal_usage[i]);
+	}
+
+	/*
+	 * Carry the shared balance value to heap scan and disable shared costing
+	 */
+	if (VacuumSharedCostBalance)
+	{
+		VacuumCostBalance = pg_atomic_read_u32(VacuumSharedCostBalance);
+		VacuumSharedCostBalance = NULL;
+		VacuumActiveNWorkers = NULL;
+	}
+}
+
+/*
+ * Index vacuum/cleanup routine used by the leader process and parallel
+ * vacuum worker processes to process the indexes in parallel.
+ */
+static void
+do_parallel_processing(LVRelState *vacrel, LVShared *lvshared)
+{
+	/*
+	 * Increment the active worker count if we are able to launch any worker.
+	 */
+	if (VacuumActiveNWorkers)
+		pg_atomic_add_fetch_u32(VacuumActiveNWorkers, 1);
+
+	/* Loop until all indexes are vacuumed */
+	for (;;)
+	{
+		int			idx;
+		LVSharedIndStats *shared_istat;
+		Relation	indrel;
+		IndexBulkDeleteResult *istat;
+
+		/* Get an index number to process */
+		idx = pg_atomic_fetch_add_u32(&(lvshared->idx), 1);
+
+		/* Done for all indexes? */
+		if (idx >= vacrel->nindexes)
+			break;
+
+		/* Get the index statistics space from DSM, if any */
+		shared_istat = parallel_stats_for_idx(lvshared, idx);
+
+		/* Skip indexes not participating in parallelism */
+		if (shared_istat == NULL)
+			continue;
+
+		indrel = vacrel->indrels[idx];
+
+		/*
+		 * Skip processing indexes that are unsafe for workers (these are
+		 * processed in do_serial_processing_for_unsafe_indexes() by leader)
+		 */
+		if (!parallel_processing_is_safe(indrel, lvshared))
+			continue;
+
+		/* Do vacuum or cleanup of the index */
+		istat = (vacrel->indstats[idx]);
+		vacrel->indstats[idx] = parallel_process_one_index(indrel, istat,
+														   lvshared,
+														   shared_istat,
+														   vacrel);
+	}
+
+	/*
+	 * We have completed the index vacuum so decrement the active worker
+	 * count.
+	 */
+	if (VacuumActiveNWorkers)
+		pg_atomic_sub_fetch_u32(VacuumActiveNWorkers, 1);
+}
+
+/*
+ * Perform parallel processing of indexes in leader process.
+ *
+ * Handles index vacuuming (or index cleanup) for indexes that are not
+ * parallel safe.  It's possible that this will vary for a given index, based
+ * on details like whether we're performing for_cleanup processing right now.
+ *
+ * Also performs processing of smaller indexes that fell under the size cutoff
+ * enforced by compute_parallel_vacuum_workers().  These indexes never get a
+ * slot for statistics in DSM.
+ */
+static void
+do_serial_processing_for_unsafe_indexes(LVRelState *vacrel, LVShared *lvshared)
+{
+	Assert(!IsParallelWorker());
+
+	/*
+	 * Increment the active worker count if we are able to launch any worker.
+	 */
+	if (VacuumActiveNWorkers)
+		pg_atomic_add_fetch_u32(VacuumActiveNWorkers, 1);
+
+	for (int idx = 0; idx < vacrel->nindexes; idx++)
+	{
+		LVSharedIndStats *shared_istat;
+		Relation	indrel;
+		IndexBulkDeleteResult *istat;
+
+		shared_istat = parallel_stats_for_idx(lvshared, idx);
+		indrel = vacrel->indrels[idx];
+
+		/*
+		 * We're only here for the indexes that parallel workers won't
+		 * process.  Note that the shared_istat test ensures that we process
+		 * indexes that fell under initial size cutoff.
+		 */
+		if (shared_istat != NULL &&
+			parallel_processing_is_safe(indrel, lvshared))
+			continue;
+
+		/* Do vacuum or cleanup of the index */
+		istat = (vacrel->indstats[idx]);
+		vacrel->indstats[idx] = parallel_process_one_index(indrel, istat,
+														   lvshared,
+														   shared_istat,
+														   vacrel);
+	}
+
+	/*
+	 * We have completed the index vacuum so decrement the active worker
+	 * count.
+	 */
+	if (VacuumActiveNWorkers)
+		pg_atomic_sub_fetch_u32(VacuumActiveNWorkers, 1);
+}
+
+/*
+ * Vacuum or cleanup index either by leader process or by one of the worker
+ * process.  After processing the index this function copies the index
+ * statistics returned from ambulkdelete and amvacuumcleanup to the DSM
+ * segment.
+ */
+static IndexBulkDeleteResult *
+parallel_process_one_index(Relation indrel,
+						   IndexBulkDeleteResult *istat,
+						   LVShared *lvshared,
+						   LVSharedIndStats *shared_istat,
+						   LVRelState *vacrel)
+{
+	IndexBulkDeleteResult *istat_res;
+
+	/*
+	 * Update the pointer to the corresponding bulk-deletion result if someone
+	 * has already updated it
+	 */
+	if (shared_istat && shared_istat->updated && istat == NULL)
+		istat = &shared_istat->istat;
+
+	/* Do vacuum or cleanup of the index */
+	if (lvshared->for_cleanup)
+		istat_res = lazy_cleanup_one_index(indrel, istat, lvshared->reltuples,
+										   lvshared->estimated_count, vacrel);
+	else
+		istat_res = lazy_vacuum_one_index(indrel, istat, lvshared->reltuples,
+										  vacrel);
+
+	/*
+	 * Copy the index bulk-deletion result returned from ambulkdelete and
+	 * amvacuumcleanup to the DSM segment if it's the first cycle because they
+	 * allocate locally and it's possible that an index will be vacuumed by a
+	 * different vacuum process the next cycle.  Copying the result normally
+	 * happens only the first time an index is vacuumed.  For any additional
+	 * vacuum pass, we directly point to the result on the DSM segment and
+	 * pass it to vacuum index APIs so that workers can update it directly.
+	 *
+	 * Since all vacuum workers write the bulk-deletion result at different
+	 * slots we can write them without locking.
+	 */
+	if (shared_istat && !shared_istat->updated && istat_res != NULL)
+	{
+		memcpy(&shared_istat->istat, istat_res, sizeof(IndexBulkDeleteResult));
+		shared_istat->updated = true;
+
+		/* Free the locally-allocated bulk-deletion result */
+		pfree(istat_res);
+
+		/* return the pointer to the result from shared memory */
+		return &shared_istat->istat;
+	}
+
+	return istat_res;
+}
+
+/*
+ *	lazy_cleanup_all_indexes() -- cleanup all indexes of relation.
+ */
+static void
+lazy_cleanup_all_indexes(LVRelState *vacrel)
+{
+	Assert(!IsParallelWorker());
+	Assert(vacrel->nindexes > 0);
+
+	/* Report that we are now cleaning up indexes */
+	pgstat_progress_update_param(PROGRESS_VACUUM_PHASE,
+								 PROGRESS_VACUUM_PHASE_INDEX_CLEANUP);
+
+	if (!ParallelVacuumIsActive(vacrel))
+	{
+		double		reltuples = vacrel->new_rel_tuples;
+		bool		estimated_count =
+		vacrel->tupcount_pages < vacrel->rel_pages;
+
+		for (int idx = 0; idx < vacrel->nindexes; idx++)
+		{
+			Relation	indrel = vacrel->indrels[idx];
+			IndexBulkDeleteResult *istat = vacrel->indstats[idx];
+
+			vacrel->indstats[idx] =
+				lazy_cleanup_one_index(indrel, istat, reltuples,
+									   estimated_count, vacrel);
+		}
+	}
+	else
+	{
+		/* Outsource everything to parallel variant */
+		do_parallel_lazy_cleanup_all_indexes(vacrel);
+	}
+}
+
+/*
+ *	lazy_vacuum_one_index() -- vacuum index relation.
+ *
+ *		Delete all the index entries pointing to tuples listed in
+ *		dead_tuples, and update running statistics.
+ *
+ *		reltuples is the number of heap tuples to be passed to the
+ *		bulkdelete callback.  It's always assumed to be estimated.
+ *
+ * Returns bulk delete stats derived from input stats
+ */
+static IndexBulkDeleteResult *
+lazy_vacuum_one_index(Relation indrel, IndexBulkDeleteResult *istat,
+					  double reltuples, LVRelState *vacrel)
+{
+	IndexVacuumInfo ivinfo;
+	PGRUsage	ru0;
+	LVSavedErrInfo saved_err_info;
+
+	pg_rusage_init(&ru0);
+
+	ivinfo.index = indrel;
+	ivinfo.analyze_only = false;
+	ivinfo.report_progress = false;
+	ivinfo.estimated_count = true;
+	ivinfo.message_level = elevel;
+	ivinfo.num_heap_tuples = reltuples;
+	ivinfo.strategy = vacrel->bstrategy;
+
+	/*
+	 * Update error traceback information.
+	 *
+	 * The index name is saved during this phase and restored immediately
+	 * after this phase.  See vacuum_error_callback.
+	 */
+	Assert(vacrel->indname == NULL);
+	vacrel->indname = pstrdup(RelationGetRelationName(indrel));
+	update_vacuum_error_info(vacrel, &saved_err_info,
+							 VACUUM_ERRCB_PHASE_VACUUM_INDEX,
+							 InvalidBlockNumber, InvalidOffsetNumber);
+
+	/* Do bulk deletion */
+	istat = index_bulk_delete(&ivinfo, istat, lazy_tid_reaped,
+							  (void *) vacrel->dead_tuples);
+
+	ereport(elevel,
+			(errmsg("scanned index \"%s\" to remove %d row versions",
+					vacrel->indname, vacrel->dead_tuples->num_tuples),
+			 errdetail_internal("%s", pg_rusage_show(&ru0))));
+
+	/* Revert to the previous phase information for error traceback */
+	restore_vacuum_error_info(vacrel, &saved_err_info);
+	pfree(vacrel->indname);
+	vacrel->indname = NULL;
+
+	return istat;
+}
+
+/*
+ *	lazy_cleanup_one_index() -- do post-vacuum cleanup for index relation.
+ *
+ *		reltuples is the number of heap tuples and estimated_count is true
+ *		if reltuples is an estimated value.
+ *
+ * Returns bulk delete stats derived from input stats
+ */
+static IndexBulkDeleteResult *
+lazy_cleanup_one_index(Relation indrel, IndexBulkDeleteResult *istat,
+					   double reltuples, bool estimated_count,
+					   LVRelState *vacrel)
+{
+	IndexVacuumInfo ivinfo;
+	PGRUsage	ru0;
+	LVSavedErrInfo saved_err_info;
+
+	pg_rusage_init(&ru0);
+
+	ivinfo.index = indrel;
+	ivinfo.analyze_only = false;
+	ivinfo.report_progress = false;
+	ivinfo.estimated_count = estimated_count;
+	ivinfo.message_level = elevel;
+
+	ivinfo.num_heap_tuples = reltuples;
+	ivinfo.strategy = vacrel->bstrategy;
+
+	/*
+	 * Update error traceback information.
+	 *
+	 * The index name is saved during this phase and restored immediately
+	 * after this phase.  See vacuum_error_callback.
+	 */
+	Assert(vacrel->indname == NULL);
+	vacrel->indname = pstrdup(RelationGetRelationName(indrel));
+	update_vacuum_error_info(vacrel, &saved_err_info,
+							 VACUUM_ERRCB_PHASE_INDEX_CLEANUP,
+							 InvalidBlockNumber, InvalidOffsetNumber);
+
+	istat = index_vacuum_cleanup(&ivinfo, istat);
+
+	if (istat)
+	{
+		ereport(elevel,
+				(errmsg("index \"%s\" now contains %.0f row versions in %u pages",
+						RelationGetRelationName(indrel),
+						(istat)->num_index_tuples,
+						(istat)->num_pages),
+				 errdetail("%.0f index row versions were removed.\n"
+						   "%u index pages were newly deleted.\n"
+						   "%u index pages are currently deleted, of which %u are currently reusable.\n"
+						   "%s.",
+						   (istat)->tuples_removed,
+						   (istat)->pages_newly_deleted,
+						   (istat)->pages_deleted, (istat)->pages_free,
+						   pg_rusage_show(&ru0))));
+	}
+
+	/* Revert to the previous phase information for error traceback */
+	restore_vacuum_error_info(vacrel, &saved_err_info);
+	pfree(vacrel->indname);
+	vacrel->indname = NULL;
+
+	return istat;
+}
+
+/*
+ * should_attempt_truncation - should we attempt to truncate the heap?
+ *
+ * Don't even think about it unless we have a shot at releasing a goodly
+ * number of pages.  Otherwise, the time taken isn't worth it.
+ *
+ * Also don't attempt it if wraparound failsafe is in effect.  It's hard to
+ * predict how long lazy_truncate_heap will take.  Don't take any chances.
+ * There is very little chance of truncation working out when the failsafe is
+ * in effect in any case.  lazy_scan_prune makes the optimistic assumption
+ * that any LP_DEAD items it encounters will always be LP_UNUSED by the time
+ * we're called.
+ *
+ * Also don't attempt it if we are doing early pruning/vacuuming, because a
+ * scan which cannot find a truncated heap page cannot determine that the
+ * snapshot is too old to read that page.
+ *
+ * This is split out so that we can test whether truncation is going to be
+ * called for before we actually do it.  If you change the logic here, be
+ * careful to depend only on fields that lazy_scan_heap updates on-the-fly.
+ */
+static bool
+should_attempt_truncation(LVRelState *vacrel)
+{
+	BlockNumber possibly_freeable;
+
+	if (!vacrel->do_rel_truncate || vacrel->failsafe_active)
+		return false;
+
+	possibly_freeable = vacrel->rel_pages - vacrel->nonempty_pages;
+	if (possibly_freeable > 0 &&
+		(possibly_freeable >= REL_TRUNCATE_MINIMUM ||
+		 possibly_freeable >= vacrel->rel_pages / REL_TRUNCATE_FRACTION) &&
+		old_snapshot_threshold < 0)
+		return true;
+	else
+		return false;
+}
+
+/*
+ * lazy_truncate_heap - try to truncate off any empty pages at the end
+ */
+static void
+lazy_truncate_heap(LVRelState *vacrel)
+{
+	BlockNumber old_rel_pages = vacrel->rel_pages;
+	BlockNumber new_rel_pages;
+	bool		lock_waiter_detected;
+	int			lock_retry;
+
+	/* Report that we are now truncating */
+	pgstat_progress_update_param(PROGRESS_VACUUM_PHASE,
+								 PROGRESS_VACUUM_PHASE_TRUNCATE);
+
+	/*
+	 * Loop until no more truncating can be done.
+	 */
+	do
+	{
+		PGRUsage	ru0;
+
+		pg_rusage_init(&ru0);
+
+		/*
+		 * We need full exclusive lock on the relation in order to do
+		 * truncation. If we can't get it, give up rather than waiting --- we
+		 * don't want to block other backends, and we don't want to deadlock
+		 * (which is quite possible considering we already hold a lower-grade
+		 * lock).
+		 */
+		lock_waiter_detected = false;
+		lock_retry = 0;
+		while (true)
+		{
+			if (ConditionalLockRelation(vacrel->rel, AccessExclusiveLock))
+				break;
+
+			/*
+			 * Check for interrupts while trying to (re-)acquire the exclusive
+			 * lock.
+			 */
+			CHECK_FOR_INTERRUPTS();
+
+			if (++lock_retry > (VACUUM_TRUNCATE_LOCK_TIMEOUT /
+								VACUUM_TRUNCATE_LOCK_WAIT_INTERVAL))
+			{
+				/*
+				 * We failed to establish the lock in the specified number of
+				 * retries. This means we give up truncating.
+				 */
+				ereport(elevel,
+						(errmsg("\"%s\": stopping truncate due to conflicting lock request",
+								vacrel->relname)));
+				return;
+			}
+
+			pg_usleep(VACUUM_TRUNCATE_LOCK_WAIT_INTERVAL * 1000L);
+		}
+
+		/*
+		 * Now that we have exclusive lock, look to see if the rel has grown
+		 * whilst we were vacuuming with non-exclusive lock.  If so, give up;
+		 * the newly added pages presumably contain non-deletable tuples.
+		 */
+		new_rel_pages = RelationGetNumberOfBlocks(vacrel->rel);
+		if (new_rel_pages != old_rel_pages)
+		{
+			/*
+			 * Note: we intentionally don't update vacrel->rel_pages with the
+			 * new rel size here.  If we did, it would amount to assuming that
+			 * the new pages are empty, which is unlikely. Leaving the numbers
+			 * alone amounts to assuming that the new pages have the same
+			 * tuple density as existing ones, which is less unlikely.
+			 */
+			UnlockRelation(vacrel->rel, AccessExclusiveLock);
+			return;
+		}
+
+		/*
+		 * Scan backwards from the end to verify that the end pages actually
+		 * contain no tuples.  This is *necessary*, not optional, because
+		 * other backends could have added tuples to these pages whilst we
+		 * were vacuuming.
+		 */
+		new_rel_pages = count_nondeletable_pages(vacrel, &lock_waiter_detected);
+		vacrel->blkno = new_rel_pages;
+
+		if (new_rel_pages >= old_rel_pages)
+		{
+			/* can't do anything after all */
+			UnlockRelation(vacrel->rel, AccessExclusiveLock);
+			return;
+		}
+
+		/*
+		 * Okay to truncate.
+		 */
+		RelationTruncate(vacrel->rel, new_rel_pages);
+
+		/*
+		 * We can release the exclusive lock as soon as we have truncated.
+		 * Other backends can't safely access the relation until they have
+		 * processed the smgr invalidation that smgrtruncate sent out ... but
+		 * that should happen as part of standard invalidation processing once
+		 * they acquire lock on the relation.
+		 */
+		UnlockRelation(vacrel->rel, AccessExclusiveLock);
+
+		/*
+		 * Update statistics.  Here, it *is* correct to adjust rel_pages
+		 * without also touching reltuples, since the tuple count wasn't
+		 * changed by the truncation.
+		 */
+		vacrel->pages_removed += old_rel_pages - new_rel_pages;
+		vacrel->rel_pages = new_rel_pages;
+
+		ereport(elevel,
+				(errmsg("table \"%s\": truncated %u to %u pages",
+						vacrel->relname,
+						old_rel_pages, new_rel_pages),
+				 errdetail_internal("%s",
+									pg_rusage_show(&ru0))));
+		old_rel_pages = new_rel_pages;
+	} while (new_rel_pages > vacrel->nonempty_pages && lock_waiter_detected);
+}
+
+/*
+ * Rescan end pages to verify that they are (still) empty of tuples.
+ *
+ * Returns number of nondeletable pages (last nonempty page + 1).
+ */
+static BlockNumber
+count_nondeletable_pages(LVRelState *vacrel, bool *lock_waiter_detected)
+{
+	BlockNumber blkno;
+	BlockNumber prefetchedUntil;
+	instr_time	starttime;
+
+	/* Initialize the starttime if we check for conflicting lock requests */
+	INSTR_TIME_SET_CURRENT(starttime);
+
+	/*
+	 * Start checking blocks at what we believe relation end to be and move
+	 * backwards.  (Strange coding of loop control is needed because blkno is
+	 * unsigned.)  To make the scan faster, we prefetch a few blocks at a time
+	 * in forward direction, so that OS-level readahead can kick in.
+	 */
+	blkno = vacrel->rel_pages;
+	StaticAssertStmt((PREFETCH_SIZE & (PREFETCH_SIZE - 1)) == 0,
+					 "prefetch size must be power of 2");
+	prefetchedUntil = InvalidBlockNumber;
+	while (blkno > vacrel->nonempty_pages)
+	{
+		Buffer		buf;
+		Page		page;
+		OffsetNumber offnum,
+					maxoff;
+		bool		hastup;
+
+		/*
+		 * Check if another process requests a lock on our relation. We are
+		 * holding an AccessExclusiveLock here, so they will be waiting. We
+		 * only do this once per VACUUM_TRUNCATE_LOCK_CHECK_INTERVAL, and we
+		 * only check if that interval has elapsed once every 32 blocks to
+		 * keep the number of system calls and actual shared lock table
+		 * lookups to a minimum.
+		 */
+		if ((blkno % 32) == 0)
+		{
+			instr_time	currenttime;
+			instr_time	elapsed;
+
+			INSTR_TIME_SET_CURRENT(currenttime);
+			elapsed = currenttime;
+			INSTR_TIME_SUBTRACT(elapsed, starttime);
+			if ((INSTR_TIME_GET_MICROSEC(elapsed) / 1000)
+				>= VACUUM_TRUNCATE_LOCK_CHECK_INTERVAL)
+			{
+				if (LockHasWaitersRelation(vacrel->rel, AccessExclusiveLock))
+				{
+					ereport(elevel,
+							(errmsg("table \"%s\": suspending truncate due to conflicting lock request",
+									vacrel->relname)));
+
+					*lock_waiter_detected = true;
+					return blkno;
+				}
+				starttime = currenttime;
+			}
+		}
+
+		/*
+		 * We don't insert a vacuum delay point here, because we have an
+		 * exclusive lock on the table which we want to hold for as short a
+		 * time as possible.  We still need to check for interrupts however.
+		 */
+		CHECK_FOR_INTERRUPTS();
+
+		blkno--;
+
+		/* If we haven't prefetched this lot yet, do so now. */
+		if (prefetchedUntil > blkno)
+		{
+			BlockNumber prefetchStart;
+			BlockNumber pblkno;
+
+			prefetchStart = blkno & ~(PREFETCH_SIZE - 1);
+			for (pblkno = prefetchStart; pblkno <= blkno; pblkno++)
+			{
+				PrefetchBuffer(vacrel->rel, MAIN_FORKNUM, pblkno);
+				CHECK_FOR_INTERRUPTS();
+			}
+			prefetchedUntil = prefetchStart;
+		}
+
+		buf = ReadBufferExtended(vacrel->rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
+								 vacrel->bstrategy);
+
+		/* In this phase we only need shared access to the buffer */
+		LockBuffer(buf, BUFFER_LOCK_SHARE);
+
+		page = BufferGetPage(buf);
+
+		if (PageIsNew(page) || PageIsEmpty(page))
+		{
+			UnlockReleaseBuffer(buf);
+			continue;
+		}
+
+		hastup = false;
+		maxoff = PageGetMaxOffsetNumber(page);
+		for (offnum = FirstOffsetNumber;
+			 offnum <= maxoff;
+			 offnum = OffsetNumberNext(offnum))
+		{
+			ItemId		itemid;
+
+			itemid = PageGetItemId(page, offnum);
+
+			/*
+			 * Note: any non-unused item should be taken as a reason to keep
+			 * this page.  Even an LP_DEAD item makes truncation unsafe, since
+			 * we must not have cleaned out its index entries.
+			 */
+			if (ItemIdIsUsed(itemid))
+			{
+				hastup = true;
+				break;			/* can stop scanning */
+			}
+		}						/* scan along page */
+
+		UnlockReleaseBuffer(buf);
+
+		/* Done scanning if we found a tuple here */
+		if (hastup)
+			return blkno + 1;
+	}
+
+	/*
+	 * If we fall out of the loop, all the previously-thought-to-be-empty
+	 * pages still are; we need not bother to look at the last known-nonempty
+	 * page.
+	 */
+	return vacrel->nonempty_pages;
+}
+
+/*
+ * Return the maximum number of dead tuples we can record.
+ */
+static long
+compute_max_dead_tuples(BlockNumber relblocks, bool hasindex)
+{
+	long		maxtuples;
+	int			vac_work_mem = IsAutoVacuumWorkerProcess() &&
+	autovacuum_work_mem != -1 ?
+	autovacuum_work_mem : maintenance_work_mem;
+
+	if (hasindex)
+	{
+		maxtuples = MAXDEADTUPLES(vac_work_mem * 1024L);
+		maxtuples = Min(maxtuples, INT_MAX);
+		maxtuples = Min(maxtuples, MAXDEADTUPLES(MaxAllocSize));
+
+		/* curious coding here to ensure the multiplication can't overflow */
+		if ((BlockNumber) (maxtuples / LAZY_ALLOC_TUPLES) > relblocks)
+			maxtuples = relblocks * LAZY_ALLOC_TUPLES;
+
+		/* stay sane if small maintenance_work_mem */
+		maxtuples = Max(maxtuples, MaxHeapTuplesPerPage);
+	}
+	else
+		maxtuples = MaxHeapTuplesPerPage;
+
+	return maxtuples;
+}
+
+/*
+ * lazy_space_alloc - space allocation decisions for lazy vacuum
+ *
+ * See the comments at the head of this file for rationale.
+ */
+static void
+lazy_space_alloc(LVRelState *vacrel, int nworkers, BlockNumber nblocks)
+{
+	LVDeadTuples *dead_tuples;
+	long		maxtuples;
+
+	/*
+	 * Initialize state for a parallel vacuum.  As of now, only one worker can
+	 * be used for an index, so we invoke parallelism only if there are at
+	 * least two indexes on a table.
+	 */
+	if (nworkers >= 0 && vacrel->nindexes > 1 && vacrel->do_index_vacuuming)
+	{
+		/*
+		 * Since parallel workers cannot access data in temporary tables, we
+		 * can't perform parallel vacuum on them.
+		 */
+		if (RelationUsesLocalBuffers(vacrel->rel))
+		{
+			/*
+			 * Give warning only if the user explicitly tries to perform a
+			 * parallel vacuum on the temporary table.
+			 */
+			if (nworkers > 0)
+				ereport(WARNING,
+						(errmsg("disabling parallel option of vacuum on \"%s\" --- cannot vacuum temporary tables in parallel",
+								vacrel->relname)));
+		}
+		else
+			vacrel->lps = begin_parallel_vacuum(vacrel, nblocks, nworkers);
+
+		/* If parallel mode started, we're done */
+		if (ParallelVacuumIsActive(vacrel))
+			return;
+	}
+
+	maxtuples = compute_max_dead_tuples(nblocks, vacrel->nindexes > 0);
+
+	dead_tuples = (LVDeadTuples *) palloc(SizeOfDeadTuples(maxtuples));
+	dead_tuples->num_tuples = 0;
+	dead_tuples->max_tuples = (int) maxtuples;
+
+	vacrel->dead_tuples = dead_tuples;
+}
+
+/*
+ * lazy_space_free - free space allocated in lazy_space_alloc
+ */
+static void
+lazy_space_free(LVRelState *vacrel)
+{
+	if (!ParallelVacuumIsActive(vacrel))
+		return;
+
+	/*
+	 * End parallel mode before updating index statistics as we cannot write
+	 * during parallel mode.
+	 */
+	end_parallel_vacuum(vacrel);
+}
+
+/*
+ *	lazy_tid_reaped() -- is a particular tid deletable?
+ *
+ *		This has the right signature to be an IndexBulkDeleteCallback.
+ *
+ *		Assumes dead_tuples array is in sorted order.
+ */
+static bool
+lazy_tid_reaped(ItemPointer itemptr, void *state)
+{
+	LVDeadTuples *dead_tuples = (LVDeadTuples *) state;
+	int64		litem,
+				ritem,
+				item;
+	ItemPointer res;
+
+	litem = itemptr_encode(&dead_tuples->itemptrs[0]);
+	ritem = itemptr_encode(&dead_tuples->itemptrs[dead_tuples->num_tuples - 1]);
+	item = itemptr_encode(itemptr);
+
+	/*
+	 * Doing a simple bound check before bsearch() is useful to avoid the
+	 * extra cost of bsearch(), especially if dead tuples on the heap are
+	 * concentrated in a certain range.  Since this function is called for
+	 * every index tuple, it pays to be really fast.
+	 */
+	if (item < litem || item > ritem)
+		return false;
+
+	res = (ItemPointer) bsearch((void *) itemptr,
+								(void *) dead_tuples->itemptrs,
+								dead_tuples->num_tuples,
+								sizeof(ItemPointerData),
+								vac_cmp_itemptr);
+
+	return (res != NULL);
+}
+
+/*
+ * Comparator routines for use with qsort() and bsearch().
+ */
+static int
+vac_cmp_itemptr(const void *left, const void *right)
+{
+	BlockNumber lblk,
+				rblk;
+	OffsetNumber loff,
+				roff;
+
+	lblk = ItemPointerGetBlockNumber((ItemPointer) left);
+	rblk = ItemPointerGetBlockNumber((ItemPointer) right);
+
+	if (lblk < rblk)
+		return -1;
+	if (lblk > rblk)
+		return 1;
+
+	loff = ItemPointerGetOffsetNumber((ItemPointer) left);
+	roff = ItemPointerGetOffsetNumber((ItemPointer) right);
+
+	if (loff < roff)
+		return -1;
+	if (loff > roff)
+		return 1;
+
+	return 0;
+}
+
+/*
+ * Check if every tuple in the given page is visible to all current and future
+ * transactions. Also return the visibility_cutoff_xid which is the highest
+ * xmin amongst the visible tuples.  Set *all_frozen to true if every tuple
+ * on this page is frozen.
+ */
+static bool
+heap_page_is_all_visible(LVRelState *vacrel, Buffer buf,
+						 TransactionId *visibility_cutoff_xid,
+						 bool *all_frozen)
+{
+	Page		page = BufferGetPage(buf);
+	BlockNumber blockno = BufferGetBlockNumber(buf);
+	OffsetNumber offnum,
+				maxoff;
+	bool		all_visible = true;
+
+	*visibility_cutoff_xid = InvalidTransactionId;
+	*all_frozen = true;
+
+	/*
+	 * This is a stripped down version of the line pointer scan in
+	 * lazy_scan_heap(). So if you change anything here, also check that code.
+	 */
+	maxoff = PageGetMaxOffsetNumber(page);
+	for (offnum = FirstOffsetNumber;
+		 offnum <= maxoff && all_visible;
+		 offnum = OffsetNumberNext(offnum))
+	{
+		ItemId		itemid;
+		HeapTupleData tuple;
+
+		/*
+		 * Set the offset number so that we can display it along with any
+		 * error that occurred while processing this tuple.
+		 */
+		vacrel->offnum = offnum;
+		itemid = PageGetItemId(page, offnum);
+
+		/* Unused or redirect line pointers are of no interest */
+		if (!ItemIdIsUsed(itemid) || ItemIdIsRedirected(itemid))
+			continue;
+
+		ItemPointerSet(&(tuple.t_self), blockno, offnum);
+
+		/*
+		 * Dead line pointers can have index pointers pointing to them. So
+		 * they can't be treated as visible
+		 */
+		if (ItemIdIsDead(itemid))
+		{
+			all_visible = false;
+			*all_frozen = false;
+			break;
+		}
+
+		Assert(ItemIdIsNormal(itemid));
+
+		tuple.t_data = (HeapTupleHeader) PageGetItem(page, itemid);
+		tuple.t_len = ItemIdGetLength(itemid);
+		tuple.t_tableOid = RelationGetRelid(vacrel->rel);
+
+		switch (HeapTupleSatisfiesVacuum(&tuple, vacrel->OldestXmin, buf))
+		{
+			case HEAPTUPLE_LIVE:
+				{
+					TransactionId xmin;
+
+					/* Check comments in lazy_scan_heap. */
+					if (!HeapTupleHeaderXminCommitted(tuple.t_data))
+					{
+						all_visible = false;
+						*all_frozen = false;
+						break;
+					}
+
+					/*
+					 * The inserter definitely committed. But is it old enough
+					 * that everyone sees it as committed?
+					 */
+					xmin = HeapTupleHeaderGetXmin(tuple.t_data);
+					if (!TransactionIdPrecedes(xmin, vacrel->OldestXmin))
+					{
+						all_visible = false;
+						*all_frozen = false;
+						break;
+					}
+
+					/* Track newest xmin on page. */
+					if (TransactionIdFollows(xmin, *visibility_cutoff_xid))
+						*visibility_cutoff_xid = xmin;
+
+					/* Check whether this tuple is already frozen or not */
+					if (all_visible && *all_frozen &&
+						heap_tuple_needs_eventual_freeze(tuple.t_data))
+						*all_frozen = false;
+				}
+				break;
+
+			case HEAPTUPLE_DEAD:
+			case HEAPTUPLE_RECENTLY_DEAD:
+			case HEAPTUPLE_INSERT_IN_PROGRESS:
+			case HEAPTUPLE_DELETE_IN_PROGRESS:
+				{
+					all_visible = false;
+					*all_frozen = false;
+					break;
+				}
+			default:
+				elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
+				break;
+		}
+	}							/* scan along page */
+
+	/* Clear the offset information once we have processed the given page. */
+	vacrel->offnum = InvalidOffsetNumber;
+
+	return all_visible;
+}
+
+/*
+ * Compute the number of parallel worker processes to request.  Both index
+ * vacuum and index cleanup can be executed with parallel workers.  The index
+ * is eligible for parallel vacuum iff its size is greater than
+ * min_parallel_index_scan_size as invoking workers for very small indexes
+ * can hurt performance.
+ *
+ * nrequested is the number of parallel workers that user requested.  If
+ * nrequested is 0, we compute the parallel degree based on nindexes, that is
+ * the number of indexes that support parallel vacuum.  This function also
+ * sets will_parallel_vacuum to remember indexes that participate in parallel
+ * vacuum.
+ */
+static int
+compute_parallel_vacuum_workers(LVRelState *vacrel, int nrequested,
+								bool *will_parallel_vacuum)
+{
+	int			nindexes_parallel = 0;
+	int			nindexes_parallel_bulkdel = 0;
+	int			nindexes_parallel_cleanup = 0;
+	int			parallel_workers;
+
+	/*
+	 * We don't allow performing parallel operation in standalone backend or
+	 * when parallelism is disabled.
+	 */
+	if (!IsUnderPostmaster || max_parallel_maintenance_workers == 0)
+		return 0;
+
+	/*
+	 * Compute the number of indexes that can participate in parallel vacuum.
+	 */
+	for (int idx = 0; idx < vacrel->nindexes; idx++)
+	{
+		Relation	indrel = vacrel->indrels[idx];
+		uint8		vacoptions = indrel->rd_indam->amparallelvacuumoptions;
+
+		if (vacoptions == VACUUM_OPTION_NO_PARALLEL ||
+			RelationGetNumberOfBlocks(indrel) < min_parallel_index_scan_size)
+			continue;
+
+		will_parallel_vacuum[idx] = true;
+
+		if ((vacoptions & VACUUM_OPTION_PARALLEL_BULKDEL) != 0)
+			nindexes_parallel_bulkdel++;
+		if (((vacoptions & VACUUM_OPTION_PARALLEL_CLEANUP) != 0) ||
+			((vacoptions & VACUUM_OPTION_PARALLEL_COND_CLEANUP) != 0))
+			nindexes_parallel_cleanup++;
+	}
+
+	nindexes_parallel = Max(nindexes_parallel_bulkdel,
+							nindexes_parallel_cleanup);
+
+	/* The leader process takes one index */
+	nindexes_parallel--;
+
+	/* No index supports parallel vacuum */
+	if (nindexes_parallel <= 0)
+		return 0;
+
+	/* Compute the parallel degree */
+	parallel_workers = (nrequested > 0) ?
+		Min(nrequested, nindexes_parallel) : nindexes_parallel;
+
+	/* Cap by max_parallel_maintenance_workers */
+	parallel_workers = Min(parallel_workers, max_parallel_maintenance_workers);
+
+	return parallel_workers;
+}
+
+/*
+ * Update index statistics in pg_class if the statistics are accurate.
+ */
+static void
+update_index_statistics(LVRelState *vacrel)
+{
+	Relation   *indrels = vacrel->indrels;
+	int			nindexes = vacrel->nindexes;
+	IndexBulkDeleteResult **indstats = vacrel->indstats;
+
+	Assert(!IsInParallelMode());
+
+	for (int idx = 0; idx < nindexes; idx++)
+	{
+		Relation	indrel = indrels[idx];
+		IndexBulkDeleteResult *istat = indstats[idx];
+
+		if (istat == NULL || istat->estimated_count)
+			continue;
+
+		/* Update index statistics */
+		vac_update_relstats(indrel,
+							istat->num_pages,
+							istat->num_index_tuples,
+							0,
+							false,
+							InvalidTransactionId,
+							InvalidMultiXactId,
+							false);
+	}
+}
+
+/*
+ * This function prepares and returns parallel vacuum state if we can launch
+ * even one worker.  This function is responsible for entering parallel mode,
+ * create a parallel context, and then initialize the DSM segment.
+ */
+static LVParallelState *
+begin_parallel_vacuum(LVRelState *vacrel, BlockNumber nblocks,
+					  int nrequested)
+{
+	LVParallelState *lps = NULL;
+	Relation   *indrels = vacrel->indrels;
+	int			nindexes = vacrel->nindexes;
+	ParallelContext *pcxt;
+	LVShared   *shared;
+	LVDeadTuples *dead_tuples;
+	BufferUsage *buffer_usage;
+	WalUsage   *wal_usage;
+	bool	   *will_parallel_vacuum;
+	long		maxtuples;
+	Size		est_shared;
+	Size		est_deadtuples;
+	int			nindexes_mwm = 0;
+	int			parallel_workers = 0;
+	int			querylen;
+
+	/*
+	 * A parallel vacuum must be requested and there must be indexes on the
+	 * relation
+	 */
+	Assert(nrequested >= 0);
+	Assert(nindexes > 0);
+
+	/*
+	 * Compute the number of parallel vacuum workers to launch
+	 */
+	will_parallel_vacuum = (bool *) palloc0(sizeof(bool) * nindexes);
+	parallel_workers = compute_parallel_vacuum_workers(vacrel,
+													   nrequested,
+													   will_parallel_vacuum);
+
+	/* Can't perform vacuum in parallel */
+	if (parallel_workers <= 0)
+	{
+		pfree(will_parallel_vacuum);
+		return lps;
+	}
+
+	lps = (LVParallelState *) palloc0(sizeof(LVParallelState));
+
+	EnterParallelMode();
+	pcxt = CreateParallelContext("postgres", "parallel_vacuum_main",
+								 parallel_workers);
+	Assert(pcxt->nworkers > 0);
+	lps->pcxt = pcxt;
+
+	/* Estimate size for shared information -- PARALLEL_VACUUM_KEY_SHARED */
+	est_shared = MAXALIGN(add_size(SizeOfLVShared, BITMAPLEN(nindexes)));
+	for (int idx = 0; idx < nindexes; idx++)
+	{
+		Relation	indrel = indrels[idx];
+		uint8		vacoptions = indrel->rd_indam->amparallelvacuumoptions;
+
+		/*
+		 * Cleanup option should be either disabled, always performing in
+		 * parallel or conditionally performing in parallel.
+		 */
+		Assert(((vacoptions & VACUUM_OPTION_PARALLEL_CLEANUP) == 0) ||
+			   ((vacoptions & VACUUM_OPTION_PARALLEL_COND_CLEANUP) == 0));
+		Assert(vacoptions <= VACUUM_OPTION_MAX_VALID_VALUE);
+
+		/* Skip indexes that don't participate in parallel vacuum */
+		if (!will_parallel_vacuum[idx])
+			continue;
+
+		if (indrel->rd_indam->amusemaintenanceworkmem)
+			nindexes_mwm++;
+
+		est_shared = add_size(est_shared, sizeof(LVSharedIndStats));
+
+		/*
+		 * Remember the number of indexes that support parallel operation for
+		 * each phase.
+		 */
+		if ((vacoptions & VACUUM_OPTION_PARALLEL_BULKDEL) != 0)
+			lps->nindexes_parallel_bulkdel++;
+		if ((vacoptions & VACUUM_OPTION_PARALLEL_CLEANUP) != 0)
+			lps->nindexes_parallel_cleanup++;
+		if ((vacoptions & VACUUM_OPTION_PARALLEL_COND_CLEANUP) != 0)
+			lps->nindexes_parallel_condcleanup++;
+	}
+	shm_toc_estimate_chunk(&pcxt->estimator, est_shared);
+	shm_toc_estimate_keys(&pcxt->estimator, 1);
+
+	/* Estimate size for dead tuples -- PARALLEL_VACUUM_KEY_DEAD_TUPLES */
+	maxtuples = compute_max_dead_tuples(nblocks, true);
+	est_deadtuples = MAXALIGN(SizeOfDeadTuples(maxtuples));
+	shm_toc_estimate_chunk(&pcxt->estimator, est_deadtuples);
+	shm_toc_estimate_keys(&pcxt->estimator, 1);
+
+	/*
+	 * Estimate space for BufferUsage and WalUsage --
+	 * PARALLEL_VACUUM_KEY_BUFFER_USAGE and PARALLEL_VACUUM_KEY_WAL_USAGE.
+	 *
+	 * If there are no extensions loaded that care, we could skip this.  We
+	 * have no way of knowing whether anyone's looking at pgBufferUsage or
+	 * pgWalUsage, so do it unconditionally.
+	 */
+	shm_toc_estimate_chunk(&pcxt->estimator,
+						   mul_size(sizeof(BufferUsage), pcxt->nworkers));
+	shm_toc_estimate_keys(&pcxt->estimator, 1);
+	shm_toc_estimate_chunk(&pcxt->estimator,
+						   mul_size(sizeof(WalUsage), pcxt->nworkers));
+	shm_toc_estimate_keys(&pcxt->estimator, 1);
+
+	/* Finally, estimate PARALLEL_VACUUM_KEY_QUERY_TEXT space */
+	if (debug_query_string)
+	{
+		querylen = strlen(debug_query_string);
+		shm_toc_estimate_chunk(&pcxt->estimator, querylen + 1);
+		shm_toc_estimate_keys(&pcxt->estimator, 1);
+	}
+	else
+		querylen = 0;			/* keep compiler quiet */
+
+	InitializeParallelDSM(pcxt);
+
+	/* Prepare shared information */
+	shared = (LVShared *) shm_toc_allocate(pcxt->toc, est_shared);
+	MemSet(shared, 0, est_shared);
+	shared->relid = RelationGetRelid(vacrel->rel);
+	shared->elevel = elevel;
+	shared->maintenance_work_mem_worker =
+		(nindexes_mwm > 0) ?
+		maintenance_work_mem / Min(parallel_workers, nindexes_mwm) :
+		maintenance_work_mem;
+
+	pg_atomic_init_u32(&(shared->cost_balance), 0);
+	pg_atomic_init_u32(&(shared->active_nworkers), 0);
+	pg_atomic_init_u32(&(shared->idx), 0);
+	shared->offset = MAXALIGN(add_size(SizeOfLVShared, BITMAPLEN(nindexes)));
+
+	/*
+	 * Initialize variables for shared index statistics, set NULL bitmap and
+	 * the size of stats for each index.
+	 */
+	memset(shared->bitmap, 0x00, BITMAPLEN(nindexes));
+	for (int idx = 0; idx < nindexes; idx++)
+	{
+		if (!will_parallel_vacuum[idx])
+			continue;
+
+		/* Set NOT NULL as this index does support parallelism */
+		shared->bitmap[idx >> 3] |= 1 << (idx & 0x07);
+	}
+
+	shm_toc_insert(pcxt->toc, PARALLEL_VACUUM_KEY_SHARED, shared);
+	lps->lvshared = shared;
+
+	/* Prepare the dead tuple space */
+	dead_tuples = (LVDeadTuples *) shm_toc_allocate(pcxt->toc, est_deadtuples);
+	dead_tuples->max_tuples = maxtuples;
+	dead_tuples->num_tuples = 0;
+	MemSet(dead_tuples->itemptrs, 0, sizeof(ItemPointerData) * maxtuples);
+	shm_toc_insert(pcxt->toc, PARALLEL_VACUUM_KEY_DEAD_TUPLES, dead_tuples);
+	vacrel->dead_tuples = dead_tuples;
+
+	/*
+	 * Allocate space for each worker's BufferUsage and WalUsage; no need to
+	 * initialize
+	 */
+	buffer_usage = shm_toc_allocate(pcxt->toc,
+									mul_size(sizeof(BufferUsage), pcxt->nworkers));
+	shm_toc_insert(pcxt->toc, PARALLEL_VACUUM_KEY_BUFFER_USAGE, buffer_usage);
+	lps->buffer_usage = buffer_usage;
+	wal_usage = shm_toc_allocate(pcxt->toc,
+								 mul_size(sizeof(WalUsage), pcxt->nworkers));
+	shm_toc_insert(pcxt->toc, PARALLEL_VACUUM_KEY_WAL_USAGE, wal_usage);
+	lps->wal_usage = wal_usage;
+
+	/* Store query string for workers */
+	if (debug_query_string)
+	{
+		char	   *sharedquery;
+
+		sharedquery = (char *) shm_toc_allocate(pcxt->toc, querylen + 1);
+		memcpy(sharedquery, debug_query_string, querylen + 1);
+		sharedquery[querylen] = '\0';
+		shm_toc_insert(pcxt->toc,
+					   PARALLEL_VACUUM_KEY_QUERY_TEXT, sharedquery);
+	}
+
+	pfree(will_parallel_vacuum);
+	return lps;
+}
+
+/*
+ * Destroy the parallel context, and end parallel mode.
+ *
+ * Since writes are not allowed during parallel mode, copy the
+ * updated index statistics from DSM into local memory and then later use that
+ * to update the index statistics.  One might think that we can exit from
+ * parallel mode, update the index statistics and then destroy parallel
+ * context, but that won't be safe (see ExitParallelMode).
+ */
+static void
+end_parallel_vacuum(LVRelState *vacrel)
+{
+	IndexBulkDeleteResult **indstats = vacrel->indstats;
+	LVParallelState *lps = vacrel->lps;
+	int			nindexes = vacrel->nindexes;
+
+	Assert(!IsParallelWorker());
+
+	/* Copy the updated statistics */
+	for (int idx = 0; idx < nindexes; idx++)
+	{
+		LVSharedIndStats *shared_istat;
+
+		shared_istat = parallel_stats_for_idx(lps->lvshared, idx);
+
+		/*
+		 * Skip index -- it must have been processed by the leader, from
+		 * inside do_serial_processing_for_unsafe_indexes()
+		 */
+		if (shared_istat == NULL)
+			continue;
+
+		if (shared_istat->updated)
+		{
+			indstats[idx] = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));
+			memcpy(indstats[idx], &(shared_istat->istat), sizeof(IndexBulkDeleteResult));
+		}
+		else
+			indstats[idx] = NULL;
+	}
+
+	DestroyParallelContext(lps->pcxt);
+	ExitParallelMode();
+
+	/* Deactivate parallel vacuum */
+	pfree(lps);
+	vacrel->lps = NULL;
+}
+
+/*
+ * Return shared memory statistics for index at offset 'getidx', if any
+ *
+ * Returning NULL indicates that compute_parallel_vacuum_workers() determined
+ * that the index is a totally unsuitable target for all parallel processing
+ * up front.  For example, the index could be < min_parallel_index_scan_size
+ * cutoff.
+ */
+static LVSharedIndStats *
+parallel_stats_for_idx(LVShared *lvshared, int getidx)
+{
+	char	   *p;
+
+	if (IndStatsIsNull(lvshared, getidx))
+		return NULL;
+
+	p = (char *) GetSharedIndStats(lvshared);
+	for (int idx = 0; idx < getidx; idx++)
+	{
+		if (IndStatsIsNull(lvshared, idx))
+			continue;
+
+		p += sizeof(LVSharedIndStats);
+	}
+
+	return (LVSharedIndStats *) p;
+}
+
+/*
+ * Returns false, if the given index can't participate in parallel index
+ * vacuum or parallel index cleanup
+ */
+static bool
+parallel_processing_is_safe(Relation indrel, LVShared *lvshared)
+{
+	uint8		vacoptions = indrel->rd_indam->amparallelvacuumoptions;
+
+	/* first_time must be true only if for_cleanup is true */
+	Assert(lvshared->for_cleanup || !lvshared->first_time);
+
+	if (lvshared->for_cleanup)
+	{
+		/* Skip, if the index does not support parallel cleanup */
+		if (((vacoptions & VACUUM_OPTION_PARALLEL_CLEANUP) == 0) &&
+			((vacoptions & VACUUM_OPTION_PARALLEL_COND_CLEANUP) == 0))
+			return false;
+
+		/*
+		 * Skip, if the index supports parallel cleanup conditionally, but we
+		 * have already processed the index (for bulkdelete).  See the
+		 * comments for option VACUUM_OPTION_PARALLEL_COND_CLEANUP to know
+		 * when indexes support parallel cleanup conditionally.
+		 */
+		if (!lvshared->first_time &&
+			((vacoptions & VACUUM_OPTION_PARALLEL_COND_CLEANUP) != 0))
+			return false;
+	}
+	else if ((vacoptions & VACUUM_OPTION_PARALLEL_BULKDEL) == 0)
+	{
+		/* Skip if the index does not support parallel bulk deletion */
+		return false;
+	}
+
+	return true;
+}
+
+/*
+ * Perform work within a launched parallel process.
+ *
+ * Since parallel vacuum workers perform only index vacuum or index cleanup,
+ * we don't need to report progress information.
+ */
+void
+parallel_vacuum_main(dsm_segment *seg, shm_toc *toc)
+{
+	Relation	rel;
+	Relation   *indrels;
+	LVShared   *lvshared;
+	LVDeadTuples *dead_tuples;
+	BufferUsage *buffer_usage;
+	WalUsage   *wal_usage;
+	int			nindexes;
+	char	   *sharedquery;
+	LVRelState	vacrel;
+	ErrorContextCallback errcallback;
+
+	/*
+	 * A parallel vacuum worker must have only PROC_IN_VACUUM flag since we
+	 * don't support parallel vacuum for autovacuum as of now.
+	 */
+	Assert(MyProc->statusFlags == PROC_IN_VACUUM);
+
+	lvshared = (LVShared *) shm_toc_lookup(toc, PARALLEL_VACUUM_KEY_SHARED,
+										   false);
+	elevel = lvshared->elevel;
+
+	if (lvshared->for_cleanup)
+		elog(DEBUG1, "starting parallel vacuum worker for cleanup");
+	else
+		elog(DEBUG1, "starting parallel vacuum worker for bulk delete");
+
+	/* Set debug_query_string for individual workers */
+	sharedquery = shm_toc_lookup(toc, PARALLEL_VACUUM_KEY_QUERY_TEXT, true);
+	debug_query_string = sharedquery;
+	pgstat_report_activity(STATE_RUNNING, debug_query_string);
+
+	/*
+	 * Open table.  The lock mode is the same as the leader process.  It's
+	 * okay because the lock mode does not conflict among the parallel
+	 * workers.
+	 */
+	rel = table_open(lvshared->relid, ShareUpdateExclusiveLock);
+
+	/*
+	 * Open all indexes. indrels are sorted in order by OID, which should be
+	 * matched to the leader's one.
+	 */
+	vac_open_indexes(rel, RowExclusiveLock, &nindexes, &indrels);
+	Assert(nindexes > 0);
+
+	/* Set dead tuple space */
+	dead_tuples = (LVDeadTuples *) shm_toc_lookup(toc,
+												  PARALLEL_VACUUM_KEY_DEAD_TUPLES,
+												  false);
+
+	/* Set cost-based vacuum delay */
+	VacuumCostActive = (VacuumCostDelay > 0);
+	VacuumCostBalance = 0;
+	VacuumPageHit = 0;
+	VacuumPageMiss = 0;
+	VacuumPageDirty = 0;
+	VacuumCostBalanceLocal = 0;
+	VacuumSharedCostBalance = &(lvshared->cost_balance);
+	VacuumActiveNWorkers = &(lvshared->active_nworkers);
+
+	vacrel.rel = rel;
+	vacrel.indrels = indrels;
+	vacrel.nindexes = nindexes;
+	/* Each parallel VACUUM worker gets its own access strategy */
+	vacrel.bstrategy = GetAccessStrategy(BAS_VACUUM);
+	vacrel.indstats = (IndexBulkDeleteResult **)
+		palloc0(nindexes * sizeof(IndexBulkDeleteResult *));
+
+	if (lvshared->maintenance_work_mem_worker > 0)
+		maintenance_work_mem = lvshared->maintenance_work_mem_worker;
+
+	/*
+	 * Initialize vacrel for use as error callback arg by parallel worker.
+	 */
+	vacrel.relnamespace = get_namespace_name(RelationGetNamespace(rel));
+	vacrel.relname = pstrdup(RelationGetRelationName(rel));
+	vacrel.indname = NULL;
+	vacrel.phase = VACUUM_ERRCB_PHASE_UNKNOWN;	/* Not yet processing */
+	vacrel.dead_tuples = dead_tuples;
+
+	/* Setup error traceback support for ereport() */
+	errcallback.callback = vacuum_error_callback;
+	errcallback.arg = &vacrel;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* Prepare to track buffer usage during parallel execution */
+	InstrStartParallelQuery();
+
+	/* Process indexes to perform vacuum/cleanup */
+	do_parallel_processing(&vacrel, lvshared);
+
+	/* Report buffer/WAL usage during parallel execution */
+	buffer_usage = shm_toc_lookup(toc, PARALLEL_VACUUM_KEY_BUFFER_USAGE, false);
+	wal_usage = shm_toc_lookup(toc, PARALLEL_VACUUM_KEY_WAL_USAGE, false);
+	InstrEndParallelQuery(&buffer_usage[ParallelWorkerNumber],
+						  &wal_usage[ParallelWorkerNumber]);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+
+	vac_close_indexes(nindexes, indrels, RowExclusiveLock);
+	table_close(rel, ShareUpdateExclusiveLock);
+	FreeAccessStrategy(vacrel.bstrategy);
+	pfree(vacrel.indstats);
+}
+
+/*
+ * Error context callback for errors occurring during vacuum.
+ */
+static void
+vacuum_error_callback(void *arg)
+{
+	LVRelState *errinfo = arg;
+
+	switch (errinfo->phase)
+	{
+		case VACUUM_ERRCB_PHASE_SCAN_HEAP:
+			if (BlockNumberIsValid(errinfo->blkno))
+			{
+				if (OffsetNumberIsValid(errinfo->offnum))
+					errcontext("while scanning block %u offset %u of relation \"%s.%s\"",
+							   errinfo->blkno, errinfo->offnum, errinfo->relnamespace, errinfo->relname);
+				else
+					errcontext("while scanning block %u of relation \"%s.%s\"",
+							   errinfo->blkno, errinfo->relnamespace, errinfo->relname);
+			}
+			else
+				errcontext("while scanning relation \"%s.%s\"",
+						   errinfo->relnamespace, errinfo->relname);
+			break;
+
+		case VACUUM_ERRCB_PHASE_VACUUM_HEAP:
+			if (BlockNumberIsValid(errinfo->blkno))
+			{
+				if (OffsetNumberIsValid(errinfo->offnum))
+					errcontext("while vacuuming block %u offset %u of relation \"%s.%s\"",
+							   errinfo->blkno, errinfo->offnum, errinfo->relnamespace, errinfo->relname);
+				else
+					errcontext("while vacuuming block %u of relation \"%s.%s\"",
+							   errinfo->blkno, errinfo->relnamespace, errinfo->relname);
+			}
+			else
+				errcontext("while vacuuming relation \"%s.%s\"",
+						   errinfo->relnamespace, errinfo->relname);
+			break;
+
+		case VACUUM_ERRCB_PHASE_VACUUM_INDEX:
+			errcontext("while vacuuming index \"%s\" of relation \"%s.%s\"",
+					   errinfo->indname, errinfo->relnamespace, errinfo->relname);
+			break;
+
+		case VACUUM_ERRCB_PHASE_INDEX_CLEANUP:
+			errcontext("while cleaning up index \"%s\" of relation \"%s.%s\"",
+					   errinfo->indname, errinfo->relnamespace, errinfo->relname);
+			break;
+
+		case VACUUM_ERRCB_PHASE_TRUNCATE:
+			if (BlockNumberIsValid(errinfo->blkno))
+				errcontext("while truncating relation \"%s.%s\" to %u blocks",
+						   errinfo->relnamespace, errinfo->relname, errinfo->blkno);
+			break;
+
+		case VACUUM_ERRCB_PHASE_UNKNOWN:
+		default:
+			return;				/* do nothing; the errinfo may not be
+								 * initialized */
+	}
+}
+
+/*
+ * Updates the information required for vacuum error callback.  This also saves
+ * the current information which can be later restored via restore_vacuum_error_info.
+ */
+static void
+update_vacuum_error_info(LVRelState *vacrel, LVSavedErrInfo *saved_vacrel,
+						 int phase, BlockNumber blkno, OffsetNumber offnum)
+{
+	if (saved_vacrel)
+	{
+		saved_vacrel->offnum = vacrel->offnum;
+		saved_vacrel->blkno = vacrel->blkno;
+		saved_vacrel->phase = vacrel->phase;
+	}
+
+	vacrel->blkno = blkno;
+	vacrel->offnum = offnum;
+	vacrel->phase = phase;
+}
+
+/*
+ * Restores the vacuum information saved via a prior call to update_vacuum_error_info.
+ */
+static void
+restore_vacuum_error_info(LVRelState *vacrel,
+						  const LVSavedErrInfo *saved_vacrel)
+{
+	vacrel->blkno = saved_vacrel->blkno;
+	vacrel->offnum = saved_vacrel->offnum;
+	vacrel->phase = saved_vacrel->phase;
+}
diff --git a/src/backend/access/heap/visibilitymap.c b/src/backend/access/heap/visibilitymap.c
new file mode 100644
index 0000000..e198df6
--- /dev/null
+++ b/src/backend/access/heap/visibilitymap.c
@@ -0,0 +1,672 @@
+/*-------------------------------------------------------------------------
+ *
+ * visibilitymap.c
+ *	  bitmap for tracking visibility of heap tuples
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/heap/visibilitymap.c
+ *
+ * INTERFACE ROUTINES
+ *		visibilitymap_clear  - clear bits for one page in the visibility map
+ *		visibilitymap_pin	 - pin a map page for setting a bit
+ *		visibilitymap_pin_ok - check whether correct map page is already pinned
+ *		visibilitymap_set	 - set a bit in a previously pinned page
+ *		visibilitymap_get_status - get status of bits
+ *		visibilitymap_count  - count number of bits set in visibility map
+ *		visibilitymap_prepare_truncate -
+ *			prepare for truncation of the visibility map
+ *
+ * NOTES
+ *
+ * The visibility map is a bitmap with two bits (all-visible and all-frozen)
+ * per heap page. A set all-visible bit means that all tuples on the page are
+ * known visible to all transactions, and therefore the page doesn't need to
+ * be vacuumed. A set all-frozen bit means that all tuples on the page are
+ * completely frozen, and therefore the page doesn't need to be vacuumed even
+ * if whole table scanning vacuum is required (e.g. anti-wraparound vacuum).
+ * The all-frozen bit must be set only when the page is already all-visible.
+ *
+ * The map is conservative in the sense that we make sure that whenever a bit
+ * is set, we know the condition is true, but if a bit is not set, it might or
+ * might not be true.
+ *
+ * Clearing visibility map bits is not separately WAL-logged.  The callers
+ * must make sure that whenever a bit is cleared, the bit is cleared on WAL
+ * replay of the updating operation as well.
+ *
+ * When we *set* a visibility map during VACUUM, we must write WAL.  This may
+ * seem counterintuitive, since the bit is basically a hint: if it is clear,
+ * it may still be the case that every tuple on the page is visible to all
+ * transactions; we just don't know that for certain.  The difficulty is that
+ * there are two bits which are typically set together: the PD_ALL_VISIBLE bit
+ * on the page itself, and the visibility map bit.  If a crash occurs after the
+ * visibility map page makes it to disk and before the updated heap page makes
+ * it to disk, redo must set the bit on the heap page.  Otherwise, the next
+ * insert, update, or delete on the heap page will fail to realize that the
+ * visibility map bit must be cleared, possibly causing index-only scans to
+ * return wrong answers.
+ *
+ * VACUUM will normally skip pages for which the visibility map bit is set;
+ * such pages can't contain any dead tuples and therefore don't need vacuuming.
+ *
+ * LOCKING
+ *
+ * In heapam.c, whenever a page is modified so that not all tuples on the
+ * page are visible to everyone anymore, the corresponding bit in the
+ * visibility map is cleared. In order to be crash-safe, we need to do this
+ * while still holding a lock on the heap page and in the same critical
+ * section that logs the page modification. However, we don't want to hold
+ * the buffer lock over any I/O that may be required to read in the visibility
+ * map page.  To avoid this, we examine the heap page before locking it;
+ * if the page-level PD_ALL_VISIBLE bit is set, we pin the visibility map
+ * bit.  Then, we lock the buffer.  But this creates a race condition: there
+ * is a possibility that in the time it takes to lock the buffer, the
+ * PD_ALL_VISIBLE bit gets set.  If that happens, we have to unlock the
+ * buffer, pin the visibility map page, and relock the buffer.  This shouldn't
+ * happen often, because only VACUUM currently sets visibility map bits,
+ * and the race will only occur if VACUUM processes a given page at almost
+ * exactly the same time that someone tries to further modify it.
+ *
+ * To set a bit, you need to hold a lock on the heap page. That prevents
+ * the race condition where VACUUM sees that all tuples on the page are
+ * visible to everyone, but another backend modifies the page before VACUUM
+ * sets the bit in the visibility map.
+ *
+ * When a bit is set, the LSN of the visibility map page is updated to make
+ * sure that the visibility map update doesn't get written to disk before the
+ * WAL record of the changes that made it possible to set the bit is flushed.
+ * But when a bit is cleared, we don't have to do that because it's always
+ * safe to clear a bit in the map from correctness point of view.
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/heapam_xlog.h"
+#include "access/visibilitymap.h"
+#include "access/xlog.h"
+#include "miscadmin.h"
+#include "port/pg_bitutils.h"
+#include "storage/bufmgr.h"
+#include "storage/lmgr.h"
+#include "storage/smgr.h"
+#include "utils/inval.h"
+
+
+/*#define TRACE_VISIBILITYMAP */
+
+/*
+ * Size of the bitmap on each visibility map page, in bytes. There's no
+ * extra headers, so the whole page minus the standard page header is
+ * used for the bitmap.
+ */
+#define MAPSIZE (BLCKSZ - MAXALIGN(SizeOfPageHeaderData))
+
+/* Number of heap blocks we can represent in one byte */
+#define HEAPBLOCKS_PER_BYTE (BITS_PER_BYTE / BITS_PER_HEAPBLOCK)
+
+/* Number of heap blocks we can represent in one visibility map page. */
+#define HEAPBLOCKS_PER_PAGE (MAPSIZE * HEAPBLOCKS_PER_BYTE)
+
+/* Mapping from heap block number to the right bit in the visibility map */
+#define HEAPBLK_TO_MAPBLOCK(x) ((x) / HEAPBLOCKS_PER_PAGE)
+#define HEAPBLK_TO_MAPBYTE(x) (((x) % HEAPBLOCKS_PER_PAGE) / HEAPBLOCKS_PER_BYTE)
+#define HEAPBLK_TO_OFFSET(x) (((x) % HEAPBLOCKS_PER_BYTE) * BITS_PER_HEAPBLOCK)
+
+/* Masks for counting subsets of bits in the visibility map. */
+#define VISIBLE_MASK64	UINT64CONST(0x5555555555555555) /* The lower bit of each
+														 * bit pair */
+#define FROZEN_MASK64	UINT64CONST(0xaaaaaaaaaaaaaaaa) /* The upper bit of each
+														 * bit pair */
+
+/* prototypes for internal routines */
+static Buffer vm_readbuf(Relation rel, BlockNumber blkno, bool extend);
+static void vm_extend(Relation rel, BlockNumber vm_nblocks);
+
+
+/*
+ *	visibilitymap_clear - clear specified bits for one page in visibility map
+ *
+ * You must pass a buffer containing the correct map page to this function.
+ * Call visibilitymap_pin first to pin the right one. This function doesn't do
+ * any I/O.  Returns true if any bits have been cleared and false otherwise.
+ */
+bool
+visibilitymap_clear(Relation rel, BlockNumber heapBlk, Buffer buf, uint8 flags)
+{
+	BlockNumber mapBlock = HEAPBLK_TO_MAPBLOCK(heapBlk);
+	int			mapByte = HEAPBLK_TO_MAPBYTE(heapBlk);
+	int			mapOffset = HEAPBLK_TO_OFFSET(heapBlk);
+	uint8		mask = flags << mapOffset;
+	char	   *map;
+	bool		cleared = false;
+
+	Assert(flags & VISIBILITYMAP_VALID_BITS);
+
+#ifdef TRACE_VISIBILITYMAP
+	elog(DEBUG1, "vm_clear %s %d", RelationGetRelationName(rel), heapBlk);
+#endif
+
+	if (!BufferIsValid(buf) || BufferGetBlockNumber(buf) != mapBlock)
+		elog(ERROR, "wrong buffer passed to visibilitymap_clear");
+
+	LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
+	map = PageGetContents(BufferGetPage(buf));
+
+	if (map[mapByte] & mask)
+	{
+		map[mapByte] &= ~mask;
+
+		MarkBufferDirty(buf);
+		cleared = true;
+	}
+
+	LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+
+	return cleared;
+}
+
+/*
+ *	visibilitymap_pin - pin a map page for setting a bit
+ *
+ * Setting a bit in the visibility map is a two-phase operation. First, call
+ * visibilitymap_pin, to pin the visibility map page containing the bit for
+ * the heap page. Because that can require I/O to read the map page, you
+ * shouldn't hold a lock on the heap page while doing that. Then, call
+ * visibilitymap_set to actually set the bit.
+ *
+ * On entry, *buf should be InvalidBuffer or a valid buffer returned by
+ * an earlier call to visibilitymap_pin or visibilitymap_get_status on the same
+ * relation. On return, *buf is a valid buffer with the map page containing
+ * the bit for heapBlk.
+ *
+ * If the page doesn't exist in the map file yet, it is extended.
+ */
+void
+visibilitymap_pin(Relation rel, BlockNumber heapBlk, Buffer *buf)
+{
+	BlockNumber mapBlock = HEAPBLK_TO_MAPBLOCK(heapBlk);
+
+	/* Reuse the old pinned buffer if possible */
+	if (BufferIsValid(*buf))
+	{
+		if (BufferGetBlockNumber(*buf) == mapBlock)
+			return;
+
+		ReleaseBuffer(*buf);
+	}
+	*buf = vm_readbuf(rel, mapBlock, true);
+}
+
+/*
+ *	visibilitymap_pin_ok - do we already have the correct page pinned?
+ *
+ * On entry, buf should be InvalidBuffer or a valid buffer returned by
+ * an earlier call to visibilitymap_pin or visibilitymap_get_status on the same
+ * relation.  The return value indicates whether the buffer covers the
+ * given heapBlk.
+ */
+bool
+visibilitymap_pin_ok(BlockNumber heapBlk, Buffer buf)
+{
+	BlockNumber mapBlock = HEAPBLK_TO_MAPBLOCK(heapBlk);
+
+	return BufferIsValid(buf) && BufferGetBlockNumber(buf) == mapBlock;
+}
+
+/*
+ *	visibilitymap_set - set bit(s) on a previously pinned page
+ *
+ * recptr is the LSN of the XLOG record we're replaying, if we're in recovery,
+ * or InvalidXLogRecPtr in normal running.  The page LSN is advanced to the
+ * one provided; in normal running, we generate a new XLOG record and set the
+ * page LSN to that value.  cutoff_xid is the largest xmin on the page being
+ * marked all-visible; it is needed for Hot Standby, and can be
+ * InvalidTransactionId if the page contains no tuples.  It can also be set
+ * to InvalidTransactionId when a page that is already all-visible is being
+ * marked all-frozen.
+ *
+ * Caller is expected to set the heap page's PD_ALL_VISIBLE bit before calling
+ * this function. Except in recovery, caller should also pass the heap
+ * buffer. When checksums are enabled and we're not in recovery, we must add
+ * the heap buffer to the WAL chain to protect it from being torn.
+ *
+ * You must pass a buffer containing the correct map page to this function.
+ * Call visibilitymap_pin first to pin the right one. This function doesn't do
+ * any I/O.
+ */
+void
+visibilitymap_set(Relation rel, BlockNumber heapBlk, Buffer heapBuf,
+				  XLogRecPtr recptr, Buffer vmBuf, TransactionId cutoff_xid,
+				  uint8 flags)
+{
+	BlockNumber mapBlock = HEAPBLK_TO_MAPBLOCK(heapBlk);
+	uint32		mapByte = HEAPBLK_TO_MAPBYTE(heapBlk);
+	uint8		mapOffset = HEAPBLK_TO_OFFSET(heapBlk);
+	Page		page;
+	uint8	   *map;
+
+#ifdef TRACE_VISIBILITYMAP
+	elog(DEBUG1, "vm_set %s %d", RelationGetRelationName(rel), heapBlk);
+#endif
+
+	Assert(InRecovery || XLogRecPtrIsInvalid(recptr));
+	Assert(InRecovery || BufferIsValid(heapBuf));
+	Assert(flags & VISIBILITYMAP_VALID_BITS);
+
+	/* Check that we have the right heap page pinned, if present */
+	if (BufferIsValid(heapBuf) && BufferGetBlockNumber(heapBuf) != heapBlk)
+		elog(ERROR, "wrong heap buffer passed to visibilitymap_set");
+
+	/* Check that we have the right VM page pinned */
+	if (!BufferIsValid(vmBuf) || BufferGetBlockNumber(vmBuf) != mapBlock)
+		elog(ERROR, "wrong VM buffer passed to visibilitymap_set");
+
+	page = BufferGetPage(vmBuf);
+	map = (uint8 *) PageGetContents(page);
+	LockBuffer(vmBuf, BUFFER_LOCK_EXCLUSIVE);
+
+	if (flags != (map[mapByte] >> mapOffset & VISIBILITYMAP_VALID_BITS))
+	{
+		START_CRIT_SECTION();
+
+		map[mapByte] |= (flags << mapOffset);
+		MarkBufferDirty(vmBuf);
+
+		if (RelationNeedsWAL(rel))
+		{
+			if (XLogRecPtrIsInvalid(recptr))
+			{
+				Assert(!InRecovery);
+				recptr = log_heap_visible(rel->rd_node, heapBuf, vmBuf,
+										  cutoff_xid, flags);
+
+				/*
+				 * If data checksums are enabled (or wal_log_hints=on), we
+				 * need to protect the heap page from being torn.
+				 */
+				if (XLogHintBitIsNeeded())
+				{
+					Page		heapPage = BufferGetPage(heapBuf);
+
+					/* caller is expected to set PD_ALL_VISIBLE first */
+					Assert(PageIsAllVisible(heapPage));
+					PageSetLSN(heapPage, recptr);
+				}
+			}
+			PageSetLSN(page, recptr);
+		}
+
+		END_CRIT_SECTION();
+	}
+
+	LockBuffer(vmBuf, BUFFER_LOCK_UNLOCK);
+}
+
+/*
+ *	visibilitymap_get_status - get status of bits
+ *
+ * Are all tuples on heapBlk visible to all or are marked frozen, according
+ * to the visibility map?
+ *
+ * On entry, *buf should be InvalidBuffer or a valid buffer returned by an
+ * earlier call to visibilitymap_pin or visibilitymap_get_status on the same
+ * relation. On return, *buf is a valid buffer with the map page containing
+ * the bit for heapBlk, or InvalidBuffer. The caller is responsible for
+ * releasing *buf after it's done testing and setting bits.
+ *
+ * NOTE: This function is typically called without a lock on the heap page,
+ * so somebody else could change the bit just after we look at it.  In fact,
+ * since we don't lock the visibility map page either, it's even possible that
+ * someone else could have changed the bit just before we look at it, but yet
+ * we might see the old value.  It is the caller's responsibility to deal with
+ * all concurrency issues!
+ */
+uint8
+visibilitymap_get_status(Relation rel, BlockNumber heapBlk, Buffer *buf)
+{
+	BlockNumber mapBlock = HEAPBLK_TO_MAPBLOCK(heapBlk);
+	uint32		mapByte = HEAPBLK_TO_MAPBYTE(heapBlk);
+	uint8		mapOffset = HEAPBLK_TO_OFFSET(heapBlk);
+	char	   *map;
+	uint8		result;
+
+#ifdef TRACE_VISIBILITYMAP
+	elog(DEBUG1, "vm_get_status %s %d", RelationGetRelationName(rel), heapBlk);
+#endif
+
+	/* Reuse the old pinned buffer if possible */
+	if (BufferIsValid(*buf))
+	{
+		if (BufferGetBlockNumber(*buf) != mapBlock)
+		{
+			ReleaseBuffer(*buf);
+			*buf = InvalidBuffer;
+		}
+	}
+
+	if (!BufferIsValid(*buf))
+	{
+		*buf = vm_readbuf(rel, mapBlock, false);
+		if (!BufferIsValid(*buf))
+			return false;
+	}
+
+	map = PageGetContents(BufferGetPage(*buf));
+
+	/*
+	 * A single byte read is atomic.  There could be memory-ordering effects
+	 * here, but for performance reasons we make it the caller's job to worry
+	 * about that.
+	 */
+	result = ((map[mapByte] >> mapOffset) & VISIBILITYMAP_VALID_BITS);
+	return result;
+}
+
+/*
+ *	visibilitymap_count  - count number of bits set in visibility map
+ *
+ * Note: we ignore the possibility of race conditions when the table is being
+ * extended concurrently with the call.  New pages added to the table aren't
+ * going to be marked all-visible or all-frozen, so they won't affect the result.
+ */
+void
+visibilitymap_count(Relation rel, BlockNumber *all_visible, BlockNumber *all_frozen)
+{
+	BlockNumber mapBlock;
+	BlockNumber nvisible = 0;
+	BlockNumber nfrozen = 0;
+
+	/* all_visible must be specified */
+	Assert(all_visible);
+
+	for (mapBlock = 0;; mapBlock++)
+	{
+		Buffer		mapBuffer;
+		uint64	   *map;
+		int			i;
+
+		/*
+		 * Read till we fall off the end of the map.  We assume that any extra
+		 * bytes in the last page are zeroed, so we don't bother excluding
+		 * them from the count.
+		 */
+		mapBuffer = vm_readbuf(rel, mapBlock, false);
+		if (!BufferIsValid(mapBuffer))
+			break;
+
+		/*
+		 * We choose not to lock the page, since the result is going to be
+		 * immediately stale anyway if anyone is concurrently setting or
+		 * clearing bits, and we only really need an approximate value.
+		 */
+		map = (uint64 *) PageGetContents(BufferGetPage(mapBuffer));
+
+		StaticAssertStmt(MAPSIZE % sizeof(uint64) == 0,
+						 "unsupported MAPSIZE");
+		if (all_frozen == NULL)
+		{
+			for (i = 0; i < MAPSIZE / sizeof(uint64); i++)
+				nvisible += pg_popcount64(map[i] & VISIBLE_MASK64);
+		}
+		else
+		{
+			for (i = 0; i < MAPSIZE / sizeof(uint64); i++)
+			{
+				nvisible += pg_popcount64(map[i] & VISIBLE_MASK64);
+				nfrozen += pg_popcount64(map[i] & FROZEN_MASK64);
+			}
+		}
+
+		ReleaseBuffer(mapBuffer);
+	}
+
+	*all_visible = nvisible;
+	if (all_frozen)
+		*all_frozen = nfrozen;
+}
+
+/*
+ *	visibilitymap_prepare_truncate -
+ *			prepare for truncation of the visibility map
+ *
+ * nheapblocks is the new size of the heap.
+ *
+ * Return the number of blocks of new visibility map.
+ * If it's InvalidBlockNumber, there is nothing to truncate;
+ * otherwise the caller is responsible for calling smgrtruncate()
+ * to truncate the visibility map pages.
+ */
+BlockNumber
+visibilitymap_prepare_truncate(Relation rel, BlockNumber nheapblocks)
+{
+	BlockNumber newnblocks;
+
+	/* last remaining block, byte, and bit */
+	BlockNumber truncBlock = HEAPBLK_TO_MAPBLOCK(nheapblocks);
+	uint32		truncByte = HEAPBLK_TO_MAPBYTE(nheapblocks);
+	uint8		truncOffset = HEAPBLK_TO_OFFSET(nheapblocks);
+
+#ifdef TRACE_VISIBILITYMAP
+	elog(DEBUG1, "vm_truncate %s %d", RelationGetRelationName(rel), nheapblocks);
+#endif
+
+	RelationOpenSmgr(rel);
+
+	/*
+	 * If no visibility map has been created yet for this relation, there's
+	 * nothing to truncate.
+	 */
+	if (!smgrexists(rel->rd_smgr, VISIBILITYMAP_FORKNUM))
+		return InvalidBlockNumber;
+
+	/*
+	 * Unless the new size is exactly at a visibility map page boundary, the
+	 * tail bits in the last remaining map page, representing truncated heap
+	 * blocks, need to be cleared. This is not only tidy, but also necessary
+	 * because we don't get a chance to clear the bits if the heap is extended
+	 * again.
+	 */
+	if (truncByte != 0 || truncOffset != 0)
+	{
+		Buffer		mapBuffer;
+		Page		page;
+		char	   *map;
+
+		newnblocks = truncBlock + 1;
+
+		mapBuffer = vm_readbuf(rel, truncBlock, false);
+		if (!BufferIsValid(mapBuffer))
+		{
+			/* nothing to do, the file was already smaller */
+			return InvalidBlockNumber;
+		}
+
+		page = BufferGetPage(mapBuffer);
+		map = PageGetContents(page);
+
+		LockBuffer(mapBuffer, BUFFER_LOCK_EXCLUSIVE);
+
+		/* NO EREPORT(ERROR) from here till changes are logged */
+		START_CRIT_SECTION();
+
+		/* Clear out the unwanted bytes. */
+		MemSet(&map[truncByte + 1], 0, MAPSIZE - (truncByte + 1));
+
+		/*----
+		 * Mask out the unwanted bits of the last remaining byte.
+		 *
+		 * ((1 << 0) - 1) = 00000000
+		 * ((1 << 1) - 1) = 00000001
+		 * ...
+		 * ((1 << 6) - 1) = 00111111
+		 * ((1 << 7) - 1) = 01111111
+		 *----
+		 */
+		map[truncByte] &= (1 << truncOffset) - 1;
+
+		/*
+		 * Truncation of a relation is WAL-logged at a higher-level, and we
+		 * will be called at WAL replay. But if checksums are enabled, we need
+		 * to still write a WAL record to protect against a torn page, if the
+		 * page is flushed to disk before the truncation WAL record. We cannot
+		 * use MarkBufferDirtyHint here, because that will not dirty the page
+		 * during recovery.
+		 */
+		MarkBufferDirty(mapBuffer);
+		if (!InRecovery && RelationNeedsWAL(rel) && XLogHintBitIsNeeded())
+			log_newpage_buffer(mapBuffer, false);
+
+		END_CRIT_SECTION();
+
+		UnlockReleaseBuffer(mapBuffer);
+	}
+	else
+		newnblocks = truncBlock;
+
+	if (smgrnblocks(rel->rd_smgr, VISIBILITYMAP_FORKNUM) <= newnblocks)
+	{
+		/* nothing to do, the file was already smaller than requested size */
+		return InvalidBlockNumber;
+	}
+
+	return newnblocks;
+}
+
+/*
+ * Read a visibility map page.
+ *
+ * If the page doesn't exist, InvalidBuffer is returned, or if 'extend' is
+ * true, the visibility map file is extended.
+ */
+static Buffer
+vm_readbuf(Relation rel, BlockNumber blkno, bool extend)
+{
+	Buffer		buf;
+
+	/*
+	 * We might not have opened the relation at the smgr level yet, or we
+	 * might have been forced to close it by a sinval message.  The code below
+	 * won't necessarily notice relation extension immediately when extend =
+	 * false, so we rely on sinval messages to ensure that our ideas about the
+	 * size of the map aren't too far out of date.
+	 */
+	RelationOpenSmgr(rel);
+
+	/*
+	 * If we haven't cached the size of the visibility map fork yet, check it
+	 * first.
+	 */
+	if (rel->rd_smgr->smgr_cached_nblocks[VISIBILITYMAP_FORKNUM] == InvalidBlockNumber)
+	{
+		if (smgrexists(rel->rd_smgr, VISIBILITYMAP_FORKNUM))
+			smgrnblocks(rel->rd_smgr, VISIBILITYMAP_FORKNUM);
+		else
+			rel->rd_smgr->smgr_cached_nblocks[VISIBILITYMAP_FORKNUM] = 0;
+	}
+
+	/* Handle requests beyond EOF */
+	if (blkno >= rel->rd_smgr->smgr_cached_nblocks[VISIBILITYMAP_FORKNUM])
+	{
+		if (extend)
+			vm_extend(rel, blkno + 1);
+		else
+			return InvalidBuffer;
+	}
+
+	/*
+	 * Use ZERO_ON_ERROR mode, and initialize the page if necessary. It's
+	 * always safe to clear bits, so it's better to clear corrupt pages than
+	 * error out.
+	 *
+	 * The initialize-the-page part is trickier than it looks, because of the
+	 * possibility of multiple backends doing this concurrently, and our
+	 * desire to not uselessly take the buffer lock in the normal path where
+	 * the page is OK.  We must take the lock to initialize the page, so
+	 * recheck page newness after we have the lock, in case someone else
+	 * already did it.  Also, because we initially check PageIsNew with no
+	 * lock, it's possible to fall through and return the buffer while someone
+	 * else is still initializing the page (i.e., we might see pd_upper as set
+	 * but other page header fields are still zeroes).  This is harmless for
+	 * callers that will take a buffer lock themselves, but some callers
+	 * inspect the page without any lock at all.  The latter is OK only so
+	 * long as it doesn't depend on the page header having correct contents.
+	 * Current usage is safe because PageGetContents() does not require that.
+	 */
+	buf = ReadBufferExtended(rel, VISIBILITYMAP_FORKNUM, blkno,
+							 RBM_ZERO_ON_ERROR, NULL);
+	if (PageIsNew(BufferGetPage(buf)))
+	{
+		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
+		if (PageIsNew(BufferGetPage(buf)))
+			PageInit(BufferGetPage(buf), BLCKSZ, 0);
+		LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+	}
+	return buf;
+}
+
+/*
+ * Ensure that the visibility map fork is at least vm_nblocks long, extending
+ * it if necessary with zeroed pages.
+ */
+static void
+vm_extend(Relation rel, BlockNumber vm_nblocks)
+{
+	BlockNumber vm_nblocks_now;
+	PGAlignedBlock pg;
+
+	PageInit((Page) pg.data, BLCKSZ, 0);
+
+	/*
+	 * We use the relation extension lock to lock out other backends trying to
+	 * extend the visibility map at the same time. It also locks out extension
+	 * of the main fork, unnecessarily, but extending the visibility map
+	 * happens seldom enough that it doesn't seem worthwhile to have a
+	 * separate lock tag type for it.
+	 *
+	 * Note that another backend might have extended or created the relation
+	 * by the time we get the lock.
+	 */
+	LockRelationForExtension(rel, ExclusiveLock);
+
+	/* Might have to re-open if a cache flush happened */
+	RelationOpenSmgr(rel);
+
+	/*
+	 * Create the file first if it doesn't exist.  If smgr_vm_nblocks is
+	 * positive then it must exist, no need for an smgrexists call.
+	 */
+	if ((rel->rd_smgr->smgr_cached_nblocks[VISIBILITYMAP_FORKNUM] == 0 ||
+		 rel->rd_smgr->smgr_cached_nblocks[VISIBILITYMAP_FORKNUM] == InvalidBlockNumber) &&
+		!smgrexists(rel->rd_smgr, VISIBILITYMAP_FORKNUM))
+		smgrcreate(rel->rd_smgr, VISIBILITYMAP_FORKNUM, false);
+
+	/* Invalidate cache so that smgrnblocks() asks the kernel. */
+	rel->rd_smgr->smgr_cached_nblocks[VISIBILITYMAP_FORKNUM] = InvalidBlockNumber;
+	vm_nblocks_now = smgrnblocks(rel->rd_smgr, VISIBILITYMAP_FORKNUM);
+
+	/* Now extend the file */
+	while (vm_nblocks_now < vm_nblocks)
+	{
+		PageSetChecksumInplace((Page) pg.data, vm_nblocks_now);
+
+		smgrextend(rel->rd_smgr, VISIBILITYMAP_FORKNUM, vm_nblocks_now,
+				   pg.data, false);
+		vm_nblocks_now++;
+	}
+
+	/*
+	 * Send a shared-inval message to force other backends to close any smgr
+	 * references they may have for this rel, which we are about to change.
+	 * This is a useful optimization because it means that backends don't have
+	 * to keep checking for creation or extension of the file, which happens
+	 * infrequently.
+	 */
+	CacheInvalidateSmgr(rel->rd_smgr->smgr_rnode);
+
+	UnlockRelationForExtension(rel, ExclusiveLock);
+}