Adding upstream version 14.5.upstream/14.5upstream

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

1 files changed, 5156 insertions, 0 deletions

diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
new file mode 100644
index 0000000..e59d139
--- /dev/null
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -0,0 +1,5156 @@
+/*-------------------------------------------------------------------------
+ *
+ * reorderbuffer.c
+ *	  PostgreSQL logical replay/reorder buffer management
+ *
+ *
+ * Copyright (c) 2012-2021, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/reorderbuffer.c
+ *
+ * NOTES
+ *	  This module gets handed individual pieces of transactions in the order
+ *	  they are written to the WAL and is responsible to reassemble them into
+ *	  toplevel transaction sized pieces. When a transaction is completely
+ *	  reassembled - signaled by reading the transaction commit record - it
+ *	  will then call the output plugin (cf. ReorderBufferCommit()) with the
+ *	  individual changes. The output plugins rely on snapshots built by
+ *	  snapbuild.c which hands them to us.
+ *
+ *	  Transactions and subtransactions/savepoints in postgres are not
+ *	  immediately linked to each other from outside the performing
+ *	  backend. Only at commit/abort (or special xact_assignment records) they
+ *	  are linked together. Which means that we will have to splice together a
+ *	  toplevel transaction from its subtransactions. To do that efficiently we
+ *	  build a binary heap indexed by the smallest current lsn of the individual
+ *	  subtransactions' changestreams. As the individual streams are inherently
+ *	  ordered by LSN - since that is where we build them from - the transaction
+ *	  can easily be reassembled by always using the subtransaction with the
+ *	  smallest current LSN from the heap.
+ *
+ *	  In order to cope with large transactions - which can be several times as
+ *	  big as the available memory - this module supports spooling the contents
+ *	  of a large transactions to disk. When the transaction is replayed the
+ *	  contents of individual (sub-)transactions will be read from disk in
+ *	  chunks.
+ *
+ *	  This module also has to deal with reassembling toast records from the
+ *	  individual chunks stored in WAL. When a new (or initial) version of a
+ *	  tuple is stored in WAL it will always be preceded by the toast chunks
+ *	  emitted for the columns stored out of line. Within a single toplevel
+ *	  transaction there will be no other data carrying records between a row's
+ *	  toast chunks and the row data itself. See ReorderBufferToast* for
+ *	  details.
+ *
+ *	  ReorderBuffer uses two special memory context types - SlabContext for
+ *	  allocations of fixed-length structures (changes and transactions), and
+ *	  GenerationContext for the variable-length transaction data (allocated
+ *	  and freed in groups with similar lifespans).
+ *
+ *	  To limit the amount of memory used by decoded changes, we track memory
+ *	  used at the reorder buffer level (i.e. total amount of memory), and for
+ *	  each transaction. When the total amount of used memory exceeds the
+ *	  limit, the transaction consuming the most memory is then serialized to
+ *	  disk.
+ *
+ *	  Only decoded changes are evicted from memory (spilled to disk), not the
+ *	  transaction records. The number of toplevel transactions is limited,
+ *	  but a transaction with many subtransactions may still consume significant
+ *	  amounts of memory. However, the transaction records are fairly small and
+ *	  are not included in the memory limit.
+ *
+ *	  The current eviction algorithm is very simple - the transaction is
+ *	  picked merely by size, while it might be useful to also consider age
+ *	  (LSN) of the changes for example. With the new Generational memory
+ *	  allocator, evicting the oldest changes would make it more likely the
+ *	  memory gets actually freed.
+ *
+ *	  We still rely on max_changes_in_memory when loading serialized changes
+ *	  back into memory. At that point we can't use the memory limit directly
+ *	  as we load the subxacts independently. One option to deal with this
+ *	  would be to count the subxacts, and allow each to allocate 1/N of the
+ *	  memory limit. That however does not seem very appealing, because with
+ *	  many subtransactions it may easily cause thrashing (short cycles of
+ *	  deserializing and applying very few changes). We probably should give
+ *	  a bit more memory to the oldest subtransactions, because it's likely
+ *	  they are the source for the next sequence of changes.
+ *
+ * -------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <unistd.h>
+#include <sys/stat.h>
+
+#include "access/detoast.h"
+#include "access/heapam.h"
+#include "access/rewriteheap.h"
+#include "access/transam.h"
+#include "access/xact.h"
+#include "access/xlog_internal.h"
+#include "catalog/catalog.h"
+#include "lib/binaryheap.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "replication/logical.h"
+#include "replication/reorderbuffer.h"
+#include "replication/slot.h"
+#include "replication/snapbuild.h"	/* just for SnapBuildSnapDecRefcount */
+#include "storage/bufmgr.h"
+#include "storage/fd.h"
+#include "storage/sinval.h"
+#include "utils/builtins.h"
+#include "utils/combocid.h"
+#include "utils/memdebug.h"
+#include "utils/memutils.h"
+#include "utils/rel.h"
+#include "utils/relfilenodemap.h"
+
+
+/* entry for a hash table we use to map from xid to our transaction state */
+typedef struct ReorderBufferTXNByIdEnt
+{
+	TransactionId xid;
+	ReorderBufferTXN *txn;
+} ReorderBufferTXNByIdEnt;
+
+/* data structures for (relfilenode, ctid) => (cmin, cmax) mapping */
+typedef struct ReorderBufferTupleCidKey
+{
+	RelFileNode relnode;
+	ItemPointerData tid;
+} ReorderBufferTupleCidKey;
+
+typedef struct ReorderBufferTupleCidEnt
+{
+	ReorderBufferTupleCidKey key;
+	CommandId	cmin;
+	CommandId	cmax;
+	CommandId	combocid;		/* just for debugging */
+} ReorderBufferTupleCidEnt;
+
+/* Virtual file descriptor with file offset tracking */
+typedef struct TXNEntryFile
+{
+	File		vfd;			/* -1 when the file is closed */
+	off_t		curOffset;		/* offset for next write or read. Reset to 0
+								 * when vfd is opened. */
+} TXNEntryFile;
+
+/* k-way in-order change iteration support structures */
+typedef struct ReorderBufferIterTXNEntry
+{
+	XLogRecPtr	lsn;
+	ReorderBufferChange *change;
+	ReorderBufferTXN *txn;
+	TXNEntryFile file;
+	XLogSegNo	segno;
+} ReorderBufferIterTXNEntry;
+
+typedef struct ReorderBufferIterTXNState
+{
+	binaryheap *heap;
+	Size		nr_txns;
+	dlist_head	old_change;
+	ReorderBufferIterTXNEntry entries[FLEXIBLE_ARRAY_MEMBER];
+} ReorderBufferIterTXNState;
+
+/* toast datastructures */
+typedef struct ReorderBufferToastEnt
+{
+	Oid			chunk_id;		/* toast_table.chunk_id */
+	int32		last_chunk_seq; /* toast_table.chunk_seq of the last chunk we
+								 * have seen */
+	Size		num_chunks;		/* number of chunks we've already seen */
+	Size		size;			/* combined size of chunks seen */
+	dlist_head	chunks;			/* linked list of chunks */
+	struct varlena *reconstructed;	/* reconstructed varlena now pointed to in
+									 * main tup */
+} ReorderBufferToastEnt;
+
+/* Disk serialization support datastructures */
+typedef struct ReorderBufferDiskChange
+{
+	Size		size;
+	ReorderBufferChange change;
+	/* data follows */
+} ReorderBufferDiskChange;
+
+#define IsSpecInsert(action) \
+( \
+	((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT) \
+)
+#define IsSpecConfirmOrAbort(action) \
+( \
+	(((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM) || \
+	((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT)) \
+)
+#define IsInsertOrUpdate(action) \
+( \
+	(((action) == REORDER_BUFFER_CHANGE_INSERT) || \
+	((action) == REORDER_BUFFER_CHANGE_UPDATE) || \
+	((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT)) \
+)
+
+/*
+ * Maximum number of changes kept in memory, per transaction. After that,
+ * changes are spooled to disk.
+ *
+ * The current value should be sufficient to decode the entire transaction
+ * without hitting disk in OLTP workloads, while starting to spool to disk in
+ * other workloads reasonably fast.
+ *
+ * At some point in the future it probably makes sense to have a more elaborate
+ * resource management here, but it's not entirely clear what that would look
+ * like.
+ */
+int			logical_decoding_work_mem;
+static const Size max_changes_in_memory = 4096; /* XXX for restore only */
+
+/* ---------------------------------------
+ * primary reorderbuffer support routines
+ * ---------------------------------------
+ */
+static ReorderBufferTXN *ReorderBufferGetTXN(ReorderBuffer *rb);
+static void ReorderBufferReturnTXN(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static ReorderBufferTXN *ReorderBufferTXNByXid(ReorderBuffer *rb,
+											   TransactionId xid, bool create, bool *is_new,
+											   XLogRecPtr lsn, bool create_as_top);
+static void ReorderBufferTransferSnapToParent(ReorderBufferTXN *txn,
+											  ReorderBufferTXN *subtxn);
+
+static void AssertTXNLsnOrder(ReorderBuffer *rb);
+
+/* ---------------------------------------
+ * support functions for lsn-order iterating over the ->changes of a
+ * transaction and its subtransactions
+ *
+ * used for iteration over the k-way heap merge of a transaction and its
+ * subtransactions
+ * ---------------------------------------
+ */
+static void ReorderBufferIterTXNInit(ReorderBuffer *rb, ReorderBufferTXN *txn,
+									 ReorderBufferIterTXNState *volatile *iter_state);
+static ReorderBufferChange *ReorderBufferIterTXNNext(ReorderBuffer *rb, ReorderBufferIterTXNState *state);
+static void ReorderBufferIterTXNFinish(ReorderBuffer *rb,
+									   ReorderBufferIterTXNState *state);
+static void ReorderBufferExecuteInvalidations(uint32 nmsgs, SharedInvalidationMessage *msgs);
+
+/*
+ * ---------------------------------------
+ * Disk serialization support functions
+ * ---------------------------------------
+ */
+static void ReorderBufferCheckMemoryLimit(ReorderBuffer *rb);
+static void ReorderBufferSerializeTXN(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static void ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+										 int fd, ReorderBufferChange *change);
+static Size ReorderBufferRestoreChanges(ReorderBuffer *rb, ReorderBufferTXN *txn,
+										TXNEntryFile *file, XLogSegNo *segno);
+static void ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+									   char *change);
+static void ReorderBufferRestoreCleanup(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static void ReorderBufferTruncateTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
+									 bool txn_prepared);
+static void ReorderBufferCleanupSerializedTXNs(const char *slotname);
+static void ReorderBufferSerializedPath(char *path, ReplicationSlot *slot,
+										TransactionId xid, XLogSegNo segno);
+
+static void ReorderBufferFreeSnap(ReorderBuffer *rb, Snapshot snap);
+static Snapshot ReorderBufferCopySnap(ReorderBuffer *rb, Snapshot orig_snap,
+									  ReorderBufferTXN *txn, CommandId cid);
+
+/*
+ * ---------------------------------------
+ * Streaming support functions
+ * ---------------------------------------
+ */
+static inline bool ReorderBufferCanStream(ReorderBuffer *rb);
+static inline bool ReorderBufferCanStartStreaming(ReorderBuffer *rb);
+static void ReorderBufferStreamTXN(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static void ReorderBufferStreamCommit(ReorderBuffer *rb, ReorderBufferTXN *txn);
+
+/* ---------------------------------------
+ * toast reassembly support
+ * ---------------------------------------
+ */
+static void ReorderBufferToastInitHash(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static void ReorderBufferToastReset(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static void ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
+									  Relation relation, ReorderBufferChange *change);
+static void ReorderBufferToastAppendChunk(ReorderBuffer *rb, ReorderBufferTXN *txn,
+										  Relation relation, ReorderBufferChange *change);
+
+/*
+ * ---------------------------------------
+ * memory accounting
+ * ---------------------------------------
+ */
+static Size ReorderBufferChangeSize(ReorderBufferChange *change);
+static void ReorderBufferChangeMemoryUpdate(ReorderBuffer *rb,
+											ReorderBufferChange *change,
+											bool addition, Size sz);
+
+/*
+ * Allocate a new ReorderBuffer and clean out any old serialized state from
+ * prior ReorderBuffer instances for the same slot.
+ */
+ReorderBuffer *
+ReorderBufferAllocate(void)
+{
+	ReorderBuffer *buffer;
+	HASHCTL		hash_ctl;
+	MemoryContext new_ctx;
+
+	Assert(MyReplicationSlot != NULL);
+
+	/* allocate memory in own context, to have better accountability */
+	new_ctx = AllocSetContextCreate(CurrentMemoryContext,
+									"ReorderBuffer",
+									ALLOCSET_DEFAULT_SIZES);
+
+	buffer =
+		(ReorderBuffer *) MemoryContextAlloc(new_ctx, sizeof(ReorderBuffer));
+
+	memset(&hash_ctl, 0, sizeof(hash_ctl));
+
+	buffer->context = new_ctx;
+
+	buffer->change_context = SlabContextCreate(new_ctx,
+											   "Change",
+											   SLAB_DEFAULT_BLOCK_SIZE,
+											   sizeof(ReorderBufferChange));
+
+	buffer->txn_context = SlabContextCreate(new_ctx,
+											"TXN",
+											SLAB_DEFAULT_BLOCK_SIZE,
+											sizeof(ReorderBufferTXN));
+
+	buffer->tup_context = GenerationContextCreate(new_ctx,
+												  "Tuples",
+												  SLAB_LARGE_BLOCK_SIZE);
+
+	hash_ctl.keysize = sizeof(TransactionId);
+	hash_ctl.entrysize = sizeof(ReorderBufferTXNByIdEnt);
+	hash_ctl.hcxt = buffer->context;
+
+	buffer->by_txn = hash_create("ReorderBufferByXid", 1000, &hash_ctl,
+								 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	buffer->by_txn_last_xid = InvalidTransactionId;
+	buffer->by_txn_last_txn = NULL;
+
+	buffer->outbuf = NULL;
+	buffer->outbufsize = 0;
+	buffer->size = 0;
+
+	buffer->spillTxns = 0;
+	buffer->spillCount = 0;
+	buffer->spillBytes = 0;
+	buffer->streamTxns = 0;
+	buffer->streamCount = 0;
+	buffer->streamBytes = 0;
+	buffer->totalTxns = 0;
+	buffer->totalBytes = 0;
+
+	buffer->current_restart_decoding_lsn = InvalidXLogRecPtr;
+
+	dlist_init(&buffer->toplevel_by_lsn);
+	dlist_init(&buffer->txns_by_base_snapshot_lsn);
+
+	/*
+	 * Ensure there's no stale data from prior uses of this slot, in case some
+	 * prior exit avoided calling ReorderBufferFree. Failure to do this can
+	 * produce duplicated txns, and it's very cheap if there's nothing there.
+	 */
+	ReorderBufferCleanupSerializedTXNs(NameStr(MyReplicationSlot->data.name));
+
+	return buffer;
+}
+
+/*
+ * Free a ReorderBuffer
+ */
+void
+ReorderBufferFree(ReorderBuffer *rb)
+{
+	MemoryContext context = rb->context;
+
+	/*
+	 * We free separately allocated data by entirely scrapping reorderbuffer's
+	 * memory context.
+	 */
+	MemoryContextDelete(context);
+
+	/* Free disk space used by unconsumed reorder buffers */
+	ReorderBufferCleanupSerializedTXNs(NameStr(MyReplicationSlot->data.name));
+}
+
+/*
+ * Get an unused, possibly preallocated, ReorderBufferTXN.
+ */
+static ReorderBufferTXN *
+ReorderBufferGetTXN(ReorderBuffer *rb)
+{
+	ReorderBufferTXN *txn;
+
+	txn = (ReorderBufferTXN *)
+		MemoryContextAlloc(rb->txn_context, sizeof(ReorderBufferTXN));
+
+	memset(txn, 0, sizeof(ReorderBufferTXN));
+
+	dlist_init(&txn->changes);
+	dlist_init(&txn->tuplecids);
+	dlist_init(&txn->subtxns);
+
+	/* InvalidCommandId is not zero, so set it explicitly */
+	txn->command_id = InvalidCommandId;
+	txn->output_plugin_private = NULL;
+
+	return txn;
+}
+
+/*
+ * Free a ReorderBufferTXN.
+ */
+static void
+ReorderBufferReturnTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	/* clean the lookup cache if we were cached (quite likely) */
+	if (rb->by_txn_last_xid == txn->xid)
+	{
+		rb->by_txn_last_xid = InvalidTransactionId;
+		rb->by_txn_last_txn = NULL;
+	}
+
+	/* free data that's contained */
+
+	if (txn->gid != NULL)
+	{
+		pfree(txn->gid);
+		txn->gid = NULL;
+	}
+
+	if (txn->tuplecid_hash != NULL)
+	{
+		hash_destroy(txn->tuplecid_hash);
+		txn->tuplecid_hash = NULL;
+	}
+
+	if (txn->invalidations)
+	{
+		pfree(txn->invalidations);
+		txn->invalidations = NULL;
+	}
+
+	/* Reset the toast hash */
+	ReorderBufferToastReset(rb, txn);
+
+	pfree(txn);
+}
+
+/*
+ * Get a fresh ReorderBufferChange.
+ */
+ReorderBufferChange *
+ReorderBufferGetChange(ReorderBuffer *rb)
+{
+	ReorderBufferChange *change;
+
+	change = (ReorderBufferChange *)
+		MemoryContextAlloc(rb->change_context, sizeof(ReorderBufferChange));
+
+	memset(change, 0, sizeof(ReorderBufferChange));
+	return change;
+}
+
+/*
+ * Free a ReorderBufferChange and update memory accounting, if requested.
+ */
+void
+ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change,
+						  bool upd_mem)
+{
+	/* update memory accounting info */
+	if (upd_mem)
+		ReorderBufferChangeMemoryUpdate(rb, change, false,
+										ReorderBufferChangeSize(change));
+
+	/* free contained data */
+	switch (change->action)
+	{
+		case REORDER_BUFFER_CHANGE_INSERT:
+		case REORDER_BUFFER_CHANGE_UPDATE:
+		case REORDER_BUFFER_CHANGE_DELETE:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
+			if (change->data.tp.newtuple)
+			{
+				ReorderBufferReturnTupleBuf(rb, change->data.tp.newtuple);
+				change->data.tp.newtuple = NULL;
+			}
+
+			if (change->data.tp.oldtuple)
+			{
+				ReorderBufferReturnTupleBuf(rb, change->data.tp.oldtuple);
+				change->data.tp.oldtuple = NULL;
+			}
+			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.prefix != NULL)
+				pfree(change->data.msg.prefix);
+			change->data.msg.prefix = NULL;
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
+		case REORDER_BUFFER_CHANGE_INVALIDATION:
+			if (change->data.inval.invalidations)
+				pfree(change->data.inval.invalidations);
+			change->data.inval.invalidations = NULL;
+			break;
+		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
+			if (change->data.snapshot)
+			{
+				ReorderBufferFreeSnap(rb, change->data.snapshot);
+				change->data.snapshot = NULL;
+			}
+			break;
+			/* no data in addition to the struct itself */
+		case REORDER_BUFFER_CHANGE_TRUNCATE:
+			if (change->data.truncate.relids != NULL)
+			{
+				ReorderBufferReturnRelids(rb, change->data.truncate.relids);
+				change->data.truncate.relids = NULL;
+			}
+			break;
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
+		case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
+		case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
+			break;
+	}
+
+	pfree(change);
+}
+
+/*
+ * Get a fresh ReorderBufferTupleBuf fitting at least a tuple of size
+ * tuple_len (excluding header overhead).
+ */
+ReorderBufferTupleBuf *
+ReorderBufferGetTupleBuf(ReorderBuffer *rb, Size tuple_len)
+{
+	ReorderBufferTupleBuf *tuple;
+	Size		alloc_len;
+
+	alloc_len = tuple_len + SizeofHeapTupleHeader;
+
+	tuple = (ReorderBufferTupleBuf *)
+		MemoryContextAlloc(rb->tup_context,
+						   sizeof(ReorderBufferTupleBuf) +
+						   MAXIMUM_ALIGNOF + alloc_len);
+	tuple->alloc_tuple_size = alloc_len;
+	tuple->tuple.t_data = ReorderBufferTupleBufData(tuple);
+
+	return tuple;
+}
+
+/*
+ * Free a ReorderBufferTupleBuf.
+ */
+void
+ReorderBufferReturnTupleBuf(ReorderBuffer *rb, ReorderBufferTupleBuf *tuple)
+{
+	pfree(tuple);
+}
+
+/*
+ * Get an array for relids of truncated relations.
+ *
+ * We use the global memory context (for the whole reorder buffer), because
+ * none of the existing ones seems like a good match (some are SLAB, so we
+ * can't use those, and tup_context is meant for tuple data, not relids). We
+ * could add yet another context, but it seems like an overkill - TRUNCATE is
+ * not particularly common operation, so it does not seem worth it.
+ */
+Oid *
+ReorderBufferGetRelids(ReorderBuffer *rb, int nrelids)
+{
+	Oid		   *relids;
+	Size		alloc_len;
+
+	alloc_len = sizeof(Oid) * nrelids;
+
+	relids = (Oid *) MemoryContextAlloc(rb->context, alloc_len);
+
+	return relids;
+}
+
+/*
+ * Free an array of relids.
+ */
+void
+ReorderBufferReturnRelids(ReorderBuffer *rb, Oid *relids)
+{
+	pfree(relids);
+}
+
+/*
+ * Return the ReorderBufferTXN from the given buffer, specified by Xid.
+ * If create is true, and a transaction doesn't already exist, create it
+ * (with the given LSN, and as top transaction if that's specified);
+ * when this happens, is_new is set to true.
+ */
+static ReorderBufferTXN *
+ReorderBufferTXNByXid(ReorderBuffer *rb, TransactionId xid, bool create,
+					  bool *is_new, XLogRecPtr lsn, bool create_as_top)
+{
+	ReorderBufferTXN *txn;
+	ReorderBufferTXNByIdEnt *ent;
+	bool		found;
+
+	Assert(TransactionIdIsValid(xid));
+
+	/*
+	 * Check the one-entry lookup cache first
+	 */
+	if (TransactionIdIsValid(rb->by_txn_last_xid) &&
+		rb->by_txn_last_xid == xid)
+	{
+		txn = rb->by_txn_last_txn;
+
+		if (txn != NULL)
+		{
+			/* found it, and it's valid */
+			if (is_new)
+				*is_new = false;
+			return txn;
+		}
+
+		/*
+		 * cached as non-existent, and asked not to create? Then nothing else
+		 * to do.
+		 */
+		if (!create)
+			return NULL;
+		/* otherwise fall through to create it */
+	}
+
+	/*
+	 * If the cache wasn't hit or it yielded a "does-not-exist" and we want
+	 * to create an entry.
+	 */
+
+	/* search the lookup table */
+	ent = (ReorderBufferTXNByIdEnt *)
+		hash_search(rb->by_txn,
+					(void *) &xid,
+					create ? HASH_ENTER : HASH_FIND,
+					&found);
+	if (found)
+		txn = ent->txn;
+	else if (create)
+	{
+		/* initialize the new entry, if creation was requested */
+		Assert(ent != NULL);
+		Assert(lsn != InvalidXLogRecPtr);
+
+		ent->txn = ReorderBufferGetTXN(rb);
+		ent->txn->xid = xid;
+		txn = ent->txn;
+		txn->first_lsn = lsn;
+		txn->restart_decoding_lsn = rb->current_restart_decoding_lsn;
+
+		if (create_as_top)
+		{
+			dlist_push_tail(&rb->toplevel_by_lsn, &txn->node);
+			AssertTXNLsnOrder(rb);
+		}
+	}
+	else
+		txn = NULL;				/* not found and not asked to create */
+
+	/* update cache */
+	rb->by_txn_last_xid = xid;
+	rb->by_txn_last_txn = txn;
+
+	if (is_new)
+		*is_new = !found;
+
+	Assert(!create || txn != NULL);
+	return txn;
+}
+
+/*
+ * Record the partial change for the streaming of in-progress transactions.  We
+ * can stream only complete changes so if we have a partial change like toast
+ * table insert or speculative insert then we mark such a 'txn' so that it
+ * can't be streamed.  We also ensure that if the changes in such a 'txn' are
+ * above logical_decoding_work_mem threshold then we stream them as soon as we
+ * have a complete change.
+ */
+static void
+ReorderBufferProcessPartialChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+								  ReorderBufferChange *change,
+								  bool toast_insert)
+{
+	ReorderBufferTXN *toptxn;
+
+	/*
+	 * The partial changes need to be processed only while streaming
+	 * in-progress transactions.
+	 */
+	if (!ReorderBufferCanStream(rb))
+		return;
+
+	/* Get the top transaction. */
+	if (txn->toptxn != NULL)
+		toptxn = txn->toptxn;
+	else
+		toptxn = txn;
+
+	/*
+	 * Indicate a partial change for toast inserts.  The change will be
+	 * considered as complete once we get the insert or update on the main
+	 * table and we are sure that the pending toast chunks are not required
+	 * anymore.
+	 *
+	 * If we allow streaming when there are pending toast chunks then such
+	 * chunks won't be released till the insert (multi_insert) is complete and
+	 * we expect the txn to have streamed all changes after streaming.  This
+	 * restriction is mainly to ensure the correctness of streamed
+	 * transactions and it doesn't seem worth uplifting such a restriction
+	 * just to allow this case because anyway we will stream the transaction
+	 * once such an insert is complete.
+	 */
+	if (toast_insert)
+		toptxn->txn_flags |= RBTXN_HAS_PARTIAL_CHANGE;
+	else if (rbtxn_has_partial_change(toptxn) &&
+			 IsInsertOrUpdate(change->action) &&
+			 change->data.tp.clear_toast_afterwards)
+		toptxn->txn_flags &= ~RBTXN_HAS_PARTIAL_CHANGE;
+
+	/*
+	 * Indicate a partial change for speculative inserts.  The change will be
+	 * considered as complete once we get the speculative confirm or abort
+	 * token.
+	 */
+	if (IsSpecInsert(change->action))
+		toptxn->txn_flags |= RBTXN_HAS_PARTIAL_CHANGE;
+	else if (rbtxn_has_partial_change(toptxn) &&
+			 IsSpecConfirmOrAbort(change->action))
+		toptxn->txn_flags &= ~RBTXN_HAS_PARTIAL_CHANGE;
+
+	/*
+	 * Stream the transaction if it is serialized before and the changes are
+	 * now complete in the top-level transaction.
+	 *
+	 * The reason for doing the streaming of such a transaction as soon as we
+	 * get the complete change for it is that previously it would have reached
+	 * the memory threshold and wouldn't get streamed because of incomplete
+	 * changes.  Delaying such transactions would increase apply lag for them.
+	 */
+	if (ReorderBufferCanStartStreaming(rb) &&
+		!(rbtxn_has_partial_change(toptxn)) &&
+		rbtxn_is_serialized(txn))
+		ReorderBufferStreamTXN(rb, toptxn);
+}
+
+/*
+ * Queue a change into a transaction so it can be replayed upon commit or will be
+ * streamed when we reach logical_decoding_work_mem threshold.
+ */
+void
+ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+						 ReorderBufferChange *change, bool toast_insert)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+	/*
+	 * While streaming the previous changes we have detected that the
+	 * transaction is aborted.  So there is no point in collecting further
+	 * changes for it.
+	 */
+	if (txn->concurrent_abort)
+	{
+		/*
+		 * We don't need to update memory accounting for this change as we
+		 * have not added it to the queue yet.
+		 */
+		ReorderBufferReturnChange(rb, change, false);
+		return;
+	}
+
+	change->lsn = lsn;
+	change->txn = txn;
+
+	Assert(InvalidXLogRecPtr != lsn);
+	dlist_push_tail(&txn->changes, &change->node);
+	txn->nentries++;
+	txn->nentries_mem++;
+
+	/* update memory accounting information */
+	ReorderBufferChangeMemoryUpdate(rb, change, true,
+									ReorderBufferChangeSize(change));
+
+	/* process partial change */
+	ReorderBufferProcessPartialChange(rb, txn, change, toast_insert);
+
+	/* check the memory limits and evict something if needed */
+	ReorderBufferCheckMemoryLimit(rb);
+}
+
+/*
+ * A transactional message is queued to be processed upon commit and a
+ * non-transactional message gets processed immediately.
+ */
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid,
+						  Snapshot snapshot, XLogRecPtr lsn,
+						  bool transactional, const char *prefix,
+						  Size message_size, const char *message)
+{
+	if (transactional)
+	{
+		MemoryContext oldcontext;
+		ReorderBufferChange *change;
+
+		Assert(xid != InvalidTransactionId);
+
+		oldcontext = MemoryContextSwitchTo(rb->context);
+
+		change = ReorderBufferGetChange(rb);
+		change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+		change->data.msg.prefix = pstrdup(prefix);
+		change->data.msg.message_size = message_size;
+		change->data.msg.message = palloc(message_size);
+		memcpy(change->data.msg.message, message, message_size);
+
+		ReorderBufferQueueChange(rb, xid, lsn, change, false);
+
+		MemoryContextSwitchTo(oldcontext);
+	}
+	else
+	{
+		ReorderBufferTXN *txn = NULL;
+		volatile Snapshot snapshot_now = snapshot;
+
+		if (xid != InvalidTransactionId)
+			txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+		/* setup snapshot to allow catalog access */
+		SetupHistoricSnapshot(snapshot_now, NULL);
+		PG_TRY();
+		{
+			rb->message(rb, txn, lsn, false, prefix, message_size, message);
+
+			TeardownHistoricSnapshot(false);
+		}
+		PG_CATCH();
+		{
+			TeardownHistoricSnapshot(true);
+			PG_RE_THROW();
+		}
+		PG_END_TRY();
+	}
+}
+
+/*
+ * AssertTXNLsnOrder
+ *		Verify LSN ordering of transaction lists in the reorderbuffer
+ *
+ * Other LSN-related invariants are checked too.
+ *
+ * No-op if assertions are not in use.
+ */
+static void
+AssertTXNLsnOrder(ReorderBuffer *rb)
+{
+#ifdef USE_ASSERT_CHECKING
+	dlist_iter	iter;
+	XLogRecPtr	prev_first_lsn = InvalidXLogRecPtr;
+	XLogRecPtr	prev_base_snap_lsn = InvalidXLogRecPtr;
+
+	dlist_foreach(iter, &rb->toplevel_by_lsn)
+	{
+		ReorderBufferTXN *cur_txn = dlist_container(ReorderBufferTXN, node,
+													iter.cur);
+
+		/* start LSN must be set */
+		Assert(cur_txn->first_lsn != InvalidXLogRecPtr);
+
+		/* If there is an end LSN, it must be higher than start LSN */
+		if (cur_txn->end_lsn != InvalidXLogRecPtr)
+			Assert(cur_txn->first_lsn <= cur_txn->end_lsn);
+
+		/* Current initial LSN must be strictly higher than previous */
+		if (prev_first_lsn != InvalidXLogRecPtr)
+			Assert(prev_first_lsn < cur_txn->first_lsn);
+
+		/* known-as-subtxn txns must not be listed */
+		Assert(!rbtxn_is_known_subxact(cur_txn));
+
+		prev_first_lsn = cur_txn->first_lsn;
+	}
+
+	dlist_foreach(iter, &rb->txns_by_base_snapshot_lsn)
+	{
+		ReorderBufferTXN *cur_txn = dlist_container(ReorderBufferTXN,
+													base_snapshot_node,
+													iter.cur);
+
+		/* base snapshot (and its LSN) must be set */
+		Assert(cur_txn->base_snapshot != NULL);
+		Assert(cur_txn->base_snapshot_lsn != InvalidXLogRecPtr);
+
+		/* current LSN must be strictly higher than previous */
+		if (prev_base_snap_lsn != InvalidXLogRecPtr)
+			Assert(prev_base_snap_lsn < cur_txn->base_snapshot_lsn);
+
+		/* known-as-subtxn txns must not be listed */
+		Assert(!rbtxn_is_known_subxact(cur_txn));
+
+		prev_base_snap_lsn = cur_txn->base_snapshot_lsn;
+	}
+#endif
+}
+
+/*
+ * AssertChangeLsnOrder
+ *
+ * Check ordering of changes in the (sub)transaction.
+ */
+static void
+AssertChangeLsnOrder(ReorderBufferTXN *txn)
+{
+#ifdef USE_ASSERT_CHECKING
+	dlist_iter	iter;
+	XLogRecPtr	prev_lsn = txn->first_lsn;
+
+	dlist_foreach(iter, &txn->changes)
+	{
+		ReorderBufferChange *cur_change;
+
+		cur_change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+		Assert(txn->first_lsn != InvalidXLogRecPtr);
+		Assert(cur_change->lsn != InvalidXLogRecPtr);
+		Assert(txn->first_lsn <= cur_change->lsn);
+
+		if (txn->end_lsn != InvalidXLogRecPtr)
+			Assert(cur_change->lsn <= txn->end_lsn);
+
+		Assert(prev_lsn <= cur_change->lsn);
+
+		prev_lsn = cur_change->lsn;
+	}
+#endif
+}
+
+/*
+ * ReorderBufferGetOldestTXN
+ *		Return oldest transaction in reorderbuffer
+ */
+ReorderBufferTXN *
+ReorderBufferGetOldestTXN(ReorderBuffer *rb)
+{
+	ReorderBufferTXN *txn;
+
+	AssertTXNLsnOrder(rb);
+
+	if (dlist_is_empty(&rb->toplevel_by_lsn))
+		return NULL;
+
+	txn = dlist_head_element(ReorderBufferTXN, node, &rb->toplevel_by_lsn);
+
+	Assert(!rbtxn_is_known_subxact(txn));
+	Assert(txn->first_lsn != InvalidXLogRecPtr);
+	return txn;
+}
+
+/*
+ * ReorderBufferGetOldestXmin
+ *		Return oldest Xmin in reorderbuffer
+ *
+ * Returns oldest possibly running Xid from the point of view of snapshots
+ * used in the transactions kept by reorderbuffer, or InvalidTransactionId if
+ * there are none.
+ *
+ * Since snapshots are assigned monotonically, this equals the Xmin of the
+ * base snapshot with minimal base_snapshot_lsn.
+ */
+TransactionId
+ReorderBufferGetOldestXmin(ReorderBuffer *rb)
+{
+	ReorderBufferTXN *txn;
+
+	AssertTXNLsnOrder(rb);
+
+	if (dlist_is_empty(&rb->txns_by_base_snapshot_lsn))
+		return InvalidTransactionId;
+
+	txn = dlist_head_element(ReorderBufferTXN, base_snapshot_node,
+							 &rb->txns_by_base_snapshot_lsn);
+	return txn->base_snapshot->xmin;
+}
+
+void
+ReorderBufferSetRestartPoint(ReorderBuffer *rb, XLogRecPtr ptr)
+{
+	rb->current_restart_decoding_lsn = ptr;
+}
+
+/*
+ * ReorderBufferAssignChild
+ *
+ * Make note that we know that subxid is a subtransaction of xid, seen as of
+ * the given lsn.
+ */
+void
+ReorderBufferAssignChild(ReorderBuffer *rb, TransactionId xid,
+						 TransactionId subxid, XLogRecPtr lsn)
+{
+	ReorderBufferTXN *txn;
+	ReorderBufferTXN *subtxn;
+	bool		new_top;
+	bool		new_sub;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, &new_top, lsn, true);
+	subtxn = ReorderBufferTXNByXid(rb, subxid, true, &new_sub, lsn, false);
+
+	if (!new_sub)
+	{
+		if (rbtxn_is_known_subxact(subtxn))
+		{
+			/* already associated, nothing to do */
+			return;
+		}
+		else
+		{
+			/*
+			 * We already saw this transaction, but initially added it to the
+			 * list of top-level txns.  Now that we know it's not top-level,
+			 * remove it from there.
+			 */
+			dlist_delete(&subtxn->node);
+		}
+	}
+
+	subtxn->txn_flags |= RBTXN_IS_SUBXACT;
+	subtxn->toplevel_xid = xid;
+	Assert(subtxn->nsubtxns == 0);
+
+	/* set the reference to top-level transaction */
+	subtxn->toptxn = txn;
+
+	/* add to subtransaction list */
+	dlist_push_tail(&txn->subtxns, &subtxn->node);
+	txn->nsubtxns++;
+
+	/* Possibly transfer the subtxn's snapshot to its top-level txn. */
+	ReorderBufferTransferSnapToParent(txn, subtxn);
+
+	/* Verify LSN-ordering invariant */
+	AssertTXNLsnOrder(rb);
+}
+
+/*
+ * ReorderBufferTransferSnapToParent
+ *		Transfer base snapshot from subtxn to top-level txn, if needed
+ *
+ * This is done if the top-level txn doesn't have a base snapshot, or if the
+ * subtxn's base snapshot has an earlier LSN than the top-level txn's base
+ * snapshot's LSN.  This can happen if there are no changes in the toplevel
+ * txn but there are some in the subtxn, or the first change in subtxn has
+ * earlier LSN than first change in the top-level txn and we learned about
+ * their kinship only now.
+ *
+ * The subtransaction's snapshot is cleared regardless of the transfer
+ * happening, since it's not needed anymore in either case.
+ *
+ * We do this as soon as we become aware of their kinship, to avoid queueing
+ * extra snapshots to txns known-as-subtxns -- only top-level txns will
+ * receive further snapshots.
+ */
+static void
+ReorderBufferTransferSnapToParent(ReorderBufferTXN *txn,
+								  ReorderBufferTXN *subtxn)
+{
+	Assert(subtxn->toplevel_xid == txn->xid);
+
+	if (subtxn->base_snapshot != NULL)
+	{
+		if (txn->base_snapshot == NULL ||
+			subtxn->base_snapshot_lsn < txn->base_snapshot_lsn)
+		{
+			/*
+			 * If the toplevel transaction already has a base snapshot but
+			 * it's newer than the subxact's, purge it.
+			 */
+			if (txn->base_snapshot != NULL)
+			{
+				SnapBuildSnapDecRefcount(txn->base_snapshot);
+				dlist_delete(&txn->base_snapshot_node);
+			}
+
+			/*
+			 * The snapshot is now the top transaction's; transfer it, and
+			 * adjust the list position of the top transaction in the list by
+			 * moving it to where the subtransaction is.
+			 */
+			txn->base_snapshot = subtxn->base_snapshot;
+			txn->base_snapshot_lsn = subtxn->base_snapshot_lsn;
+			dlist_insert_before(&subtxn->base_snapshot_node,
+								&txn->base_snapshot_node);
+
+			/*
+			 * The subtransaction doesn't have a snapshot anymore (so it
+			 * mustn't be in the list.)
+			 */
+			subtxn->base_snapshot = NULL;
+			subtxn->base_snapshot_lsn = InvalidXLogRecPtr;
+			dlist_delete(&subtxn->base_snapshot_node);
+		}
+		else
+		{
+			/* Base snap of toplevel is fine, so subxact's is not needed */
+			SnapBuildSnapDecRefcount(subtxn->base_snapshot);
+			dlist_delete(&subtxn->base_snapshot_node);
+			subtxn->base_snapshot = NULL;
+			subtxn->base_snapshot_lsn = InvalidXLogRecPtr;
+		}
+	}
+}
+
+/*
+ * Associate a subtransaction with its toplevel transaction at commit
+ * time. There may be no further changes added after this.
+ */
+void
+ReorderBufferCommitChild(ReorderBuffer *rb, TransactionId xid,
+						 TransactionId subxid, XLogRecPtr commit_lsn,
+						 XLogRecPtr end_lsn)
+{
+	ReorderBufferTXN *subtxn;
+
+	subtxn = ReorderBufferTXNByXid(rb, subxid, false, NULL,
+								   InvalidXLogRecPtr, false);
+
+	/*
+	 * No need to do anything if that subtxn didn't contain any changes
+	 */
+	if (!subtxn)
+		return;
+
+	subtxn->final_lsn = commit_lsn;
+	subtxn->end_lsn = end_lsn;
+
+	/*
+	 * Assign this subxact as a child of the toplevel xact (no-op if already
+	 * done.)
+	 */
+	ReorderBufferAssignChild(rb, xid, subxid, InvalidXLogRecPtr);
+}
+
+
+/*
+ * Support for efficiently iterating over a transaction's and its
+ * subtransactions' changes.
+ *
+ * We do by doing a k-way merge between transactions/subtransactions. For that
+ * we model the current heads of the different transactions as a binary heap
+ * so we easily know which (sub-)transaction has the change with the smallest
+ * lsn next.
+ *
+ * We assume the changes in individual transactions are already sorted by LSN.
+ */
+
+/*
+ * Binary heap comparison function.
+ */
+static int
+ReorderBufferIterCompare(Datum a, Datum b, void *arg)
+{
+	ReorderBufferIterTXNState *state = (ReorderBufferIterTXNState *) arg;
+	XLogRecPtr	pos_a = state->entries[DatumGetInt32(a)].lsn;
+	XLogRecPtr	pos_b = state->entries[DatumGetInt32(b)].lsn;
+
+	if (pos_a < pos_b)
+		return 1;
+	else if (pos_a == pos_b)
+		return 0;
+	return -1;
+}
+
+/*
+ * Allocate & initialize an iterator which iterates in lsn order over a
+ * transaction and all its subtransactions.
+ *
+ * Note: The iterator state is returned through iter_state parameter rather
+ * than the function's return value.  This is because the state gets cleaned up
+ * in a PG_CATCH block in the caller, so we want to make sure the caller gets
+ * back the state even if this function throws an exception.
+ */
+static void
+ReorderBufferIterTXNInit(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						 ReorderBufferIterTXNState *volatile *iter_state)
+{
+	Size		nr_txns = 0;
+	ReorderBufferIterTXNState *state;
+	dlist_iter	cur_txn_i;
+	int32		off;
+
+	*iter_state = NULL;
+
+	/* Check ordering of changes in the toplevel transaction. */
+	AssertChangeLsnOrder(txn);
+
+	/*
+	 * Calculate the size of our heap: one element for every transaction that
+	 * contains changes.  (Besides the transactions already in the reorder
+	 * buffer, we count the one we were directly passed.)
+	 */
+	if (txn->nentries > 0)
+		nr_txns++;
+
+	dlist_foreach(cur_txn_i, &txn->subtxns)
+	{
+		ReorderBufferTXN *cur_txn;
+
+		cur_txn = dlist_container(ReorderBufferTXN, node, cur_txn_i.cur);
+
+		/* Check ordering of changes in this subtransaction. */
+		AssertChangeLsnOrder(cur_txn);
+
+		if (cur_txn->nentries > 0)
+			nr_txns++;
+	}
+
+	/* allocate iteration state */
+	state = (ReorderBufferIterTXNState *)
+		MemoryContextAllocZero(rb->context,
+							   sizeof(ReorderBufferIterTXNState) +
+							   sizeof(ReorderBufferIterTXNEntry) * nr_txns);
+
+	state->nr_txns = nr_txns;
+	dlist_init(&state->old_change);
+
+	for (off = 0; off < state->nr_txns; off++)
+	{
+		state->entries[off].file.vfd = -1;
+		state->entries[off].segno = 0;
+	}
+
+	/* allocate heap */
+	state->heap = binaryheap_allocate(state->nr_txns,
+									  ReorderBufferIterCompare,
+									  state);
+
+	/* Now that the state fields are initialized, it is safe to return it. */
+	*iter_state = state;
+
+	/*
+	 * Now insert items into the binary heap, in an unordered fashion.  (We
+	 * will run a heap assembly step at the end; this is more efficient.)
+	 */
+
+	off = 0;
+
+	/* add toplevel transaction if it contains changes */
+	if (txn->nentries > 0)
+	{
+		ReorderBufferChange *cur_change;
+
+		if (rbtxn_is_serialized(txn))
+		{
+			/* serialize remaining changes */
+			ReorderBufferSerializeTXN(rb, txn);
+			ReorderBufferRestoreChanges(rb, txn, &state->entries[off].file,
+										&state->entries[off].segno);
+		}
+
+		cur_change = dlist_head_element(ReorderBufferChange, node,
+										&txn->changes);
+
+		state->entries[off].lsn = cur_change->lsn;
+		state->entries[off].change = cur_change;
+		state->entries[off].txn = txn;
+
+		binaryheap_add_unordered(state->heap, Int32GetDatum(off++));
+	}
+
+	/* add subtransactions if they contain changes */
+	dlist_foreach(cur_txn_i, &txn->subtxns)
+	{
+		ReorderBufferTXN *cur_txn;
+
+		cur_txn = dlist_container(ReorderBufferTXN, node, cur_txn_i.cur);
+
+		if (cur_txn->nentries > 0)
+		{
+			ReorderBufferChange *cur_change;
+
+			if (rbtxn_is_serialized(cur_txn))
+			{
+				/* serialize remaining changes */
+				ReorderBufferSerializeTXN(rb, cur_txn);
+				ReorderBufferRestoreChanges(rb, cur_txn,
+											&state->entries[off].file,
+											&state->entries[off].segno);
+			}
+			cur_change = dlist_head_element(ReorderBufferChange, node,
+											&cur_txn->changes);
+
+			state->entries[off].lsn = cur_change->lsn;
+			state->entries[off].change = cur_change;
+			state->entries[off].txn = cur_txn;
+
+			binaryheap_add_unordered(state->heap, Int32GetDatum(off++));
+		}
+	}
+
+	/* assemble a valid binary heap */
+	binaryheap_build(state->heap);
+}
+
+/*
+ * Return the next change when iterating over a transaction and its
+ * subtransactions.
+ *
+ * Returns NULL when no further changes exist.
+ */
+static ReorderBufferChange *
+ReorderBufferIterTXNNext(ReorderBuffer *rb, ReorderBufferIterTXNState *state)
+{
+	ReorderBufferChange *change;
+	ReorderBufferIterTXNEntry *entry;
+	int32		off;
+
+	/* nothing there anymore */
+	if (state->heap->bh_size == 0)
+		return NULL;
+
+	off = DatumGetInt32(binaryheap_first(state->heap));
+	entry = &state->entries[off];
+
+	/* free memory we might have "leaked" in the previous *Next call */
+	if (!dlist_is_empty(&state->old_change))
+	{
+		change = dlist_container(ReorderBufferChange, node,
+								 dlist_pop_head_node(&state->old_change));
+		ReorderBufferReturnChange(rb, change, true);
+		Assert(dlist_is_empty(&state->old_change));
+	}
+
+	change = entry->change;
+
+	/*
+	 * update heap with information about which transaction has the next
+	 * relevant change in LSN order
+	 */
+
+	/* there are in-memory changes */
+	if (dlist_has_next(&entry->txn->changes, &entry->change->node))
+	{
+		dlist_node *next = dlist_next_node(&entry->txn->changes, &change->node);
+		ReorderBufferChange *next_change =
+		dlist_container(ReorderBufferChange, node, next);
+
+		/* txn stays the same */
+		state->entries[off].lsn = next_change->lsn;
+		state->entries[off].change = next_change;
+
+		binaryheap_replace_first(state->heap, Int32GetDatum(off));
+		return change;
+	}
+
+	/* try to load changes from disk */
+	if (entry->txn->nentries != entry->txn->nentries_mem)
+	{
+		/*
+		 * Ugly: restoring changes will reuse *Change records, thus delete the
+		 * current one from the per-tx list and only free in the next call.
+		 */
+		dlist_delete(&change->node);
+		dlist_push_tail(&state->old_change, &change->node);
+
+		/*
+		 * Update the total bytes processed by the txn for which we are
+		 * releasing the current set of changes and restoring the new set of
+		 * changes.
+		 */
+		rb->totalBytes += entry->txn->size;
+		if (ReorderBufferRestoreChanges(rb, entry->txn, &entry->file,
+										&state->entries[off].segno))
+		{
+			/* successfully restored changes from disk */
+			ReorderBufferChange *next_change =
+			dlist_head_element(ReorderBufferChange, node,
+							   &entry->txn->changes);
+
+			elog(DEBUG2, "restored %u/%u changes from disk",
+				 (uint32) entry->txn->nentries_mem,
+				 (uint32) entry->txn->nentries);
+
+			Assert(entry->txn->nentries_mem);
+			/* txn stays the same */
+			state->entries[off].lsn = next_change->lsn;
+			state->entries[off].change = next_change;
+			binaryheap_replace_first(state->heap, Int32GetDatum(off));
+
+			return change;
+		}
+	}
+
+	/* ok, no changes there anymore, remove */
+	binaryheap_remove_first(state->heap);
+
+	return change;
+}
+
+/*
+ * Deallocate the iterator
+ */
+static void
+ReorderBufferIterTXNFinish(ReorderBuffer *rb,
+						   ReorderBufferIterTXNState *state)
+{
+	int32		off;
+
+	for (off = 0; off < state->nr_txns; off++)
+	{
+		if (state->entries[off].file.vfd != -1)
+			FileClose(state->entries[off].file.vfd);
+	}
+
+	/* free memory we might have "leaked" in the last *Next call */
+	if (!dlist_is_empty(&state->old_change))
+	{
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node,
+								 dlist_pop_head_node(&state->old_change));
+		ReorderBufferReturnChange(rb, change, true);
+		Assert(dlist_is_empty(&state->old_change));
+	}
+
+	binaryheap_free(state->heap);
+	pfree(state);
+}
+
+/*
+ * Cleanup the contents of a transaction, usually after the transaction
+ * committed or aborted.
+ */
+static void
+ReorderBufferCleanupTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	bool		found;
+	dlist_mutable_iter iter;
+
+	/* cleanup subtransactions & their changes */
+	dlist_foreach_modify(iter, &txn->subtxns)
+	{
+		ReorderBufferTXN *subtxn;
+
+		subtxn = dlist_container(ReorderBufferTXN, node, iter.cur);
+
+		/*
+		 * Subtransactions are always associated to the toplevel TXN, even if
+		 * they originally were happening inside another subtxn, so we won't
+		 * ever recurse more than one level deep here.
+		 */
+		Assert(rbtxn_is_known_subxact(subtxn));
+		Assert(subtxn->nsubtxns == 0);
+
+		ReorderBufferCleanupTXN(rb, subtxn);
+	}
+
+	/* cleanup changes in the txn */
+	dlist_foreach_modify(iter, &txn->changes)
+	{
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+		/* Check we're not mixing changes from different transactions. */
+		Assert(change->txn == txn);
+
+		ReorderBufferReturnChange(rb, change, true);
+	}
+
+	/*
+	 * Cleanup the tuplecids we stored for decoding catalog snapshot access.
+	 * They are always stored in the toplevel transaction.
+	 */
+	dlist_foreach_modify(iter, &txn->tuplecids)
+	{
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+		/* Check we're not mixing changes from different transactions. */
+		Assert(change->txn == txn);
+		Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
+
+		ReorderBufferReturnChange(rb, change, true);
+	}
+
+	/*
+	 * Cleanup the base snapshot, if set.
+	 */
+	if (txn->base_snapshot != NULL)
+	{
+		SnapBuildSnapDecRefcount(txn->base_snapshot);
+		dlist_delete(&txn->base_snapshot_node);
+	}
+
+	/*
+	 * Cleanup the snapshot for the last streamed run.
+	 */
+	if (txn->snapshot_now != NULL)
+	{
+		Assert(rbtxn_is_streamed(txn));
+		ReorderBufferFreeSnap(rb, txn->snapshot_now);
+	}
+
+	/*
+	 * Remove TXN from its containing list.
+	 *
+	 * Note: if txn is known as subxact, we are deleting the TXN from its
+	 * parent's list of known subxacts; this leaves the parent's nsubxacts
+	 * count too high, but we don't care.  Otherwise, we are deleting the TXN
+	 * from the LSN-ordered list of toplevel TXNs.
+	 */
+	dlist_delete(&txn->node);
+
+	/* now remove reference from buffer */
+	hash_search(rb->by_txn,
+				(void *) &txn->xid,
+				HASH_REMOVE,
+				&found);
+	Assert(found);
+
+	/* remove entries spilled to disk */
+	if (rbtxn_is_serialized(txn))
+		ReorderBufferRestoreCleanup(rb, txn);
+
+	/* deallocate */
+	ReorderBufferReturnTXN(rb, txn);
+}
+
+/*
+ * Discard changes from a transaction (and subtransactions), either after
+ * streaming or decoding them at PREPARE. Keep the remaining info -
+ * transactions, tuplecids, invalidations and snapshots.
+ *
+ * We additionaly remove tuplecids after decoding the transaction at prepare
+ * time as we only need to perform invalidation at rollback or commit prepared.
+ *
+ * 'txn_prepared' indicates that we have decoded the transaction at prepare
+ * time.
+ */
+static void
+ReorderBufferTruncateTXN(ReorderBuffer *rb, ReorderBufferTXN *txn, bool txn_prepared)
+{
+	dlist_mutable_iter iter;
+
+	/* cleanup subtransactions & their changes */
+	dlist_foreach_modify(iter, &txn->subtxns)
+	{
+		ReorderBufferTXN *subtxn;
+
+		subtxn = dlist_container(ReorderBufferTXN, node, iter.cur);
+
+		/*
+		 * Subtransactions are always associated to the toplevel TXN, even if
+		 * they originally were happening inside another subtxn, so we won't
+		 * ever recurse more than one level deep here.
+		 */
+		Assert(rbtxn_is_known_subxact(subtxn));
+		Assert(subtxn->nsubtxns == 0);
+
+		ReorderBufferTruncateTXN(rb, subtxn, txn_prepared);
+	}
+
+	/* cleanup changes in the txn */
+	dlist_foreach_modify(iter, &txn->changes)
+	{
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+		/* Check we're not mixing changes from different transactions. */
+		Assert(change->txn == txn);
+
+		/* remove the change from it's containing list */
+		dlist_delete(&change->node);
+
+		ReorderBufferReturnChange(rb, change, true);
+	}
+
+	/*
+	 * Mark the transaction as streamed.
+	 *
+	 * The toplevel transaction, identified by (toptxn==NULL), is marked as
+	 * streamed always, even if it does not contain any changes (that is, when
+	 * all the changes are in subtransactions).
+	 *
+	 * For subtransactions, we only mark them as streamed when there are
+	 * changes in them.
+	 *
+	 * We do it this way because of aborts - we don't want to send aborts for
+	 * XIDs the downstream is not aware of. And of course, it always knows
+	 * about the toplevel xact (we send the XID in all messages), but we never
+	 * stream XIDs of empty subxacts.
+	 */
+	if ((!txn_prepared) && ((!txn->toptxn) || (txn->nentries_mem != 0)))
+		txn->txn_flags |= RBTXN_IS_STREAMED;
+
+	if (txn_prepared)
+	{
+		/*
+		 * If this is a prepared txn, cleanup the tuplecids we stored for
+		 * decoding catalog snapshot access. They are always stored in the
+		 * toplevel transaction.
+		 */
+		dlist_foreach_modify(iter, &txn->tuplecids)
+		{
+			ReorderBufferChange *change;
+
+			change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+			/* Check we're not mixing changes from different transactions. */
+			Assert(change->txn == txn);
+			Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
+
+			/* Remove the change from its containing list. */
+			dlist_delete(&change->node);
+
+			ReorderBufferReturnChange(rb, change, true);
+		}
+	}
+
+	/*
+	 * Destroy the (relfilenode, ctid) hashtable, so that we don't leak any
+	 * memory. We could also keep the hash table and update it with new ctid
+	 * values, but this seems simpler and good enough for now.
+	 */
+	if (txn->tuplecid_hash != NULL)
+	{
+		hash_destroy(txn->tuplecid_hash);
+		txn->tuplecid_hash = NULL;
+	}
+
+	/* If this txn is serialized then clean the disk space. */
+	if (rbtxn_is_serialized(txn))
+	{
+		ReorderBufferRestoreCleanup(rb, txn);
+		txn->txn_flags &= ~RBTXN_IS_SERIALIZED;
+
+		/*
+		 * We set this flag to indicate if the transaction is ever serialized.
+		 * We need this to accurately update the stats as otherwise the same
+		 * transaction can be counted as serialized multiple times.
+		 */
+		txn->txn_flags |= RBTXN_IS_SERIALIZED_CLEAR;
+	}
+
+	/* also reset the number of entries in the transaction */
+	txn->nentries_mem = 0;
+	txn->nentries = 0;
+}
+
+/*
+ * Build a hash with a (relfilenode, ctid) -> (cmin, cmax) mapping for use by
+ * HeapTupleSatisfiesHistoricMVCC.
+ */
+static void
+ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	dlist_iter	iter;
+	HASHCTL		hash_ctl;
+
+	if (!rbtxn_has_catalog_changes(txn) || dlist_is_empty(&txn->tuplecids))
+		return;
+
+	hash_ctl.keysize = sizeof(ReorderBufferTupleCidKey);
+	hash_ctl.entrysize = sizeof(ReorderBufferTupleCidEnt);
+	hash_ctl.hcxt = rb->context;
+
+	/*
+	 * create the hash with the exact number of to-be-stored tuplecids from
+	 * the start
+	 */
+	txn->tuplecid_hash =
+		hash_create("ReorderBufferTupleCid", txn->ntuplecids, &hash_ctl,
+					HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	dlist_foreach(iter, &txn->tuplecids)
+	{
+		ReorderBufferTupleCidKey key;
+		ReorderBufferTupleCidEnt *ent;
+		bool		found;
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+		Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
+
+		/* be careful about padding */
+		memset(&key, 0, sizeof(ReorderBufferTupleCidKey));
+
+		key.relnode = change->data.tuplecid.node;
+
+		ItemPointerCopy(&change->data.tuplecid.tid,
+						&key.tid);
+
+		ent = (ReorderBufferTupleCidEnt *)
+			hash_search(txn->tuplecid_hash,
+						(void *) &key,
+						HASH_ENTER,
+						&found);
+		if (!found)
+		{
+			ent->cmin = change->data.tuplecid.cmin;
+			ent->cmax = change->data.tuplecid.cmax;
+			ent->combocid = change->data.tuplecid.combocid;
+		}
+		else
+		{
+			/*
+			 * Maybe we already saw this tuple before in this transaction, but
+			 * if so it must have the same cmin.
+			 */
+			Assert(ent->cmin == change->data.tuplecid.cmin);
+
+			/*
+			 * cmax may be initially invalid, but once set it can only grow,
+			 * and never become invalid again.
+			 */
+			Assert((ent->cmax == InvalidCommandId) ||
+				   ((change->data.tuplecid.cmax != InvalidCommandId) &&
+					(change->data.tuplecid.cmax > ent->cmax)));
+			ent->cmax = change->data.tuplecid.cmax;
+		}
+	}
+}
+
+/*
+ * Copy a provided snapshot so we can modify it privately. This is needed so
+ * that catalog modifying transactions can look into intermediate catalog
+ * states.
+ */
+static Snapshot
+ReorderBufferCopySnap(ReorderBuffer *rb, Snapshot orig_snap,
+					  ReorderBufferTXN *txn, CommandId cid)
+{
+	Snapshot	snap;
+	dlist_iter	iter;
+	int			i = 0;
+	Size		size;
+
+	size = sizeof(SnapshotData) +
+		sizeof(TransactionId) * orig_snap->xcnt +
+		sizeof(TransactionId) * (txn->nsubtxns + 1);
+
+	snap = MemoryContextAllocZero(rb->context, size);
+	memcpy(snap, orig_snap, sizeof(SnapshotData));
+
+	snap->copied = true;
+	snap->active_count = 1;		/* mark as active so nobody frees it */
+	snap->regd_count = 0;
+	snap->xip = (TransactionId *) (snap + 1);
+
+	memcpy(snap->xip, orig_snap->xip, sizeof(TransactionId) * snap->xcnt);
+
+	/*
+	 * snap->subxip contains all txids that belong to our transaction which we
+	 * need to check via cmin/cmax. That's why we store the toplevel
+	 * transaction in there as well.
+	 */
+	snap->subxip = snap->xip + snap->xcnt;
+	snap->subxip[i++] = txn->xid;
+
+	/*
+	 * subxcnt isn't decreased when subtransactions abort, so count manually.
+	 * Since it's an upper boundary it is safe to use it for the allocation
+	 * above.
+	 */
+	snap->subxcnt = 1;
+
+	dlist_foreach(iter, &txn->subtxns)
+	{
+		ReorderBufferTXN *sub_txn;
+
+		sub_txn = dlist_container(ReorderBufferTXN, node, iter.cur);
+		snap->subxip[i++] = sub_txn->xid;
+		snap->subxcnt++;
+	}
+
+	/* sort so we can bsearch() later */
+	qsort(snap->subxip, snap->subxcnt, sizeof(TransactionId), xidComparator);
+
+	/* store the specified current CommandId */
+	snap->curcid = cid;
+
+	return snap;
+}
+
+/*
+ * Free a previously ReorderBufferCopySnap'ed snapshot
+ */
+static void
+ReorderBufferFreeSnap(ReorderBuffer *rb, Snapshot snap)
+{
+	if (snap->copied)
+		pfree(snap);
+	else
+		SnapBuildSnapDecRefcount(snap);
+}
+
+/*
+ * If the transaction was (partially) streamed, we need to prepare or commit
+ * it in a 'streamed' way.  That is, we first stream the remaining part of the
+ * transaction, and then invoke stream_prepare or stream_commit message as per
+ * the case.
+ */
+static void
+ReorderBufferStreamCommit(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	/* we should only call this for previously streamed transactions */
+	Assert(rbtxn_is_streamed(txn));
+
+	ReorderBufferStreamTXN(rb, txn);
+
+	if (rbtxn_prepared(txn))
+	{
+		/*
+		 * Note, we send stream prepare even if a concurrent abort is
+		 * detected. See DecodePrepare for more information.
+		 */
+		rb->stream_prepare(rb, txn, txn->final_lsn);
+
+		/*
+		 * This is a PREPARED transaction, part of a two-phase commit. The
+		 * full cleanup will happen as part of the COMMIT PREPAREDs, so now
+		 * just truncate txn by removing changes and tuple_cids.
+		 */
+		ReorderBufferTruncateTXN(rb, txn, true);
+		/* Reset the CheckXidAlive */
+		CheckXidAlive = InvalidTransactionId;
+	}
+	else
+	{
+		rb->stream_commit(rb, txn, txn->final_lsn);
+		ReorderBufferCleanupTXN(rb, txn);
+	}
+}
+
+/*
+ * Set xid to detect concurrent aborts.
+ *
+ * While streaming an in-progress transaction or decoding a prepared
+ * transaction there is a possibility that the (sub)transaction might get
+ * aborted concurrently.  In such case if the (sub)transaction has catalog
+ * update then we might decode the tuple using wrong catalog version.  For
+ * example, suppose there is one catalog tuple with (xmin: 500, xmax: 0).  Now,
+ * the transaction 501 updates the catalog tuple and after that we will have
+ * two tuples (xmin: 500, xmax: 501) and (xmin: 501, xmax: 0).  Now, if 501 is
+ * aborted and some other transaction say 502 updates the same catalog tuple
+ * then the first tuple will be changed to (xmin: 500, xmax: 502).  So, the
+ * problem is that when we try to decode the tuple inserted/updated in 501
+ * after the catalog update, we will see the catalog tuple with (xmin: 500,
+ * xmax: 502) as visible because it will consider that the tuple is deleted by
+ * xid 502 which is not visible to our snapshot.  And when we will try to
+ * decode with that catalog tuple, it can lead to a wrong result or a crash.
+ * So, it is necessary to detect concurrent aborts to allow streaming of
+ * in-progress transactions or decoding of prepared  transactions.
+ *
+ * For detecting the concurrent abort we set CheckXidAlive to the current
+ * (sub)transaction's xid for which this change belongs to.  And, during
+ * catalog scan we can check the status of the xid and if it is aborted we will
+ * report a specific error so that we can stop streaming current transaction
+ * and discard the already streamed changes on such an error.  We might have
+ * already streamed some of the changes for the aborted (sub)transaction, but
+ * that is fine because when we decode the abort we will stream abort message
+ * to truncate the changes in the subscriber. Similarly, for prepared
+ * transactions, we stop decoding if concurrent abort is detected and then
+ * rollback the changes when rollback prepared is encountered. See
+ * DecodePrepare.
+ */
+static inline void
+SetupCheckXidLive(TransactionId xid)
+{
+	/*
+	 * If the input transaction id is already set as a CheckXidAlive then
+	 * nothing to do.
+	 */
+	if (TransactionIdEquals(CheckXidAlive, xid))
+		return;
+
+	/*
+	 * setup CheckXidAlive if it's not committed yet.  We don't check if the
+	 * xid is aborted.  That will happen during catalog access.
+	 */
+	if (!TransactionIdDidCommit(xid))
+		CheckXidAlive = xid;
+	else
+		CheckXidAlive = InvalidTransactionId;
+}
+
+/*
+ * Helper function for ReorderBufferProcessTXN for applying change.
+ */
+static inline void
+ReorderBufferApplyChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						 Relation relation, ReorderBufferChange *change,
+						 bool streaming)
+{
+	if (streaming)
+		rb->stream_change(rb, txn, relation, change);
+	else
+		rb->apply_change(rb, txn, relation, change);
+}
+
+/*
+ * Helper function for ReorderBufferProcessTXN for applying the truncate.
+ */
+static inline void
+ReorderBufferApplyTruncate(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						   int nrelations, Relation *relations,
+						   ReorderBufferChange *change, bool streaming)
+{
+	if (streaming)
+		rb->stream_truncate(rb, txn, nrelations, relations, change);
+	else
+		rb->apply_truncate(rb, txn, nrelations, relations, change);
+}
+
+/*
+ * Helper function for ReorderBufferProcessTXN for applying the message.
+ */
+static inline void
+ReorderBufferApplyMessage(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						  ReorderBufferChange *change, bool streaming)
+{
+	if (streaming)
+		rb->stream_message(rb, txn, change->lsn, true,
+						   change->data.msg.prefix,
+						   change->data.msg.message_size,
+						   change->data.msg.message);
+	else
+		rb->message(rb, txn, change->lsn, true,
+					change->data.msg.prefix,
+					change->data.msg.message_size,
+					change->data.msg.message);
+}
+
+/*
+ * Function to store the command id and snapshot at the end of the current
+ * stream so that we can reuse the same while sending the next stream.
+ */
+static inline void
+ReorderBufferSaveTXNSnapshot(ReorderBuffer *rb, ReorderBufferTXN *txn,
+							 Snapshot snapshot_now, CommandId command_id)
+{
+	txn->command_id = command_id;
+
+	/* Avoid copying if it's already copied. */
+	if (snapshot_now->copied)
+		txn->snapshot_now = snapshot_now;
+	else
+		txn->snapshot_now = ReorderBufferCopySnap(rb, snapshot_now,
+												  txn, command_id);
+}
+
+/*
+ * Helper function for ReorderBufferProcessTXN to handle the concurrent
+ * abort of the streaming transaction.  This resets the TXN such that it
+ * can be used to stream the remaining data of transaction being processed.
+ * This can happen when the subtransaction is aborted and we still want to
+ * continue processing the main or other subtransactions data.
+ */
+static void
+ReorderBufferResetTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
+					  Snapshot snapshot_now,
+					  CommandId command_id,
+					  XLogRecPtr last_lsn,
+					  ReorderBufferChange *specinsert)
+{
+	/* Discard the changes that we just streamed */
+	ReorderBufferTruncateTXN(rb, txn, rbtxn_prepared(txn));
+
+	/* Free all resources allocated for toast reconstruction */
+	ReorderBufferToastReset(rb, txn);
+
+	/* Return the spec insert change if it is not NULL */
+	if (specinsert != NULL)
+	{
+		ReorderBufferReturnChange(rb, specinsert, true);
+		specinsert = NULL;
+	}
+
+	/*
+	 * For the streaming case, stop the stream and remember the command ID and
+	 * snapshot for the streaming run.
+	 */
+	if (rbtxn_is_streamed(txn))
+	{
+		rb->stream_stop(rb, txn, last_lsn);
+		ReorderBufferSaveTXNSnapshot(rb, txn, snapshot_now, command_id);
+	}
+}
+
+/*
+ * Helper function for ReorderBufferReplay and ReorderBufferStreamTXN.
+ *
+ * Send data of a transaction (and its subtransactions) to the
+ * output plugin. We iterate over the top and subtransactions (using a k-way
+ * merge) and replay the changes in lsn order.
+ *
+ * If streaming is true then data will be sent using stream API.
+ *
+ * Note: "volatile" markers on some parameters are to avoid trouble with
+ * PG_TRY inside the function.
+ */
+static void
+ReorderBufferProcessTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						XLogRecPtr commit_lsn,
+						volatile Snapshot snapshot_now,
+						volatile CommandId command_id,
+						bool streaming)
+{
+	bool		using_subtxn;
+	MemoryContext ccxt = CurrentMemoryContext;
+	ReorderBufferIterTXNState *volatile iterstate = NULL;
+	volatile XLogRecPtr prev_lsn = InvalidXLogRecPtr;
+	ReorderBufferChange *volatile specinsert = NULL;
+	volatile bool stream_started = false;
+	ReorderBufferTXN *volatile curtxn = NULL;
+
+	/* build data to be able to lookup the CommandIds of catalog tuples */
+	ReorderBufferBuildTupleCidHash(rb, txn);
+
+	/* setup the initial snapshot */
+	SetupHistoricSnapshot(snapshot_now, txn->tuplecid_hash);
+
+	/*
+	 * Decoding needs access to syscaches et al., which in turn use
+	 * heavyweight locks and such. Thus we need to have enough state around to
+	 * keep track of those.  The easiest way is to simply use a transaction
+	 * internally.  That also allows us to easily enforce that nothing writes
+	 * to the database by checking for xid assignments.
+	 *
+	 * When we're called via the SQL SRF there's already a transaction
+	 * started, so start an explicit subtransaction there.
+	 */
+	using_subtxn = IsTransactionOrTransactionBlock();
+
+	PG_TRY();
+	{
+		ReorderBufferChange *change;
+
+		if (using_subtxn)
+			BeginInternalSubTransaction(streaming ? "stream" : "replay");
+		else
+			StartTransactionCommand();
+
+		/*
+		 * We only need to send begin/begin-prepare for non-streamed
+		 * transactions.
+		 */
+		if (!streaming)
+		{
+			if (rbtxn_prepared(txn))
+				rb->begin_prepare(rb, txn);
+			else
+				rb->begin(rb, txn);
+		}
+
+		ReorderBufferIterTXNInit(rb, txn, &iterstate);
+		while ((change = ReorderBufferIterTXNNext(rb, iterstate)) != NULL)
+		{
+			Relation	relation = NULL;
+			Oid			reloid;
+
+			/*
+			 * We can't call start stream callback before processing first
+			 * change.
+			 */
+			if (prev_lsn == InvalidXLogRecPtr)
+			{
+				if (streaming)
+				{
+					txn->origin_id = change->origin_id;
+					rb->stream_start(rb, txn, change->lsn);
+					stream_started = true;
+				}
+			}
+
+			/*
+			 * Enforce correct ordering of changes, merged from multiple
+			 * subtransactions. The changes may have the same LSN due to
+			 * MULTI_INSERT xlog records.
+			 */
+			Assert(prev_lsn == InvalidXLogRecPtr || prev_lsn <= change->lsn);
+
+			prev_lsn = change->lsn;
+
+			/*
+			 * Set the current xid to detect concurrent aborts. This is
+			 * required for the cases when we decode the changes before the
+			 * COMMIT record is processed.
+			 */
+			if (streaming || rbtxn_prepared(change->txn))
+			{
+				curtxn = change->txn;
+				SetupCheckXidLive(curtxn->xid);
+			}
+
+			switch (change->action)
+			{
+				case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
+
+					/*
+					 * Confirmation for speculative insertion arrived. Simply
+					 * use as a normal record. It'll be cleaned up at the end
+					 * of INSERT processing.
+					 */
+					if (specinsert == NULL)
+						elog(ERROR, "invalid ordering of speculative insertion changes");
+					Assert(specinsert->data.tp.oldtuple == NULL);
+					change = specinsert;
+					change->action = REORDER_BUFFER_CHANGE_INSERT;
+
+					/* intentionally fall through */
+				case REORDER_BUFFER_CHANGE_INSERT:
+				case REORDER_BUFFER_CHANGE_UPDATE:
+				case REORDER_BUFFER_CHANGE_DELETE:
+					Assert(snapshot_now);
+
+					reloid = RelidByRelfilenode(change->data.tp.relnode.spcNode,
+												change->data.tp.relnode.relNode);
+
+					/*
+					 * Mapped catalog tuple without data, emitted while
+					 * catalog table was in the process of being rewritten. We
+					 * can fail to look up the relfilenode, because the
+					 * relmapper has no "historic" view, in contrast to the
+					 * normal catalog during decoding. Thus repeated rewrites
+					 * can cause a lookup failure. That's OK because we do not
+					 * decode catalog changes anyway. Normally such tuples
+					 * would be skipped over below, but we can't identify
+					 * whether the table should be logically logged without
+					 * mapping the relfilenode to the oid.
+					 */
+					if (reloid == InvalidOid &&
+						change->data.tp.newtuple == NULL &&
+						change->data.tp.oldtuple == NULL)
+						goto change_done;
+					else if (reloid == InvalidOid)
+						elog(ERROR, "could not map filenode \"%s\" to relation OID",
+							 relpathperm(change->data.tp.relnode,
+										 MAIN_FORKNUM));
+
+					relation = RelationIdGetRelation(reloid);
+
+					if (!RelationIsValid(relation))
+						elog(ERROR, "could not open relation with OID %u (for filenode \"%s\")",
+							 reloid,
+							 relpathperm(change->data.tp.relnode,
+										 MAIN_FORKNUM));
+
+					if (!RelationIsLogicallyLogged(relation))
+						goto change_done;
+
+					/*
+					 * Ignore temporary heaps created during DDL unless the
+					 * plugin has asked for them.
+					 */
+					if (relation->rd_rel->relrewrite && !rb->output_rewrites)
+						goto change_done;
+
+					/*
+					 * For now ignore sequence changes entirely. Most of the
+					 * time they don't log changes using records we
+					 * understand, so it doesn't make sense to handle the few
+					 * cases we do.
+					 */
+					if (relation->rd_rel->relkind == RELKIND_SEQUENCE)
+						goto change_done;
+
+					/* user-triggered change */
+					if (!IsToastRelation(relation))
+					{
+						ReorderBufferToastReplace(rb, txn, relation, change);
+						ReorderBufferApplyChange(rb, txn, relation, change,
+												 streaming);
+
+						/*
+						 * Only clear reassembled toast chunks if we're sure
+						 * they're not required anymore. The creator of the
+						 * tuple tells us.
+						 */
+						if (change->data.tp.clear_toast_afterwards)
+							ReorderBufferToastReset(rb, txn);
+					}
+					/* we're not interested in toast deletions */
+					else if (change->action == REORDER_BUFFER_CHANGE_INSERT)
+					{
+						/*
+						 * Need to reassemble the full toasted Datum in
+						 * memory, to ensure the chunks don't get reused till
+						 * we're done remove it from the list of this
+						 * transaction's changes. Otherwise it will get
+						 * freed/reused while restoring spooled data from
+						 * disk.
+						 */
+						Assert(change->data.tp.newtuple != NULL);
+
+						dlist_delete(&change->node);
+						ReorderBufferToastAppendChunk(rb, txn, relation,
+													  change);
+					}
+
+			change_done:
+
+					/*
+					 * If speculative insertion was confirmed, the record
+					 * isn't needed anymore.
+					 */
+					if (specinsert != NULL)
+					{
+						ReorderBufferReturnChange(rb, specinsert, true);
+						specinsert = NULL;
+					}
+
+					if (RelationIsValid(relation))
+					{
+						RelationClose(relation);
+						relation = NULL;
+					}
+					break;
+
+				case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
+
+					/*
+					 * Speculative insertions are dealt with by delaying the
+					 * processing of the insert until the confirmation record
+					 * arrives. For that we simply unlink the record from the
+					 * chain, so it does not get freed/reused while restoring
+					 * spooled data from disk.
+					 *
+					 * This is safe in the face of concurrent catalog changes
+					 * because the relevant relation can't be changed between
+					 * speculative insertion and confirmation due to
+					 * CheckTableNotInUse() and locking.
+					 */
+
+					/* clear out a pending (and thus failed) speculation */
+					if (specinsert != NULL)
+					{
+						ReorderBufferReturnChange(rb, specinsert, true);
+						specinsert = NULL;
+					}
+
+					/* and memorize the pending insertion */
+					dlist_delete(&change->node);
+					specinsert = change;
+					break;
+
+				case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
+
+					/*
+					 * Abort for speculative insertion arrived. So cleanup the
+					 * specinsert tuple and toast hash.
+					 *
+					 * Note that we get the spec abort change for each toast
+					 * entry but we need to perform the cleanup only the first
+					 * time we get it for the main table.
+					 */
+					if (specinsert != NULL)
+					{
+						/*
+						 * We must clean the toast hash before processing a
+						 * completely new tuple to avoid confusion about the
+						 * previous tuple's toast chunks.
+						 */
+						Assert(change->data.tp.clear_toast_afterwards);
+						ReorderBufferToastReset(rb, txn);
+
+						/* We don't need this record anymore. */
+						ReorderBufferReturnChange(rb, specinsert, true);
+						specinsert = NULL;
+					}
+					break;
+
+				case REORDER_BUFFER_CHANGE_TRUNCATE:
+					{
+						int			i;
+						int			nrelids = change->data.truncate.nrelids;
+						int			nrelations = 0;
+						Relation   *relations;
+
+						relations = palloc0(nrelids * sizeof(Relation));
+						for (i = 0; i < nrelids; i++)
+						{
+							Oid			relid = change->data.truncate.relids[i];
+							Relation	relation;
+
+							relation = RelationIdGetRelation(relid);
+
+							if (!RelationIsValid(relation))
+								elog(ERROR, "could not open relation with OID %u", relid);
+
+							if (!RelationIsLogicallyLogged(relation))
+								continue;
+
+							relations[nrelations++] = relation;
+						}
+
+						/* Apply the truncate. */
+						ReorderBufferApplyTruncate(rb, txn, nrelations,
+												   relations, change,
+												   streaming);
+
+						for (i = 0; i < nrelations; i++)
+							RelationClose(relations[i]);
+
+						break;
+					}
+
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					ReorderBufferApplyMessage(rb, txn, change, streaming);
+					break;
+
+				case REORDER_BUFFER_CHANGE_INVALIDATION:
+					/* Execute the invalidation messages locally */
+					ReorderBufferExecuteInvalidations(
+													  change->data.inval.ninvalidations,
+													  change->data.inval.invalidations);
+					break;
+
+				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
+					/* get rid of the old */
+					TeardownHistoricSnapshot(false);
+
+					if (snapshot_now->copied)
+					{
+						ReorderBufferFreeSnap(rb, snapshot_now);
+						snapshot_now =
+							ReorderBufferCopySnap(rb, change->data.snapshot,
+												  txn, command_id);
+					}
+
+					/*
+					 * Restored from disk, need to be careful not to double
+					 * free. We could introduce refcounting for that, but for
+					 * now this seems infrequent enough not to care.
+					 */
+					else if (change->data.snapshot->copied)
+					{
+						snapshot_now =
+							ReorderBufferCopySnap(rb, change->data.snapshot,
+												  txn, command_id);
+					}
+					else
+					{
+						snapshot_now = change->data.snapshot;
+					}
+
+					/* and continue with the new one */
+					SetupHistoricSnapshot(snapshot_now, txn->tuplecid_hash);
+					break;
+
+				case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
+					Assert(change->data.command_id != InvalidCommandId);
+
+					if (command_id < change->data.command_id)
+					{
+						command_id = change->data.command_id;
+
+						if (!snapshot_now->copied)
+						{
+							/* we don't use the global one anymore */
+							snapshot_now = ReorderBufferCopySnap(rb, snapshot_now,
+																 txn, command_id);
+						}
+
+						snapshot_now->curcid = command_id;
+
+						TeardownHistoricSnapshot(false);
+						SetupHistoricSnapshot(snapshot_now, txn->tuplecid_hash);
+					}
+
+					break;
+
+				case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
+					elog(ERROR, "tuplecid value in changequeue");
+					break;
+			}
+		}
+
+		/* speculative insertion record must be freed by now */
+		Assert(!specinsert);
+
+		/* clean up the iterator */
+		ReorderBufferIterTXNFinish(rb, iterstate);
+		iterstate = NULL;
+
+		/*
+		 * Update total transaction count and total bytes processed by the
+		 * transaction and its subtransactions. Ensure to not count the
+		 * streamed transaction multiple times.
+		 *
+		 * Note that the statistics computation has to be done after
+		 * ReorderBufferIterTXNFinish as it releases the serialized change
+		 * which we have already accounted in ReorderBufferIterTXNNext.
+		 */
+		if (!rbtxn_is_streamed(txn))
+			rb->totalTxns++;
+
+		rb->totalBytes += txn->total_size;
+
+		/*
+		 * Done with current changes, send the last message for this set of
+		 * changes depending upon streaming mode.
+		 */
+		if (streaming)
+		{
+			if (stream_started)
+			{
+				rb->stream_stop(rb, txn, prev_lsn);
+				stream_started = false;
+			}
+		}
+		else
+		{
+			/*
+			 * Call either PREPARE (for two-phase transactions) or COMMIT (for
+			 * regular ones).
+			 */
+			if (rbtxn_prepared(txn))
+				rb->prepare(rb, txn, commit_lsn);
+			else
+				rb->commit(rb, txn, commit_lsn);
+		}
+
+		/* this is just a sanity check against bad output plugin behaviour */
+		if (GetCurrentTransactionIdIfAny() != InvalidTransactionId)
+			elog(ERROR, "output plugin used XID %u",
+				 GetCurrentTransactionId());
+
+		/*
+		 * Remember the command ID and snapshot for the next set of changes in
+		 * streaming mode.
+		 */
+		if (streaming)
+			ReorderBufferSaveTXNSnapshot(rb, txn, snapshot_now, command_id);
+		else if (snapshot_now->copied)
+			ReorderBufferFreeSnap(rb, snapshot_now);
+
+		/* cleanup */
+		TeardownHistoricSnapshot(false);
+
+		/*
+		 * Aborting the current (sub-)transaction as a whole has the right
+		 * semantics. We want all locks acquired in here to be released, not
+		 * reassigned to the parent and we do not want any database access
+		 * have persistent effects.
+		 */
+		AbortCurrentTransaction();
+
+		/* make sure there's no cache pollution */
+		ReorderBufferExecuteInvalidations(txn->ninvalidations, txn->invalidations);
+
+		if (using_subtxn)
+			RollbackAndReleaseCurrentSubTransaction();
+
+		/*
+		 * We are here due to one of the four reasons: 1. Decoding an
+		 * in-progress txn. 2. Decoding a prepared txn. 3. Decoding of a
+		 * prepared txn that was (partially) streamed. 4. Decoding a committed
+		 * txn.
+		 *
+		 * For 1, we allow truncation of txn data by removing the changes
+		 * already streamed but still keeping other things like invalidations,
+		 * snapshot, and tuplecids. For 2 and 3, we indicate
+		 * ReorderBufferTruncateTXN to do more elaborate truncation of txn
+		 * data as the entire transaction has been decoded except for commit.
+		 * For 4, as the entire txn has been decoded, we can fully clean up
+		 * the TXN reorder buffer.
+		 */
+		if (streaming || rbtxn_prepared(txn))
+		{
+			ReorderBufferTruncateTXN(rb, txn, rbtxn_prepared(txn));
+			/* Reset the CheckXidAlive */
+			CheckXidAlive = InvalidTransactionId;
+		}
+		else
+			ReorderBufferCleanupTXN(rb, txn);
+	}
+	PG_CATCH();
+	{
+		MemoryContext ecxt = MemoryContextSwitchTo(ccxt);
+		ErrorData  *errdata = CopyErrorData();
+
+		/* TODO: Encapsulate cleanup from the PG_TRY and PG_CATCH blocks */
+		if (iterstate)
+			ReorderBufferIterTXNFinish(rb, iterstate);
+
+		TeardownHistoricSnapshot(true);
+
+		/*
+		 * Force cache invalidation to happen outside of a valid transaction
+		 * to prevent catalog access as we just caught an error.
+		 */
+		AbortCurrentTransaction();
+
+		/* make sure there's no cache pollution */
+		ReorderBufferExecuteInvalidations(txn->ninvalidations,
+										  txn->invalidations);
+
+		if (using_subtxn)
+			RollbackAndReleaseCurrentSubTransaction();
+
+		/*
+		 * The error code ERRCODE_TRANSACTION_ROLLBACK indicates a concurrent
+		 * abort of the (sub)transaction we are streaming or preparing. We
+		 * need to do the cleanup and return gracefully on this error, see
+		 * SetupCheckXidLive.
+		 *
+		 * This error code can be thrown by one of the callbacks we call
+		 * during decoding so we need to ensure that we return gracefully only
+		 * when we are sending the data in streaming mode and the streaming is
+		 * not finished yet or when we are sending the data out on a PREPARE
+		 * during a two-phase commit.
+		 */
+		if (errdata->sqlerrcode == ERRCODE_TRANSACTION_ROLLBACK &&
+			(stream_started || rbtxn_prepared(txn)))
+		{
+			/* curtxn must be set for streaming or prepared transactions */
+			Assert(curtxn);
+
+			/* Cleanup the temporary error state. */
+			FlushErrorState();
+			FreeErrorData(errdata);
+			errdata = NULL;
+			curtxn->concurrent_abort = true;
+
+			/* Reset the TXN so that it is allowed to stream remaining data. */
+			ReorderBufferResetTXN(rb, txn, snapshot_now,
+								  command_id, prev_lsn,
+								  specinsert);
+		}
+		else
+		{
+			ReorderBufferCleanupTXN(rb, txn);
+			MemoryContextSwitchTo(ecxt);
+			PG_RE_THROW();
+		}
+	}
+	PG_END_TRY();
+}
+
+/*
+ * Perform the replay of a transaction and its non-aborted subtransactions.
+ *
+ * Subtransactions previously have to be processed by
+ * ReorderBufferCommitChild(), even if previously assigned to the toplevel
+ * transaction with ReorderBufferAssignChild.
+ *
+ * This interface is called once a prepare or toplevel commit is read for both
+ * streamed as well as non-streamed transactions.
+ */
+static void
+ReorderBufferReplay(ReorderBufferTXN *txn,
+					ReorderBuffer *rb, TransactionId xid,
+					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
+					TimestampTz commit_time,
+					RepOriginId origin_id, XLogRecPtr origin_lsn)
+{
+	Snapshot	snapshot_now;
+	CommandId	command_id = FirstCommandId;
+
+	txn->final_lsn = commit_lsn;
+	txn->end_lsn = end_lsn;
+	txn->commit_time = commit_time;
+	txn->origin_id = origin_id;
+	txn->origin_lsn = origin_lsn;
+
+	/*
+	 * If the transaction was (partially) streamed, we need to commit it in a
+	 * 'streamed' way. That is, we first stream the remaining part of the
+	 * transaction, and then invoke stream_commit message.
+	 *
+	 * Called after everything (origin ID, LSN, ...) is stored in the
+	 * transaction to avoid passing that information directly.
+	 */
+	if (rbtxn_is_streamed(txn))
+	{
+		ReorderBufferStreamCommit(rb, txn);
+		return;
+	}
+
+	/*
+	 * If this transaction has no snapshot, it didn't make any changes to the
+	 * database, so there's nothing to decode.  Note that
+	 * ReorderBufferCommitChild will have transferred any snapshots from
+	 * subtransactions if there were any.
+	 */
+	if (txn->base_snapshot == NULL)
+	{
+		Assert(txn->ninvalidations == 0);
+
+		/*
+		 * Removing this txn before a commit might result in the computation
+		 * of an incorrect restart_lsn. See SnapBuildProcessRunningXacts.
+		 */
+		if (!rbtxn_prepared(txn))
+			ReorderBufferCleanupTXN(rb, txn);
+		return;
+	}
+
+	snapshot_now = txn->base_snapshot;
+
+	/* Process and send the changes to output plugin. */
+	ReorderBufferProcessTXN(rb, txn, commit_lsn, snapshot_now,
+							command_id, false);
+}
+
+/*
+ * Commit a transaction.
+ *
+ * See comments for ReorderBufferReplay().
+ */
+void
+ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
+					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
+					TimestampTz commit_time,
+					RepOriginId origin_id, XLogRecPtr origin_lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+
+	/* unknown transaction, nothing to replay */
+	if (txn == NULL)
+		return;
+
+	ReorderBufferReplay(txn, rb, xid, commit_lsn, end_lsn, commit_time,
+						origin_id, origin_lsn);
+}
+
+/*
+ * Record the prepare information for a transaction.
+ */
+bool
+ReorderBufferRememberPrepareInfo(ReorderBuffer *rb, TransactionId xid,
+								 XLogRecPtr prepare_lsn, XLogRecPtr end_lsn,
+								 TimestampTz prepare_time,
+								 RepOriginId origin_id, XLogRecPtr origin_lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr, false);
+
+	/* unknown transaction, nothing to do */
+	if (txn == NULL)
+		return false;
+
+	/*
+	 * Remember the prepare information to be later used by commit prepared in
+	 * case we skip doing prepare.
+	 */
+	txn->final_lsn = prepare_lsn;
+	txn->end_lsn = end_lsn;
+	txn->commit_time = prepare_time;
+	txn->origin_id = origin_id;
+	txn->origin_lsn = origin_lsn;
+
+	return true;
+}
+
+/* Remember that we have skipped prepare */
+void
+ReorderBufferSkipPrepare(ReorderBuffer *rb, TransactionId xid)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr, false);
+
+	/* unknown transaction, nothing to do */
+	if (txn == NULL)
+		return;
+
+	txn->txn_flags |= RBTXN_SKIPPED_PREPARE;
+}
+
+/*
+ * Prepare a two-phase transaction.
+ *
+ * See comments for ReorderBufferReplay().
+ */
+void
+ReorderBufferPrepare(ReorderBuffer *rb, TransactionId xid,
+					 char *gid)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+
+	/* unknown transaction, nothing to replay */
+	if (txn == NULL)
+		return;
+
+	txn->txn_flags |= RBTXN_PREPARE;
+	txn->gid = pstrdup(gid);
+
+	/* The prepare info must have been updated in txn by now. */
+	Assert(txn->final_lsn != InvalidXLogRecPtr);
+
+	ReorderBufferReplay(txn, rb, xid, txn->final_lsn, txn->end_lsn,
+						txn->commit_time, txn->origin_id, txn->origin_lsn);
+
+	/*
+	 * We send the prepare for the concurrently aborted xacts so that later
+	 * when rollback prepared is decoded and sent, the downstream should be
+	 * able to rollback such a xact. See comments atop DecodePrepare.
+	 *
+	 * Note, for the concurrent_abort + streaming case a stream_prepare was
+	 * already sent within the ReorderBufferReplay call above.
+	 */
+	if (txn->concurrent_abort && !rbtxn_is_streamed(txn))
+		rb->prepare(rb, txn, txn->final_lsn);
+}
+
+/*
+ * This is used to handle COMMIT/ROLLBACK PREPARED.
+ */
+void
+ReorderBufferFinishPrepared(ReorderBuffer *rb, TransactionId xid,
+							XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
+							XLogRecPtr initial_consistent_point,
+							TimestampTz commit_time, RepOriginId origin_id,
+							XLogRecPtr origin_lsn, char *gid, bool is_commit)
+{
+	ReorderBufferTXN *txn;
+	XLogRecPtr	prepare_end_lsn;
+	TimestampTz prepare_time;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, commit_lsn, false);
+
+	/* unknown transaction, nothing to do */
+	if (txn == NULL)
+		return;
+
+	/*
+	 * By this time the txn has the prepare record information, remember it to
+	 * be later used for rollback.
+	 */
+	prepare_end_lsn = txn->end_lsn;
+	prepare_time = txn->commit_time;
+
+	/* add the gid in the txn */
+	txn->gid = pstrdup(gid);
+
+	/*
+	 * It is possible that this transaction is not decoded at prepare time
+	 * either because by that time we didn't have a consistent snapshot or it
+	 * was decoded earlier but we have restarted. We only need to send the
+	 * prepare if it was not decoded earlier. We don't need to decode the xact
+	 * for aborts if it is not done already.
+	 */
+	if ((txn->final_lsn < initial_consistent_point) && is_commit)
+	{
+		txn->txn_flags |= RBTXN_PREPARE;
+
+		/*
+		 * The prepare info must have been updated in txn even if we skip
+		 * prepare.
+		 */
+		Assert(txn->final_lsn != InvalidXLogRecPtr);
+
+		/*
+		 * By this time the txn has the prepare record information and it is
+		 * important to use that so that downstream gets the accurate
+		 * information. If instead, we have passed commit information here
+		 * then downstream can behave as it has already replayed commit
+		 * prepared after the restart.
+		 */
+		ReorderBufferReplay(txn, rb, xid, txn->final_lsn, txn->end_lsn,
+							txn->commit_time, txn->origin_id, txn->origin_lsn);
+	}
+
+	txn->final_lsn = commit_lsn;
+	txn->end_lsn = end_lsn;
+	txn->commit_time = commit_time;
+	txn->origin_id = origin_id;
+	txn->origin_lsn = origin_lsn;
+
+	if (is_commit)
+		rb->commit_prepared(rb, txn, commit_lsn);
+	else
+		rb->rollback_prepared(rb, txn, prepare_end_lsn, prepare_time);
+
+	/* cleanup: make sure there's no cache pollution */
+	ReorderBufferExecuteInvalidations(txn->ninvalidations,
+									  txn->invalidations);
+	ReorderBufferCleanupTXN(rb, txn);
+}
+
+/*
+ * Abort a transaction that possibly has previous changes. Needs to be first
+ * called for subtransactions and then for the toplevel xid.
+ *
+ * NB: Transactions handled here have to have actively aborted (i.e. have
+ * produced an abort record). Implicitly aborted transactions are handled via
+ * ReorderBufferAbortOld(); transactions we're just not interested in, but
+ * which have committed are handled in ReorderBufferForget().
+ *
+ * This function purges this transaction and its contents from memory and
+ * disk.
+ */
+void
+ReorderBufferAbort(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+
+	/* unknown, nothing to remove */
+	if (txn == NULL)
+		return;
+
+	/* For streamed transactions notify the remote node about the abort. */
+	if (rbtxn_is_streamed(txn))
+	{
+		rb->stream_abort(rb, txn, lsn);
+
+		/*
+		 * We might have decoded changes for this transaction that could load
+		 * the cache as per the current transaction's view (consider DDL's
+		 * happened in this transaction). We don't want the decoding of future
+		 * transactions to use those cache entries so execute invalidations.
+		 */
+		if (txn->ninvalidations > 0)
+			ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
+											   txn->invalidations);
+	}
+
+	/* cosmetic... */
+	txn->final_lsn = lsn;
+
+	/* remove potential on-disk data, and deallocate */
+	ReorderBufferCleanupTXN(rb, txn);
+}
+
+/*
+ * Abort all transactions that aren't actually running anymore because the
+ * server restarted.
+ *
+ * NB: These really have to be transactions that have aborted due to a server
+ * crash/immediate restart, as we don't deal with invalidations here.
+ */
+void
+ReorderBufferAbortOld(ReorderBuffer *rb, TransactionId oldestRunningXid)
+{
+	dlist_mutable_iter it;
+
+	/*
+	 * Iterate through all (potential) toplevel TXNs and abort all that are
+	 * older than what possibly can be running. Once we've found the first
+	 * that is alive we stop, there might be some that acquired an xid earlier
+	 * but started writing later, but it's unlikely and they will be cleaned
+	 * up in a later call to this function.
+	 */
+	dlist_foreach_modify(it, &rb->toplevel_by_lsn)
+	{
+		ReorderBufferTXN *txn;
+
+		txn = dlist_container(ReorderBufferTXN, node, it.cur);
+
+		if (TransactionIdPrecedes(txn->xid, oldestRunningXid))
+		{
+			elog(DEBUG2, "aborting old transaction %u", txn->xid);
+
+			/* remove potential on-disk data, and deallocate this tx */
+			ReorderBufferCleanupTXN(rb, txn);
+		}
+		else
+			return;
+	}
+}
+
+/*
+ * Forget the contents of a transaction if we aren't interested in its
+ * contents. Needs to be first called for subtransactions and then for the
+ * toplevel xid.
+ *
+ * This is significantly different to ReorderBufferAbort() because
+ * transactions that have committed need to be treated differently from aborted
+ * ones since they may have modified the catalog.
+ *
+ * Note that this is only allowed to be called in the moment a transaction
+ * commit has just been read, not earlier; otherwise later records referring
+ * to this xid might re-create the transaction incompletely.
+ */
+void
+ReorderBufferForget(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+
+	/* unknown, nothing to forget */
+	if (txn == NULL)
+		return;
+
+	/* For streamed transactions notify the remote node about the abort. */
+	if (rbtxn_is_streamed(txn))
+		rb->stream_abort(rb, txn, lsn);
+
+	/* cosmetic... */
+	txn->final_lsn = lsn;
+
+	/*
+	 * Process cache invalidation messages if there are any. Even if we're not
+	 * interested in the transaction's contents, it could have manipulated the
+	 * catalog and we need to update the caches according to that.
+	 */
+	if (txn->base_snapshot != NULL && txn->ninvalidations > 0)
+		ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
+										   txn->invalidations);
+	else
+		Assert(txn->ninvalidations == 0);
+
+	/* remove potential on-disk data, and deallocate */
+	ReorderBufferCleanupTXN(rb, txn);
+}
+
+/*
+ * Invalidate cache for those transactions that need to be skipped just in case
+ * catalogs were manipulated as part of the transaction.
+ *
+ * Note that this is a special-purpose function for prepared transactions where
+ * we don't want to clean up the TXN even when we decide to skip it. See
+ * DecodePrepare.
+ */
+void
+ReorderBufferInvalidate(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+
+	/* unknown, nothing to do */
+	if (txn == NULL)
+		return;
+
+	/*
+	 * Process cache invalidation messages if there are any. Even if we're not
+	 * interested in the transaction's contents, it could have manipulated the
+	 * catalog and we need to update the caches according to that.
+	 */
+	if (txn->base_snapshot != NULL && txn->ninvalidations > 0)
+		ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
+										   txn->invalidations);
+	else
+		Assert(txn->ninvalidations == 0);
+}
+
+
+/*
+ * Execute invalidations happening outside the context of a decoded
+ * transaction. That currently happens either for xid-less commits
+ * (cf. RecordTransactionCommit()) or for invalidations in uninteresting
+ * transactions (via ReorderBufferForget()).
+ */
+void
+ReorderBufferImmediateInvalidation(ReorderBuffer *rb, uint32 ninvalidations,
+								   SharedInvalidationMessage *invalidations)
+{
+	bool		use_subtxn = IsTransactionOrTransactionBlock();
+	int			i;
+
+	if (use_subtxn)
+		BeginInternalSubTransaction("replay");
+
+	/*
+	 * Force invalidations to happen outside of a valid transaction - that way
+	 * entries will just be marked as invalid without accessing the catalog.
+	 * That's advantageous because we don't need to setup the full state
+	 * necessary for catalog access.
+	 */
+	if (use_subtxn)
+		AbortCurrentTransaction();
+
+	for (i = 0; i < ninvalidations; i++)
+		LocalExecuteInvalidationMessage(&invalidations[i]);
+
+	if (use_subtxn)
+		RollbackAndReleaseCurrentSubTransaction();
+}
+
+/*
+ * Tell reorderbuffer about an xid seen in the WAL stream. Has to be called at
+ * least once for every xid in XLogRecord->xl_xid (other places in records
+ * may, but do not have to be passed through here).
+ *
+ * Reorderbuffer keeps some datastructures about transactions in LSN order,
+ * for efficiency. To do that it has to know about when transactions are seen
+ * first in the WAL. As many types of records are not actually interesting for
+ * logical decoding, they do not necessarily pass though here.
+ */
+void
+ReorderBufferProcessXid(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
+{
+	/* many records won't have an xid assigned, centralize check here */
+	if (xid != InvalidTransactionId)
+		ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+}
+
+/*
+ * Add a new snapshot to this transaction that may only used after lsn 'lsn'
+ * because the previous snapshot doesn't describe the catalog correctly for
+ * following rows.
+ */
+void
+ReorderBufferAddSnapshot(ReorderBuffer *rb, TransactionId xid,
+						 XLogRecPtr lsn, Snapshot snap)
+{
+	ReorderBufferChange *change = ReorderBufferGetChange(rb);
+
+	change->data.snapshot = snap;
+	change->action = REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT;
+
+	ReorderBufferQueueChange(rb, xid, lsn, change, false);
+}
+
+/*
+ * Set up the transaction's base snapshot.
+ *
+ * If we know that xid is a subtransaction, set the base snapshot on the
+ * top-level transaction instead.
+ */
+void
+ReorderBufferSetBaseSnapshot(ReorderBuffer *rb, TransactionId xid,
+							 XLogRecPtr lsn, Snapshot snap)
+{
+	ReorderBufferTXN *txn;
+	bool		is_new;
+
+	AssertArg(snap != NULL);
+
+	/*
+	 * Fetch the transaction to operate on.  If we know it's a subtransaction,
+	 * operate on its top-level transaction instead.
+	 */
+	txn = ReorderBufferTXNByXid(rb, xid, true, &is_new, lsn, true);
+	if (rbtxn_is_known_subxact(txn))
+		txn = ReorderBufferTXNByXid(rb, txn->toplevel_xid, false,
+									NULL, InvalidXLogRecPtr, false);
+	Assert(txn->base_snapshot == NULL);
+
+	txn->base_snapshot = snap;
+	txn->base_snapshot_lsn = lsn;
+	dlist_push_tail(&rb->txns_by_base_snapshot_lsn, &txn->base_snapshot_node);
+
+	AssertTXNLsnOrder(rb);
+}
+
+/*
+ * Access the catalog with this CommandId at this point in the changestream.
+ *
+ * May only be called for command ids > 1
+ */
+void
+ReorderBufferAddNewCommandId(ReorderBuffer *rb, TransactionId xid,
+							 XLogRecPtr lsn, CommandId cid)
+{
+	ReorderBufferChange *change = ReorderBufferGetChange(rb);
+
+	change->data.command_id = cid;
+	change->action = REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID;
+
+	ReorderBufferQueueChange(rb, xid, lsn, change, false);
+}
+
+/*
+ * Update memory counters to account for the new or removed change.
+ *
+ * We update two counters - in the reorder buffer, and in the transaction
+ * containing the change. The reorder buffer counter allows us to quickly
+ * decide if we reached the memory limit, the transaction counter allows
+ * us to quickly pick the largest transaction for eviction.
+ *
+ * When streaming is enabled, we need to update the toplevel transaction
+ * counters instead - we don't really care about subtransactions as we
+ * can't stream them individually anyway, and we only pick toplevel
+ * transactions for eviction. So only toplevel transactions matter.
+ */
+static void
+ReorderBufferChangeMemoryUpdate(ReorderBuffer *rb,
+								ReorderBufferChange *change,
+								bool addition, Size sz)
+{
+	ReorderBufferTXN *txn;
+	ReorderBufferTXN *toptxn;
+
+	Assert(change->txn);
+
+	/*
+	 * Ignore tuple CID changes, because those are not evicted when reaching
+	 * memory limit. So we just don't count them, because it might easily
+	 * trigger a pointless attempt to spill.
+	 */
+	if (change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID)
+		return;
+
+	txn = change->txn;
+
+	/*
+	 * Update the total size in top level as well. This is later used to
+	 * compute the decoding stats.
+	 */
+	if (txn->toptxn != NULL)
+		toptxn = txn->toptxn;
+	else
+		toptxn = txn;
+
+	if (addition)
+	{
+		txn->size += sz;
+		rb->size += sz;
+
+		/* Update the total size in the top transaction. */
+		toptxn->total_size += sz;
+	}
+	else
+	{
+		Assert((rb->size >= sz) && (txn->size >= sz));
+		txn->size -= sz;
+		rb->size -= sz;
+
+		/* Update the total size in the top transaction. */
+		toptxn->total_size -= sz;
+	}
+
+	Assert(txn->size <= rb->size);
+}
+
+/*
+ * Add new (relfilenode, tid) -> (cmin, cmax) mappings.
+ *
+ * We do not include this change type in memory accounting, because we
+ * keep CIDs in a separate list and do not evict them when reaching
+ * the memory limit.
+ */
+void
+ReorderBufferAddNewTupleCids(ReorderBuffer *rb, TransactionId xid,
+							 XLogRecPtr lsn, RelFileNode node,
+							 ItemPointerData tid, CommandId cmin,
+							 CommandId cmax, CommandId combocid)
+{
+	ReorderBufferChange *change = ReorderBufferGetChange(rb);
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+	change->data.tuplecid.node = node;
+	change->data.tuplecid.tid = tid;
+	change->data.tuplecid.cmin = cmin;
+	change->data.tuplecid.cmax = cmax;
+	change->data.tuplecid.combocid = combocid;
+	change->lsn = lsn;
+	change->txn = txn;
+	change->action = REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID;
+
+	dlist_push_tail(&txn->tuplecids, &change->node);
+	txn->ntuplecids++;
+}
+
+/*
+ * Setup the invalidation of the toplevel transaction.
+ *
+ * This needs to be called for each XLOG_XACT_INVALIDATIONS message and
+ * accumulates all the invalidation messages in the toplevel transaction as
+ * well as in the form of change in reorder buffer.  We require to record it in
+ * form of the change so that we can execute only the required invalidations
+ * instead of executing all the invalidations on each CommandId increment.  We
+ * also need to accumulate these in the toplevel transaction because in some
+ * cases we skip processing the transaction (see ReorderBufferForget), we need
+ * to execute all the invalidations together.
+ */
+void
+ReorderBufferAddInvalidations(ReorderBuffer *rb, TransactionId xid,
+							  XLogRecPtr lsn, Size nmsgs,
+							  SharedInvalidationMessage *msgs)
+{
+	ReorderBufferTXN *txn;
+	MemoryContext oldcontext;
+	ReorderBufferChange *change;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+	oldcontext = MemoryContextSwitchTo(rb->context);
+
+	/*
+	 * Collect all the invalidations under the top transaction so that we can
+	 * execute them all together.  See comment atop this function
+	 */
+	if (txn->toptxn)
+		txn = txn->toptxn;
+
+	Assert(nmsgs > 0);
+
+	/* Accumulate invalidations. */
+	if (txn->ninvalidations == 0)
+	{
+		txn->ninvalidations = nmsgs;
+		txn->invalidations = (SharedInvalidationMessage *)
+			palloc(sizeof(SharedInvalidationMessage) * nmsgs);
+		memcpy(txn->invalidations, msgs,
+			   sizeof(SharedInvalidationMessage) * nmsgs);
+	}
+	else
+	{
+		txn->invalidations = (SharedInvalidationMessage *)
+			repalloc(txn->invalidations, sizeof(SharedInvalidationMessage) *
+					 (txn->ninvalidations + nmsgs));
+
+		memcpy(txn->invalidations + txn->ninvalidations, msgs,
+			   nmsgs * sizeof(SharedInvalidationMessage));
+		txn->ninvalidations += nmsgs;
+	}
+
+	change = ReorderBufferGetChange(rb);
+	change->action = REORDER_BUFFER_CHANGE_INVALIDATION;
+	change->data.inval.ninvalidations = nmsgs;
+	change->data.inval.invalidations = (SharedInvalidationMessage *)
+		palloc(sizeof(SharedInvalidationMessage) * nmsgs);
+	memcpy(change->data.inval.invalidations, msgs,
+		   sizeof(SharedInvalidationMessage) * nmsgs);
+
+	ReorderBufferQueueChange(rb, xid, lsn, change, false);
+
+	MemoryContextSwitchTo(oldcontext);
+}
+
+/*
+ * Apply all invalidations we know. Possibly we only need parts at this point
+ * in the changestream but we don't know which those are.
+ */
+static void
+ReorderBufferExecuteInvalidations(uint32 nmsgs, SharedInvalidationMessage *msgs)
+{
+	int			i;
+
+	for (i = 0; i < nmsgs; i++)
+		LocalExecuteInvalidationMessage(&msgs[i]);
+}
+
+/*
+ * Mark a transaction as containing catalog changes
+ */
+void
+ReorderBufferXidSetCatalogChanges(ReorderBuffer *rb, TransactionId xid,
+								  XLogRecPtr lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+	txn->txn_flags |= RBTXN_HAS_CATALOG_CHANGES;
+
+	/*
+	 * Mark top-level transaction as having catalog changes too if one of its
+	 * children has so that the ReorderBufferBuildTupleCidHash can
+	 * conveniently check just top-level transaction and decide whether to
+	 * build the hash table or not.
+	 */
+	if (txn->toptxn != NULL)
+		txn->toptxn->txn_flags |= RBTXN_HAS_CATALOG_CHANGES;
+}
+
+/*
+ * Query whether a transaction is already *known* to contain catalog
+ * changes. This can be wrong until directly before the commit!
+ */
+bool
+ReorderBufferXidHasCatalogChanges(ReorderBuffer *rb, TransactionId xid)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+	if (txn == NULL)
+		return false;
+
+	return rbtxn_has_catalog_changes(txn);
+}
+
+/*
+ * ReorderBufferXidHasBaseSnapshot
+ *		Have we already set the base snapshot for the given txn/subtxn?
+ */
+bool
+ReorderBufferXidHasBaseSnapshot(ReorderBuffer *rb, TransactionId xid)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false,
+								NULL, InvalidXLogRecPtr, false);
+
+	/* transaction isn't known yet, ergo no snapshot */
+	if (txn == NULL)
+		return false;
+
+	/* a known subtxn? operate on top-level txn instead */
+	if (rbtxn_is_known_subxact(txn))
+		txn = ReorderBufferTXNByXid(rb, txn->toplevel_xid, false,
+									NULL, InvalidXLogRecPtr, false);
+
+	return txn->base_snapshot != NULL;
+}
+
+
+/*
+ * ---------------------------------------
+ * Disk serialization support
+ * ---------------------------------------
+ */
+
+/*
+ * Ensure the IO buffer is >= sz.
+ */
+static void
+ReorderBufferSerializeReserve(ReorderBuffer *rb, Size sz)
+{
+	if (!rb->outbufsize)
+	{
+		rb->outbuf = MemoryContextAlloc(rb->context, sz);
+		rb->outbufsize = sz;
+	}
+	else if (rb->outbufsize < sz)
+	{
+		rb->outbuf = repalloc(rb->outbuf, sz);
+		rb->outbufsize = sz;
+	}
+}
+
+/*
+ * Find the largest transaction (toplevel or subxact) to evict (spill to disk).
+ *
+ * XXX With many subtransactions this might be quite slow, because we'll have
+ * to walk through all of them. There are some options how we could improve
+ * that: (a) maintain some secondary structure with transactions sorted by
+ * amount of changes, (b) not looking for the entirely largest transaction,
+ * but e.g. for transaction using at least some fraction of the memory limit,
+ * and (c) evicting multiple transactions at once, e.g. to free a given portion
+ * of the memory limit (e.g. 50%).
+ */
+static ReorderBufferTXN *
+ReorderBufferLargestTXN(ReorderBuffer *rb)
+{
+	HASH_SEQ_STATUS hash_seq;
+	ReorderBufferTXNByIdEnt *ent;
+	ReorderBufferTXN *largest = NULL;
+
+	hash_seq_init(&hash_seq, rb->by_txn);
+	while ((ent = hash_seq_search(&hash_seq)) != NULL)
+	{
+		ReorderBufferTXN *txn = ent->txn;
+
+		/* if the current transaction is larger, remember it */
+		if ((!largest) || (txn->size > largest->size))
+			largest = txn;
+	}
+
+	Assert(largest);
+	Assert(largest->size > 0);
+	Assert(largest->size <= rb->size);
+
+	return largest;
+}
+
+/*
+ * Find the largest toplevel transaction to evict (by streaming).
+ *
+ * This can be seen as an optimized version of ReorderBufferLargestTXN, which
+ * should give us the same transaction (because we don't update memory account
+ * for subtransaction with streaming, so it's always 0). But we can simply
+ * iterate over the limited number of toplevel transactions that have a base
+ * snapshot. There is no use of selecting a transaction that doesn't have base
+ * snapshot because we don't decode such transactions.
+ *
+ * Note that, we skip transactions that contains incomplete changes. There
+ * is a scope of optimization here such that we can select the largest
+ * transaction which has incomplete changes.  But that will make the code and
+ * design quite complex and that might not be worth the benefit.  If we plan to
+ * stream the transactions that contains incomplete changes then we need to
+ * find a way to partially stream/truncate the transaction changes in-memory
+ * and build a mechanism to partially truncate the spilled files.
+ * Additionally, whenever we partially stream the transaction we need to
+ * maintain the last streamed lsn and next time we need to restore from that
+ * segment and the offset in WAL.  As we stream the changes from the top
+ * transaction and restore them subtransaction wise, we need to even remember
+ * the subxact from where we streamed the last change.
+ */
+static ReorderBufferTXN *
+ReorderBufferLargestTopTXN(ReorderBuffer *rb)
+{
+	dlist_iter	iter;
+	Size		largest_size = 0;
+	ReorderBufferTXN *largest = NULL;
+
+	/* Find the largest top-level transaction having a base snapshot. */
+	dlist_foreach(iter, &rb->txns_by_base_snapshot_lsn)
+	{
+		ReorderBufferTXN *txn;
+
+		txn = dlist_container(ReorderBufferTXN, base_snapshot_node, iter.cur);
+
+		/* must not be a subtxn */
+		Assert(!rbtxn_is_known_subxact(txn));
+		/* base_snapshot must be set */
+		Assert(txn->base_snapshot != NULL);
+
+		if ((largest == NULL || txn->total_size > largest_size) &&
+			(txn->total_size > 0) && !(rbtxn_has_partial_change(txn)))
+		{
+			largest = txn;
+			largest_size = txn->total_size;
+		}
+	}
+
+	return largest;
+}
+
+/*
+ * Check whether the logical_decoding_work_mem limit was reached, and if yes
+ * pick the largest (sub)transaction at-a-time to evict and spill its changes to
+ * disk until we reach under the memory limit.
+ *
+ * XXX At this point we select the transactions until we reach under the memory
+ * limit, but we might also adapt a more elaborate eviction strategy - for example
+ * evicting enough transactions to free certain fraction (e.g. 50%) of the memory
+ * limit.
+ */
+static void
+ReorderBufferCheckMemoryLimit(ReorderBuffer *rb)
+{
+	ReorderBufferTXN *txn;
+
+	/* bail out if we haven't exceeded the memory limit */
+	if (rb->size < logical_decoding_work_mem * 1024L)
+		return;
+
+	/*
+	 * Loop until we reach under the memory limit.  One might think that just
+	 * by evicting the largest (sub)transaction we will come under the memory
+	 * limit based on assumption that the selected transaction is at least as
+	 * large as the most recent change (which caused us to go over the memory
+	 * limit). However, that is not true because a user can reduce the
+	 * logical_decoding_work_mem to a smaller value before the most recent
+	 * change.
+	 */
+	while (rb->size >= logical_decoding_work_mem * 1024L)
+	{
+		/*
+		 * Pick the largest transaction (or subtransaction) and evict it from
+		 * memory by streaming, if possible.  Otherwise, spill to disk.
+		 */
+		if (ReorderBufferCanStartStreaming(rb) &&
+			(txn = ReorderBufferLargestTopTXN(rb)) != NULL)
+		{
+			/* we know there has to be one, because the size is not zero */
+			Assert(txn && !txn->toptxn);
+			Assert(txn->total_size > 0);
+			Assert(rb->size >= txn->total_size);
+
+			ReorderBufferStreamTXN(rb, txn);
+		}
+		else
+		{
+			/*
+			 * Pick the largest transaction (or subtransaction) and evict it
+			 * from memory by serializing it to disk.
+			 */
+			txn = ReorderBufferLargestTXN(rb);
+
+			/* we know there has to be one, because the size is not zero */
+			Assert(txn);
+			Assert(txn->size > 0);
+			Assert(rb->size >= txn->size);
+
+			ReorderBufferSerializeTXN(rb, txn);
+		}
+
+		/*
+		 * After eviction, the transaction should have no entries in memory,
+		 * and should use 0 bytes for changes.
+		 */
+		Assert(txn->size == 0);
+		Assert(txn->nentries_mem == 0);
+	}
+
+	/* We must be under the memory limit now. */
+	Assert(rb->size < logical_decoding_work_mem * 1024L);
+}
+
+/*
+ * Spill data of a large transaction (and its subtransactions) to disk.
+ */
+static void
+ReorderBufferSerializeTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	dlist_iter	subtxn_i;
+	dlist_mutable_iter change_i;
+	int			fd = -1;
+	XLogSegNo	curOpenSegNo = 0;
+	Size		spilled = 0;
+	Size		size = txn->size;
+
+	elog(DEBUG2, "spill %u changes in XID %u to disk",
+		 (uint32) txn->nentries_mem, txn->xid);
+
+	/* do the same to all child TXs */
+	dlist_foreach(subtxn_i, &txn->subtxns)
+	{
+		ReorderBufferTXN *subtxn;
+
+		subtxn = dlist_container(ReorderBufferTXN, node, subtxn_i.cur);
+		ReorderBufferSerializeTXN(rb, subtxn);
+	}
+
+	/* serialize changestream */
+	dlist_foreach_modify(change_i, &txn->changes)
+	{
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node, change_i.cur);
+
+		/*
+		 * store in segment in which it belongs by start lsn, don't split over
+		 * multiple segments tho
+		 */
+		if (fd == -1 ||
+			!XLByteInSeg(change->lsn, curOpenSegNo, wal_segment_size))
+		{
+			char		path[MAXPGPATH];
+
+			if (fd != -1)
+				CloseTransientFile(fd);
+
+			XLByteToSeg(change->lsn, curOpenSegNo, wal_segment_size);
+
+			/*
+			 * No need to care about TLIs here, only used during a single run,
+			 * so each LSN only maps to a specific WAL record.
+			 */
+			ReorderBufferSerializedPath(path, MyReplicationSlot, txn->xid,
+										curOpenSegNo);
+
+			/* open segment, create it if necessary */
+			fd = OpenTransientFile(path,
+								   O_CREAT | O_WRONLY | O_APPEND | PG_BINARY);
+
+			if (fd < 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not open file \"%s\": %m", path)));
+		}
+
+		ReorderBufferSerializeChange(rb, txn, fd, change);
+		dlist_delete(&change->node);
+		ReorderBufferReturnChange(rb, change, true);
+
+		spilled++;
+	}
+
+	/* update the statistics iff we have spilled anything */
+	if (spilled)
+	{
+		rb->spillCount += 1;
+		rb->spillBytes += size;
+
+		/* don't consider already serialized transactions */
+		rb->spillTxns += (rbtxn_is_serialized(txn) || rbtxn_is_serialized_clear(txn)) ? 0 : 1;
+
+		/* update the decoding stats */
+		UpdateDecodingStats((LogicalDecodingContext *) rb->private_data);
+	}
+
+	Assert(spilled == txn->nentries_mem);
+	Assert(dlist_is_empty(&txn->changes));
+	txn->nentries_mem = 0;
+	txn->txn_flags |= RBTXN_IS_SERIALIZED;
+
+	if (fd != -1)
+		CloseTransientFile(fd);
+}
+
+/*
+ * Serialize individual change to disk.
+ */
+static void
+ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+							 int fd, ReorderBufferChange *change)
+{
+	ReorderBufferDiskChange *ondisk;
+	Size		sz = sizeof(ReorderBufferDiskChange);
+
+	ReorderBufferSerializeReserve(rb, sz);
+
+	ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+	memcpy(&ondisk->change, change, sizeof(ReorderBufferChange));
+
+	switch (change->action)
+	{
+			/* fall through these, they're all similar enough */
+		case REORDER_BUFFER_CHANGE_INSERT:
+		case REORDER_BUFFER_CHANGE_UPDATE:
+		case REORDER_BUFFER_CHANGE_DELETE:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
+			{
+				char	   *data;
+				ReorderBufferTupleBuf *oldtup,
+						   *newtup;
+				Size		oldlen = 0;
+				Size		newlen = 0;
+
+				oldtup = change->data.tp.oldtuple;
+				newtup = change->data.tp.newtuple;
+
+				if (oldtup)
+				{
+					sz += sizeof(HeapTupleData);
+					oldlen = oldtup->tuple.t_len;
+					sz += oldlen;
+				}
+
+				if (newtup)
+				{
+					sz += sizeof(HeapTupleData);
+					newlen = newtup->tuple.t_len;
+					sz += newlen;
+				}
+
+				/* make sure we have enough space */
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				/* might have been reallocated above */
+				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+				if (oldlen)
+				{
+					memcpy(data, &oldtup->tuple, sizeof(HeapTupleData));
+					data += sizeof(HeapTupleData);
+
+					memcpy(data, oldtup->tuple.t_data, oldlen);
+					data += oldlen;
+				}
+
+				if (newlen)
+				{
+					memcpy(data, &newtup->tuple, sizeof(HeapTupleData));
+					data += sizeof(HeapTupleData);
+
+					memcpy(data, newtup->tuple.t_data, newlen);
+					data += newlen;
+				}
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				Size		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size +
+					sizeof(Size) + sizeof(Size);
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+
+				/* might have been reallocated above */
+				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+				/* write the prefix including the size */
+				memcpy(data, &prefix_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				data += prefix_size;
+
+				/* write the message including the size */
+				memcpy(data, &change->data.msg.message_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.message,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INVALIDATION:
+			{
+				char	   *data;
+				Size		inval_size = sizeof(SharedInvalidationMessage) *
+				change->data.inval.ninvalidations;
+
+				sz += inval_size;
+
+				ReorderBufferSerializeReserve(rb, sz);
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+
+				/* might have been reallocated above */
+				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+				memcpy(data, change->data.inval.invalidations, inval_size);
+				data += inval_size;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
+			{
+				Snapshot	snap;
+				char	   *data;
+
+				snap = change->data.snapshot;
+
+				sz += sizeof(SnapshotData) +
+					sizeof(TransactionId) * snap->xcnt +
+					sizeof(TransactionId) * snap->subxcnt;
+
+				/* make sure we have enough space */
+				ReorderBufferSerializeReserve(rb, sz);
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				/* might have been reallocated above */
+				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+				memcpy(data, snap, sizeof(SnapshotData));
+				data += sizeof(SnapshotData);
+
+				if (snap->xcnt)
+				{
+					memcpy(data, snap->xip,
+						   sizeof(TransactionId) * snap->xcnt);
+					data += sizeof(TransactionId) * snap->xcnt;
+				}
+
+				if (snap->subxcnt)
+				{
+					memcpy(data, snap->subxip,
+						   sizeof(TransactionId) * snap->subxcnt);
+					data += sizeof(TransactionId) * snap->subxcnt;
+				}
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_TRUNCATE:
+			{
+				Size		size;
+				char	   *data;
+
+				/* account for the OIDs of truncated relations */
+				size = sizeof(Oid) * change->data.truncate.nrelids;
+				sz += size;
+
+				/* make sure we have enough space */
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				/* might have been reallocated above */
+				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+				memcpy(data, change->data.truncate.relids, size);
+				data += size;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
+		case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
+		case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
+			/* ReorderBufferChange contains everything important */
+			break;
+	}
+
+	ondisk->size = sz;
+
+	errno = 0;
+	pgstat_report_wait_start(WAIT_EVENT_REORDER_BUFFER_WRITE);
+	if (write(fd, rb->outbuf, ondisk->size) != ondisk->size)
+	{
+		int			save_errno = errno;
+
+		CloseTransientFile(fd);
+
+		/* if write didn't set errno, assume problem is no disk space */
+		errno = save_errno ? save_errno : ENOSPC;
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write to data file for XID %u: %m",
+						txn->xid)));
+	}
+	pgstat_report_wait_end();
+
+	/*
+	 * Keep the transaction's final_lsn up to date with each change we send to
+	 * disk, so that ReorderBufferRestoreCleanup works correctly.  (We used to
+	 * only do this on commit and abort records, but that doesn't work if a
+	 * system crash leaves a transaction without its abort record).
+	 *
+	 * Make sure not to move it backwards.
+	 */
+	if (txn->final_lsn < change->lsn)
+		txn->final_lsn = change->lsn;
+
+	Assert(ondisk->change.action == change->action);
+}
+
+/* Returns true, if the output plugin supports streaming, false, otherwise. */
+static inline bool
+ReorderBufferCanStream(ReorderBuffer *rb)
+{
+	LogicalDecodingContext *ctx = rb->private_data;
+
+	return ctx->streaming;
+}
+
+/* Returns true, if the streaming can be started now, false, otherwise. */
+static inline bool
+ReorderBufferCanStartStreaming(ReorderBuffer *rb)
+{
+	LogicalDecodingContext *ctx = rb->private_data;
+	SnapBuild  *builder = ctx->snapshot_builder;
+
+	/* We can't start streaming unless a consistent state is reached. */
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_CONSISTENT)
+		return false;
+
+	/*
+	 * We can't start streaming immediately even if the streaming is enabled
+	 * because we previously decoded this transaction and now just are
+	 * restarting.
+	 */
+	if (ReorderBufferCanStream(rb) &&
+		!SnapBuildXactNeedsSkip(builder, ctx->reader->EndRecPtr))
+		return true;
+
+	return false;
+}
+
+/*
+ * Send data of a large transaction (and its subtransactions) to the
+ * output plugin, but using the stream API.
+ */
+static void
+ReorderBufferStreamTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	Snapshot	snapshot_now;
+	CommandId	command_id;
+	Size		stream_bytes;
+	bool		txn_is_streamed;
+
+	/* We can never reach here for a subtransaction. */
+	Assert(txn->toptxn == NULL);
+
+	/*
+	 * We can't make any assumptions about base snapshot here, similar to what
+	 * ReorderBufferCommit() does. That relies on base_snapshot getting
+	 * transferred from subxact in ReorderBufferCommitChild(), but that was
+	 * not yet called as the transaction is in-progress.
+	 *
+	 * So just walk the subxacts and use the same logic here. But we only need
+	 * to do that once, when the transaction is streamed for the first time.
+	 * After that we need to reuse the snapshot from the previous run.
+	 *
+	 * Unlike DecodeCommit which adds xids of all the subtransactions in
+	 * snapshot's xip array via SnapBuildCommittedTxn, we can't do that here
+	 * but we do add them to subxip array instead via ReorderBufferCopySnap.
+	 * This allows the catalog changes made in subtransactions decoded till
+	 * now to be visible.
+	 */
+	if (txn->snapshot_now == NULL)
+	{
+		dlist_iter	subxact_i;
+
+		/* make sure this transaction is streamed for the first time */
+		Assert(!rbtxn_is_streamed(txn));
+
+		/* at the beginning we should have invalid command ID */
+		Assert(txn->command_id == InvalidCommandId);
+
+		dlist_foreach(subxact_i, &txn->subtxns)
+		{
+			ReorderBufferTXN *subtxn;
+
+			subtxn = dlist_container(ReorderBufferTXN, node, subxact_i.cur);
+			ReorderBufferTransferSnapToParent(txn, subtxn);
+		}
+
+		/*
+		 * If this transaction has no snapshot, it didn't make any changes to
+		 * the database till now, so there's nothing to decode.
+		 */
+		if (txn->base_snapshot == NULL)
+		{
+			Assert(txn->ninvalidations == 0);
+			return;
+		}
+
+		command_id = FirstCommandId;
+		snapshot_now = ReorderBufferCopySnap(rb, txn->base_snapshot,
+											 txn, command_id);
+	}
+	else
+	{
+		/* the transaction must have been already streamed */
+		Assert(rbtxn_is_streamed(txn));
+
+		/*
+		 * Nah, we already have snapshot from the previous streaming run. We
+		 * assume new subxacts can't move the LSN backwards, and so can't beat
+		 * the LSN condition in the previous branch (so no need to walk
+		 * through subxacts again). In fact, we must not do that as we may be
+		 * using snapshot half-way through the subxact.
+		 */
+		command_id = txn->command_id;
+
+		/*
+		 * We can't use txn->snapshot_now directly because after the last
+		 * streaming run, we might have got some new sub-transactions. So we
+		 * need to add them to the snapshot.
+		 */
+		snapshot_now = ReorderBufferCopySnap(rb, txn->snapshot_now,
+											 txn, command_id);
+
+		/* Free the previously copied snapshot. */
+		Assert(txn->snapshot_now->copied);
+		ReorderBufferFreeSnap(rb, txn->snapshot_now);
+		txn->snapshot_now = NULL;
+	}
+
+	/*
+	 * Remember this information to be used later to update stats. We can't
+	 * update the stats here as an error while processing the changes would
+	 * lead to the accumulation of stats even though we haven't streamed all
+	 * the changes.
+	 */
+	txn_is_streamed = rbtxn_is_streamed(txn);
+	stream_bytes = txn->total_size;
+
+	/* Process and send the changes to output plugin. */
+	ReorderBufferProcessTXN(rb, txn, InvalidXLogRecPtr, snapshot_now,
+							command_id, true);
+
+	rb->streamCount += 1;
+	rb->streamBytes += stream_bytes;
+
+	/* Don't consider already streamed transaction. */
+	rb->streamTxns += (txn_is_streamed) ? 0 : 1;
+
+	/* update the decoding stats */
+	UpdateDecodingStats((LogicalDecodingContext *) rb->private_data);
+
+	Assert(dlist_is_empty(&txn->changes));
+	Assert(txn->nentries == 0);
+	Assert(txn->nentries_mem == 0);
+}
+
+/*
+ * Size of a change in memory.
+ */
+static Size
+ReorderBufferChangeSize(ReorderBufferChange *change)
+{
+	Size		sz = sizeof(ReorderBufferChange);
+
+	switch (change->action)
+	{
+			/* fall through these, they're all similar enough */
+		case REORDER_BUFFER_CHANGE_INSERT:
+		case REORDER_BUFFER_CHANGE_UPDATE:
+		case REORDER_BUFFER_CHANGE_DELETE:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
+			{
+				ReorderBufferTupleBuf *oldtup,
+						   *newtup;
+				Size		oldlen = 0;
+				Size		newlen = 0;
+
+				oldtup = change->data.tp.oldtuple;
+				newtup = change->data.tp.newtuple;
+
+				if (oldtup)
+				{
+					sz += sizeof(HeapTupleData);
+					oldlen = oldtup->tuple.t_len;
+					sz += oldlen;
+				}
+
+				if (newtup)
+				{
+					sz += sizeof(HeapTupleData);
+					newlen = newtup->tuple.t_len;
+					sz += newlen;
+				}
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size +
+					sizeof(Size) + sizeof(Size);
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INVALIDATION:
+			{
+				sz += sizeof(SharedInvalidationMessage) *
+					change->data.inval.ninvalidations;
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
+			{
+				Snapshot	snap;
+
+				snap = change->data.snapshot;
+
+				sz += sizeof(SnapshotData) +
+					sizeof(TransactionId) * snap->xcnt +
+					sizeof(TransactionId) * snap->subxcnt;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_TRUNCATE:
+			{
+				sz += sizeof(Oid) * change->data.truncate.nrelids;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
+		case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
+		case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
+			/* ReorderBufferChange contains everything important */
+			break;
+	}
+
+	return sz;
+}
+
+
+/*
+ * Restore a number of changes spilled to disk back into memory.
+ */
+static Size
+ReorderBufferRestoreChanges(ReorderBuffer *rb, ReorderBufferTXN *txn,
+							TXNEntryFile *file, XLogSegNo *segno)
+{
+	Size		restored = 0;
+	XLogSegNo	last_segno;
+	dlist_mutable_iter cleanup_iter;
+	File	   *fd = &file->vfd;
+
+	Assert(txn->first_lsn != InvalidXLogRecPtr);
+	Assert(txn->final_lsn != InvalidXLogRecPtr);
+
+	/* free current entries, so we have memory for more */
+	dlist_foreach_modify(cleanup_iter, &txn->changes)
+	{
+		ReorderBufferChange *cleanup =
+		dlist_container(ReorderBufferChange, node, cleanup_iter.cur);
+
+		dlist_delete(&cleanup->node);
+		ReorderBufferReturnChange(rb, cleanup, true);
+	}
+	txn->nentries_mem = 0;
+	Assert(dlist_is_empty(&txn->changes));
+
+	XLByteToSeg(txn->final_lsn, last_segno, wal_segment_size);
+
+	while (restored < max_changes_in_memory && *segno <= last_segno)
+	{
+		int			readBytes;
+		ReorderBufferDiskChange *ondisk;
+
+		if (*fd == -1)
+		{
+			char		path[MAXPGPATH];
+
+			/* first time in */
+			if (*segno == 0)
+				XLByteToSeg(txn->first_lsn, *segno, wal_segment_size);
+
+			Assert(*segno != 0 || dlist_is_empty(&txn->changes));
+
+			/*
+			 * No need to care about TLIs here, only used during a single run,
+			 * so each LSN only maps to a specific WAL record.
+			 */
+			ReorderBufferSerializedPath(path, MyReplicationSlot, txn->xid,
+										*segno);
+
+			*fd = PathNameOpenFile(path, O_RDONLY | PG_BINARY);
+
+			/* No harm in resetting the offset even in case of failure */
+			file->curOffset = 0;
+
+			if (*fd < 0 && errno == ENOENT)
+			{
+				*fd = -1;
+				(*segno)++;
+				continue;
+			}
+			else if (*fd < 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not open file \"%s\": %m",
+								path)));
+		}
+
+		/*
+		 * Read the statically sized part of a change which has information
+		 * about the total size. If we couldn't read a record, we're at the
+		 * end of this file.
+		 */
+		ReorderBufferSerializeReserve(rb, sizeof(ReorderBufferDiskChange));
+		readBytes = FileRead(file->vfd, rb->outbuf,
+							 sizeof(ReorderBufferDiskChange),
+							 file->curOffset, WAIT_EVENT_REORDER_BUFFER_READ);
+
+		/* eof */
+		if (readBytes == 0)
+		{
+			FileClose(*fd);
+			*fd = -1;
+			(*segno)++;
+			continue;
+		}
+		else if (readBytes < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from reorderbuffer spill file: %m")));
+		else if (readBytes != sizeof(ReorderBufferDiskChange))
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from reorderbuffer spill file: read %d instead of %u bytes",
+							readBytes,
+							(uint32) sizeof(ReorderBufferDiskChange))));
+
+		file->curOffset += readBytes;
+
+		ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+		ReorderBufferSerializeReserve(rb,
+									  sizeof(ReorderBufferDiskChange) + ondisk->size);
+		ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+		readBytes = FileRead(file->vfd,
+							 rb->outbuf + sizeof(ReorderBufferDiskChange),
+							 ondisk->size - sizeof(ReorderBufferDiskChange),
+							 file->curOffset,
+							 WAIT_EVENT_REORDER_BUFFER_READ);
+
+		if (readBytes < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from reorderbuffer spill file: %m")));
+		else if (readBytes != ondisk->size - sizeof(ReorderBufferDiskChange))
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from reorderbuffer spill file: read %d instead of %u bytes",
+							readBytes,
+							(uint32) (ondisk->size - sizeof(ReorderBufferDiskChange)))));
+
+		file->curOffset += readBytes;
+
+		/*
+		 * ok, read a full change from disk, now restore it into proper
+		 * in-memory format
+		 */
+		ReorderBufferRestoreChange(rb, txn, rb->outbuf);
+		restored++;
+	}
+
+	return restored;
+}
+
+/*
+ * Convert change from its on-disk format to in-memory format and queue it onto
+ * the TXN's ->changes list.
+ *
+ * Note: although "data" is declared char*, at entry it points to a
+ * maxalign'd buffer, making it safe in most of this function to assume
+ * that the pointed-to data is suitably aligned for direct access.
+ */
+static void
+ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						   char *data)
+{
+	ReorderBufferDiskChange *ondisk;
+	ReorderBufferChange *change;
+
+	ondisk = (ReorderBufferDiskChange *) data;
+
+	change = ReorderBufferGetChange(rb);
+
+	/* copy static part */
+	memcpy(change, &ondisk->change, sizeof(ReorderBufferChange));
+
+	data += sizeof(ReorderBufferDiskChange);
+
+	/* restore individual stuff */
+	switch (change->action)
+	{
+			/* fall through these, they're all similar enough */
+		case REORDER_BUFFER_CHANGE_INSERT:
+		case REORDER_BUFFER_CHANGE_UPDATE:
+		case REORDER_BUFFER_CHANGE_DELETE:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
+			if (change->data.tp.oldtuple)
+			{
+				uint32		tuplelen = ((HeapTuple) data)->t_len;
+
+				change->data.tp.oldtuple =
+					ReorderBufferGetTupleBuf(rb, tuplelen - SizeofHeapTupleHeader);
+
+				/* restore ->tuple */
+				memcpy(&change->data.tp.oldtuple->tuple, data,
+					   sizeof(HeapTupleData));
+				data += sizeof(HeapTupleData);
+
+				/* reset t_data pointer into the new tuplebuf */
+				change->data.tp.oldtuple->tuple.t_data =
+					ReorderBufferTupleBufData(change->data.tp.oldtuple);
+
+				/* restore tuple data itself */
+				memcpy(change->data.tp.oldtuple->tuple.t_data, data, tuplelen);
+				data += tuplelen;
+			}
+
+			if (change->data.tp.newtuple)
+			{
+				/* here, data might not be suitably aligned! */
+				uint32		tuplelen;
+
+				memcpy(&tuplelen, data + offsetof(HeapTupleData, t_len),
+					   sizeof(uint32));
+
+				change->data.tp.newtuple =
+					ReorderBufferGetTupleBuf(rb, tuplelen - SizeofHeapTupleHeader);
+
+				/* restore ->tuple */
+				memcpy(&change->data.tp.newtuple->tuple, data,
+					   sizeof(HeapTupleData));
+				data += sizeof(HeapTupleData);
+
+				/* reset t_data pointer into the new tuplebuf */
+				change->data.tp.newtuple->tuple.t_data =
+					ReorderBufferTupleBufData(change->data.tp.newtuple);
+
+				/* restore tuple data itself */
+				memcpy(change->data.tp.newtuple->tuple.t_data, data, tuplelen);
+				data += tuplelen;
+			}
+
+			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		prefix_size;
+
+				/* read prefix */
+				memcpy(&prefix_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.prefix = MemoryContextAlloc(rb->context,
+															 prefix_size);
+				memcpy(change->data.msg.prefix, data, prefix_size);
+				Assert(change->data.msg.prefix[prefix_size - 1] == '\0');
+				data += prefix_size;
+
+				/* read the message */
+				memcpy(&change->data.msg.message_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.message = MemoryContextAlloc(rb->context,
+															  change->data.msg.message_size);
+				memcpy(change->data.msg.message, data,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INVALIDATION:
+			{
+				Size		inval_size = sizeof(SharedInvalidationMessage) *
+				change->data.inval.ninvalidations;
+
+				change->data.inval.invalidations =
+					MemoryContextAlloc(rb->context, inval_size);
+
+				/* read the message */
+				memcpy(change->data.inval.invalidations, data, inval_size);
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
+			{
+				Snapshot	oldsnap;
+				Snapshot	newsnap;
+				Size		size;
+
+				oldsnap = (Snapshot) data;
+
+				size = sizeof(SnapshotData) +
+					sizeof(TransactionId) * oldsnap->xcnt +
+					sizeof(TransactionId) * (oldsnap->subxcnt + 0);
+
+				change->data.snapshot = MemoryContextAllocZero(rb->context, size);
+
+				newsnap = change->data.snapshot;
+
+				memcpy(newsnap, data, size);
+				newsnap->xip = (TransactionId *)
+					(((char *) newsnap) + sizeof(SnapshotData));
+				newsnap->subxip = newsnap->xip + newsnap->xcnt;
+				newsnap->copied = true;
+				break;
+			}
+			/* the base struct contains all the data, easy peasy */
+		case REORDER_BUFFER_CHANGE_TRUNCATE:
+			{
+				Oid		   *relids;
+
+				relids = ReorderBufferGetRelids(rb,
+												change->data.truncate.nrelids);
+				memcpy(relids, data, change->data.truncate.nrelids * sizeof(Oid));
+				change->data.truncate.relids = relids;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
+		case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
+		case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
+			break;
+	}
+
+	dlist_push_tail(&txn->changes, &change->node);
+	txn->nentries_mem++;
+
+	/*
+	 * Update memory accounting for the restored change.  We need to do this
+	 * although we don't check the memory limit when restoring the changes in
+	 * this branch (we only do that when initially queueing the changes after
+	 * decoding), because we will release the changes later, and that will
+	 * update the accounting too (subtracting the size from the counters). And
+	 * we don't want to underflow there.
+	 */
+	ReorderBufferChangeMemoryUpdate(rb, change, true,
+									ReorderBufferChangeSize(change));
+}
+
+/*
+ * Remove all on-disk stored for the passed in transaction.
+ */
+static void
+ReorderBufferRestoreCleanup(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	XLogSegNo	first;
+	XLogSegNo	cur;
+	XLogSegNo	last;
+
+	Assert(txn->first_lsn != InvalidXLogRecPtr);
+	Assert(txn->final_lsn != InvalidXLogRecPtr);
+
+	XLByteToSeg(txn->first_lsn, first, wal_segment_size);
+	XLByteToSeg(txn->final_lsn, last, wal_segment_size);
+
+	/* iterate over all possible filenames, and delete them */
+	for (cur = first; cur <= last; cur++)
+	{
+		char		path[MAXPGPATH];
+
+		ReorderBufferSerializedPath(path, MyReplicationSlot, txn->xid, cur);
+		if (unlink(path) != 0 && errno != ENOENT)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not remove file \"%s\": %m", path)));
+	}
+}
+
+/*
+ * Remove any leftover serialized reorder buffers from a slot directory after a
+ * prior crash or decoding session exit.
+ */
+static void
+ReorderBufferCleanupSerializedTXNs(const char *slotname)
+{
+	DIR		   *spill_dir;
+	struct dirent *spill_de;
+	struct stat statbuf;
+	char		path[MAXPGPATH * 2 + 12];
+
+	sprintf(path, "pg_replslot/%s", slotname);
+
+	/* we're only handling directories here, skip if it's not ours */
+	if (lstat(path, &statbuf) == 0 && !S_ISDIR(statbuf.st_mode))
+		return;
+
+	spill_dir = AllocateDir(path);
+	while ((spill_de = ReadDirExtended(spill_dir, path, INFO)) != NULL)
+	{
+		/* only look at names that can be ours */
+		if (strncmp(spill_de->d_name, "xid", 3) == 0)
+		{
+			snprintf(path, sizeof(path),
+					 "pg_replslot/%s/%s", slotname,
+					 spill_de->d_name);
+
+			if (unlink(path) != 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not remove file \"%s\" during removal of pg_replslot/%s/xid*: %m",
+								path, slotname)));
+		}
+	}
+	FreeDir(spill_dir);
+}
+
+/*
+ * Given a replication slot, transaction ID and segment number, fill in the
+ * corresponding spill file into 'path', which is a caller-owned buffer of size
+ * at least MAXPGPATH.
+ */
+static void
+ReorderBufferSerializedPath(char *path, ReplicationSlot *slot, TransactionId xid,
+							XLogSegNo segno)
+{
+	XLogRecPtr	recptr;
+
+	XLogSegNoOffsetToRecPtr(segno, 0, wal_segment_size, recptr);
+
+	snprintf(path, MAXPGPATH, "pg_replslot/%s/xid-%u-lsn-%X-%X.spill",
+			 NameStr(MyReplicationSlot->data.name),
+			 xid, LSN_FORMAT_ARGS(recptr));
+}
+
+/*
+ * Delete all data spilled to disk after we've restarted/crashed. It will be
+ * recreated when the respective slots are reused.
+ */
+void
+StartupReorderBuffer(void)
+{
+	DIR		   *logical_dir;
+	struct dirent *logical_de;
+
+	logical_dir = AllocateDir("pg_replslot");
+	while ((logical_de = ReadDir(logical_dir, "pg_replslot")) != NULL)
+	{
+		if (strcmp(logical_de->d_name, ".") == 0 ||
+			strcmp(logical_de->d_name, "..") == 0)
+			continue;
+
+		/* if it cannot be a slot, skip the directory */
+		if (!ReplicationSlotValidateName(logical_de->d_name, DEBUG2))
+			continue;
+
+		/*
+		 * ok, has to be a surviving logical slot, iterate and delete
+		 * everything starting with xid-*
+		 */
+		ReorderBufferCleanupSerializedTXNs(logical_de->d_name);
+	}
+	FreeDir(logical_dir);
+}
+
+/* ---------------------------------------
+ * toast reassembly support
+ * ---------------------------------------
+ */
+
+/*
+ * Initialize per tuple toast reconstruction support.
+ */
+static void
+ReorderBufferToastInitHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	HASHCTL		hash_ctl;
+
+	Assert(txn->toast_hash == NULL);
+
+	hash_ctl.keysize = sizeof(Oid);
+	hash_ctl.entrysize = sizeof(ReorderBufferToastEnt);
+	hash_ctl.hcxt = rb->context;
+	txn->toast_hash = hash_create("ReorderBufferToastHash", 5, &hash_ctl,
+								  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+}
+
+/*
+ * Per toast-chunk handling for toast reconstruction
+ *
+ * Appends a toast chunk so we can reconstruct it when the tuple "owning" the
+ * toasted Datum comes along.
+ */
+static void
+ReorderBufferToastAppendChunk(ReorderBuffer *rb, ReorderBufferTXN *txn,
+							  Relation relation, ReorderBufferChange *change)
+{
+	ReorderBufferToastEnt *ent;
+	ReorderBufferTupleBuf *newtup;
+	bool		found;
+	int32		chunksize;
+	bool		isnull;
+	Pointer		chunk;
+	TupleDesc	desc = RelationGetDescr(relation);
+	Oid			chunk_id;
+	int32		chunk_seq;
+
+	if (txn->toast_hash == NULL)
+		ReorderBufferToastInitHash(rb, txn);
+
+	Assert(IsToastRelation(relation));
+
+	newtup = change->data.tp.newtuple;
+	chunk_id = DatumGetObjectId(fastgetattr(&newtup->tuple, 1, desc, &isnull));
+	Assert(!isnull);
+	chunk_seq = DatumGetInt32(fastgetattr(&newtup->tuple, 2, desc, &isnull));
+	Assert(!isnull);
+
+	ent = (ReorderBufferToastEnt *)
+		hash_search(txn->toast_hash,
+					(void *) &chunk_id,
+					HASH_ENTER,
+					&found);
+
+	if (!found)
+	{
+		Assert(ent->chunk_id == chunk_id);
+		ent->num_chunks = 0;
+		ent->last_chunk_seq = 0;
+		ent->size = 0;
+		ent->reconstructed = NULL;
+		dlist_init(&ent->chunks);
+
+		if (chunk_seq != 0)
+			elog(ERROR, "got sequence entry %d for toast chunk %u instead of seq 0",
+				 chunk_seq, chunk_id);
+	}
+	else if (found && chunk_seq != ent->last_chunk_seq + 1)
+		elog(ERROR, "got sequence entry %d for toast chunk %u instead of seq %d",
+			 chunk_seq, chunk_id, ent->last_chunk_seq + 1);
+
+	chunk = DatumGetPointer(fastgetattr(&newtup->tuple, 3, desc, &isnull));
+	Assert(!isnull);
+
+	/* calculate size so we can allocate the right size at once later */
+	if (!VARATT_IS_EXTENDED(chunk))
+		chunksize = VARSIZE(chunk) - VARHDRSZ;
+	else if (VARATT_IS_SHORT(chunk))
+		/* could happen due to heap_form_tuple doing its thing */
+		chunksize = VARSIZE_SHORT(chunk) - VARHDRSZ_SHORT;
+	else
+		elog(ERROR, "unexpected type of toast chunk");
+
+	ent->size += chunksize;
+	ent->last_chunk_seq = chunk_seq;
+	ent->num_chunks++;
+	dlist_push_tail(&ent->chunks, &change->node);
+}
+
+/*
+ * Rejigger change->newtuple to point to in-memory toast tuples instead to
+ * on-disk toast tuples that may not longer exist (think DROP TABLE or VACUUM).
+ *
+ * We cannot replace unchanged toast tuples though, so those will still point
+ * to on-disk toast data.
+ *
+ * While updating the existing change with detoasted tuple data, we need to
+ * update the memory accounting info, because the change size will differ.
+ * Otherwise the accounting may get out of sync, triggering serialization
+ * at unexpected times.
+ *
+ * We simply subtract size of the change before rejiggering the tuple, and
+ * then adding the new size. This makes it look like the change was removed
+ * and then added back, except it only tweaks the accounting info.
+ *
+ * In particular it can't trigger serialization, which would be pointless
+ * anyway as it happens during commit processing right before handing
+ * the change to the output plugin.
+ */
+static void
+ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						  Relation relation, ReorderBufferChange *change)
+{
+	TupleDesc	desc;
+	int			natt;
+	Datum	   *attrs;
+	bool	   *isnull;
+	bool	   *free;
+	HeapTuple	tmphtup;
+	Relation	toast_rel;
+	TupleDesc	toast_desc;
+	MemoryContext oldcontext;
+	ReorderBufferTupleBuf *newtup;
+	Size		old_size;
+
+	/* no toast tuples changed */
+	if (txn->toast_hash == NULL)
+		return;
+
+	/*
+	 * We're going to modify the size of the change. So, to make sure the
+	 * accounting is correct we record the current change size and then after
+	 * re-computing the change we'll subtract the recorded size and then
+	 * re-add the new change size at the end. We don't immediately subtract
+	 * the old size because if there is any error before we add the new size,
+	 * we will release the changes and that will update the accounting info
+	 * (subtracting the size from the counters). And we don't want to
+	 * underflow there.
+	 */
+	old_size = ReorderBufferChangeSize(change);
+
+	oldcontext = MemoryContextSwitchTo(rb->context);
+
+	/* we should only have toast tuples in an INSERT or UPDATE */
+	Assert(change->data.tp.newtuple);
+
+	desc = RelationGetDescr(relation);
+
+	toast_rel = RelationIdGetRelation(relation->rd_rel->reltoastrelid);
+	if (!RelationIsValid(toast_rel))
+		elog(ERROR, "could not open toast relation with OID %u (base relation \"%s\")",
+			 relation->rd_rel->reltoastrelid, RelationGetRelationName(relation));
+
+	toast_desc = RelationGetDescr(toast_rel);
+
+	/* should we allocate from stack instead? */
+	attrs = palloc0(sizeof(Datum) * desc->natts);
+	isnull = palloc0(sizeof(bool) * desc->natts);
+	free = palloc0(sizeof(bool) * desc->natts);
+
+	newtup = change->data.tp.newtuple;
+
+	heap_deform_tuple(&newtup->tuple, desc, attrs, isnull);
+
+	for (natt = 0; natt < desc->natts; natt++)
+	{
+		Form_pg_attribute attr = TupleDescAttr(desc, natt);
+		ReorderBufferToastEnt *ent;
+		struct varlena *varlena;
+
+		/* va_rawsize is the size of the original datum -- including header */
+		struct varatt_external toast_pointer;
+		struct varatt_indirect redirect_pointer;
+		struct varlena *new_datum = NULL;
+		struct varlena *reconstructed;
+		dlist_iter	it;
+		Size		data_done = 0;
+
+		/* system columns aren't toasted */
+		if (attr->attnum < 0)
+			continue;
+
+		if (attr->attisdropped)
+			continue;
+
+		/* not a varlena datatype */
+		if (attr->attlen != -1)
+			continue;
+
+		/* no data */
+		if (isnull[natt])
+			continue;
+
+		/* ok, we know we have a toast datum */
+		varlena = (struct varlena *) DatumGetPointer(attrs[natt]);
+
+		/* no need to do anything if the tuple isn't external */
+		if (!VARATT_IS_EXTERNAL(varlena))
+			continue;
+
+		VARATT_EXTERNAL_GET_POINTER(toast_pointer, varlena);
+
+		/*
+		 * Check whether the toast tuple changed, replace if so.
+		 */
+		ent = (ReorderBufferToastEnt *)
+			hash_search(txn->toast_hash,
+						(void *) &toast_pointer.va_valueid,
+						HASH_FIND,
+						NULL);
+		if (ent == NULL)
+			continue;
+
+		new_datum =
+			(struct varlena *) palloc0(INDIRECT_POINTER_SIZE);
+
+		free[natt] = true;
+
+		reconstructed = palloc0(toast_pointer.va_rawsize);
+
+		ent->reconstructed = reconstructed;
+
+		/* stitch toast tuple back together from its parts */
+		dlist_foreach(it, &ent->chunks)
+		{
+			bool		isnull;
+			ReorderBufferChange *cchange;
+			ReorderBufferTupleBuf *ctup;
+			Pointer		chunk;
+
+			cchange = dlist_container(ReorderBufferChange, node, it.cur);
+			ctup = cchange->data.tp.newtuple;
+			chunk = DatumGetPointer(fastgetattr(&ctup->tuple, 3, toast_desc, &isnull));
+
+			Assert(!isnull);
+			Assert(!VARATT_IS_EXTERNAL(chunk));
+			Assert(!VARATT_IS_SHORT(chunk));
+
+			memcpy(VARDATA(reconstructed) + data_done,
+				   VARDATA(chunk),
+				   VARSIZE(chunk) - VARHDRSZ);
+			data_done += VARSIZE(chunk) - VARHDRSZ;
+		}
+		Assert(data_done == VARATT_EXTERNAL_GET_EXTSIZE(toast_pointer));
+
+		/* make sure its marked as compressed or not */
+		if (VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
+			SET_VARSIZE_COMPRESSED(reconstructed, data_done + VARHDRSZ);
+		else
+			SET_VARSIZE(reconstructed, data_done + VARHDRSZ);
+
+		memset(&redirect_pointer, 0, sizeof(redirect_pointer));
+		redirect_pointer.pointer = reconstructed;
+
+		SET_VARTAG_EXTERNAL(new_datum, VARTAG_INDIRECT);
+		memcpy(VARDATA_EXTERNAL(new_datum), &redirect_pointer,
+			   sizeof(redirect_pointer));
+
+		attrs[natt] = PointerGetDatum(new_datum);
+	}
+
+	/*
+	 * Build tuple in separate memory & copy tuple back into the tuplebuf
+	 * passed to the output plugin. We can't directly heap_fill_tuple() into
+	 * the tuplebuf because attrs[] will point back into the current content.
+	 */
+	tmphtup = heap_form_tuple(desc, attrs, isnull);
+	Assert(newtup->tuple.t_len <= MaxHeapTupleSize);
+	Assert(ReorderBufferTupleBufData(newtup) == newtup->tuple.t_data);
+
+	memcpy(newtup->tuple.t_data, tmphtup->t_data, tmphtup->t_len);
+	newtup->tuple.t_len = tmphtup->t_len;
+
+	/*
+	 * free resources we won't further need, more persistent stuff will be
+	 * free'd in ReorderBufferToastReset().
+	 */
+	RelationClose(toast_rel);
+	pfree(tmphtup);
+	for (natt = 0; natt < desc->natts; natt++)
+	{
+		if (free[natt])
+			pfree(DatumGetPointer(attrs[natt]));
+	}
+	pfree(attrs);
+	pfree(free);
+	pfree(isnull);
+
+	MemoryContextSwitchTo(oldcontext);
+
+	/* subtract the old change size */
+	ReorderBufferChangeMemoryUpdate(rb, change, false, old_size);
+	/* now add the change back, with the correct size */
+	ReorderBufferChangeMemoryUpdate(rb, change, true,
+									ReorderBufferChangeSize(change));
+}
+
+/*
+ * Free all resources allocated for toast reconstruction.
+ */
+static void
+ReorderBufferToastReset(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	HASH_SEQ_STATUS hstat;
+	ReorderBufferToastEnt *ent;
+
+	if (txn->toast_hash == NULL)
+		return;
+
+	/* sequentially walk over the hash and free everything */
+	hash_seq_init(&hstat, txn->toast_hash);
+	while ((ent = (ReorderBufferToastEnt *) hash_seq_search(&hstat)) != NULL)
+	{
+		dlist_mutable_iter it;
+
+		if (ent->reconstructed != NULL)
+			pfree(ent->reconstructed);
+
+		dlist_foreach_modify(it, &ent->chunks)
+		{
+			ReorderBufferChange *change =
+			dlist_container(ReorderBufferChange, node, it.cur);
+
+			dlist_delete(&change->node);
+			ReorderBufferReturnChange(rb, change, true);
+		}
+	}
+
+	hash_destroy(txn->toast_hash);
+	txn->toast_hash = NULL;
+}
+
+
+/* ---------------------------------------
+ * Visibility support for logical decoding
+ *
+ *
+ * Lookup actual cmin/cmax values when using decoding snapshot. We can't
+ * always rely on stored cmin/cmax values because of two scenarios:
+ *
+ * * A tuple got changed multiple times during a single transaction and thus
+ *	 has got a combo CID. Combo CIDs are only valid for the duration of a
+ *	 single transaction.
+ * * A tuple with a cmin but no cmax (and thus no combo CID) got
+ *	 deleted/updated in another transaction than the one which created it
+ *	 which we are looking at right now. As only one of cmin, cmax or combo CID
+ *	 is actually stored in the heap we don't have access to the value we
+ *	 need anymore.
+ *
+ * To resolve those problems we have a per-transaction hash of (cmin,
+ * cmax) tuples keyed by (relfilenode, ctid) which contains the actual
+ * (cmin, cmax) values. That also takes care of combo CIDs by simply
+ * not caring about them at all. As we have the real cmin/cmax values
+ * combo CIDs aren't interesting.
+ *
+ * As we only care about catalog tuples here the overhead of this
+ * hashtable should be acceptable.
+ *
+ * Heap rewrites complicate this a bit, check rewriteheap.c for
+ * details.
+ * -------------------------------------------------------------------------
+ */
+
+/* struct for sorting mapping files by LSN efficiently */
+typedef struct RewriteMappingFile
+{
+	XLogRecPtr	lsn;
+	char		fname[MAXPGPATH];
+} RewriteMappingFile;
+
+#ifdef NOT_USED
+static void
+DisplayMapping(HTAB *tuplecid_data)
+{
+	HASH_SEQ_STATUS hstat;
+	ReorderBufferTupleCidEnt *ent;
+
+	hash_seq_init(&hstat, tuplecid_data);
+	while ((ent = (ReorderBufferTupleCidEnt *) hash_seq_search(&hstat)) != NULL)
+	{
+		elog(DEBUG3, "mapping: node: %u/%u/%u tid: %u/%u cmin: %u, cmax: %u",
+			 ent->key.relnode.dbNode,
+			 ent->key.relnode.spcNode,
+			 ent->key.relnode.relNode,
+			 ItemPointerGetBlockNumber(&ent->key.tid),
+			 ItemPointerGetOffsetNumber(&ent->key.tid),
+			 ent->cmin,
+			 ent->cmax
+			);
+	}
+}
+#endif
+
+/*
+ * Apply a single mapping file to tuplecid_data.
+ *
+ * The mapping file has to have been verified to be a) committed b) for our
+ * transaction c) applied in LSN order.
+ */
+static void
+ApplyLogicalMappingFile(HTAB *tuplecid_data, Oid relid, const char *fname)
+{
+	char		path[MAXPGPATH];
+	int			fd;
+	int			readBytes;
+	LogicalRewriteMappingData map;
+
+	sprintf(path, "pg_logical/mappings/%s", fname);
+	fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
+	if (fd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m", path)));
+
+	while (true)
+	{
+		ReorderBufferTupleCidKey key;
+		ReorderBufferTupleCidEnt *ent;
+		ReorderBufferTupleCidEnt *new_ent;
+		bool		found;
+
+		/* be careful about padding */
+		memset(&key, 0, sizeof(ReorderBufferTupleCidKey));
+
+		/* read all mappings till the end of the file */
+		pgstat_report_wait_start(WAIT_EVENT_REORDER_LOGICAL_MAPPING_READ);
+		readBytes = read(fd, &map, sizeof(LogicalRewriteMappingData));
+		pgstat_report_wait_end();
+
+		if (readBytes < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m",
+							path)));
+		else if (readBytes == 0)	/* EOF */
+			break;
+		else if (readBytes != sizeof(LogicalRewriteMappingData))
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from file \"%s\": read %d instead of %d bytes",
+							path, readBytes,
+							(int32) sizeof(LogicalRewriteMappingData))));
+
+		key.relnode = map.old_node;
+		ItemPointerCopy(&map.old_tid,
+						&key.tid);
+
+
+		ent = (ReorderBufferTupleCidEnt *)
+			hash_search(tuplecid_data,
+						(void *) &key,
+						HASH_FIND,
+						NULL);
+
+		/* no existing mapping, no need to update */
+		if (!ent)
+			continue;
+
+		key.relnode = map.new_node;
+		ItemPointerCopy(&map.new_tid,
+						&key.tid);
+
+		new_ent = (ReorderBufferTupleCidEnt *)
+			hash_search(tuplecid_data,
+						(void *) &key,
+						HASH_ENTER,
+						&found);
+
+		if (found)
+		{
+			/*
+			 * Make sure the existing mapping makes sense. We sometime update
+			 * old records that did not yet have a cmax (e.g. pg_class' own
+			 * entry while rewriting it) during rewrites, so allow that.
+			 */
+			Assert(ent->cmin == InvalidCommandId || ent->cmin == new_ent->cmin);
+			Assert(ent->cmax == InvalidCommandId || ent->cmax == new_ent->cmax);
+		}
+		else
+		{
+			/* update mapping */
+			new_ent->cmin = ent->cmin;
+			new_ent->cmax = ent->cmax;
+			new_ent->combocid = ent->combocid;
+		}
+	}
+
+	if (CloseTransientFile(fd) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", path)));
+}
+
+
+/*
+ * Check whether the TransactionId 'xid' is in the pre-sorted array 'xip'.
+ */
+static bool
+TransactionIdInArray(TransactionId xid, TransactionId *xip, Size num)
+{
+	return bsearch(&xid, xip, num,
+				   sizeof(TransactionId), xidComparator) != NULL;
+}
+
+/*
+ * list_sort() comparator for sorting RewriteMappingFiles in LSN order.
+ */
+static int
+file_sort_by_lsn(const ListCell *a_p, const ListCell *b_p)
+{
+	RewriteMappingFile *a = (RewriteMappingFile *) lfirst(a_p);
+	RewriteMappingFile *b = (RewriteMappingFile *) lfirst(b_p);
+
+	if (a->lsn < b->lsn)
+		return -1;
+	else if (a->lsn > b->lsn)
+		return 1;
+	return 0;
+}
+
+/*
+ * Apply any existing logical remapping files if there are any targeted at our
+ * transaction for relid.
+ */
+static void
+UpdateLogicalMappings(HTAB *tuplecid_data, Oid relid, Snapshot snapshot)
+{
+	DIR		   *mapping_dir;
+	struct dirent *mapping_de;
+	List	   *files = NIL;
+	ListCell   *file;
+	Oid			dboid = IsSharedRelation(relid) ? InvalidOid : MyDatabaseId;
+
+	mapping_dir = AllocateDir("pg_logical/mappings");
+	while ((mapping_de = ReadDir(mapping_dir, "pg_logical/mappings")) != NULL)
+	{
+		Oid			f_dboid;
+		Oid			f_relid;
+		TransactionId f_mapped_xid;
+		TransactionId f_create_xid;
+		XLogRecPtr	f_lsn;
+		uint32		f_hi,
+					f_lo;
+		RewriteMappingFile *f;
+
+		if (strcmp(mapping_de->d_name, ".") == 0 ||
+			strcmp(mapping_de->d_name, "..") == 0)
+			continue;
+
+		/* Ignore files that aren't ours */
+		if (strncmp(mapping_de->d_name, "map-", 4) != 0)
+			continue;
+
+		if (sscanf(mapping_de->d_name, LOGICAL_REWRITE_FORMAT,
+				   &f_dboid, &f_relid, &f_hi, &f_lo,
+				   &f_mapped_xid, &f_create_xid) != 6)
+			elog(ERROR, "could not parse filename \"%s\"", mapping_de->d_name);
+
+		f_lsn = ((uint64) f_hi) << 32 | f_lo;
+
+		/* mapping for another database */
+		if (f_dboid != dboid)
+			continue;
+
+		/* mapping for another relation */
+		if (f_relid != relid)
+			continue;
+
+		/* did the creating transaction abort? */
+		if (!TransactionIdDidCommit(f_create_xid))
+			continue;
+
+		/* not for our transaction */
+		if (!TransactionIdInArray(f_mapped_xid, snapshot->subxip, snapshot->subxcnt))
+			continue;
+
+		/* ok, relevant, queue for apply */
+		f = palloc(sizeof(RewriteMappingFile));
+		f->lsn = f_lsn;
+		strcpy(f->fname, mapping_de->d_name);
+		files = lappend(files, f);
+	}
+	FreeDir(mapping_dir);
+
+	/* sort files so we apply them in LSN order */
+	list_sort(files, file_sort_by_lsn);
+
+	foreach(file, files)
+	{
+		RewriteMappingFile *f = (RewriteMappingFile *) lfirst(file);
+
+		elog(DEBUG1, "applying mapping: \"%s\" in %u", f->fname,
+			 snapshot->subxip[0]);
+		ApplyLogicalMappingFile(tuplecid_data, relid, f->fname);
+		pfree(f);
+	}
+}
+
+/*
+ * Lookup cmin/cmax of a tuple, during logical decoding where we can't rely on
+ * combo CIDs.
+ */
+bool
+ResolveCminCmaxDuringDecoding(HTAB *tuplecid_data,
+							  Snapshot snapshot,
+							  HeapTuple htup, Buffer buffer,
+							  CommandId *cmin, CommandId *cmax)
+{
+	ReorderBufferTupleCidKey key;
+	ReorderBufferTupleCidEnt *ent;
+	ForkNumber	forkno;
+	BlockNumber blockno;
+	bool		updated_mapping = false;
+
+	/*
+	 * Return unresolved if tuplecid_data is not valid.  That's because when
+	 * streaming in-progress transactions we may run into tuples with the CID
+	 * before actually decoding them.  Think e.g. about INSERT followed by
+	 * TRUNCATE, where the TRUNCATE may not be decoded yet when applying the
+	 * INSERT.  So in such cases, we assume the CID is from the future
+	 * command.
+	 */
+	if (tuplecid_data == NULL)
+		return false;
+
+	/* be careful about padding */
+	memset(&key, 0, sizeof(key));
+
+	Assert(!BufferIsLocal(buffer));
+
+	/*
+	 * get relfilenode from the buffer, no convenient way to access it other
+	 * than that.
+	 */
+	BufferGetTag(buffer, &key.relnode, &forkno, &blockno);
+
+	/* tuples can only be in the main fork */
+	Assert(forkno == MAIN_FORKNUM);
+	Assert(blockno == ItemPointerGetBlockNumber(&htup->t_self));
+
+	ItemPointerCopy(&htup->t_self,
+					&key.tid);
+
+restart:
+	ent = (ReorderBufferTupleCidEnt *)
+		hash_search(tuplecid_data,
+					(void *) &key,
+					HASH_FIND,
+					NULL);
+
+	/*
+	 * failed to find a mapping, check whether the table was rewritten and
+	 * apply mapping if so, but only do that once - there can be no new
+	 * mappings while we are in here since we have to hold a lock on the
+	 * relation.
+	 */
+	if (ent == NULL && !updated_mapping)
+	{
+		UpdateLogicalMappings(tuplecid_data, htup->t_tableOid, snapshot);
+		/* now check but don't update for a mapping again */
+		updated_mapping = true;
+		goto restart;
+	}
+	else if (ent == NULL)
+		return false;
+
+	if (cmin)
+		*cmin = ent->cmin;
+	if (cmax)
+		*cmax = ent->cmax;
+	return true;
+}