Adding upstream version 13.4.upstream/13.4upstream

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

1 files changed, 1505 insertions, 0 deletions

diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c
new file mode 100644
index 0000000..c37bbe5
--- /dev/null
+++ b/src/backend/access/nbtree/nbtree.c
@@ -0,0 +1,1505 @@
+/*-------------------------------------------------------------------------
+ *
+ * nbtree.c
+ *	  Implementation of Lehman and Yao's btree management algorithm for
+ *	  Postgres.
+ *
+ * NOTES
+ *	  This file contains only the public interface routines.
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/nbtree/nbtree.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/nbtree.h"
+#include "access/nbtxlog.h"
+#include "access/relscan.h"
+#include "access/xlog.h"
+#include "commands/progress.h"
+#include "commands/vacuum.h"
+#include "miscadmin.h"
+#include "nodes/execnodes.h"
+#include "pgstat.h"
+#include "postmaster/autovacuum.h"
+#include "storage/condition_variable.h"
+#include "storage/indexfsm.h"
+#include "storage/ipc.h"
+#include "storage/lmgr.h"
+#include "storage/smgr.h"
+#include "utils/builtins.h"
+#include "utils/index_selfuncs.h"
+#include "utils/memutils.h"
+
+
+/* Working state needed by btvacuumpage */
+typedef struct
+{
+	IndexVacuumInfo *info;
+	IndexBulkDeleteResult *stats;
+	IndexBulkDeleteCallback callback;
+	void	   *callback_state;
+	BTCycleId	cycleid;
+	BlockNumber totFreePages;	/* true total # of free pages */
+	TransactionId oldestBtpoXact;
+	MemoryContext pagedelcontext;
+} BTVacState;
+
+/*
+ * BTPARALLEL_NOT_INITIALIZED indicates that the scan has not started.
+ *
+ * BTPARALLEL_ADVANCING indicates that some process is advancing the scan to
+ * a new page; others must wait.
+ *
+ * BTPARALLEL_IDLE indicates that no backend is currently advancing the scan
+ * to a new page; some process can start doing that.
+ *
+ * BTPARALLEL_DONE indicates that the scan is complete (including error exit).
+ * We reach this state once for every distinct combination of array keys.
+ */
+typedef enum
+{
+	BTPARALLEL_NOT_INITIALIZED,
+	BTPARALLEL_ADVANCING,
+	BTPARALLEL_IDLE,
+	BTPARALLEL_DONE
+} BTPS_State;
+
+/*
+ * BTParallelScanDescData contains btree specific shared information required
+ * for parallel scan.
+ */
+typedef struct BTParallelScanDescData
+{
+	BlockNumber btps_scanPage;	/* latest or next page to be scanned */
+	BTPS_State	btps_pageStatus;	/* indicates whether next page is
+									 * available for scan. see above for
+									 * possible states of parallel scan. */
+	int			btps_arrayKeyCount; /* count indicating number of array scan
+									 * keys processed by parallel scan */
+	slock_t		btps_mutex;		/* protects above variables */
+	ConditionVariable btps_cv;	/* used to synchronize parallel scan */
+}			BTParallelScanDescData;
+
+typedef struct BTParallelScanDescData *BTParallelScanDesc;
+
+
+static void btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
+						 IndexBulkDeleteCallback callback, void *callback_state,
+						 BTCycleId cycleid);
+static void btvacuumpage(BTVacState *vstate, BlockNumber scanblkno);
+static BTVacuumPosting btreevacuumposting(BTVacState *vstate,
+										  IndexTuple posting,
+										  OffsetNumber updatedoffset,
+										  int *nremaining);
+
+
+/*
+ * Btree handler function: return IndexAmRoutine with access method parameters
+ * and callbacks.
+ */
+Datum
+bthandler(PG_FUNCTION_ARGS)
+{
+	IndexAmRoutine *amroutine = makeNode(IndexAmRoutine);
+
+	amroutine->amstrategies = BTMaxStrategyNumber;
+	amroutine->amsupport = BTNProcs;
+	amroutine->amoptsprocnum = BTOPTIONS_PROC;
+	amroutine->amcanorder = true;
+	amroutine->amcanorderbyop = false;
+	amroutine->amcanbackward = true;
+	amroutine->amcanunique = true;
+	amroutine->amcanmulticol = true;
+	amroutine->amoptionalkey = true;
+	amroutine->amsearcharray = true;
+	amroutine->amsearchnulls = true;
+	amroutine->amstorage = false;
+	amroutine->amclusterable = true;
+	amroutine->ampredlocks = true;
+	amroutine->amcanparallel = true;
+	amroutine->amcaninclude = true;
+	amroutine->amusemaintenanceworkmem = false;
+	amroutine->amparallelvacuumoptions =
+		VACUUM_OPTION_PARALLEL_BULKDEL | VACUUM_OPTION_PARALLEL_COND_CLEANUP;
+	amroutine->amkeytype = InvalidOid;
+
+	amroutine->ambuild = btbuild;
+	amroutine->ambuildempty = btbuildempty;
+	amroutine->aminsert = btinsert;
+	amroutine->ambulkdelete = btbulkdelete;
+	amroutine->amvacuumcleanup = btvacuumcleanup;
+	amroutine->amcanreturn = btcanreturn;
+	amroutine->amcostestimate = btcostestimate;
+	amroutine->amoptions = btoptions;
+	amroutine->amproperty = btproperty;
+	amroutine->ambuildphasename = btbuildphasename;
+	amroutine->amvalidate = btvalidate;
+	amroutine->ambeginscan = btbeginscan;
+	amroutine->amrescan = btrescan;
+	amroutine->amgettuple = btgettuple;
+	amroutine->amgetbitmap = btgetbitmap;
+	amroutine->amendscan = btendscan;
+	amroutine->ammarkpos = btmarkpos;
+	amroutine->amrestrpos = btrestrpos;
+	amroutine->amestimateparallelscan = btestimateparallelscan;
+	amroutine->aminitparallelscan = btinitparallelscan;
+	amroutine->amparallelrescan = btparallelrescan;
+
+	PG_RETURN_POINTER(amroutine);
+}
+
+/*
+ *	btbuildempty() -- build an empty btree index in the initialization fork
+ */
+void
+btbuildempty(Relation index)
+{
+	Page		metapage;
+
+	/* Construct metapage. */
+	metapage = (Page) palloc(BLCKSZ);
+	_bt_initmetapage(metapage, P_NONE, 0, _bt_allequalimage(index, false));
+
+	/*
+	 * Write the page and log it.  It might seem that an immediate sync would
+	 * be sufficient to guarantee that the file exists on disk, but recovery
+	 * itself might remove it while replaying, for example, an
+	 * XLOG_DBASE_CREATE or XLOG_TBLSPC_CREATE record.  Therefore, we need
+	 * this even when wal_level=minimal.
+	 */
+	PageSetChecksumInplace(metapage, BTREE_METAPAGE);
+	smgrwrite(index->rd_smgr, INIT_FORKNUM, BTREE_METAPAGE,
+			  (char *) metapage, true);
+	log_newpage(&index->rd_smgr->smgr_rnode.node, INIT_FORKNUM,
+				BTREE_METAPAGE, metapage, true);
+
+	/*
+	 * An immediate sync is required even if we xlog'd the page, because the
+	 * write did not go through shared_buffers and therefore a concurrent
+	 * checkpoint may have moved the redo pointer past our xlog record.
+	 */
+	smgrimmedsync(index->rd_smgr, INIT_FORKNUM);
+}
+
+/*
+ *	btinsert() -- insert an index tuple into a btree.
+ *
+ *		Descend the tree recursively, find the appropriate location for our
+ *		new tuple, and put it there.
+ */
+bool
+btinsert(Relation rel, Datum *values, bool *isnull,
+		 ItemPointer ht_ctid, Relation heapRel,
+		 IndexUniqueCheck checkUnique,
+		 IndexInfo *indexInfo)
+{
+	bool		result;
+	IndexTuple	itup;
+
+	/* generate an index tuple */
+	itup = index_form_tuple(RelationGetDescr(rel), values, isnull);
+	itup->t_tid = *ht_ctid;
+
+	result = _bt_doinsert(rel, itup, checkUnique, heapRel);
+
+	pfree(itup);
+
+	return result;
+}
+
+/*
+ *	btgettuple() -- Get the next tuple in the scan.
+ */
+bool
+btgettuple(IndexScanDesc scan, ScanDirection dir)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+	bool		res;
+
+	/* btree indexes are never lossy */
+	scan->xs_recheck = false;
+
+	/*
+	 * If we have any array keys, initialize them during first call for a
+	 * scan.  We can't do this in btrescan because we don't know the scan
+	 * direction at that time.
+	 */
+	if (so->numArrayKeys && !BTScanPosIsValid(so->currPos))
+	{
+		/* punt if we have any unsatisfiable array keys */
+		if (so->numArrayKeys < 0)
+			return false;
+
+		_bt_start_array_keys(scan, dir);
+	}
+
+	/* This loop handles advancing to the next array elements, if any */
+	do
+	{
+		/*
+		 * If we've already initialized this scan, we can just advance it in
+		 * the appropriate direction.  If we haven't done so yet, we call
+		 * _bt_first() to get the first item in the scan.
+		 */
+		if (!BTScanPosIsValid(so->currPos))
+			res = _bt_first(scan, dir);
+		else
+		{
+			/*
+			 * Check to see if we should kill the previously-fetched tuple.
+			 */
+			if (scan->kill_prior_tuple)
+			{
+				/*
+				 * Yes, remember it for later. (We'll deal with all such
+				 * tuples at once right before leaving the index page.)  The
+				 * test for numKilled overrun is not just paranoia: if the
+				 * caller reverses direction in the indexscan then the same
+				 * item might get entered multiple times. It's not worth
+				 * trying to optimize that, so we don't detect it, but instead
+				 * just forget any excess entries.
+				 */
+				if (so->killedItems == NULL)
+					so->killedItems = (int *)
+						palloc(MaxTIDsPerBTreePage * sizeof(int));
+				if (so->numKilled < MaxTIDsPerBTreePage)
+					so->killedItems[so->numKilled++] = so->currPos.itemIndex;
+			}
+
+			/*
+			 * Now continue the scan.
+			 */
+			res = _bt_next(scan, dir);
+		}
+
+		/* If we have a tuple, return it ... */
+		if (res)
+			break;
+		/* ... otherwise see if we have more array keys to deal with */
+	} while (so->numArrayKeys && _bt_advance_array_keys(scan, dir));
+
+	return res;
+}
+
+/*
+ * btgetbitmap() -- gets all matching tuples, and adds them to a bitmap
+ */
+int64
+btgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+	int64		ntids = 0;
+	ItemPointer heapTid;
+
+	/*
+	 * If we have any array keys, initialize them.
+	 */
+	if (so->numArrayKeys)
+	{
+		/* punt if we have any unsatisfiable array keys */
+		if (so->numArrayKeys < 0)
+			return ntids;
+
+		_bt_start_array_keys(scan, ForwardScanDirection);
+	}
+
+	/* This loop handles advancing to the next array elements, if any */
+	do
+	{
+		/* Fetch the first page & tuple */
+		if (_bt_first(scan, ForwardScanDirection))
+		{
+			/* Save tuple ID, and continue scanning */
+			heapTid = &scan->xs_heaptid;
+			tbm_add_tuples(tbm, heapTid, 1, false);
+			ntids++;
+
+			for (;;)
+			{
+				/*
+				 * Advance to next tuple within page.  This is the same as the
+				 * easy case in _bt_next().
+				 */
+				if (++so->currPos.itemIndex > so->currPos.lastItem)
+				{
+					/* let _bt_next do the heavy lifting */
+					if (!_bt_next(scan, ForwardScanDirection))
+						break;
+				}
+
+				/* Save tuple ID, and continue scanning */
+				heapTid = &so->currPos.items[so->currPos.itemIndex].heapTid;
+				tbm_add_tuples(tbm, heapTid, 1, false);
+				ntids++;
+			}
+		}
+		/* Now see if we have more array keys to deal with */
+	} while (so->numArrayKeys && _bt_advance_array_keys(scan, ForwardScanDirection));
+
+	return ntids;
+}
+
+/*
+ *	btbeginscan() -- start a scan on a btree index
+ */
+IndexScanDesc
+btbeginscan(Relation rel, int nkeys, int norderbys)
+{
+	IndexScanDesc scan;
+	BTScanOpaque so;
+
+	/* no order by operators allowed */
+	Assert(norderbys == 0);
+
+	/* get the scan */
+	scan = RelationGetIndexScan(rel, nkeys, norderbys);
+
+	/* allocate private workspace */
+	so = (BTScanOpaque) palloc(sizeof(BTScanOpaqueData));
+	BTScanPosInvalidate(so->currPos);
+	BTScanPosInvalidate(so->markPos);
+	if (scan->numberOfKeys > 0)
+		so->keyData = (ScanKey) palloc(scan->numberOfKeys * sizeof(ScanKeyData));
+	else
+		so->keyData = NULL;
+
+	so->arrayKeyData = NULL;	/* assume no array keys for now */
+	so->numArrayKeys = 0;
+	so->arrayKeys = NULL;
+	so->arrayContext = NULL;
+
+	so->killedItems = NULL;		/* until needed */
+	so->numKilled = 0;
+
+	/*
+	 * We don't know yet whether the scan will be index-only, so we do not
+	 * allocate the tuple workspace arrays until btrescan.  However, we set up
+	 * scan->xs_itupdesc whether we'll need it or not, since that's so cheap.
+	 */
+	so->currTuples = so->markTuples = NULL;
+
+	scan->xs_itupdesc = RelationGetDescr(rel);
+
+	scan->opaque = so;
+
+	return scan;
+}
+
+/*
+ *	btrescan() -- rescan an index relation
+ */
+void
+btrescan(IndexScanDesc scan, ScanKey scankey, int nscankeys,
+		 ScanKey orderbys, int norderbys)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+
+	/* we aren't holding any read locks, but gotta drop the pins */
+	if (BTScanPosIsValid(so->currPos))
+	{
+		/* Before leaving current page, deal with any killed items */
+		if (so->numKilled > 0)
+			_bt_killitems(scan);
+		BTScanPosUnpinIfPinned(so->currPos);
+		BTScanPosInvalidate(so->currPos);
+	}
+
+	so->markItemIndex = -1;
+	so->arrayKeyCount = 0;
+	BTScanPosUnpinIfPinned(so->markPos);
+	BTScanPosInvalidate(so->markPos);
+
+	/*
+	 * Allocate tuple workspace arrays, if needed for an index-only scan and
+	 * not already done in a previous rescan call.  To save on palloc
+	 * overhead, both workspaces are allocated as one palloc block; only this
+	 * function and btendscan know that.
+	 *
+	 * NOTE: this data structure also makes it safe to return data from a
+	 * "name" column, even though btree name_ops uses an underlying storage
+	 * datatype of cstring.  The risk there is that "name" is supposed to be
+	 * padded to NAMEDATALEN, but the actual index tuple is probably shorter.
+	 * However, since we only return data out of tuples sitting in the
+	 * currTuples array, a fetch of NAMEDATALEN bytes can at worst pull some
+	 * data out of the markTuples array --- running off the end of memory for
+	 * a SIGSEGV is not possible.  Yeah, this is ugly as sin, but it beats
+	 * adding special-case treatment for name_ops elsewhere.
+	 */
+	if (scan->xs_want_itup && so->currTuples == NULL)
+	{
+		so->currTuples = (char *) palloc(BLCKSZ * 2);
+		so->markTuples = so->currTuples + BLCKSZ;
+	}
+
+	/*
+	 * Reset the scan keys. Note that keys ordering stuff moved to _bt_first.
+	 * - vadim 05/05/97
+	 */
+	if (scankey && scan->numberOfKeys > 0)
+		memmove(scan->keyData,
+				scankey,
+				scan->numberOfKeys * sizeof(ScanKeyData));
+	so->numberOfKeys = 0;		/* until _bt_preprocess_keys sets it */
+
+	/* If any keys are SK_SEARCHARRAY type, set up array-key info */
+	_bt_preprocess_array_keys(scan);
+}
+
+/*
+ *	btendscan() -- close down a scan
+ */
+void
+btendscan(IndexScanDesc scan)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+
+	/* we aren't holding any read locks, but gotta drop the pins */
+	if (BTScanPosIsValid(so->currPos))
+	{
+		/* Before leaving current page, deal with any killed items */
+		if (so->numKilled > 0)
+			_bt_killitems(scan);
+		BTScanPosUnpinIfPinned(so->currPos);
+	}
+
+	so->markItemIndex = -1;
+	BTScanPosUnpinIfPinned(so->markPos);
+
+	/* No need to invalidate positions, the RAM is about to be freed. */
+
+	/* Release storage */
+	if (so->keyData != NULL)
+		pfree(so->keyData);
+	/* so->arrayKeyData and so->arrayKeys are in arrayContext */
+	if (so->arrayContext != NULL)
+		MemoryContextDelete(so->arrayContext);
+	if (so->killedItems != NULL)
+		pfree(so->killedItems);
+	if (so->currTuples != NULL)
+		pfree(so->currTuples);
+	/* so->markTuples should not be pfree'd, see btrescan */
+	pfree(so);
+}
+
+/*
+ *	btmarkpos() -- save current scan position
+ */
+void
+btmarkpos(IndexScanDesc scan)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+
+	/* There may be an old mark with a pin (but no lock). */
+	BTScanPosUnpinIfPinned(so->markPos);
+
+	/*
+	 * Just record the current itemIndex.  If we later step to next page
+	 * before releasing the marked position, _bt_steppage makes a full copy of
+	 * the currPos struct in markPos.  If (as often happens) the mark is moved
+	 * before we leave the page, we don't have to do that work.
+	 */
+	if (BTScanPosIsValid(so->currPos))
+		so->markItemIndex = so->currPos.itemIndex;
+	else
+	{
+		BTScanPosInvalidate(so->markPos);
+		so->markItemIndex = -1;
+	}
+
+	/* Also record the current positions of any array keys */
+	if (so->numArrayKeys)
+		_bt_mark_array_keys(scan);
+}
+
+/*
+ *	btrestrpos() -- restore scan to last saved position
+ */
+void
+btrestrpos(IndexScanDesc scan)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+
+	/* Restore the marked positions of any array keys */
+	if (so->numArrayKeys)
+		_bt_restore_array_keys(scan);
+
+	if (so->markItemIndex >= 0)
+	{
+		/*
+		 * The scan has never moved to a new page since the last mark.  Just
+		 * restore the itemIndex.
+		 *
+		 * NB: In this case we can't count on anything in so->markPos to be
+		 * accurate.
+		 */
+		so->currPos.itemIndex = so->markItemIndex;
+	}
+	else
+	{
+		/*
+		 * The scan moved to a new page after last mark or restore, and we are
+		 * now restoring to the marked page.  We aren't holding any read
+		 * locks, but if we're still holding the pin for the current position,
+		 * we must drop it.
+		 */
+		if (BTScanPosIsValid(so->currPos))
+		{
+			/* Before leaving current page, deal with any killed items */
+			if (so->numKilled > 0)
+				_bt_killitems(scan);
+			BTScanPosUnpinIfPinned(so->currPos);
+		}
+
+		if (BTScanPosIsValid(so->markPos))
+		{
+			/* bump pin on mark buffer for assignment to current buffer */
+			if (BTScanPosIsPinned(so->markPos))
+				IncrBufferRefCount(so->markPos.buf);
+			memcpy(&so->currPos, &so->markPos,
+				   offsetof(BTScanPosData, items[1]) +
+				   so->markPos.lastItem * sizeof(BTScanPosItem));
+			if (so->currTuples)
+				memcpy(so->currTuples, so->markTuples,
+					   so->markPos.nextTupleOffset);
+		}
+		else
+			BTScanPosInvalidate(so->currPos);
+	}
+}
+
+/*
+ * btestimateparallelscan -- estimate storage for BTParallelScanDescData
+ */
+Size
+btestimateparallelscan(void)
+{
+	return sizeof(BTParallelScanDescData);
+}
+
+/*
+ * btinitparallelscan -- initialize BTParallelScanDesc for parallel btree scan
+ */
+void
+btinitparallelscan(void *target)
+{
+	BTParallelScanDesc bt_target = (BTParallelScanDesc) target;
+
+	SpinLockInit(&bt_target->btps_mutex);
+	bt_target->btps_scanPage = InvalidBlockNumber;
+	bt_target->btps_pageStatus = BTPARALLEL_NOT_INITIALIZED;
+	bt_target->btps_arrayKeyCount = 0;
+	ConditionVariableInit(&bt_target->btps_cv);
+}
+
+/*
+ *	btparallelrescan() -- reset parallel scan
+ */
+void
+btparallelrescan(IndexScanDesc scan)
+{
+	BTParallelScanDesc btscan;
+	ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
+
+	Assert(parallel_scan);
+
+	btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
+												  parallel_scan->ps_offset);
+
+	/*
+	 * In theory, we don't need to acquire the spinlock here, because there
+	 * shouldn't be any other workers running at this point, but we do so for
+	 * consistency.
+	 */
+	SpinLockAcquire(&btscan->btps_mutex);
+	btscan->btps_scanPage = InvalidBlockNumber;
+	btscan->btps_pageStatus = BTPARALLEL_NOT_INITIALIZED;
+	btscan->btps_arrayKeyCount = 0;
+	SpinLockRelease(&btscan->btps_mutex);
+}
+
+/*
+ * _bt_parallel_seize() -- Begin the process of advancing the scan to a new
+ *		page.  Other scans must wait until we call _bt_parallel_release()
+ *		or _bt_parallel_done().
+ *
+ * The return value is true if we successfully seized the scan and false
+ * if we did not.  The latter case occurs if no pages remain for the current
+ * set of scankeys.
+ *
+ * If the return value is true, *pageno returns the next or current page
+ * of the scan (depending on the scan direction).  An invalid block number
+ * means the scan hasn't yet started, and P_NONE means we've reached the end.
+ * The first time a participating process reaches the last page, it will return
+ * true and set *pageno to P_NONE; after that, further attempts to seize the
+ * scan will return false.
+ *
+ * Callers should ignore the value of pageno if the return value is false.
+ */
+bool
+_bt_parallel_seize(IndexScanDesc scan, BlockNumber *pageno)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+	BTPS_State	pageStatus;
+	bool		exit_loop = false;
+	bool		status = true;
+	ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
+	BTParallelScanDesc btscan;
+
+	*pageno = P_NONE;
+
+	btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
+												  parallel_scan->ps_offset);
+
+	while (1)
+	{
+		SpinLockAcquire(&btscan->btps_mutex);
+		pageStatus = btscan->btps_pageStatus;
+
+		if (so->arrayKeyCount < btscan->btps_arrayKeyCount)
+		{
+			/* Parallel scan has already advanced to a new set of scankeys. */
+			status = false;
+		}
+		else if (pageStatus == BTPARALLEL_DONE)
+		{
+			/*
+			 * We're done with this set of scankeys.  This may be the end, or
+			 * there could be more sets to try.
+			 */
+			status = false;
+		}
+		else if (pageStatus != BTPARALLEL_ADVANCING)
+		{
+			/*
+			 * We have successfully seized control of the scan for the purpose
+			 * of advancing it to a new page!
+			 */
+			btscan->btps_pageStatus = BTPARALLEL_ADVANCING;
+			*pageno = btscan->btps_scanPage;
+			exit_loop = true;
+		}
+		SpinLockRelease(&btscan->btps_mutex);
+		if (exit_loop || !status)
+			break;
+		ConditionVariableSleep(&btscan->btps_cv, WAIT_EVENT_BTREE_PAGE);
+	}
+	ConditionVariableCancelSleep();
+
+	return status;
+}
+
+/*
+ * _bt_parallel_release() -- Complete the process of advancing the scan to a
+ *		new page.  We now have the new value btps_scanPage; some other backend
+ *		can now begin advancing the scan.
+ */
+void
+_bt_parallel_release(IndexScanDesc scan, BlockNumber scan_page)
+{
+	ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
+	BTParallelScanDesc btscan;
+
+	btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
+												  parallel_scan->ps_offset);
+
+	SpinLockAcquire(&btscan->btps_mutex);
+	btscan->btps_scanPage = scan_page;
+	btscan->btps_pageStatus = BTPARALLEL_IDLE;
+	SpinLockRelease(&btscan->btps_mutex);
+	ConditionVariableSignal(&btscan->btps_cv);
+}
+
+/*
+ * _bt_parallel_done() -- Mark the parallel scan as complete.
+ *
+ * When there are no pages left to scan, this function should be called to
+ * notify other workers.  Otherwise, they might wait forever for the scan to
+ * advance to the next page.
+ */
+void
+_bt_parallel_done(IndexScanDesc scan)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+	ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
+	BTParallelScanDesc btscan;
+	bool		status_changed = false;
+
+	/* Do nothing, for non-parallel scans */
+	if (parallel_scan == NULL)
+		return;
+
+	btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
+												  parallel_scan->ps_offset);
+
+	/*
+	 * Mark the parallel scan as done for this combination of scan keys,
+	 * unless some other process already did so.  See also
+	 * _bt_advance_array_keys.
+	 */
+	SpinLockAcquire(&btscan->btps_mutex);
+	if (so->arrayKeyCount >= btscan->btps_arrayKeyCount &&
+		btscan->btps_pageStatus != BTPARALLEL_DONE)
+	{
+		btscan->btps_pageStatus = BTPARALLEL_DONE;
+		status_changed = true;
+	}
+	SpinLockRelease(&btscan->btps_mutex);
+
+	/* wake up all the workers associated with this parallel scan */
+	if (status_changed)
+		ConditionVariableBroadcast(&btscan->btps_cv);
+}
+
+/*
+ * _bt_parallel_advance_array_keys() -- Advances the parallel scan for array
+ *			keys.
+ *
+ * Updates the count of array keys processed for both local and parallel
+ * scans.
+ */
+void
+_bt_parallel_advance_array_keys(IndexScanDesc scan)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+	ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
+	BTParallelScanDesc btscan;
+
+	btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
+												  parallel_scan->ps_offset);
+
+	so->arrayKeyCount++;
+	SpinLockAcquire(&btscan->btps_mutex);
+	if (btscan->btps_pageStatus == BTPARALLEL_DONE)
+	{
+		btscan->btps_scanPage = InvalidBlockNumber;
+		btscan->btps_pageStatus = BTPARALLEL_NOT_INITIALIZED;
+		btscan->btps_arrayKeyCount++;
+	}
+	SpinLockRelease(&btscan->btps_mutex);
+}
+
+/*
+ * _bt_vacuum_needs_cleanup() -- Checks if index needs cleanup
+ *
+ * Called by btvacuumcleanup when btbulkdelete was never called because no
+ * tuples need to be deleted.
+ *
+ * When we return false, VACUUM can even skip the cleanup-only call to
+ * btvacuumscan (i.e. there will be no btvacuumscan call for this index at
+ * all).  Otherwise, a cleanup-only btvacuumscan call is required.
+ *
+ * Postgres 13 ignores btm_last_cleanup_num_heap_tuples value here following
+ * backbranch disabling of vacuum_cleanup_index_scale_factor.
+ */
+static bool
+_bt_vacuum_needs_cleanup(IndexVacuumInfo *info)
+{
+	Buffer		metabuf;
+	Page		metapg;
+	BTMetaPageData *metad;
+	uint32		btm_version;
+	TransactionId prev_btm_oldest_btpo_xact;
+
+	/*
+	 * Copy details from metapage to local variables quickly.
+	 *
+	 * Note that we deliberately avoid using cached version of metapage here.
+	 */
+	metabuf = _bt_getbuf(info->index, BTREE_METAPAGE, BT_READ);
+	metapg = BufferGetPage(metabuf);
+	metad = BTPageGetMeta(metapg);
+	btm_version = metad->btm_version;
+
+	if (btm_version < BTREE_NOVAC_VERSION)
+	{
+		/*
+		 * Metapage needs to be dynamically upgraded to store fields that are
+		 * only present when btm_version >= BTREE_NOVAC_VERSION
+		 */
+		_bt_relbuf(info->index, metabuf);
+		return true;
+	}
+
+	prev_btm_oldest_btpo_xact = metad->btm_oldest_btpo_xact;
+	_bt_relbuf(info->index, metabuf);
+
+	if (TransactionIdIsValid(prev_btm_oldest_btpo_xact) &&
+		TransactionIdPrecedes(prev_btm_oldest_btpo_xact, RecentGlobalXmin))
+	{
+		/*
+		 * If any oldest btpo.xact from a previously deleted page in the index
+		 * is older than RecentGlobalXmin, then at least one deleted page can
+		 * be recycled -- don't skip cleanup.
+		 */
+		return true;
+	}
+
+	return false;
+}
+
+/*
+ * Bulk deletion of all index entries pointing to a set of heap tuples.
+ * The set of target tuples is specified via a callback routine that tells
+ * whether any given heap tuple (identified by ItemPointer) is being deleted.
+ *
+ * Result: a palloc'd struct containing statistical info for VACUUM displays.
+ */
+IndexBulkDeleteResult *
+btbulkdelete(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
+			 IndexBulkDeleteCallback callback, void *callback_state)
+{
+	Relation	rel = info->index;
+	BTCycleId	cycleid;
+
+	/* allocate stats if first time through, else re-use existing struct */
+	if (stats == NULL)
+		stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));
+
+	/* Establish the vacuum cycle ID to use for this scan */
+	/* The ENSURE stuff ensures we clean up shared memory on failure */
+	PG_ENSURE_ERROR_CLEANUP(_bt_end_vacuum_callback, PointerGetDatum(rel));
+	{
+		cycleid = _bt_start_vacuum(rel);
+
+		btvacuumscan(info, stats, callback, callback_state, cycleid);
+	}
+	PG_END_ENSURE_ERROR_CLEANUP(_bt_end_vacuum_callback, PointerGetDatum(rel));
+	_bt_end_vacuum(rel);
+
+	return stats;
+}
+
+/*
+ * Post-VACUUM cleanup.
+ *
+ * Result: a palloc'd struct containing statistical info for VACUUM displays.
+ */
+IndexBulkDeleteResult *
+btvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats)
+{
+	/* No-op in ANALYZE ONLY mode */
+	if (info->analyze_only)
+		return stats;
+
+	/*
+	 * If btbulkdelete was called, we need not do anything, just return the
+	 * stats from the latest btbulkdelete call.  If it wasn't called, we might
+	 * still need to do a pass over the index, to recycle any newly-recyclable
+	 * pages or to obtain index statistics.  _bt_vacuum_needs_cleanup
+	 * determines if either are needed.
+	 */
+	if (stats == NULL)
+	{
+		/* Check if we need a cleanup */
+		if (!_bt_vacuum_needs_cleanup(info))
+			return NULL;
+
+		/*
+		 * Since we aren't going to actually delete any leaf items, there's no
+		 * need to go through all the vacuum-cycle-ID pushups here.
+		 *
+		 * Posting list tuples are a source of inaccuracy for cleanup-only
+		 * scans.  btvacuumscan() will assume that the number of index tuples
+		 * from each page can be used as num_index_tuples, even though
+		 * num_index_tuples is supposed to represent the number of TIDs in the
+		 * index.  This naive approach can underestimate the number of tuples
+		 * in the index significantly.
+		 *
+		 * We handle the problem by making num_index_tuples an estimate in
+		 * cleanup-only case.
+		 */
+		stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));
+		btvacuumscan(info, stats, NULL, NULL, 0);
+		stats->estimated_count = true;
+	}
+
+	/*
+	 * It's quite possible for us to be fooled by concurrent page splits into
+	 * double-counting some index tuples, so disbelieve any total that exceeds
+	 * the underlying heap's count ... if we know that accurately.  Otherwise
+	 * this might just make matters worse.
+	 */
+	if (!info->estimated_count)
+	{
+		if (stats->num_index_tuples > info->num_heap_tuples)
+			stats->num_index_tuples = info->num_heap_tuples;
+	}
+
+	return stats;
+}
+
+/*
+ * btvacuumscan --- scan the index for VACUUMing purposes
+ *
+ * This combines the functions of looking for leaf tuples that are deletable
+ * according to the vacuum callback, looking for empty pages that can be
+ * deleted, and looking for old deleted pages that can be recycled.  Both
+ * btbulkdelete and btvacuumcleanup invoke this (the latter only if no
+ * btbulkdelete call occurred and _bt_vacuum_needs_cleanup returned true).
+ * Note that this is also where the metadata used by _bt_vacuum_needs_cleanup
+ * is maintained.
+ *
+ * The caller is responsible for initially allocating/zeroing a stats struct
+ * and for obtaining a vacuum cycle ID if necessary.
+ */
+static void
+btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
+			 IndexBulkDeleteCallback callback, void *callback_state,
+			 BTCycleId cycleid)
+{
+	Relation	rel = info->index;
+	BTVacState	vstate;
+	BlockNumber num_pages;
+	BlockNumber scanblkno;
+	bool		needLock;
+
+	/*
+	 * Reset counts that will be incremented during the scan; needed in case
+	 * of multiple scans during a single VACUUM command
+	 */
+	stats->num_index_tuples = 0;
+	stats->pages_deleted = 0;
+
+	/* Set up info to pass down to btvacuumpage */
+	vstate.info = info;
+	vstate.stats = stats;
+	vstate.callback = callback;
+	vstate.callback_state = callback_state;
+	vstate.cycleid = cycleid;
+	vstate.totFreePages = 0;
+	vstate.oldestBtpoXact = InvalidTransactionId;
+
+	/* Create a temporary memory context to run _bt_pagedel in */
+	vstate.pagedelcontext = AllocSetContextCreate(CurrentMemoryContext,
+												  "_bt_pagedel",
+												  ALLOCSET_DEFAULT_SIZES);
+
+	/*
+	 * The outer loop iterates over all index pages except the metapage, in
+	 * physical order (we hope the kernel will cooperate in providing
+	 * read-ahead for speed).  It is critical that we visit all leaf pages,
+	 * including ones added after we start the scan, else we might fail to
+	 * delete some deletable tuples.  Hence, we must repeatedly check the
+	 * relation length.  We must acquire the relation-extension lock while
+	 * doing so to avoid a race condition: if someone else is extending the
+	 * relation, there is a window where bufmgr/smgr have created a new
+	 * all-zero page but it hasn't yet been write-locked by _bt_getbuf(). If
+	 * we manage to scan such a page here, we'll improperly assume it can be
+	 * recycled.  Taking the lock synchronizes things enough to prevent a
+	 * problem: either num_pages won't include the new page, or _bt_getbuf
+	 * already has write lock on the buffer and it will be fully initialized
+	 * before we can examine it.  (See also vacuumlazy.c, which has the same
+	 * issue.)	Also, we need not worry if a page is added immediately after
+	 * we look; the page splitting code already has write-lock on the left
+	 * page before it adds a right page, so we must already have processed any
+	 * tuples due to be moved into such a page.
+	 *
+	 * We can skip locking for new or temp relations, however, since no one
+	 * else could be accessing them.
+	 */
+	needLock = !RELATION_IS_LOCAL(rel);
+
+	scanblkno = BTREE_METAPAGE + 1;
+	for (;;)
+	{
+		/* Get the current relation length */
+		if (needLock)
+			LockRelationForExtension(rel, ExclusiveLock);
+		num_pages = RelationGetNumberOfBlocks(rel);
+		if (needLock)
+			UnlockRelationForExtension(rel, ExclusiveLock);
+
+		if (info->report_progress)
+			pgstat_progress_update_param(PROGRESS_SCAN_BLOCKS_TOTAL,
+										 num_pages);
+
+		/* Quit if we've scanned the whole relation */
+		if (scanblkno >= num_pages)
+			break;
+		/* Iterate over pages, then loop back to recheck length */
+		for (; scanblkno < num_pages; scanblkno++)
+		{
+			btvacuumpage(&vstate, scanblkno);
+			if (info->report_progress)
+				pgstat_progress_update_param(PROGRESS_SCAN_BLOCKS_DONE,
+											 scanblkno);
+		}
+	}
+
+	MemoryContextDelete(vstate.pagedelcontext);
+
+	/*
+	 * If we found any recyclable pages (and recorded them in the FSM), then
+	 * forcibly update the upper-level FSM pages to ensure that searchers can
+	 * find them.  It's possible that the pages were also found during
+	 * previous scans and so this is a waste of time, but it's cheap enough
+	 * relative to scanning the index that it shouldn't matter much, and
+	 * making sure that free pages are available sooner not later seems
+	 * worthwhile.
+	 *
+	 * Note that if no recyclable pages exist, we don't bother vacuuming the
+	 * FSM at all.
+	 */
+	if (vstate.totFreePages > 0)
+		IndexFreeSpaceMapVacuum(rel);
+
+	/*
+	 * Maintain the oldest btpo.xact using _bt_update_meta_cleanup_info, for
+	 * the benefit of _bt_vacuum_needs_cleanup.
+	 *
+	 * Note: We deliberately don't store the count of heap tuples here
+	 * anymore.  The numHeapTuples argument to _bt_update_meta_cleanup_info()
+	 * is left in place on Postgres 13.
+	 *
+	 * The page with the oldest btpo.xact is typically a page deleted by this
+	 * VACUUM operation, since pages deleted by a previous VACUUM operation
+	 * tend to be placed in the FSM (by the current VACUUM operation) -- such
+	 * pages are not candidates to be the oldest btpo.xact.  (Note that pages
+	 * placed in the FSM are reported as deleted pages in the bulk delete
+	 * statistics, despite not counting as deleted pages for the purposes of
+	 * determining the oldest btpo.xact.)
+	 */
+	_bt_update_meta_cleanup_info(rel, vstate.oldestBtpoXact, -1);
+
+	/* update statistics */
+	stats->num_pages = num_pages;
+	stats->pages_free = vstate.totFreePages;
+}
+
+/*
+ * btvacuumpage --- VACUUM one page
+ *
+ * This processes a single page for btvacuumscan().  In some cases we must
+ * backtrack to re-examine and VACUUM pages that were the scanblkno during
+ * a previous call here.  This is how we handle page splits (that happened
+ * after our cycleid was acquired) whose right half page happened to reuse
+ * a block that we might have processed at some point before it was
+ * recycled (i.e. before the page split).
+ */
+static void
+btvacuumpage(BTVacState *vstate, BlockNumber scanblkno)
+{
+	IndexVacuumInfo *info = vstate->info;
+	IndexBulkDeleteResult *stats = vstate->stats;
+	IndexBulkDeleteCallback callback = vstate->callback;
+	void	   *callback_state = vstate->callback_state;
+	Relation	rel = info->index;
+	bool		attempt_pagedel;
+	BlockNumber blkno,
+				backtrack_to;
+	Buffer		buf;
+	Page		page;
+	BTPageOpaque opaque;
+
+	blkno = scanblkno;
+
+backtrack:
+
+	attempt_pagedel = false;
+	backtrack_to = P_NONE;
+
+	/* call vacuum_delay_point while not holding any buffer lock */
+	vacuum_delay_point();
+
+	/*
+	 * We can't use _bt_getbuf() here because it always applies
+	 * _bt_checkpage(), which will barf on an all-zero page. We want to
+	 * recycle all-zero pages, not fail.  Also, we want to use a nondefault
+	 * buffer access strategy.
+	 */
+	buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
+							 info->strategy);
+	LockBuffer(buf, BT_READ);
+	page = BufferGetPage(buf);
+	opaque = NULL;
+	if (!PageIsNew(page))
+	{
+		_bt_checkpage(rel, buf);
+		opaque = (BTPageOpaque) PageGetSpecialPointer(page);
+	}
+
+	Assert(blkno <= scanblkno);
+	if (blkno != scanblkno)
+	{
+		/*
+		 * We're backtracking.
+		 *
+		 * We followed a right link to a sibling leaf page (a page that
+		 * happens to be from a block located before scanblkno).  The only
+		 * case we want to do anything with is a live leaf page having the
+		 * current vacuum cycle ID.
+		 *
+		 * The page had better be in a state that's consistent with what we
+		 * expect.  Check for conditions that imply corruption in passing.  It
+		 * can't be half-dead because only an interrupted VACUUM process can
+		 * leave pages in that state, so we'd definitely have dealt with it
+		 * back when the page was the scanblkno page (half-dead pages are
+		 * always marked fully deleted by _bt_pagedel()).  This assumes that
+		 * there can be only one vacuum process running at a time.
+		 */
+		if (!opaque || !P_ISLEAF(opaque) || P_ISHALFDEAD(opaque))
+		{
+			Assert(false);
+			ereport(LOG,
+					(errcode(ERRCODE_INDEX_CORRUPTED),
+					 errmsg_internal("right sibling %u of scanblkno %u unexpectedly in an inconsistent state in index \"%s\"",
+									 blkno, scanblkno, RelationGetRelationName(rel))));
+			_bt_relbuf(rel, buf);
+			return;
+		}
+
+		/*
+		 * We may have already processed the page in an earlier call, when the
+		 * page was scanblkno.  This happens when the leaf page split occurred
+		 * after the scan began, but before the right sibling page became the
+		 * scanblkno.
+		 *
+		 * Page may also have been deleted by current btvacuumpage() call,
+		 * since _bt_pagedel() sometimes deletes the right sibling page of
+		 * scanblkno in passing (it does so after we decided where to
+		 * backtrack to).  We don't need to process this page as a deleted
+		 * page a second time now (in fact, it would be wrong to count it as a
+		 * deleted page in the bulk delete statistics a second time).
+		 */
+		if (opaque->btpo_cycleid != vstate->cycleid || P_ISDELETED(opaque))
+		{
+			/* Done with current scanblkno (and all lower split pages) */
+			_bt_relbuf(rel, buf);
+			return;
+		}
+	}
+
+	/* Page is valid, see what to do with it */
+	if (_bt_page_recyclable(page))
+	{
+		/* Okay to recycle this page (which could be leaf or internal) */
+		RecordFreeIndexPage(rel, blkno);
+		vstate->totFreePages++;
+		stats->pages_deleted++;
+	}
+	else if (P_ISDELETED(opaque))
+	{
+		/*
+		 * Already deleted page (which could be leaf or internal).  Can't
+		 * recycle yet.
+		 */
+		stats->pages_deleted++;
+
+		/* Maintain the oldest btpo.xact */
+		if (!TransactionIdIsValid(vstate->oldestBtpoXact) ||
+			TransactionIdPrecedes(opaque->btpo.xact, vstate->oldestBtpoXact))
+			vstate->oldestBtpoXact = opaque->btpo.xact;
+	}
+	else if (P_ISHALFDEAD(opaque))
+	{
+		/*
+		 * Half-dead leaf page.  Try to delete now.  Might update
+		 * oldestBtpoXact and pages_deleted below.
+		 */
+		attempt_pagedel = true;
+	}
+	else if (P_ISLEAF(opaque))
+	{
+		OffsetNumber deletable[MaxIndexTuplesPerPage];
+		int			ndeletable;
+		BTVacuumPosting updatable[MaxIndexTuplesPerPage];
+		int			nupdatable;
+		OffsetNumber offnum,
+					minoff,
+					maxoff;
+		int			nhtidsdead,
+					nhtidslive;
+
+		/*
+		 * Trade in the initial read lock for a super-exclusive write lock on
+		 * this page.  We must get such a lock on every leaf page over the
+		 * course of the vacuum scan, whether or not it actually contains any
+		 * deletable tuples --- see nbtree/README.
+		 */
+		LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+		LockBufferForCleanup(buf);
+
+		/*
+		 * Check whether we need to backtrack to earlier pages.  What we are
+		 * concerned about is a page split that happened since we started the
+		 * vacuum scan.  If the split moved tuples on the right half of the
+		 * split (i.e. the tuples that sort high) to a block that we already
+		 * passed over, then we might have missed the tuples.  We need to
+		 * backtrack now.  (Must do this before possibly clearing btpo_cycleid
+		 * or deleting scanblkno page below!)
+		 */
+		if (vstate->cycleid != 0 &&
+			opaque->btpo_cycleid == vstate->cycleid &&
+			!(opaque->btpo_flags & BTP_SPLIT_END) &&
+			!P_RIGHTMOST(opaque) &&
+			opaque->btpo_next < scanblkno)
+			backtrack_to = opaque->btpo_next;
+
+		/*
+		 * When each VACUUM begins, it determines an OldestXmin cutoff value.
+		 * Tuples before the cutoff are removed by VACUUM.  Scan over all
+		 * items to see which ones need to be deleted according to cutoff
+		 * point using callback.
+		 */
+		ndeletable = 0;
+		nupdatable = 0;
+		minoff = P_FIRSTDATAKEY(opaque);
+		maxoff = PageGetMaxOffsetNumber(page);
+		nhtidsdead = 0;
+		nhtidslive = 0;
+		if (callback)
+		{
+			for (offnum = minoff;
+				 offnum <= maxoff;
+				 offnum = OffsetNumberNext(offnum))
+			{
+				IndexTuple	itup;
+
+				itup = (IndexTuple) PageGetItem(page,
+												PageGetItemId(page, offnum));
+
+				/*
+				 * Hot Standby assumes that it's okay that XLOG_BTREE_VACUUM
+				 * records do not produce their own conflicts.  This is safe
+				 * as long as the callback function only considers whether the
+				 * index tuple refers to pre-cutoff heap tuples that were
+				 * certainly already pruned away during VACUUM's initial heap
+				 * scan by the time we get here. (XLOG_HEAP2_CLEANUP_INFO
+				 * records produce conflicts using a latestRemovedXid value
+				 * for the entire VACUUM, so there is no need to produce our
+				 * own conflict now.)
+				 *
+				 * Backends with snapshots acquired after a VACUUM starts but
+				 * before it finishes could have a RecentGlobalXmin with a
+				 * later xid than the VACUUM's OldestXmin cutoff.  These
+				 * backends might happen to opportunistically mark some index
+				 * tuples LP_DEAD before we reach them, even though they may
+				 * be after our cutoff.  We don't try to kill these "extra"
+				 * index tuples in _bt_delitems_vacuum().  This keep things
+				 * simple, and allows us to always avoid generating our own
+				 * conflicts.
+				 */
+				Assert(!BTreeTupleIsPivot(itup));
+				if (!BTreeTupleIsPosting(itup))
+				{
+					/* Regular tuple, standard table TID representation */
+					if (callback(&itup->t_tid, callback_state))
+					{
+						deletable[ndeletable++] = offnum;
+						nhtidsdead++;
+					}
+					else
+						nhtidslive++;
+				}
+				else
+				{
+					BTVacuumPosting vacposting;
+					int			nremaining;
+
+					/* Posting list tuple */
+					vacposting = btreevacuumposting(vstate, itup, offnum,
+													&nremaining);
+					if (vacposting == NULL)
+					{
+						/*
+						 * All table TIDs from the posting tuple remain, so no
+						 * delete or update required
+						 */
+						Assert(nremaining == BTreeTupleGetNPosting(itup));
+					}
+					else if (nremaining > 0)
+					{
+
+						/*
+						 * Store metadata about posting list tuple in
+						 * updatable array for entire page.  Existing tuple
+						 * will be updated during the later call to
+						 * _bt_delitems_vacuum().
+						 */
+						Assert(nremaining < BTreeTupleGetNPosting(itup));
+						updatable[nupdatable++] = vacposting;
+						nhtidsdead += BTreeTupleGetNPosting(itup) - nremaining;
+					}
+					else
+					{
+						/*
+						 * All table TIDs from the posting list must be
+						 * deleted.  We'll delete the index tuple completely
+						 * (no update required).
+						 */
+						Assert(nremaining == 0);
+						deletable[ndeletable++] = offnum;
+						nhtidsdead += BTreeTupleGetNPosting(itup);
+						pfree(vacposting);
+					}
+
+					nhtidslive += nremaining;
+				}
+			}
+		}
+
+		/*
+		 * Apply any needed deletes or updates.  We issue just one
+		 * _bt_delitems_vacuum() call per page, so as to minimize WAL traffic.
+		 */
+		if (ndeletable > 0 || nupdatable > 0)
+		{
+			Assert(nhtidsdead >= ndeletable + nupdatable);
+			_bt_delitems_vacuum(rel, buf, deletable, ndeletable, updatable,
+								nupdatable);
+
+			stats->tuples_removed += nhtidsdead;
+			/* must recompute maxoff */
+			maxoff = PageGetMaxOffsetNumber(page);
+
+			/* can't leak memory here */
+			for (int i = 0; i < nupdatable; i++)
+				pfree(updatable[i]);
+		}
+		else
+		{
+			/*
+			 * If the leaf page has been split during this vacuum cycle, it
+			 * seems worth expending a write to clear btpo_cycleid even if we
+			 * don't have any deletions to do.  (If we do, _bt_delitems_vacuum
+			 * takes care of this.)  This ensures we won't process the page
+			 * again.
+			 *
+			 * We treat this like a hint-bit update because there's no need to
+			 * WAL-log it.
+			 */
+			Assert(nhtidsdead == 0);
+			if (vstate->cycleid != 0 &&
+				opaque->btpo_cycleid == vstate->cycleid)
+			{
+				opaque->btpo_cycleid = 0;
+				MarkBufferDirtyHint(buf, true);
+			}
+		}
+
+		/*
+		 * If the leaf page is now empty, try to delete it; else count the
+		 * live tuples (live table TIDs in posting lists are counted as
+		 * separate live tuples).  We don't delete when backtracking, though,
+		 * since that would require teaching _bt_pagedel() about backtracking
+		 * (doesn't seem worth adding more complexity to deal with that).
+		 *
+		 * We don't count the number of live TIDs during cleanup-only calls to
+		 * btvacuumscan (i.e. when callback is not set).  We count the number
+		 * of index tuples directly instead.  This avoids the expense of
+		 * directly examining all of the tuples on each page.  VACUUM will
+		 * treat num_index_tuples as an estimate in cleanup-only case, so it
+		 * doesn't matter that this underestimates num_index_tuples
+		 * significantly in some cases.
+		 */
+		if (minoff > maxoff)
+			attempt_pagedel = (blkno == scanblkno);
+		else if (callback)
+			stats->num_index_tuples += nhtidslive;
+		else
+			stats->num_index_tuples += maxoff - minoff + 1;
+
+		Assert(!attempt_pagedel || nhtidslive == 0);
+	}
+
+	if (attempt_pagedel)
+	{
+		MemoryContext oldcontext;
+
+		/* Run pagedel in a temp context to avoid memory leakage */
+		MemoryContextReset(vstate->pagedelcontext);
+		oldcontext = MemoryContextSwitchTo(vstate->pagedelcontext);
+
+		/*
+		 * We trust the _bt_pagedel return value because it does not include
+		 * any page that a future call here from btvacuumscan is expected to
+		 * count.  There will be no double-counting.
+		 */
+		Assert(blkno == scanblkno);
+		stats->pages_deleted += _bt_pagedel(rel, buf, &vstate->oldestBtpoXact);
+
+		MemoryContextSwitchTo(oldcontext);
+		/* pagedel released buffer, so we shouldn't */
+	}
+	else
+		_bt_relbuf(rel, buf);
+
+	if (backtrack_to != P_NONE)
+	{
+		blkno = backtrack_to;
+		goto backtrack;
+	}
+}
+
+/*
+ * btreevacuumposting --- determine TIDs still needed in posting list
+ *
+ * Returns metadata describing how to build replacement tuple without the TIDs
+ * that VACUUM needs to delete.  Returned value is NULL in the common case
+ * where no changes are needed to caller's posting list tuple (we avoid
+ * allocating memory here as an optimization).
+ *
+ * The number of TIDs that should remain in the posting list tuple is set for
+ * caller in *nremaining.
+ */
+static BTVacuumPosting
+btreevacuumposting(BTVacState *vstate, IndexTuple posting,
+				   OffsetNumber updatedoffset, int *nremaining)
+{
+	int			live = 0;
+	int			nitem = BTreeTupleGetNPosting(posting);
+	ItemPointer items = BTreeTupleGetPosting(posting);
+	BTVacuumPosting vacposting = NULL;
+
+	for (int i = 0; i < nitem; i++)
+	{
+		if (!vstate->callback(items + i, vstate->callback_state))
+		{
+			/* Live table TID */
+			live++;
+		}
+		else if (vacposting == NULL)
+		{
+			/*
+			 * First dead table TID encountered.
+			 *
+			 * It's now clear that we need to delete one or more dead table
+			 * TIDs, so start maintaining metadata describing how to update
+			 * existing posting list tuple.
+			 */
+			vacposting = palloc(offsetof(BTVacuumPostingData, deletetids) +
+								nitem * sizeof(uint16));
+
+			vacposting->itup = posting;
+			vacposting->updatedoffset = updatedoffset;
+			vacposting->ndeletedtids = 0;
+			vacposting->deletetids[vacposting->ndeletedtids++] = i;
+		}
+		else
+		{
+			/* Second or subsequent dead table TID */
+			vacposting->deletetids[vacposting->ndeletedtids++] = i;
+		}
+	}
+
+	*nremaining = live;
+	return vacposting;
+}
+
+/*
+ *	btcanreturn() -- Check whether btree indexes support index-only scans.
+ *
+ * btrees always do, so this is trivial.
+ */
+bool
+btcanreturn(Relation index, int attno)
+{
+	return true;
+}