postgres/src/backend/access/heap/heapam.c

/*-------------------------------------------------------------------------
 *
 * heapam.c
 *	  heap access method code
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/access/heap/heapam.c
 *
 *
 * INTERFACE ROUTINES
 *		relation_open	- open any relation by relation OID
 *		relation_openrv - open any relation specified by a RangeVar
 *		relation_close	- close any relation
 *		heap_open		- open a heap relation by relation OID
 *		heap_openrv		- open a heap relation specified by a RangeVar
 *		heap_close		- (now just a macro for relation_close)
 *		heap_beginscan	- begin relation scan
 *		heap_rescan		- restart a relation scan
 *		heap_endscan	- end relation scan
 *		heap_getnext	- retrieve next tuple in scan
 *		heap_fetch		- retrieve tuple with given tid
 *		heap_insert		- insert tuple into a relation
 *		heap_multi_insert - insert multiple tuples into a relation
 *		heap_delete		- delete a tuple from a relation
 *		heap_update		- replace a tuple in a relation with another tuple
 *		heap_markpos	- mark scan position
 *		heap_restrpos	- restore position to marked location
 *		heap_sync		- sync heap, for when no WAL has been written
 *
 * NOTES
 *	  This file contains the heap_ routines which implement
 *	  the POSTGRES heap access method used for all POSTGRES
 *	  relations.
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "access/heapam_xlog.h"
#include "access/hio.h"
#include "access/multixact.h"
#include "access/relscan.h"
#include "access/sysattr.h"
#include "access/transam.h"
#include "access/tuptoaster.h"
#include "access/valid.h"
#include "access/visibilitymap.h"
#include "access/xact.h"
#include "access/xlogutils.h"
#include "catalog/catalog.h"
#include "catalog/namespace.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/bufmgr.h"
#include "storage/freespace.h"
#include "storage/lmgr.h"
#include "storage/predicate.h"
#include "storage/procarray.h"
#include "storage/smgr.h"
#include "storage/standby.h"
#include "utils/datum.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/relcache.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
#include "utils/tqual.h"


/* GUC variable */
bool		synchronize_seqscans = true;


static HeapScanDesc heap_beginscan_internal(Relation relation,
						Snapshot snapshot,
						int nkeys, ScanKey key,
						bool allow_strat, bool allow_sync,
						bool is_bitmapscan);
static HeapTuple heap_prepare_insert(Relation relation, HeapTuple tup,
					TransactionId xid, CommandId cid, int options);
static XLogRecPtr log_heap_update(Relation reln, Buffer oldbuf,
				Buffer newbuf, HeapTuple oldtup,
				HeapTuple newtup, bool all_visible_cleared,
				bool new_all_visible_cleared);
static void HeapSatisfiesHOTandKeyUpdate(Relation relation,
							 Bitmapset *hot_attrs, Bitmapset *key_attrs,
							 bool *satisfies_hot, bool *satisfies_key,
							 HeapTuple oldtup, HeapTuple newtup);
static void compute_new_xmax_infomask(TransactionId xmax, uint16 old_infomask,
						  uint16 old_infomask2, TransactionId add_to_xmax,
						  LockTupleMode mode, bool is_update,
						  TransactionId *result_xmax, uint16 *result_infomask,
						  uint16 *result_infomask2);
static HTSU_Result heap_lock_updated_tuple(Relation rel, HeapTuple tuple,
						ItemPointer ctid, TransactionId xid,
						LockTupleMode mode);
static void GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
					   uint16 *new_infomask2);
static TransactionId MultiXactIdGetUpdateXid(TransactionId xmax,
						uint16 t_infomask);
static void MultiXactIdWait(MultiXactId multi, MultiXactStatus status,
				int *remaining, uint16 infomask);
static bool ConditionalMultiXactIdWait(MultiXactId multi,
						   MultiXactStatus status, int *remaining,
						   uint16 infomask);


/*
 * Each tuple lock mode has a corresponding heavyweight lock, and one or two
 * corresponding MultiXactStatuses (one to merely lock tuples, another one to
 * update them).  This table (and the macros below) helps us determine the
 * heavyweight lock mode and MultiXactStatus values to use for any particular
 * tuple lock strength.
 */
static const struct
{
	LOCKMODE	hwlock;
	MultiXactStatus	lockstatus;
	MultiXactStatus	updstatus;
}
tupleLockExtraInfo[MaxLockTupleMode + 1] =
{
	{	/* LockTupleKeyShare */
		AccessShareLock,
		MultiXactStatusForKeyShare,
		-1	/* KeyShare does not allow updating tuples */
	},
	{	/* LockTupleShare */
		RowShareLock,
		MultiXactStatusForShare,
		-1	/* Share does not allow updating tuples */
	},
	{	/* LockTupleNoKeyExclusive */
		ExclusiveLock,
		MultiXactStatusForNoKeyUpdate,
		MultiXactStatusNoKeyUpdate
	},
	{	/* LockTupleExclusive */
		AccessExclusiveLock,
		MultiXactStatusForUpdate,
		MultiXactStatusUpdate
	}
};
/* Get the LOCKMODE for a given MultiXactStatus */
#define LOCKMODE_from_mxstatus(status) \
			(tupleLockExtraInfo[TUPLOCK_from_mxstatus((status))].hwlock)

/*
 * Acquire heavyweight locks on tuples, using a LockTupleMode strength value.
 * This is more readable than having every caller translate it to lock.h's
 * LOCKMODE.
 */
#define LockTupleTuplock(rel, tup, mode) \
	LockTuple((rel), (tup), tupleLockExtraInfo[mode].hwlock)
#define UnlockTupleTuplock(rel, tup, mode) \
	UnlockTuple((rel), (tup), tupleLockExtraInfo[mode].hwlock)
#define ConditionalLockTupleTuplock(rel, tup, mode) \
	ConditionalLockTuple((rel), (tup), tupleLockExtraInfo[mode].hwlock)

/*
 * This table maps tuple lock strength values for each particular
 * MultiXactStatus value.
 */
static const int MultiXactStatusLock[MaxMultiXactStatus + 1] =
{
	LockTupleKeyShare,		/* ForKeyShare */
	LockTupleShare,			/* ForShare */
	LockTupleNoKeyExclusive,		/* ForNoKeyUpdate */
	LockTupleExclusive,		/* ForUpdate */
	LockTupleNoKeyExclusive,		/* NoKeyUpdate */
	LockTupleExclusive		/* Update */
};

/* Get the LockTupleMode for a given MultiXactStatus */
#define TUPLOCK_from_mxstatus(status) \
			(MultiXactStatusLock[(status)])
/* Get the is_update bit for a given MultiXactStatus */
#define ISUPDATE_from_mxstatus(status) \
			((status) > MultiXactStatusForUpdate)

/* ----------------------------------------------------------------
 *						 heap support routines
 * ----------------------------------------------------------------
 */

/* ----------------
 *		initscan - scan code common to heap_beginscan and heap_rescan
 * ----------------
 */
static void
initscan(HeapScanDesc scan, ScanKey key, bool is_rescan)
{
	bool		allow_strat;
	bool		allow_sync;

	/*
	 * Determine the number of blocks we have to scan.
	 *
	 * It is sufficient to do this once at scan start, since any tuples added
	 * while the scan is in progress will be invisible to my snapshot anyway.
	 * (That is not true when using a non-MVCC snapshot.  However, we couldn't
	 * guarantee to return tuples added after scan start anyway, since they
	 * might go into pages we already scanned.	To guarantee consistent
	 * results for a non-MVCC snapshot, the caller must hold some higher-level
	 * lock that ensures the interesting tuple(s) won't change.)
	 */
	scan->rs_nblocks = RelationGetNumberOfBlocks(scan->rs_rd);

	/*
	 * If the table is large relative to NBuffers, use a bulk-read access
	 * strategy and enable synchronized scanning (see syncscan.c).	Although
	 * the thresholds for these features could be different, we make them the
	 * same so that there are only two behaviors to tune rather than four.
	 * (However, some callers need to be able to disable one or both of these
	 * behaviors, independently of the size of the table; also there is a GUC
	 * variable that can disable synchronized scanning.)
	 *
	 * During a rescan, don't make a new strategy object if we don't have to.
	 */
	if (!RelationUsesLocalBuffers(scan->rs_rd) &&
		scan->rs_nblocks > NBuffers / 4)
	{
		allow_strat = scan->rs_allow_strat;
		allow_sync = scan->rs_allow_sync;
	}
	else
		allow_strat = allow_sync = false;

	if (allow_strat)
	{
		if (scan->rs_strategy == NULL)
			scan->rs_strategy = GetAccessStrategy(BAS_BULKREAD);
	}
	else
	{
		if (scan->rs_strategy != NULL)
			FreeAccessStrategy(scan->rs_strategy);
		scan->rs_strategy = NULL;
	}

	if (is_rescan)
	{
		/*
		 * If rescan, keep the previous startblock setting so that rewinding a
		 * cursor doesn't generate surprising results.  Reset the syncscan
		 * setting, though.
		 */
		scan->rs_syncscan = (allow_sync && synchronize_seqscans);
	}
	else if (allow_sync && synchronize_seqscans)
	{
		scan->rs_syncscan = true;
		scan->rs_startblock = ss_get_location(scan->rs_rd, scan->rs_nblocks);
	}
	else
	{
		scan->rs_syncscan = false;
		scan->rs_startblock = 0;
	}

	scan->rs_inited = false;
	scan->rs_ctup.t_data = NULL;
	ItemPointerSetInvalid(&scan->rs_ctup.t_self);
	scan->rs_cbuf = InvalidBuffer;
	scan->rs_cblock = InvalidBlockNumber;

	/* we don't have a marked position... */
	ItemPointerSetInvalid(&(scan->rs_mctid));

	/* page-at-a-time fields are always invalid when not rs_inited */

	/*
	 * copy the scan key, if appropriate
	 */
	if (key != NULL)
		memcpy(scan->rs_key, key, scan->rs_nkeys * sizeof(ScanKeyData));

	/*
	 * Currently, we don't have a stats counter for bitmap heap scans (but the
	 * underlying bitmap index scans will be counted).
	 */
	if (!scan->rs_bitmapscan)
		pgstat_count_heap_scan(scan->rs_rd);
}

/*
 * heapgetpage - subroutine for heapgettup()
 *
 * This routine reads and pins the specified page of the relation.
 * In page-at-a-time mode it performs additional work, namely determining
 * which tuples on the page are visible.
 */
static void
heapgetpage(HeapScanDesc scan, BlockNumber page)
{
	Buffer		buffer;
	Snapshot	snapshot;
	Page		dp;
	int			lines;
	int			ntup;
	OffsetNumber lineoff;
	ItemId		lpp;
	bool		all_visible;

	Assert(page < scan->rs_nblocks);

	/* release previous scan buffer, if any */
	if (BufferIsValid(scan->rs_cbuf))
	{
		ReleaseBuffer(scan->rs_cbuf);
		scan->rs_cbuf = InvalidBuffer;
	}

	/*
	 * Be sure to check for interrupts at least once per page.	Checks at
	 * higher code levels won't be able to stop a seqscan that encounters many
	 * pages' worth of consecutive dead tuples.
	 */
	CHECK_FOR_INTERRUPTS();

	/* read page using selected strategy */
	scan->rs_cbuf = ReadBufferExtended(scan->rs_rd, MAIN_FORKNUM, page,
									   RBM_NORMAL, scan->rs_strategy);
	scan->rs_cblock = page;

	if (!scan->rs_pageatatime)
		return;

	buffer = scan->rs_cbuf;
	snapshot = scan->rs_snapshot;

	/*
	 * Prune and repair fragmentation for the whole page, if possible.
	 */
	Assert(TransactionIdIsValid(RecentGlobalXmin));
	heap_page_prune_opt(scan->rs_rd, buffer, RecentGlobalXmin);

	/*
	 * We must hold share lock on the buffer content while examining tuple
	 * visibility.	Afterwards, however, the tuples we have found to be
	 * visible are guaranteed good as long as we hold the buffer pin.
	 */
	LockBuffer(buffer, BUFFER_LOCK_SHARE);

	dp = (Page) BufferGetPage(buffer);
	lines = PageGetMaxOffsetNumber(dp);
	ntup = 0;

	/*
	 * If the all-visible flag indicates that all tuples on the page are
	 * visible to everyone, we can skip the per-tuple visibility tests.
	 *
	 * Note: In hot standby, a tuple that's already visible to all
	 * transactions in the master might still be invisible to a read-only
	 * transaction in the standby. We partly handle this problem by tracking
	 * the minimum xmin of visible tuples as the cut-off XID while marking a
	 * page all-visible on master and WAL log that along with the visibility
	 * map SET operation. In hot standby, we wait for (or abort) all
	 * transactions that can potentially may not see one or more tuples on the
	 * page. That's how index-only scans work fine in hot standby. A crucial
	 * difference between index-only scans and heap scans is that the
	 * index-only scan completely relies on the visibility map where as heap
	 * scan looks at the page-level PD_ALL_VISIBLE flag. We are not sure if the
	 * page-level flag can be trusted in the same way, because it might get
	 * propagated somehow without being explicitly WAL-logged, e.g. via a full
	 * page write. Until we can prove that beyond doubt, let's check each
	 * tuple for visibility the hard way.
	 */
	all_visible = PageIsAllVisible(dp) && !snapshot->takenDuringRecovery;

	for (lineoff = FirstOffsetNumber, lpp = PageGetItemId(dp, lineoff);
		 lineoff <= lines;
		 lineoff++, lpp++)
	{
		if (ItemIdIsNormal(lpp))
		{
			HeapTupleData loctup;
			bool		valid;

			loctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
			loctup.t_len = ItemIdGetLength(lpp);
			ItemPointerSet(&(loctup.t_self), page, lineoff);

			if (all_visible)
				valid = true;
			else
				valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer);

			CheckForSerializableConflictOut(valid, scan->rs_rd, &loctup,
											buffer, snapshot);

			if (valid)
				scan->rs_vistuples[ntup++] = lineoff;
		}
	}

	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

	Assert(ntup <= MaxHeapTuplesPerPage);
	scan->rs_ntuples = ntup;
}

/* ----------------
 *		heapgettup - fetch next heap tuple
 *
 *		Initialize the scan if not already done; then advance to the next
 *		tuple as indicated by "dir"; return the next tuple in scan->rs_ctup,
 *		or set scan->rs_ctup.t_data = NULL if no more tuples.
 *
 * dir == NoMovementScanDirection means "re-fetch the tuple indicated
 * by scan->rs_ctup".
 *
 * Note: the reason nkeys/key are passed separately, even though they are
 * kept in the scan descriptor, is that the caller may not want us to check
 * the scankeys.
 *
 * Note: when we fall off the end of the scan in either direction, we
 * reset rs_inited.  This means that a further request with the same
 * scan direction will restart the scan, which is a bit odd, but a
 * request with the opposite scan direction will start a fresh scan
 * in the proper direction.  The latter is required behavior for cursors,
 * while the former case is generally undefined behavior in Postgres
 * so we don't care too much.
 * ----------------
 */
static void
heapgettup(HeapScanDesc scan,
		   ScanDirection dir,
		   int nkeys,
		   ScanKey key)
{
	HeapTuple	tuple = &(scan->rs_ctup);
	Snapshot	snapshot = scan->rs_snapshot;
	bool		backward = ScanDirectionIsBackward(dir);
	BlockNumber page;
	bool		finished;
	Page		dp;
	int			lines;
	OffsetNumber lineoff;
	int			linesleft;
	ItemId		lpp;

	/*
	 * calculate next starting lineoff, given scan direction
	 */
	if (ScanDirectionIsForward(dir))
	{
		if (!scan->rs_inited)
		{
			/*
			 * return null immediately if relation is empty
			 */
			if (scan->rs_nblocks == 0)
			{
				Assert(!BufferIsValid(scan->rs_cbuf));
				tuple->t_data = NULL;
				return;
			}
			page = scan->rs_startblock; /* first page */
			heapgetpage(scan, page);
			lineoff = FirstOffsetNumber;		/* first offnum */
			scan->rs_inited = true;
		}
		else
		{
			/* continue from previously returned page/tuple */
			page = scan->rs_cblock;		/* current page */
			lineoff =			/* next offnum */
				OffsetNumberNext(ItemPointerGetOffsetNumber(&(tuple->t_self)));
		}

		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);

		dp = (Page) BufferGetPage(scan->rs_cbuf);
		lines = PageGetMaxOffsetNumber(dp);
		/* page and lineoff now reference the physically next tid */

		linesleft = lines - lineoff + 1;
	}
	else if (backward)
	{
		if (!scan->rs_inited)
		{
			/*
			 * return null immediately if relation is empty
			 */
			if (scan->rs_nblocks == 0)
			{
				Assert(!BufferIsValid(scan->rs_cbuf));
				tuple->t_data = NULL;
				return;
			}

			/*
			 * Disable reporting to syncscan logic in a backwards scan; it's
			 * not very likely anyone else is doing the same thing at the same
			 * time, and much more likely that we'll just bollix things for
			 * forward scanners.
			 */
			scan->rs_syncscan = false;
			/* start from last page of the scan */
			if (scan->rs_startblock > 0)
				page = scan->rs_startblock - 1;
			else
				page = scan->rs_nblocks - 1;
			heapgetpage(scan, page);
		}
		else
		{
			/* continue from previously returned page/tuple */
			page = scan->rs_cblock;		/* current page */
		}

		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);

		dp = (Page) BufferGetPage(scan->rs_cbuf);
		lines = PageGetMaxOffsetNumber(dp);

		if (!scan->rs_inited)
		{
			lineoff = lines;	/* final offnum */
			scan->rs_inited = true;
		}
		else
		{
			lineoff =			/* previous offnum */
				OffsetNumberPrev(ItemPointerGetOffsetNumber(&(tuple->t_self)));
		}
		/* page and lineoff now reference the physically previous tid */

		linesleft = lineoff;
	}
	else
	{
		/*
		 * ``no movement'' scan direction: refetch prior tuple
		 */
		if (!scan->rs_inited)
		{
			Assert(!BufferIsValid(scan->rs_cbuf));
			tuple->t_data = NULL;
			return;
		}

		page = ItemPointerGetBlockNumber(&(tuple->t_self));
		if (page != scan->rs_cblock)
			heapgetpage(scan, page);

		/* Since the tuple was previously fetched, needn't lock page here */
		dp = (Page) BufferGetPage(scan->rs_cbuf);
		lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
		lpp = PageGetItemId(dp, lineoff);
		Assert(ItemIdIsNormal(lpp));

		tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
		tuple->t_len = ItemIdGetLength(lpp);

		return;
	}

	/*
	 * advance the scan until we find a qualifying tuple or run out of stuff
	 * to scan
	 */
	lpp = PageGetItemId(dp, lineoff);
	for (;;)
	{
		while (linesleft > 0)
		{
			if (ItemIdIsNormal(lpp))
			{
				bool		valid;

				tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
				tuple->t_len = ItemIdGetLength(lpp);
				ItemPointerSet(&(tuple->t_self), page, lineoff);

				/*
				 * if current tuple qualifies, return it.
				 */
				valid = HeapTupleSatisfiesVisibility(tuple,
													 snapshot,
													 scan->rs_cbuf);

				CheckForSerializableConflictOut(valid, scan->rs_rd, tuple,
												scan->rs_cbuf, snapshot);

				if (valid && key != NULL)
					HeapKeyTest(tuple, RelationGetDescr(scan->rs_rd),
								nkeys, key, valid);

				if (valid)
				{
					LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
					return;
				}
			}

			/*
			 * otherwise move to the next item on the page
			 */
			--linesleft;
			if (backward)
			{
				--lpp;			/* move back in this page's ItemId array */
				--lineoff;
			}
			else
			{
				++lpp;			/* move forward in this page's ItemId array */
				++lineoff;
			}
		}

		/*
		 * if we get here, it means we've exhausted the items on this page and
		 * it's time to move to the next.
		 */
		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);

		/*
		 * advance to next/prior page and detect end of scan
		 */
		if (backward)
		{
			finished = (page == scan->rs_startblock);
			if (page == 0)
				page = scan->rs_nblocks;
			page--;
		}
		else
		{
			page++;
			if (page >= scan->rs_nblocks)
				page = 0;
			finished = (page == scan->rs_startblock);

			/*
			 * Report our new scan position for synchronization purposes. We
			 * don't do that when moving backwards, however. That would just
			 * mess up any other forward-moving scanners.
			 *
			 * Note: we do this before checking for end of scan so that the
			 * final state of the position hint is back at the start of the
			 * rel.  That's not strictly necessary, but otherwise when you run
			 * the same query multiple times the starting position would shift
			 * a little bit backwards on every invocation, which is confusing.
			 * We don't guarantee any specific ordering in general, though.
			 */
			if (scan->rs_syncscan)
				ss_report_location(scan->rs_rd, page);
		}

		/*
		 * return NULL if we've exhausted all the pages
		 */
		if (finished)
		{
			if (BufferIsValid(scan->rs_cbuf))
				ReleaseBuffer(scan->rs_cbuf);
			scan->rs_cbuf = InvalidBuffer;
			scan->rs_cblock = InvalidBlockNumber;
			tuple->t_data = NULL;
			scan->rs_inited = false;
			return;
		}

		heapgetpage(scan, page);

		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);

		dp = (Page) BufferGetPage(scan->rs_cbuf);
		lines = PageGetMaxOffsetNumber((Page) dp);
		linesleft = lines;
		if (backward)
		{
			lineoff = lines;
			lpp = PageGetItemId(dp, lines);
		}
		else
		{
			lineoff = FirstOffsetNumber;
			lpp = PageGetItemId(dp, FirstOffsetNumber);
		}
	}
}

/* ----------------
 *		heapgettup_pagemode - fetch next heap tuple in page-at-a-time mode
 *
 *		Same API as heapgettup, but used in page-at-a-time mode
 *
 * The internal logic is much the same as heapgettup's too, but there are some
 * differences: we do not take the buffer content lock (that only needs to
 * happen inside heapgetpage), and we iterate through just the tuples listed
 * in rs_vistuples[] rather than all tuples on the page.  Notice that
 * lineindex is 0-based, where the corresponding loop variable lineoff in
 * heapgettup is 1-based.
 * ----------------
 */
static void
heapgettup_pagemode(HeapScanDesc scan,
					ScanDirection dir,
					int nkeys,
					ScanKey key)
{
	HeapTuple	tuple = &(scan->rs_ctup);
	bool		backward = ScanDirectionIsBackward(dir);
	BlockNumber page;
	bool		finished;
	Page		dp;
	int			lines;
	int			lineindex;
	OffsetNumber lineoff;
	int			linesleft;
	ItemId		lpp;

	/*
	 * calculate next starting lineindex, given scan direction
	 */
	if (ScanDirectionIsForward(dir))
	{
		if (!scan->rs_inited)
		{
			/*
			 * return null immediately if relation is empty
			 */
			if (scan->rs_nblocks == 0)
			{
				Assert(!BufferIsValid(scan->rs_cbuf));
				tuple->t_data = NULL;
				return;
			}
			page = scan->rs_startblock; /* first page */
			heapgetpage(scan, page);
			lineindex = 0;
			scan->rs_inited = true;
		}
		else
		{
			/* continue from previously returned page/tuple */
			page = scan->rs_cblock;		/* current page */
			lineindex = scan->rs_cindex + 1;
		}

		dp = (Page) BufferGetPage(scan->rs_cbuf);
		lines = scan->rs_ntuples;
		/* page and lineindex now reference the next visible tid */

		linesleft = lines - lineindex;
	}
	else if (backward)
	{
		if (!scan->rs_inited)
		{
			/*
			 * return null immediately if relation is empty
			 */
			if (scan->rs_nblocks == 0)
			{
				Assert(!BufferIsValid(scan->rs_cbuf));
				tuple->t_data = NULL;
				return;
			}

			/*
			 * Disable reporting to syncscan logic in a backwards scan; it's
			 * not very likely anyone else is doing the same thing at the same
			 * time, and much more likely that we'll just bollix things for
			 * forward scanners.
			 */
			scan->rs_syncscan = false;
			/* start from last page of the scan */
			if (scan->rs_startblock > 0)
				page = scan->rs_startblock - 1;
			else
				page = scan->rs_nblocks - 1;
			heapgetpage(scan, page);
		}
		else
		{
			/* continue from previously returned page/tuple */
			page = scan->rs_cblock;		/* current page */
		}

		dp = (Page) BufferGetPage(scan->rs_cbuf);
		lines = scan->rs_ntuples;

		if (!scan->rs_inited)
		{
			lineindex = lines - 1;
			scan->rs_inited = true;
		}
		else
		{
			lineindex = scan->rs_cindex - 1;
		}
		/* page and lineindex now reference the previous visible tid */

		linesleft = lineindex + 1;
	}
	else
	{
		/*
		 * ``no movement'' scan direction: refetch prior tuple
		 */
		if (!scan->rs_inited)
		{
			Assert(!BufferIsValid(scan->rs_cbuf));
			tuple->t_data = NULL;
			return;
		}

		page = ItemPointerGetBlockNumber(&(tuple->t_self));
		if (page != scan->rs_cblock)
			heapgetpage(scan, page);

		/* Since the tuple was previously fetched, needn't lock page here */
		dp = (Page) BufferGetPage(scan->rs_cbuf);
		lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
		lpp = PageGetItemId(dp, lineoff);
		Assert(ItemIdIsNormal(lpp));

		tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
		tuple->t_len = ItemIdGetLength(lpp);

		/* check that rs_cindex is in sync */
		Assert(scan->rs_cindex < scan->rs_ntuples);
		Assert(lineoff == scan->rs_vistuples[scan->rs_cindex]);

		return;
	}

	/*
	 * advance the scan until we find a qualifying tuple or run out of stuff
	 * to scan
	 */
	for (;;)
	{
		while (linesleft > 0)
		{
			lineoff = scan->rs_vistuples[lineindex];
			lpp = PageGetItemId(dp, lineoff);
			Assert(ItemIdIsNormal(lpp));

			tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
			tuple->t_len = ItemIdGetLength(lpp);
			ItemPointerSet(&(tuple->t_self), page, lineoff);

			/*
			 * if current tuple qualifies, return it.
			 */
			if (key != NULL)
			{
				bool		valid;

				HeapKeyTest(tuple, RelationGetDescr(scan->rs_rd),
							nkeys, key, valid);
				if (valid)
				{
					scan->rs_cindex = lineindex;
					return;
				}
			}
			else
			{
				scan->rs_cindex = lineindex;
				return;
			}

			/*
			 * otherwise move to the next item on the page
			 */
			--linesleft;
			if (backward)
				--lineindex;
			else
				++lineindex;
		}

		/*
		 * if we get here, it means we've exhausted the items on this page and
		 * it's time to move to the next.
		 */
		if (backward)
		{
			finished = (page == scan->rs_startblock);
			if (page == 0)
				page = scan->rs_nblocks;
			page--;
		}
		else
		{
			page++;
			if (page >= scan->rs_nblocks)
				page = 0;
			finished = (page == scan->rs_startblock);

			/*
			 * Report our new scan position for synchronization purposes. We
			 * don't do that when moving backwards, however. That would just
			 * mess up any other forward-moving scanners.
			 *
			 * Note: we do this before checking for end of scan so that the
			 * final state of the position hint is back at the start of the
			 * rel.  That's not strictly necessary, but otherwise when you run
			 * the same query multiple times the starting position would shift
			 * a little bit backwards on every invocation, which is confusing.
			 * We don't guarantee any specific ordering in general, though.
			 */
			if (scan->rs_syncscan)
				ss_report_location(scan->rs_rd, page);
		}

		/*
		 * return NULL if we've exhausted all the pages
		 */
		if (finished)
		{
			if (BufferIsValid(scan->rs_cbuf))
				ReleaseBuffer(scan->rs_cbuf);
			scan->rs_cbuf = InvalidBuffer;
			scan->rs_cblock = InvalidBlockNumber;
			tuple->t_data = NULL;
			scan->rs_inited = false;
			return;
		}

		heapgetpage(scan, page);

		dp = (Page) BufferGetPage(scan->rs_cbuf);
		lines = scan->rs_ntuples;
		linesleft = lines;
		if (backward)
			lineindex = lines - 1;
		else
			lineindex = 0;
	}
}


#if defined(DISABLE_COMPLEX_MACRO)
/*
 * This is formatted so oddly so that the correspondence to the macro
 * definition in access/htup.h is maintained.
 */
Datum
fastgetattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
			bool *isnull)
{
	return (
			(attnum) > 0 ?
			(
			 (*(isnull) = false),
			 HeapTupleNoNulls(tup) ?
			 (
			  (tupleDesc)->attrs[(attnum) - 1]->attcacheoff >= 0 ?
			  (
			   fetchatt((tupleDesc)->attrs[(attnum) - 1],
						(char *) (tup)->t_data + (tup)->t_data->t_hoff +
						(tupleDesc)->attrs[(attnum) - 1]->attcacheoff)
			   )
			  :
			  nocachegetattr((tup), (attnum), (tupleDesc))
			  )
			 :
			 (
			  att_isnull((attnum) - 1, (tup)->t_data->t_bits) ?
			  (
			   (*(isnull) = true),
			   (Datum) NULL
			   )
			  :
			  (
			   nocachegetattr((tup), (attnum), (tupleDesc))
			   )
			  )
			 )
			:
			(
			 (Datum) NULL
			 )
		);
}
#endif   /* defined(DISABLE_COMPLEX_MACRO) */


/* ----------------------------------------------------------------
 *					 heap access method interface
 * ----------------------------------------------------------------
 */

/* ----------------
 *		relation_open - open any relation by relation OID
 *
 *		If lockmode is not "NoLock", the specified kind of lock is
 *		obtained on the relation.  (Generally, NoLock should only be
 *		used if the caller knows it has some appropriate lock on the
 *		relation already.)
 *
 *		An error is raised if the relation does not exist.
 *
 *		NB: a "relation" is anything with a pg_class entry.  The caller is
 *		expected to check whether the relkind is something it can handle.
 * ----------------
 */
Relation
relation_open(Oid relationId, LOCKMODE lockmode)
{
	Relation	r;

	Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);

	/* Get the lock before trying to open the relcache entry */
	if (lockmode != NoLock)
		LockRelationOid(relationId, lockmode);

	/* The relcache does all the real work... */
	r = RelationIdGetRelation(relationId);

	if (!RelationIsValid(r))
		elog(ERROR, "could not open relation with OID %u", relationId);

	/* Make note that we've accessed a temporary relation */
	if (RelationUsesLocalBuffers(r))
		MyXactAccessedTempRel = true;

	pgstat_initstats(r);

	return r;
}

/* ----------------
 *		try_relation_open - open any relation by relation OID
 *
 *		Same as relation_open, except return NULL instead of failing
 *		if the relation does not exist.
 * ----------------
 */
Relation
try_relation_open(Oid relationId, LOCKMODE lockmode)
{
	Relation	r;

	Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);

	/* Get the lock first */
	if (lockmode != NoLock)
		LockRelationOid(relationId, lockmode);

	/*
	 * Now that we have the lock, probe to see if the relation really exists
	 * or not.
	 */
	if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(relationId)))
	{
		/* Release useless lock */
		if (lockmode != NoLock)
			UnlockRelationOid(relationId, lockmode);

		return NULL;
	}

	/* Should be safe to do a relcache load */
	r = RelationIdGetRelation(relationId);

	if (!RelationIsValid(r))
		elog(ERROR, "could not open relation with OID %u", relationId);

	/* Make note that we've accessed a temporary relation */
	if (RelationUsesLocalBuffers(r))
		MyXactAccessedTempRel = true;

	pgstat_initstats(r);

	return r;
}

/* ----------------
 *		relation_openrv - open any relation specified by a RangeVar
 *
 *		Same as relation_open, but the relation is specified by a RangeVar.
 * ----------------
 */
Relation
relation_openrv(const RangeVar *relation, LOCKMODE lockmode)
{
	Oid			relOid;

	/*
	 * Check for shared-cache-inval messages before trying to open the
	 * relation.  This is needed even if we already hold a lock on the
	 * relation, because GRANT/REVOKE are executed without taking any lock on
	 * the target relation, and we want to be sure we see current ACL
	 * information.  We can skip this if asked for NoLock, on the assumption
	 * that such a call is not the first one in the current command, and so we
	 * should be reasonably up-to-date already.  (XXX this all could stand to
	 * be redesigned, but for the moment we'll keep doing this like it's been
	 * done historically.)
	 */
	if (lockmode != NoLock)
		AcceptInvalidationMessages();

	/* Look up and lock the appropriate relation using namespace search */
	relOid = RangeVarGetRelid(relation, lockmode, false);

	/* Let relation_open do the rest */
	return relation_open(relOid, NoLock);
}

/* ----------------
 *		relation_openrv_extended - open any relation specified by a RangeVar
 *
 *		Same as relation_openrv, but with an additional missing_ok argument
 *		allowing a NULL return rather than an error if the relation is not
 *		found.	(Note that some other causes, such as permissions problems,
 *		will still result in an ereport.)
 * ----------------
 */
Relation
relation_openrv_extended(const RangeVar *relation, LOCKMODE lockmode,
						 bool missing_ok)
{
	Oid			relOid;

	/*
	 * Check for shared-cache-inval messages before trying to open the
	 * relation.  See comments in relation_openrv().
	 */
	if (lockmode != NoLock)
		AcceptInvalidationMessages();

	/* Look up and lock the appropriate relation using namespace search */
	relOid = RangeVarGetRelid(relation, lockmode, missing_ok);

	/* Return NULL on not-found */
	if (!OidIsValid(relOid))
		return NULL;

	/* Let relation_open do the rest */
	return relation_open(relOid, NoLock);
}

/* ----------------
 *		relation_close - close any relation
 *
 *		If lockmode is not "NoLock", we then release the specified lock.
 *
 *		Note that it is often sensible to hold a lock beyond relation_close;
 *		in that case, the lock is released automatically at xact end.
 * ----------------
 */
void
relation_close(Relation relation, LOCKMODE lockmode)
{
	LockRelId	relid = relation->rd_lockInfo.lockRelId;

	Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);

	/* The relcache does the real work... */
	RelationClose(relation);

	if (lockmode != NoLock)
		UnlockRelationId(&relid, lockmode);
}


/* ----------------
 *		heap_open - open a heap relation by relation OID
 *
 *		This is essentially relation_open plus check that the relation
 *		is not an index nor a composite type.  (The caller should also
 *		check that it's not a view or foreign table before assuming it has
 *		storage.)
 * ----------------
 */
Relation
heap_open(Oid relationId, LOCKMODE lockmode)
{
	Relation	r;

	r = relation_open(relationId, lockmode);

	if (r->rd_rel->relkind == RELKIND_INDEX)
		ereport(ERROR,
				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
				 errmsg("\"%s\" is an index",
						RelationGetRelationName(r))));
	else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
		ereport(ERROR,
				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
				 errmsg("\"%s\" is a composite type",
						RelationGetRelationName(r))));

	return r;
}

/* ----------------
 *		heap_openrv - open a heap relation specified
 *		by a RangeVar node
 *
 *		As above, but relation is specified by a RangeVar.
 * ----------------
 */
Relation
heap_openrv(const RangeVar *relation, LOCKMODE lockmode)
{
	Relation	r;

	r = relation_openrv(relation, lockmode);

	if (r->rd_rel->relkind == RELKIND_INDEX)
		ereport(ERROR,
				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
				 errmsg("\"%s\" is an index",
						RelationGetRelationName(r))));
	else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
		ereport(ERROR,
				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
				 errmsg("\"%s\" is a composite type",
						RelationGetRelationName(r))));

	return r;
}

/* ----------------
 *		heap_openrv_extended - open a heap relation specified
 *		by a RangeVar node
 *
 *		As above, but optionally return NULL instead of failing for
 *		relation-not-found.
 * ----------------
 */
Relation
heap_openrv_extended(const RangeVar *relation, LOCKMODE lockmode,
					 bool missing_ok)
{
	Relation	r;

	r = relation_openrv_extended(relation, lockmode, missing_ok);

	if (r)
	{
		if (r->rd_rel->relkind == RELKIND_INDEX)
			ereport(ERROR,
					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
					 errmsg("\"%s\" is an index",
							RelationGetRelationName(r))));
		else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
			ereport(ERROR,
					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
					 errmsg("\"%s\" is a composite type",
							RelationGetRelationName(r))));
	}

	return r;
}


/* ----------------
 *		heap_beginscan	- begin relation scan
 *
 * heap_beginscan_strat offers an extended API that lets the caller control
 * whether a nondefault buffer access strategy can be used, and whether
 * syncscan can be chosen (possibly resulting in the scan not starting from
 * block zero).  Both of these default to TRUE with plain heap_beginscan.
 *
 * heap_beginscan_bm is an alternative entry point for setting up a
 * HeapScanDesc for a bitmap heap scan.  Although that scan technology is
 * really quite unlike a standard seqscan, there is just enough commonality
 * to make it worth using the same data structure.
 * ----------------
 */
HeapScanDesc
heap_beginscan(Relation relation, Snapshot snapshot,
			   int nkeys, ScanKey key)
{
	return heap_beginscan_internal(relation, snapshot, nkeys, key,
								   true, true, false);
}

HeapScanDesc
heap_beginscan_strat(Relation relation, Snapshot snapshot,
					 int nkeys, ScanKey key,
					 bool allow_strat, bool allow_sync)
{
	return heap_beginscan_internal(relation, snapshot, nkeys, key,
								   allow_strat, allow_sync, false);
}

HeapScanDesc
heap_beginscan_bm(Relation relation, Snapshot snapshot,
				  int nkeys, ScanKey key)
{
	return heap_beginscan_internal(relation, snapshot, nkeys, key,
								   false, false, true);
}

static HeapScanDesc
heap_beginscan_internal(Relation relation, Snapshot snapshot,
						int nkeys, ScanKey key,
						bool allow_strat, bool allow_sync,
						bool is_bitmapscan)
{
	HeapScanDesc scan;

	/*
	 * increment relation ref count while scanning relation
	 *
	 * This is just to make really sure the relcache entry won't go away while
	 * the scan has a pointer to it.  Caller should be holding the rel open
	 * anyway, so this is redundant in all normal scenarios...
	 */
	RelationIncrementReferenceCount(relation);

	/*
	 * allocate and initialize scan descriptor
	 */
	scan = (HeapScanDesc) palloc(sizeof(HeapScanDescData));

	scan->rs_rd = relation;
	scan->rs_snapshot = snapshot;
	scan->rs_nkeys = nkeys;
	scan->rs_bitmapscan = is_bitmapscan;
	scan->rs_strategy = NULL;	/* set in initscan */
	scan->rs_allow_strat = allow_strat;
	scan->rs_allow_sync = allow_sync;

	/*
	 * we can use page-at-a-time mode if it's an MVCC-safe snapshot
	 */
	scan->rs_pageatatime = IsMVCCSnapshot(snapshot);

	/*
	 * For a seqscan in a serializable transaction, acquire a predicate lock
	 * on the entire relation. This is required not only to lock all the
	 * matching tuples, but also to conflict with new insertions into the
	 * table. In an indexscan, we take page locks on the index pages covering
	 * the range specified in the scan qual, but in a heap scan there is
	 * nothing more fine-grained to lock. A bitmap scan is a different story,
	 * there we have already scanned the index and locked the index pages
	 * covering the predicate. But in that case we still have to lock any
	 * matching heap tuples.
	 */
	if (!is_bitmapscan)
		PredicateLockRelation(relation, snapshot);

	/* we only need to set this up once */
	scan->rs_ctup.t_tableOid = RelationGetRelid(relation);

	/*
	 * we do this here instead of in initscan() because heap_rescan also calls
	 * initscan() and we don't want to allocate memory again
	 */
	if (nkeys > 0)
		scan->rs_key = (ScanKey) palloc(sizeof(ScanKeyData) * nkeys);
	else
		scan->rs_key = NULL;

	initscan(scan, key, false);

	return scan;
}

/* ----------------
 *		heap_rescan		- restart a relation scan
 * ----------------
 */
void
heap_rescan(HeapScanDesc scan,
			ScanKey key)
{
	/*
	 * unpin scan buffers
	 */
	if (BufferIsValid(scan->rs_cbuf))
		ReleaseBuffer(scan->rs_cbuf);

	/*
	 * reinitialize scan descriptor
	 */
	initscan(scan, key, true);
}

/* ----------------
 *		heap_endscan	- end relation scan
 *
 *		See how to integrate with index scans.
 *		Check handling if reldesc caching.
 * ----------------
 */
void
heap_endscan(HeapScanDesc scan)
{
	/* Note: no locking manipulations needed */

	/*
	 * unpin scan buffers
	 */
	if (BufferIsValid(scan->rs_cbuf))
		ReleaseBuffer(scan->rs_cbuf);

	/*
	 * decrement relation reference count and free scan descriptor storage
	 */
	RelationDecrementReferenceCount(scan->rs_rd);

	if (scan->rs_key)
		pfree(scan->rs_key);

	if (scan->rs_strategy != NULL)
		FreeAccessStrategy(scan->rs_strategy);

	pfree(scan);
}

/* ----------------
 *		heap_getnext	- retrieve next tuple in scan
 *
 *		Fix to work with index relations.
 *		We don't return the buffer anymore, but you can get it from the
 *		returned HeapTuple.
 * ----------------
 */

#ifdef HEAPDEBUGALL
#define HEAPDEBUG_1 \
	elog(DEBUG2, "heap_getnext([%s,nkeys=%d],dir=%d) called", \
		 RelationGetRelationName(scan->rs_rd), scan->rs_nkeys, (int) direction)
#define HEAPDEBUG_2 \
	elog(DEBUG2, "heap_getnext returning EOS")
#define HEAPDEBUG_3 \
	elog(DEBUG2, "heap_getnext returning tuple")
#else
#define HEAPDEBUG_1
#define HEAPDEBUG_2
#define HEAPDEBUG_3
#endif   /* !defined(HEAPDEBUGALL) */


HeapTuple
heap_getnext(HeapScanDesc scan, ScanDirection direction)
{
	/* Note: no locking manipulations needed */

	HEAPDEBUG_1;				/* heap_getnext( info ) */

	if (scan->rs_pageatatime)
		heapgettup_pagemode(scan, direction,
							scan->rs_nkeys, scan->rs_key);
	else
		heapgettup(scan, direction, scan->rs_nkeys, scan->rs_key);

	if (scan->rs_ctup.t_data == NULL)
	{
		HEAPDEBUG_2;			/* heap_getnext returning EOS */
		return NULL;
	}

	/*
	 * if we get here it means we have a new current scan tuple, so point to
	 * the proper return buffer and return the tuple.
	 */
	HEAPDEBUG_3;				/* heap_getnext returning tuple */

	pgstat_count_heap_getnext(scan->rs_rd);

	return &(scan->rs_ctup);
}

/*
 *	heap_fetch		- retrieve tuple with given tid
 *
 * On entry, tuple->t_self is the TID to fetch.  We pin the buffer holding
 * the tuple, fill in the remaining fields of *tuple, and check the tuple
 * against the specified snapshot.
 *
 * If successful (tuple found and passes snapshot time qual), then *userbuf
 * is set to the buffer holding the tuple and TRUE is returned.  The caller
 * must unpin the buffer when done with the tuple.
 *
 * If the tuple is not found (ie, item number references a deleted slot),
 * then tuple->t_data is set to NULL and FALSE is returned.
 *
 * If the tuple is found but fails the time qual check, then FALSE is returned
 * but tuple->t_data is left pointing to the tuple.
 *
 * keep_buf determines what is done with the buffer in the FALSE-result cases.
 * When the caller specifies keep_buf = true, we retain the pin on the buffer
 * and return it in *userbuf (so the caller must eventually unpin it); when
 * keep_buf = false, the pin is released and *userbuf is set to InvalidBuffer.
 *
 * stats_relation is the relation to charge the heap_fetch operation against
 * for statistical purposes.  (This could be the heap rel itself, an
 * associated index, or NULL to not count the fetch at all.)
 *
 * heap_fetch does not follow HOT chains: only the exact TID requested will
 * be fetched.
 *
 * It is somewhat inconsistent that we ereport() on invalid block number but
 * return false on invalid item number.  There are a couple of reasons though.
 * One is that the caller can relatively easily check the block number for
 * validity, but cannot check the item number without reading the page
 * himself.  Another is that when we are following a t_ctid link, we can be
 * reasonably confident that the page number is valid (since VACUUM shouldn't
 * truncate off the destination page without having killed the referencing
 * tuple first), but the item number might well not be good.
 */
bool
heap_fetch(Relation relation,
		   Snapshot snapshot,
		   HeapTuple tuple,
		   Buffer *userbuf,
		   bool keep_buf,
		   Relation stats_relation)
{
	ItemPointer tid = &(tuple->t_self);
	ItemId		lp;
	Buffer		buffer;
	Page		page;
	OffsetNumber offnum;
	bool		valid;

	/*
	 * Fetch and pin the appropriate page of the relation.
	 */
	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));

	/*
	 * Need share lock on buffer to examine tuple commit status.
	 */
	LockBuffer(buffer, BUFFER_LOCK_SHARE);
	page = BufferGetPage(buffer);

	/*
	 * We'd better check for out-of-range offnum in case of VACUUM since the
	 * TID was obtained.
	 */
	offnum = ItemPointerGetOffsetNumber(tid);
	if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(page))
	{
		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
		if (keep_buf)
			*userbuf = buffer;
		else
		{
			ReleaseBuffer(buffer);
			*userbuf = InvalidBuffer;
		}
		tuple->t_data = NULL;
		return false;
	}

	/*
	 * get the item line pointer corresponding to the requested tid
	 */
	lp = PageGetItemId(page, offnum);

	/*
	 * Must check for deleted tuple.
	 */
	if (!ItemIdIsNormal(lp))
	{
		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
		if (keep_buf)
			*userbuf = buffer;
		else
		{
			ReleaseBuffer(buffer);
			*userbuf = InvalidBuffer;
		}
		tuple->t_data = NULL;
		return false;
	}

	/*
	 * fill in *tuple fields
	 */
	tuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
	tuple->t_len = ItemIdGetLength(lp);
	tuple->t_tableOid = RelationGetRelid(relation);

	/*
	 * check time qualification of tuple, then release lock
	 */
	valid = HeapTupleSatisfiesVisibility(tuple, snapshot, buffer);

	if (valid)
		PredicateLockTuple(relation, tuple, snapshot);

	CheckForSerializableConflictOut(valid, relation, tuple, buffer, snapshot);

	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

	if (valid)
	{
		/*
		 * All checks passed, so return the tuple as valid. Caller is now
		 * responsible for releasing the buffer.
		 */
		*userbuf = buffer;

		/* Count the successful fetch against appropriate rel, if any */
		if (stats_relation != NULL)
			pgstat_count_heap_fetch(stats_relation);

		return true;
	}

	/* Tuple failed time qual, but maybe caller wants to see it anyway. */
	if (keep_buf)
		*userbuf = buffer;
	else
	{
		ReleaseBuffer(buffer);
		*userbuf = InvalidBuffer;
	}

	return false;
}

/*
 *	heap_hot_search_buffer	- search HOT chain for tuple satisfying snapshot
 *
 * On entry, *tid is the TID of a tuple (either a simple tuple, or the root
 * of a HOT chain), and buffer is the buffer holding this tuple.  We search
 * for the first chain member satisfying the given snapshot.  If one is
 * found, we update *tid to reference that tuple's offset number, and
 * return TRUE.  If no match, return FALSE without modifying *tid.
 *
 * heapTuple is a caller-supplied buffer.  When a match is found, we return
 * the tuple here, in addition to updating *tid.  If no match is found, the
 * contents of this buffer on return are undefined.
 *
 * If all_dead is not NULL, we check non-visible tuples to see if they are
 * globally dead; *all_dead is set TRUE if all members of the HOT chain
 * are vacuumable, FALSE if not.
 *
 * Unlike heap_fetch, the caller must already have pin and (at least) share
 * lock on the buffer; it is still pinned/locked at exit.  Also unlike
 * heap_fetch, we do not report any pgstats count; caller may do so if wanted.
 */
bool
heap_hot_search_buffer(ItemPointer tid, Relation relation, Buffer buffer,
					   Snapshot snapshot, HeapTuple heapTuple,
					   bool *all_dead, bool first_call)
{
	Page		dp = (Page) BufferGetPage(buffer);
	TransactionId prev_xmax = InvalidTransactionId;
	OffsetNumber offnum;
	bool		at_chain_start;
	bool		valid;
	bool		skip;

	/* If this is not the first call, previous call returned a (live!) tuple */
	if (all_dead)
		*all_dead = first_call;

	Assert(TransactionIdIsValid(RecentGlobalXmin));

	Assert(ItemPointerGetBlockNumber(tid) == BufferGetBlockNumber(buffer));
	offnum = ItemPointerGetOffsetNumber(tid);
	at_chain_start = first_call;
	skip = !first_call;

	/* Scan through possible multiple members of HOT-chain */
	for (;;)
	{
		ItemId		lp;

		/* check for bogus TID */
		if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(dp))
			break;

		lp = PageGetItemId(dp, offnum);

		/* check for unused, dead, or redirected items */
		if (!ItemIdIsNormal(lp))
		{
			/* We should only see a redirect at start of chain */
			if (ItemIdIsRedirected(lp) && at_chain_start)
			{
				/* Follow the redirect */
				offnum = ItemIdGetRedirect(lp);
				at_chain_start = false;
				continue;
			}
			/* else must be end of chain */
			break;
		}

		heapTuple->t_data = (HeapTupleHeader) PageGetItem(dp, lp);
		heapTuple->t_len = ItemIdGetLength(lp);
		heapTuple->t_tableOid = relation->rd_id;
		heapTuple->t_self = *tid;

		/*
		 * Shouldn't see a HEAP_ONLY tuple at chain start.
		 */
		if (at_chain_start && HeapTupleIsHeapOnly(heapTuple))
			break;

		/*
		 * The xmin should match the previous xmax value, else chain is
		 * broken.
		 */
		if (TransactionIdIsValid(prev_xmax) &&
			!TransactionIdEquals(prev_xmax,
								 HeapTupleHeaderGetXmin(heapTuple->t_data)))
			break;

		/*
		 * When first_call is true (and thus, skip is initially false) we'll
		 * return the first tuple we find.	But on later passes, heapTuple
		 * will initially be pointing to the tuple we returned last time.
		 * Returning it again would be incorrect (and would loop forever), so
		 * we skip it and return the next match we find.
		 */
		if (!skip)
		{
			/* If it's visible per the snapshot, we must return it */
			valid = HeapTupleSatisfiesVisibility(heapTuple, snapshot, buffer);
			CheckForSerializableConflictOut(valid, relation, heapTuple,
											buffer, snapshot);
			if (valid)
			{
				ItemPointerSetOffsetNumber(tid, offnum);
				PredicateLockTuple(relation, heapTuple, snapshot);
				if (all_dead)
					*all_dead = false;
				return true;
			}
		}
		skip = false;

		/*
		 * If we can't see it, maybe no one else can either.  At caller
		 * request, check whether all chain members are dead to all
		 * transactions.
		 */
		if (all_dead && *all_dead &&
			!HeapTupleIsSurelyDead(heapTuple->t_data, RecentGlobalXmin))
			*all_dead = false;

		/*
		 * Check to see if HOT chain continues past this tuple; if so fetch
		 * the next offnum and loop around.
		 */
		if (HeapTupleIsHotUpdated(heapTuple))
		{
			Assert(ItemPointerGetBlockNumber(&heapTuple->t_data->t_ctid) ==
				   ItemPointerGetBlockNumber(tid));
			offnum = ItemPointerGetOffsetNumber(&heapTuple->t_data->t_ctid);
			at_chain_start = false;
			prev_xmax = HeapTupleHeaderGetUpdateXid(heapTuple->t_data);
		}
		else
			break;				/* end of chain */
	}

	return false;
}

/*
 *	heap_hot_search		- search HOT chain for tuple satisfying snapshot
 *
 * This has the same API as heap_hot_search_buffer, except that the caller
 * does not provide the buffer containing the page, rather we access it
 * locally.
 */
bool
heap_hot_search(ItemPointer tid, Relation relation, Snapshot snapshot,
				bool *all_dead)
{
	bool		result;
	Buffer		buffer;
	HeapTupleData heapTuple;

	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
	LockBuffer(buffer, BUFFER_LOCK_SHARE);
	result = heap_hot_search_buffer(tid, relation, buffer, snapshot,
									&heapTuple, all_dead, true);
	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
	ReleaseBuffer(buffer);
	return result;
}

/*
 *	heap_get_latest_tid -  get the latest tid of a specified tuple
 *
 * Actually, this gets the latest version that is visible according to
 * the passed snapshot.  You can pass SnapshotDirty to get the very latest,
 * possibly uncommitted version.
 *
 * *tid is both an input and an output parameter: it is updated to
 * show the latest version of the row.	Note that it will not be changed
 * if no version of the row passes the snapshot test.
 */
void
heap_get_latest_tid(Relation relation,
					Snapshot snapshot,
					ItemPointer tid)
{
	BlockNumber blk;
	ItemPointerData ctid;
	TransactionId priorXmax;

	/* this is to avoid Assert failures on bad input */
	if (!ItemPointerIsValid(tid))
		return;

	/*
	 * Since this can be called with user-supplied TID, don't trust the input
	 * too much.  (RelationGetNumberOfBlocks is an expensive check, so we
	 * don't check t_ctid links again this way.  Note that it would not do to
	 * call it just once and save the result, either.)
	 */
	blk = ItemPointerGetBlockNumber(tid);
	if (blk >= RelationGetNumberOfBlocks(relation))
		elog(ERROR, "block number %u is out of range for relation \"%s\"",
			 blk, RelationGetRelationName(relation));

	/*
	 * Loop to chase down t_ctid links.  At top of loop, ctid is the tuple we
	 * need to examine, and *tid is the TID we will return if ctid turns out
	 * to be bogus.
	 *
	 * Note that we will loop until we reach the end of the t_ctid chain.
	 * Depending on the snapshot passed, there might be at most one visible
	 * version of the row, but we don't try to optimize for that.
	 */
	ctid = *tid;
	priorXmax = InvalidTransactionId;	/* cannot check first XMIN */
	for (;;)
	{
		Buffer		buffer;
		Page		page;
		OffsetNumber offnum;
		ItemId		lp;
		HeapTupleData tp;
		bool		valid;

		/*
		 * Read, pin, and lock the page.
		 */
		buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&ctid));
		LockBuffer(buffer, BUFFER_LOCK_SHARE);
		page = BufferGetPage(buffer);

		/*
		 * Check for bogus item number.  This is not treated as an error
		 * condition because it can happen while following a t_ctid link. We
		 * just assume that the prior tid is OK and return it unchanged.
		 */
		offnum = ItemPointerGetOffsetNumber(&ctid);
		if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(page))
		{
			UnlockReleaseBuffer(buffer);
			break;
		}
		lp = PageGetItemId(page, offnum);
		if (!ItemIdIsNormal(lp))
		{
			UnlockReleaseBuffer(buffer);
			break;
		}

		/* OK to access the tuple */
		tp.t_self = ctid;
		tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
		tp.t_len = ItemIdGetLength(lp);

		/*
		 * After following a t_ctid link, we might arrive at an unrelated
		 * tuple.  Check for XMIN match.
		 */
		if (TransactionIdIsValid(priorXmax) &&
			!TransactionIdEquals(priorXmax, HeapTupleHeaderGetXmin(tp.t_data)))
		{
			UnlockReleaseBuffer(buffer);
			break;
		}

		/*
		 * Check time qualification of tuple; if visible, set it as the new
		 * result candidate.
		 */
		valid = HeapTupleSatisfiesVisibility(&tp, snapshot, buffer);
		CheckForSerializableConflictOut(valid, relation, &tp, buffer, snapshot);
		if (valid)
			*tid = ctid;

		/*
		 * If there's a valid t_ctid link, follow it, else we're done.
		 */
		if ((tp.t_data->t_infomask & HEAP_XMAX_INVALID) ||
			HeapTupleHeaderIsOnlyLocked(tp.t_data) ||
			ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid))
		{
			UnlockReleaseBuffer(buffer);
			break;
		}

		ctid = tp.t_data->t_ctid;
		priorXmax = HeapTupleHeaderGetUpdateXid(tp.t_data);
		UnlockReleaseBuffer(buffer);
	}							/* end of loop */
}


/*
 * UpdateXmaxHintBits - update tuple hint bits after xmax transaction ends
 *
 * This is called after we have waited for the XMAX transaction to terminate.
 * If the transaction aborted, we guarantee the XMAX_INVALID hint bit will
 * be set on exit.	If the transaction committed, we set the XMAX_COMMITTED
 * hint bit if possible --- but beware that that may not yet be possible,
 * if the transaction committed asynchronously.
 *
 * Note that if the transaction was a locker only, we set HEAP_XMAX_INVALID
 * even if it commits.
 *
 * Hence callers should look only at XMAX_INVALID.
 *
 * Note this is not allowed for tuples whose xmax is a multixact.
 */
static void
UpdateXmaxHintBits(HeapTupleHeader tuple, Buffer buffer, TransactionId xid)
{
	Assert(TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple), xid));
	Assert(!(tuple->t_infomask & HEAP_XMAX_IS_MULTI));

	if (!(tuple->t_infomask & (HEAP_XMAX_COMMITTED | HEAP_XMAX_INVALID)))
	{
		if (!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask) &&
			TransactionIdDidCommit(xid))
			HeapTupleSetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
								 xid);
		else
			HeapTupleSetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
								 InvalidTransactionId);
	}
}


/*
 * GetBulkInsertState - prepare status object for a bulk insert
 */
BulkInsertState
GetBulkInsertState(void)
{
	BulkInsertState bistate;

	bistate = (BulkInsertState) palloc(sizeof(BulkInsertStateData));
	bistate->strategy = GetAccessStrategy(BAS_BULKWRITE);
	bistate->current_buf = InvalidBuffer;
	return bistate;
}

/*
 * FreeBulkInsertState - clean up after finishing a bulk insert
 */
void
FreeBulkInsertState(BulkInsertState bistate)
{
	if (bistate->current_buf != InvalidBuffer)
		ReleaseBuffer(bistate->current_buf);
	FreeAccessStrategy(bistate->strategy);
	pfree(bistate);
}


/*
 *	heap_insert		- insert tuple into a heap
 *
 * The new tuple is stamped with current transaction ID and the specified
 * command ID.
 *
 * If the HEAP_INSERT_SKIP_WAL option is specified, the new tuple is not
 * logged in WAL, even for a non-temp relation.  Safe usage of this behavior
 * requires that we arrange that all new tuples go into new pages not
 * containing any tuples from other transactions, and that the relation gets
 * fsync'd before commit.  (See also heap_sync() comments)
 *
 * The HEAP_INSERT_SKIP_FSM option is passed directly to
 * RelationGetBufferForTuple, which see for more info.
 *
 * HEAP_INSERT_FROZEN should only be specified for inserts into
 * relfilenodes created during the current subtransaction and when
 * there are no prior snapshots or pre-existing portals open.
 * This causes rows to be frozen, which is an MVCC violation and
 * requires explicit options chosen by user.
 *
 * Note that these options will be applied when inserting into the heap's
 * TOAST table, too, if the tuple requires any out-of-line data.
 *
 * The BulkInsertState object (if any; bistate can be NULL for default
 * behavior) is also just passed through to RelationGetBufferForTuple.
 *
 * The return value is the OID assigned to the tuple (either here or by the
 * caller), or InvalidOid if no OID.  The header fields of *tup are updated
 * to match the stored tuple; in particular tup->t_self receives the actual
 * TID where the tuple was stored.	But note that any toasting of fields
 * within the tuple data is NOT reflected into *tup.
 */
Oid
heap_insert(Relation relation, HeapTuple tup, CommandId cid,
			int options, BulkInsertState bistate)
{
	TransactionId xid = GetCurrentTransactionId();
	HeapTuple	heaptup;
	Buffer		buffer;
	Buffer		vmbuffer = InvalidBuffer;
	bool		all_visible_cleared = false;

	/*
	 * Fill in tuple header fields, assign an OID, and toast the tuple if
	 * necessary.
	 *
	 * Note: below this point, heaptup is the data we actually intend to store
	 * into the relation; tup is the caller's original untoasted data.
	 */
	heaptup = heap_prepare_insert(relation, tup, xid, cid, options);

	/*
	 * We're about to do the actual insert -- but check for conflict first, to
	 * avoid possibly having to roll back work we've just done.
	 *
	 * For a heap insert, we only need to check for table-level SSI locks. Our
	 * new tuple can't possibly conflict with existing tuple locks, and heap
	 * page locks are only consolidated versions of tuple locks; they do not
	 * lock "gaps" as index page locks do.	So we don't need to identify a
	 * buffer before making the call.
	 */
	CheckForSerializableConflictIn(relation, NULL, InvalidBuffer);

	/*
	 * Find buffer to insert this tuple into.  If the page is all visible,
	 * this will also pin the requisite visibility map page.
	 */
	buffer = RelationGetBufferForTuple(relation, heaptup->t_len,
									   InvalidBuffer, options, bistate,
									   &vmbuffer, NULL);

	/* NO EREPORT(ERROR) from here till changes are logged */
	START_CRIT_SECTION();

	RelationPutHeapTuple(relation, buffer, heaptup);

	if (PageIsAllVisible(BufferGetPage(buffer)))
	{
		all_visible_cleared = true;
		PageClearAllVisible(BufferGetPage(buffer));
		visibilitymap_clear(relation,
							ItemPointerGetBlockNumber(&(heaptup->t_self)),
							vmbuffer);
	}

	/*
	 * XXX Should we set PageSetPrunable on this page ?
	 *
	 * The inserting transaction may eventually abort thus making this tuple
	 * DEAD and hence available for pruning. Though we don't want to optimize
	 * for aborts, if no other tuple in this page is UPDATEd/DELETEd, the
	 * aborted tuple will never be pruned until next vacuum is triggered.
	 *
	 * If you do add PageSetPrunable here, add it in heap_xlog_insert too.
	 */

	MarkBufferDirty(buffer);

	/* XLOG stuff */
	if (!(options & HEAP_INSERT_SKIP_WAL) && RelationNeedsWAL(relation))
	{
		xl_heap_insert xlrec;
		xl_heap_header xlhdr;
		XLogRecPtr	recptr;
		XLogRecData rdata[3];
		Page		page = BufferGetPage(buffer);
		uint8		info = XLOG_HEAP_INSERT;

		xlrec.all_visible_cleared = all_visible_cleared;
		xlrec.target.node = relation->rd_node;
		xlrec.target.tid = heaptup->t_self;
		rdata[0].data = (char *) &xlrec;
		rdata[0].len = SizeOfHeapInsert;
		rdata[0].buffer = InvalidBuffer;
		rdata[0].next = &(rdata[1]);

		xlhdr.t_infomask2 = heaptup->t_data->t_infomask2;
		xlhdr.t_infomask = heaptup->t_data->t_infomask;
		xlhdr.t_hoff = heaptup->t_data->t_hoff;

		/*
		 * note we mark rdata[1] as belonging to buffer; if XLogInsert decides
		 * to write the whole page to the xlog, we don't need to store
		 * xl_heap_header in the xlog.
		 */
		rdata[1].data = (char *) &xlhdr;
		rdata[1].len = SizeOfHeapHeader;
		rdata[1].buffer = buffer;
		rdata[1].buffer_std = true;
		rdata[1].next = &(rdata[2]);

		/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
		rdata[2].data = (char *) heaptup->t_data + offsetof(HeapTupleHeaderData, t_bits);
		rdata[2].len = heaptup->t_len - offsetof(HeapTupleHeaderData, t_bits);
		rdata[2].buffer = buffer;
		rdata[2].buffer_std = true;
		rdata[2].next = NULL;

		/*
		 * If this is the single and first tuple on page, we can reinit the
		 * page instead of restoring the whole thing.  Set flag, and hide
		 * buffer references from XLogInsert.
		 */
		if (ItemPointerGetOffsetNumber(&(heaptup->t_self)) == FirstOffsetNumber &&
			PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
		{
			info |= XLOG_HEAP_INIT_PAGE;
			rdata[1].buffer = rdata[2].buffer = InvalidBuffer;
		}

		recptr = XLogInsert(RM_HEAP_ID, info, rdata);

		PageSetLSN(page, recptr);
	}

	END_CRIT_SECTION();

	UnlockReleaseBuffer(buffer);
	if (vmbuffer != InvalidBuffer)
		ReleaseBuffer(vmbuffer);

	/*
	 * If tuple is cachable, mark it for invalidation from the caches in case
	 * we abort.  Note it is OK to do this after releasing the buffer, because
	 * the heaptup data structure is all in local memory, not in the shared
	 * buffer.
	 */
	CacheInvalidateHeapTuple(relation, heaptup, NULL);

	pgstat_count_heap_insert(relation, 1);

	/*
	 * If heaptup is a private copy, release it.  Don't forget to copy t_self
	 * back to the caller's image, too.
	 */
	if (heaptup != tup)
	{
		tup->t_self = heaptup->t_self;
		heap_freetuple(heaptup);
	}

	return HeapTupleGetOid(tup);
}

/*
 * Subroutine for heap_insert(). Prepares a tuple for insertion. This sets the
 * tuple header fields, assigns an OID, and toasts the tuple if necessary.
 * Returns a toasted version of the tuple if it was toasted, or the original
 * tuple if not. Note that in any case, the header fields are also set in
 * the original tuple.
 */
static HeapTuple
heap_prepare_insert(Relation relation, HeapTuple tup, TransactionId xid,
					CommandId cid, int options)
{
	if (relation->rd_rel->relhasoids)
	{
#ifdef NOT_USED
		/* this is redundant with an Assert in HeapTupleSetOid */
		Assert(tup->t_data->t_infomask & HEAP_HASOID);
#endif

		/*
		 * If the object id of this tuple has already been assigned, trust the
		 * caller.	There are a couple of ways this can happen.  At initial db
		 * creation, the backend program sets oids for tuples. When we define
		 * an index, we set the oid.  Finally, in the future, we may allow
		 * users to set their own object ids in order to support a persistent
		 * object store (objects need to contain pointers to one another).
		 */
		if (!OidIsValid(HeapTupleGetOid(tup)))
			HeapTupleSetOid(tup, GetNewOid(relation));
	}
	else
	{
		/* check there is not space for an OID */
		Assert(!(tup->t_data->t_infomask & HEAP_HASOID));
	}

	tup->t_data->t_infomask &= ~(HEAP_XACT_MASK);
	tup->t_data->t_infomask2 &= ~(HEAP2_XACT_MASK);
	tup->t_data->t_infomask |= HEAP_XMAX_INVALID;
	if (options & HEAP_INSERT_FROZEN)
	{
		tup->t_data->t_infomask |= HEAP_XMIN_COMMITTED;
		HeapTupleHeaderSetXmin(tup->t_data, FrozenTransactionId);
	}
	else
		HeapTupleHeaderSetXmin(tup->t_data, xid);
	HeapTupleHeaderSetCmin(tup->t_data, cid);
	HeapTupleHeaderSetXmax(tup->t_data, 0);		/* for cleanliness */
	tup->t_tableOid = RelationGetRelid(relation);

	/*
	 * If the new tuple is too big for storage or contains already toasted
	 * out-of-line attributes from some other relation, invoke the toaster.
	 */
	if (relation->rd_rel->relkind != RELKIND_RELATION &&
		relation->rd_rel->relkind != RELKIND_MATVIEW)
	{
		/* toast table entries should never be recursively toasted */
		Assert(!HeapTupleHasExternal(tup));
		return tup;
	}
	else if (HeapTupleHasExternal(tup) || tup->t_len > TOAST_TUPLE_THRESHOLD)
		return toast_insert_or_update(relation, tup, NULL, options);
	else
		return tup;
}

/*
 *	heap_multi_insert	- insert multiple tuple into a heap
 *
 * This is like heap_insert(), but inserts multiple tuples in one operation.
 * That's faster than calling heap_insert() in a loop, because when multiple
 * tuples can be inserted on a single page, we can write just a single WAL
 * record covering all of them, and only need to lock/unlock the page once.
 *
 * Note: this leaks memory into the current memory context. You can create a
 * temporary context before calling this, if that's a problem.
 */
void
heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
				  CommandId cid, int options, BulkInsertState bistate)
{
	TransactionId xid = GetCurrentTransactionId();
	HeapTuple  *heaptuples;
	int			i;
	int			ndone;
	char	   *scratch = NULL;
	Page		page;
	bool		needwal;
	Size		saveFreeSpace;

	needwal = !(options & HEAP_INSERT_SKIP_WAL) && RelationNeedsWAL(relation);
	saveFreeSpace = RelationGetTargetPageFreeSpace(relation,
												   HEAP_DEFAULT_FILLFACTOR);

	/* Toast and set header data in all the tuples */
	heaptuples = palloc(ntuples * sizeof(HeapTuple));
	for (i = 0; i < ntuples; i++)
		heaptuples[i] = heap_prepare_insert(relation, tuples[i],
											xid, cid, options);

	/*
	 * Allocate some memory to use for constructing the WAL record. Using
	 * palloc() within a critical section is not safe, so we allocate this
	 * beforehand.
	 */
	if (needwal)
		scratch = palloc(BLCKSZ);

	/*
	 * We're about to do the actual inserts -- but check for conflict first,
	 * to avoid possibly having to roll back work we've just done.
	 *
	 * For a heap insert, we only need to check for table-level SSI locks. Our
	 * new tuple can't possibly conflict with existing tuple locks, and heap
	 * page locks are only consolidated versions of tuple locks; they do not
	 * lock "gaps" as index page locks do.	So we don't need to identify a
	 * buffer before making the call.
	 */
	CheckForSerializableConflictIn(relation, NULL, InvalidBuffer);

	ndone = 0;
	while (ndone < ntuples)
	{
		Buffer		buffer;
		Buffer		vmbuffer = InvalidBuffer;
		bool		all_visible_cleared = false;
		int			nthispage;

		/*
		 * Find buffer where at least the next tuple will fit.	If the page is
		 * all-visible, this will also pin the requisite visibility map page.
		 */
		buffer = RelationGetBufferForTuple(relation, heaptuples[ndone]->t_len,
										   InvalidBuffer, options, bistate,
										   &vmbuffer, NULL);
		page = BufferGetPage(buffer);

		/* NO EREPORT(ERROR) from here till changes are logged */
		START_CRIT_SECTION();

		/*
		 * RelationGetBufferForTuple has ensured that the first tuple fits.
		 * Put that on the page, and then as many other tuples as fit.
		 */
		RelationPutHeapTuple(relation, buffer, heaptuples[ndone]);
		for (nthispage = 1; ndone + nthispage < ntuples; nthispage++)
		{
			HeapTuple	heaptup = heaptuples[ndone + nthispage];

			if (PageGetHeapFreeSpace(page) < MAXALIGN(heaptup->t_len) + saveFreeSpace)
				break;

			RelationPutHeapTuple(relation, buffer, heaptup);
		}

		if (PageIsAllVisible(page))
		{
			all_visible_cleared = true;
			PageClearAllVisible(page);
			visibilitymap_clear(relation,
								BufferGetBlockNumber(buffer),
								vmbuffer);
		}

		/*
		 * XXX Should we set PageSetPrunable on this page ? See heap_insert()
		 */

		MarkBufferDirty(buffer);

		/* XLOG stuff */
		if (needwal)
		{
			XLogRecPtr	recptr;
			xl_heap_multi_insert *xlrec;
			XLogRecData rdata[2];
			uint8		info = XLOG_HEAP2_MULTI_INSERT;
			char	   *tupledata;
			int			totaldatalen;
			char	   *scratchptr = scratch;
			bool		init;

			/*
			 * If the page was previously empty, we can reinit the page
			 * instead of restoring the whole thing.
			 */
			init = (ItemPointerGetOffsetNumber(&(heaptuples[ndone]->t_self)) == FirstOffsetNumber &&
					PageGetMaxOffsetNumber(page) == FirstOffsetNumber + nthispage - 1);

			/* allocate xl_heap_multi_insert struct from the scratch area */
			xlrec = (xl_heap_multi_insert *) scratchptr;
			scratchptr += SizeOfHeapMultiInsert;

			/*
			 * Allocate offsets array. Unless we're reinitializing the page,
			 * in that case the tuples are stored in order starting at
			 * FirstOffsetNumber and we don't need to store the offsets
			 * explicitly.
			 */
			if (!init)
				scratchptr += nthispage * sizeof(OffsetNumber);

			/* the rest of the scratch space is used for tuple data */
			tupledata = scratchptr;

			xlrec->all_visible_cleared = all_visible_cleared;
			xlrec->node = relation->rd_node;
			xlrec->blkno = BufferGetBlockNumber(buffer);
			xlrec->ntuples = nthispage;

			/*
			 * Write out an xl_multi_insert_tuple and the tuple data itself
			 * for each tuple.
			 */
			for (i = 0; i < nthispage; i++)
			{
				HeapTuple	heaptup = heaptuples[ndone + i];
				xl_multi_insert_tuple *tuphdr;
				int			datalen;

				if (!init)
					xlrec->offsets[i] = ItemPointerGetOffsetNumber(&heaptup->t_self);
				/* xl_multi_insert_tuple needs two-byte alignment. */
				tuphdr = (xl_multi_insert_tuple *) SHORTALIGN(scratchptr);
				scratchptr = ((char *) tuphdr) + SizeOfMultiInsertTuple;

				tuphdr->t_infomask2 = heaptup->t_data->t_infomask2;
				tuphdr->t_infomask = heaptup->t_data->t_infomask;
				tuphdr->t_hoff = heaptup->t_data->t_hoff;

				/* write bitmap [+ padding] [+ oid] + data */
				datalen = heaptup->t_len - offsetof(HeapTupleHeaderData, t_bits);
				memcpy(scratchptr,
					   (char *) heaptup->t_data + offsetof(HeapTupleHeaderData, t_bits),
					   datalen);
				tuphdr->datalen = datalen;
				scratchptr += datalen;
			}
			totaldatalen = scratchptr - tupledata;
			Assert((scratchptr - scratch) < BLCKSZ);

			rdata[0].data = (char *) xlrec;
			rdata[0].len = tupledata - scratch;
			rdata[0].buffer = InvalidBuffer;
			rdata[0].next = &rdata[1];

			rdata[1].data = tupledata;
			rdata[1].len = totaldatalen;
			rdata[1].buffer = buffer;
			rdata[1].buffer_std = true;
			rdata[1].next = NULL;

			/*
			 * If we're going to reinitialize the whole page using the WAL
			 * record, hide buffer reference from XLogInsert.
			 */
			if (init)
			{
				rdata[1].buffer = InvalidBuffer;
				info |= XLOG_HEAP_INIT_PAGE;
			}

			recptr = XLogInsert(RM_HEAP2_ID, info, rdata);

			PageSetLSN(page, recptr);
		}

		END_CRIT_SECTION();

		UnlockReleaseBuffer(buffer);
		if (vmbuffer != InvalidBuffer)
			ReleaseBuffer(vmbuffer);

		ndone += nthispage;
	}

	/*
	 * If tuples are cachable, mark them for invalidation from the caches in
	 * case we abort.  Note it is OK to do this after releasing the buffer,
	 * because the heaptuples data structure is all in local memory, not in
	 * the shared buffer.
	 */
	if (IsSystemRelation(relation))
	{
		for (i = 0; i < ntuples; i++)
			CacheInvalidateHeapTuple(relation, heaptuples[i], NULL);
	}

	/*
	 * Copy t_self fields back to the caller's original tuples. This does
	 * nothing for untoasted tuples (tuples[i] == heaptuples[i)], but it's
	 * probably faster to always copy than check.
	 */
	for (i = 0; i < ntuples; i++)
		tuples[i]->t_self = heaptuples[i]->t_self;

	pgstat_count_heap_insert(relation, ntuples);
}

/*
 *	simple_heap_insert - insert a tuple
 *
 * Currently, this routine differs from heap_insert only in supplying
 * a default command ID and not allowing access to the speedup options.
 *
 * This should be used rather than using heap_insert directly in most places
 * where we are modifying system catalogs.
 */
Oid
simple_heap_insert(Relation relation, HeapTuple tup)
{
	return heap_insert(relation, tup, GetCurrentCommandId(true), 0, NULL);
}

/*
 * Given infomask/infomask2, compute the bits that must be saved in the
 * "infobits" field of xl_heap_delete, xl_heap_update, xl_heap_lock,
 * xl_heap_lock_updated WAL records.
 *
 * See fix_infomask_from_infobits.
 */
static uint8
compute_infobits(uint16 infomask, uint16 infomask2)
{
	return
		((infomask & HEAP_XMAX_IS_MULTI) != 0 ? XLHL_XMAX_IS_MULTI : 0) |
		((infomask & HEAP_XMAX_LOCK_ONLY) != 0 ? XLHL_XMAX_LOCK_ONLY : 0) |
		((infomask & HEAP_XMAX_EXCL_LOCK) != 0 ? XLHL_XMAX_EXCL_LOCK : 0) |
		/* note we ignore HEAP_XMAX_SHR_LOCK here */
		((infomask & HEAP_XMAX_KEYSHR_LOCK) != 0 ? XLHL_XMAX_KEYSHR_LOCK : 0) |
		((infomask2 & HEAP_KEYS_UPDATED) != 0 ?
		 XLHL_KEYS_UPDATED : 0);
}

/*
 *	heap_delete - delete a tuple
 *
 * NB: do not call this directly unless you are prepared to deal with
 * concurrent-update conditions.  Use simple_heap_delete instead.
 *
 *	relation - table to be modified (caller must hold suitable lock)
 *	tid - TID of tuple to be deleted
 *	cid - delete command ID (used for visibility test, and stored into
 *		cmax if successful)
 *	crosscheck - if not InvalidSnapshot, also check tuple against this
 *	wait - true if should wait for any conflicting update to commit/abort
 *	hufd - output parameter, filled in failure cases (see below)
 *
 * Normal, successful return value is HeapTupleMayBeUpdated, which
 * actually means we did delete it.  Failure return codes are
 * HeapTupleSelfUpdated, HeapTupleUpdated, or HeapTupleBeingUpdated
 * (the last only possible if wait == false).
 *
 * In the failure cases, the routine fills *hufd with the tuple's t_ctid,
 * t_xmax (resolving a possible MultiXact, if necessary), and t_cmax
 * (the last only for HeapTupleSelfUpdated, since we
 * cannot obtain cmax from a combocid generated by another transaction).
 * See comments for struct HeapUpdateFailureData for additional info.
 */
HTSU_Result
heap_delete(Relation relation, ItemPointer tid,
			CommandId cid, Snapshot crosscheck, bool wait,
			HeapUpdateFailureData *hufd)
{
	HTSU_Result result;
	TransactionId xid = GetCurrentTransactionId();
	ItemId		lp;
	HeapTupleData tp;
	Page		page;
	BlockNumber block;
	Buffer		buffer;
	Buffer		vmbuffer = InvalidBuffer;
	TransactionId new_xmax;
	uint16		new_infomask,
				new_infomask2;
	bool		have_tuple_lock = false;
	bool		iscombo;
	bool		all_visible_cleared = false;

	Assert(ItemPointerIsValid(tid));

	block = ItemPointerGetBlockNumber(tid);
	buffer = ReadBuffer(relation, block);
	page = BufferGetPage(buffer);

	/*
	 * Before locking the buffer, pin the visibility map page if it appears to
	 * be necessary.  Since we haven't got the lock yet, someone else might be
	 * in the middle of changing this, so we'll need to recheck after we have
	 * the lock.
	 */
	if (PageIsAllVisible(page))
		visibilitymap_pin(relation, block, &vmbuffer);

	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

	/*
	 * If we didn't pin the visibility map page and the page has become all
	 * visible while we were busy locking the buffer, we'll have to unlock and
	 * re-lock, to avoid holding the buffer lock across an I/O.  That's a bit
	 * unfortunate, but hopefully shouldn't happen often.
	 */
	if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
	{
		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
		visibilitymap_pin(relation, block, &vmbuffer);
		LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
	}

	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
	Assert(ItemIdIsNormal(lp));

	tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
	tp.t_len = ItemIdGetLength(lp);
	tp.t_self = *tid;

l1:
	result = HeapTupleSatisfiesUpdate(tp.t_data, cid, buffer);

	if (result == HeapTupleInvisible)
	{
		UnlockReleaseBuffer(buffer);
		elog(ERROR, "attempted to delete invisible tuple");
	}
	else if (result == HeapTupleBeingUpdated && wait)
	{
		TransactionId xwait;
		uint16		infomask;

		/* must copy state data before unlocking buffer */
		xwait = HeapTupleHeaderGetRawXmax(tp.t_data);
		infomask = tp.t_data->t_infomask;

		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

		/*
		 * Acquire tuple lock to establish our priority for the tuple (see
		 * heap_lock_tuple).  LockTuple will release us when we are
		 * next-in-line for the tuple.
		 *
		 * If we are forced to "start over" below, we keep the tuple lock;
		 * this arranges that we stay at the head of the line while rechecking
		 * tuple state.
		 */
		if (!have_tuple_lock)
		{
			LockTupleTuplock(relation, &(tp.t_self), LockTupleExclusive);
			have_tuple_lock = true;
		}

		/*
		 * Sleep until concurrent transaction ends.  Note that we don't care
		 * which lock mode the locker has, because we need the strongest one.
		 */

		if (infomask & HEAP_XMAX_IS_MULTI)
		{
			/* wait for multixact */
			MultiXactIdWait((MultiXactId) xwait, MultiXactStatusUpdate,
							NULL, infomask);
			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

			/*
			 * If xwait had just locked the tuple then some other xact could
			 * update this tuple before we get to this point.  Check for xmax
			 * change, and start over if so.
			 */
			if (!(tp.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
				!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tp.t_data),
									 xwait))
				goto l1;

			/*
			 * You might think the multixact is necessarily done here, but not
			 * so: it could have surviving members, namely our own xact or
			 * other subxacts of this backend.	It is legal for us to delete
			 * the tuple in either case, however (the latter case is
			 * essentially a situation of upgrading our former shared lock to
			 * exclusive).	We don't bother changing the on-disk hint bits
			 * since we are about to overwrite the xmax altogether.
			 */
		}
		else
		{
			/* wait for regular transaction to end */
			XactLockTableWait(xwait);
			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

			/*
			 * xwait is done, but if xwait had just locked the tuple then some
			 * other xact could update this tuple before we get to this point.
			 * Check for xmax change, and start over if so.
			 */
			if ((tp.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
				!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tp.t_data),
									 xwait))
				goto l1;

			/* Otherwise check if it committed or aborted */
			UpdateXmaxHintBits(tp.t_data, buffer, xwait);
		}

		/*
		 * We may overwrite if previous xmax aborted, or if it committed but
		 * only locked the tuple without updating it.
		 */
		if ((tp.t_data->t_infomask & HEAP_XMAX_INVALID) ||
			HEAP_XMAX_IS_LOCKED_ONLY(tp.t_data->t_infomask) ||
			HeapTupleHeaderIsOnlyLocked(tp.t_data))
			result = HeapTupleMayBeUpdated;
		else
			result = HeapTupleUpdated;
	}

	if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
	{
		/* Perform additional check for transaction-snapshot mode RI updates */
		if (!HeapTupleSatisfiesVisibility(&tp, crosscheck, buffer))
			result = HeapTupleUpdated;
	}

	if (result != HeapTupleMayBeUpdated)
	{
		Assert(result == HeapTupleSelfUpdated ||
			   result == HeapTupleUpdated ||
			   result == HeapTupleBeingUpdated);
		Assert(!(tp.t_data->t_infomask & HEAP_XMAX_INVALID));
		hufd->ctid = tp.t_data->t_ctid;
		hufd->xmax = HeapTupleHeaderGetUpdateXid(tp.t_data);
		if (result == HeapTupleSelfUpdated)
			hufd->cmax = HeapTupleHeaderGetCmax(tp.t_data);
		else
			hufd->cmax = 0;		/* for lack of an InvalidCommandId value */
		UnlockReleaseBuffer(buffer);
		if (have_tuple_lock)
			UnlockTupleTuplock(relation, &(tp.t_self), LockTupleExclusive);
		if (vmbuffer != InvalidBuffer)
			ReleaseBuffer(vmbuffer);
		return result;
	}

	/*
	 * We're about to do the actual delete -- check for conflict first, to
	 * avoid possibly having to roll back work we've just done.
	 */
	CheckForSerializableConflictIn(relation, &tp, buffer);

	/* replace cid with a combo cid if necessary */
	HeapTupleHeaderAdjustCmax(tp.t_data, &cid, &iscombo);

	START_CRIT_SECTION();

	/*
	 * If this transaction commits, the tuple will become DEAD sooner or
	 * later.  Set flag that this page is a candidate for pruning once our xid
	 * falls below the OldestXmin horizon.	If the transaction finally aborts,
	 * the subsequent page pruning will be a no-op and the hint will be
	 * cleared.
	 */
	PageSetPrunable(page, xid);

	if (PageIsAllVisible(page))
	{
		all_visible_cleared = true;
		PageClearAllVisible(page);
		visibilitymap_clear(relation, BufferGetBlockNumber(buffer),
							vmbuffer);
	}

	/*
	 * If this is the first possibly-multixact-able operation in the
	 * current transaction, set my per-backend OldestMemberMXactId setting.
	 * We can be certain that the transaction will never become a member of
	 * any older MultiXactIds than that.  (We have to do this even if we
	 * end up just using our own TransactionId below, since some other
	 * backend could incorporate our XID into a MultiXact immediately
	 * afterwards.)
	 */
	MultiXactIdSetOldestMember();

	compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(tp.t_data),
							  tp.t_data->t_infomask, tp.t_data->t_infomask2,
							  xid, LockTupleExclusive, true,
							  &new_xmax, &new_infomask, &new_infomask2);

	/* store transaction information of xact deleting the tuple */
	tp.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
	tp.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
	tp.t_data->t_infomask |= new_infomask;
	tp.t_data->t_infomask2 |= new_infomask2;
	HeapTupleHeaderClearHotUpdated(tp.t_data);
	HeapTupleHeaderSetXmax(tp.t_data, new_xmax);
	HeapTupleHeaderSetCmax(tp.t_data, cid, iscombo);
	/* Make sure there is no forward chain link in t_ctid */
	tp.t_data->t_ctid = tp.t_self;

	MarkBufferDirty(buffer);

	/* XLOG stuff */
	if (RelationNeedsWAL(relation))
	{
		xl_heap_delete xlrec;
		XLogRecPtr	recptr;
		XLogRecData rdata[2];

		xlrec.all_visible_cleared = all_visible_cleared;
		xlrec.infobits_set = compute_infobits(tp.t_data->t_infomask,
											  tp.t_data->t_infomask2);
		xlrec.target.node = relation->rd_node;
		xlrec.target.tid = tp.t_self;
		xlrec.xmax = new_xmax;
		rdata[0].data = (char *) &xlrec;
		rdata[0].len = SizeOfHeapDelete;
		rdata[0].buffer = InvalidBuffer;
		rdata[0].next = &(rdata[1]);

		rdata[1].data = NULL;
		rdata[1].len = 0;
		rdata[1].buffer = buffer;
		rdata[1].buffer_std = true;
		rdata[1].next = NULL;

		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_DELETE, rdata);

		PageSetLSN(page, recptr);
	}

	END_CRIT_SECTION();

	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

	if (vmbuffer != InvalidBuffer)
		ReleaseBuffer(vmbuffer);

	/*
	 * If the tuple has toasted out-of-line attributes, we need to delete
	 * those items too.  We have to do this before releasing the buffer
	 * because we need to look at the contents of the tuple, but it's OK to
	 * release the content lock on the buffer first.
	 */
	if (relation->rd_rel->relkind != RELKIND_RELATION &&
		relation->rd_rel->relkind != RELKIND_MATVIEW)
	{
		/* toast table entries should never be recursively toasted */
		Assert(!HeapTupleHasExternal(&tp));
	}
	else if (HeapTupleHasExternal(&tp))
		toast_delete(relation, &tp);

	/*
	 * Mark tuple for invalidation from system caches at next command
	 * boundary. We have to do this before releasing the buffer because we
	 * need to look at the contents of the tuple.
	 */
	CacheInvalidateHeapTuple(relation, &tp, NULL);

	/* Now we can release the buffer */
	ReleaseBuffer(buffer);

	/*
	 * Release the lmgr tuple lock, if we had it.
	 */
	if (have_tuple_lock)
		UnlockTupleTuplock(relation, &(tp.t_self), LockTupleExclusive);

	pgstat_count_heap_delete(relation);

	return HeapTupleMayBeUpdated;
}

/*
 *	simple_heap_delete - delete a tuple
 *
 * This routine may be used to delete a tuple when concurrent updates of
 * the target tuple are not expected (for example, because we have a lock
 * on the relation associated with the tuple).	Any failure is reported
 * via ereport().
 */
void
simple_heap_delete(Relation relation, ItemPointer tid)
{
	HTSU_Result result;
	HeapUpdateFailureData hufd;

	result = heap_delete(relation, tid,
						 GetCurrentCommandId(true), InvalidSnapshot,
						 true /* wait for commit */,
						 &hufd);
	switch (result)
	{
		case HeapTupleSelfUpdated:
			/* Tuple was already updated in current command? */
			elog(ERROR, "tuple already updated by self");
			break;

		case HeapTupleMayBeUpdated:
			/* done successfully */
			break;

		case HeapTupleUpdated:
			elog(ERROR, "tuple concurrently updated");
			break;

		default:
			elog(ERROR, "unrecognized heap_delete status: %u", result);
			break;
	}
}

/*
 *	heap_update - replace a tuple
 *
 * NB: do not call this directly unless you are prepared to deal with
 * concurrent-update conditions.  Use simple_heap_update instead.
 *
 *	relation - table to be modified (caller must hold suitable lock)
 *	otid - TID of old tuple to be replaced
 *	newtup - newly constructed tuple data to store
 *	cid - update command ID (used for visibility test, and stored into
 *		cmax/cmin if successful)
 *	crosscheck - if not InvalidSnapshot, also check old tuple against this
 *	wait - true if should wait for any conflicting update to commit/abort
 *	hufd - output parameter, filled in failure cases (see below)
 *	lockmode - output parameter, filled with lock mode acquired on tuple
 *
 * Normal, successful return value is HeapTupleMayBeUpdated, which
 * actually means we *did* update it.  Failure return codes are
 * HeapTupleSelfUpdated, HeapTupleUpdated, or HeapTupleBeingUpdated
 * (the last only possible if wait == false).
 *
 * On success, the header fields of *newtup are updated to match the new
 * stored tuple; in particular, newtup->t_self is set to the TID where the
 * new tuple was inserted, and its HEAP_ONLY_TUPLE flag is set iff a HOT
 * update was done.  However, any TOAST changes in the new tuple's
 * data are not reflected into *newtup.
 *
 * In the failure cases, the routine fills *hufd with the tuple's t_ctid,
 * t_xmax (resolving a possible MultiXact, if necessary), and t_cmax
 * (the last only for HeapTupleSelfUpdated, since we
 * cannot obtain cmax from a combocid generated by another transaction).
 * See comments for struct HeapUpdateFailureData for additional info.
 */
HTSU_Result
heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
			CommandId cid, Snapshot crosscheck, bool wait,
			HeapUpdateFailureData *hufd, LockTupleMode *lockmode)
{
	HTSU_Result result;
	TransactionId xid = GetCurrentTransactionId();
	Bitmapset  *hot_attrs;
	Bitmapset  *key_attrs;
	ItemId		lp;
	HeapTupleData oldtup;
	HeapTuple	heaptup;
	Page		page;
	BlockNumber block;
	MultiXactStatus mxact_status;
	Buffer		buffer,
				newbuf,
				vmbuffer = InvalidBuffer,
				vmbuffer_new = InvalidBuffer;
	bool		need_toast,
				already_marked;
	Size		newtupsize,
				pagefree;
	bool		have_tuple_lock = false;
	bool		iscombo;
	bool		satisfies_hot;
	bool		satisfies_key;
	bool		use_hot_update = false;
	bool		key_intact;
	bool		all_visible_cleared = false;
	bool		all_visible_cleared_new = false;
	bool		checked_lockers;
	bool		locker_remains;
	TransactionId xmax_new_tuple,
				  xmax_old_tuple;
	uint16		infomask_old_tuple,
				infomask2_old_tuple,
				infomask_new_tuple,
				infomask2_new_tuple;

	Assert(ItemPointerIsValid(otid));

	/*
	 * Fetch the list of attributes to be checked for HOT update.  This is
	 * wasted effort if we fail to update or have to put the new tuple on a
	 * different page.	But we must compute the list before obtaining buffer
	 * lock --- in the worst case, if we are doing an update on one of the
	 * relevant system catalogs, we could deadlock if we try to fetch the list
	 * later.  In any case, the relcache caches the data so this is usually
	 * pretty cheap.
	 *
	 * Note that we get a copy here, so we need not worry about relcache flush
	 * happening midway through.
	 */
	hot_attrs = RelationGetIndexAttrBitmap(relation, false);
	key_attrs = RelationGetIndexAttrBitmap(relation, true);

	block = ItemPointerGetBlockNumber(otid);
	buffer = ReadBuffer(relation, block);
	page = BufferGetPage(buffer);

	/*
	 * Before locking the buffer, pin the visibility map page if it appears to
	 * be necessary.  Since we haven't got the lock yet, someone else might be
	 * in the middle of changing this, so we'll need to recheck after we have
	 * the lock.
	 */
	if (PageIsAllVisible(page))
		visibilitymap_pin(relation, block, &vmbuffer);

	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(otid));
	Assert(ItemIdIsNormal(lp));

	/*
	 * Fill in enough data in oldtup for HeapSatisfiesHOTandKeyUpdate to work
	 * properly.
	 */
	oldtup.t_tableOid = RelationGetRelid(relation);
	oldtup.t_data = (HeapTupleHeader) PageGetItem(page, lp);
	oldtup.t_len = ItemIdGetLength(lp);
	oldtup.t_self = *otid;

	/* the new tuple is ready, except for this: */
	newtup->t_tableOid = RelationGetRelid(relation);

	/* Fill in OID for newtup */
	if (relation->rd_rel->relhasoids)
	{
#ifdef NOT_USED
		/* this is redundant with an Assert in HeapTupleSetOid */
		Assert(newtup->t_data->t_infomask & HEAP_HASOID);
#endif
		HeapTupleSetOid(newtup, HeapTupleGetOid(&oldtup));
	}
	else
	{
		/* check there is not space for an OID */
		Assert(!(newtup->t_data->t_infomask & HEAP_HASOID));
	}

	/*
	 * If we're not updating any "key" column, we can grab a weaker lock type.
	 * This allows for more concurrency when we are running simultaneously with
	 * foreign key checks.
	 *
	 * Note that if a column gets detoasted while executing the update, but the
	 * value ends up being the same, this test will fail and we will use the
	 * stronger lock.  This is acceptable; the important case to optimize is
	 * updates that don't manipulate key columns, not those that
	 * serendipitiously arrive at the same key values.
	 */
	HeapSatisfiesHOTandKeyUpdate(relation, hot_attrs, key_attrs,
								 &satisfies_hot, &satisfies_key,
								 &oldtup, newtup);
	if (satisfies_key)
	{
		*lockmode = LockTupleNoKeyExclusive;
		mxact_status = MultiXactStatusNoKeyUpdate;
		key_intact = true;

		/*
		 * If this is the first possibly-multixact-able operation in the
		 * current transaction, set my per-backend OldestMemberMXactId setting.
		 * We can be certain that the transaction will never become a member of
		 * any older MultiXactIds than that.  (We have to do this even if we
		 * end up just using our own TransactionId below, since some other
		 * backend could incorporate our XID into a MultiXact immediately
		 * afterwards.)
		 */
		MultiXactIdSetOldestMember();
	}
	else
	{
		*lockmode = LockTupleExclusive;
		mxact_status = MultiXactStatusUpdate;
		key_intact = false;
	}

	/*
	 * Note: beyond this point, use oldtup not otid to refer to old tuple.
	 * otid may very well point at newtup->t_self, which we will overwrite
	 * with the new tuple's location, so there's great risk of confusion if we
	 * use otid anymore.
	 */

l2:
	checked_lockers = false;
	locker_remains = false;
	result = HeapTupleSatisfiesUpdate(oldtup.t_data, cid, buffer);

	/* see below about the "no wait" case */
	Assert(result != HeapTupleBeingUpdated || wait);

	if (result == HeapTupleInvisible)
	{
		UnlockReleaseBuffer(buffer);
		elog(ERROR, "attempted to update invisible tuple");
	}
	else if (result == HeapTupleBeingUpdated && wait)
	{
		TransactionId	xwait;
		uint16		infomask;
		bool		can_continue = false;

		checked_lockers = true;

		/*
		 * XXX note that we don't consider the "no wait" case here.  This
		 * isn't a problem currently because no caller uses that case, but it
		 * should be fixed if such a caller is introduced.  It wasn't a problem
		 * previously because this code would always wait, but now that some
		 * tuple locks do not conflict with one of the lock modes we use, it is
		 * possible that this case is interesting to handle specially.
		 *
		 * This may cause failures with third-party code that calls heap_update
		 * directly.
		 */

		/* must copy state data before unlocking buffer */
		xwait = HeapTupleHeaderGetRawXmax(oldtup.t_data);
		infomask = oldtup.t_data->t_infomask;

		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

		/*
		 * Acquire tuple lock to establish our priority for the tuple (see
		 * heap_lock_tuple).  LockTuple will release us when we are
		 * next-in-line for the tuple.
		 *
		 * If we are forced to "start over" below, we keep the tuple lock;
		 * this arranges that we stay at the head of the line while rechecking
		 * tuple state.
		 */
		if (!have_tuple_lock)
		{
			LockTupleTuplock(relation, &(oldtup.t_self), *lockmode);
			have_tuple_lock = true;
		}

		/*
		 * Now we have to do something about the existing locker.  If it's a
		 * multi, sleep on it; we might be awakened before it is completely
		 * gone (or even not sleep at all in some cases); we need to preserve
		 * it as locker, unless it is gone completely.
		 *
		 * If it's not a multi, we need to check for sleeping conditions before
		 * actually going to sleep.  If the update doesn't conflict with the
		 * locks, we just continue without sleeping (but making sure it is
		 * preserved).
		 */
		if (infomask & HEAP_XMAX_IS_MULTI)
		{
			TransactionId	update_xact;
			int				remain;

			/* wait for multixact */
			MultiXactIdWait((MultiXactId) xwait, mxact_status, &remain,
							infomask);
			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

			/*
			 * If xwait had just locked the tuple then some other xact could
			 * update this tuple before we get to this point.  Check for xmax
			 * change, and start over if so.
			 */
			if (!(oldtup.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
				!TransactionIdEquals(HeapTupleHeaderGetRawXmax(oldtup.t_data),
									 xwait))
				goto l2;

			/*
			 * Note that the multixact may not be done by now.  It could have
			 * surviving members; our own xact or other subxacts of this
			 * backend, and also any other concurrent transaction that locked
			 * the tuple with KeyShare if we only got TupleLockUpdate.  If this
			 * is the case, we have to be careful to mark the updated tuple
			 * with the surviving members in Xmax.
			 *
			 * Note that there could have been another update in the MultiXact.
			 * In that case, we need to check whether it committed or aborted.
			 * If it aborted we are safe to update it again; otherwise there is
			 * an update conflict, and we have to return HeapTupleUpdated
			 * below.
			 *
			 * In the LockTupleExclusive case, we still need to preserve the
			 * surviving members: those would include the tuple locks we had
			 * before this one, which are important to keep in case this
			 * subxact aborts.
			 */
			update_xact = InvalidTransactionId;
			if (!HEAP_XMAX_IS_LOCKED_ONLY(oldtup.t_data->t_infomask))
				update_xact = HeapTupleGetUpdateXid(oldtup.t_data);

			/* there was no UPDATE in the MultiXact; or it aborted. */
			if (!TransactionIdIsValid(update_xact) ||
				TransactionIdDidAbort(update_xact))
				can_continue = true;

			locker_remains = remain != 0;
		}
		else
		{
			/*
			 * If it's just a key-share locker, and we're not changing the
			 * key columns, we don't need to wait for it to end; but we
			 * need to preserve it as locker.
			 */
			if (HEAP_XMAX_IS_KEYSHR_LOCKED(infomask) && key_intact)
			{
				LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

				/*
				 * recheck the locker; if someone else changed the tuple while we
				 * weren't looking, start over.
				 */
				if ((oldtup.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
					!TransactionIdEquals(HeapTupleHeaderGetRawXmax(oldtup.t_data),
										 xwait))
					goto l2;

				can_continue = true;
				locker_remains = true;
			}
			else
			{
				/* wait for regular transaction to end */
				XactLockTableWait(xwait);
				LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

				/*
				 * xwait is done, but if xwait had just locked the tuple then some
				 * other xact could update this tuple before we get to this point.
				 * Check for xmax change, and start over if so.
				 */
				if ((oldtup.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
					!TransactionIdEquals(HeapTupleHeaderGetRawXmax(oldtup.t_data),
										 xwait))
					goto l2;

				/* Otherwise check if it committed or aborted */
				UpdateXmaxHintBits(oldtup.t_data, buffer, xwait);
				if (oldtup.t_data->t_infomask & HEAP_XMAX_INVALID)
					can_continue = true;
			}
		}

		result = can_continue ? HeapTupleMayBeUpdated : HeapTupleUpdated;
	}

	if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
	{
		/* Perform additional check for transaction-snapshot mode RI updates */
		if (!HeapTupleSatisfiesVisibility(&oldtup, crosscheck, buffer))
			result = HeapTupleUpdated;
	}

	if (result != HeapTupleMayBeUpdated)
	{
		Assert(result == HeapTupleSelfUpdated ||
			   result == HeapTupleUpdated ||
			   result == HeapTupleBeingUpdated);
		Assert(!(oldtup.t_data->t_infomask & HEAP_XMAX_INVALID));
		hufd->ctid = oldtup.t_data->t_ctid;
		hufd->xmax = HeapTupleHeaderGetUpdateXid(oldtup.t_data);
		if (result == HeapTupleSelfUpdated)
			hufd->cmax = HeapTupleHeaderGetCmax(oldtup.t_data);
		else
			hufd->cmax = 0;		/* for lack of an InvalidCommandId value */
		UnlockReleaseBuffer(buffer);
		if (have_tuple_lock)
			UnlockTupleTuplock(relation, &(oldtup.t_self), *lockmode);
		if (vmbuffer != InvalidBuffer)
			ReleaseBuffer(vmbuffer);
		bms_free(hot_attrs);
		bms_free(key_attrs);
		return result;
	}

	/*
	 * If we didn't pin the visibility map page and the page has become all
	 * visible while we were busy locking the buffer, or during some
	 * subsequent window during which we had it unlocked, we'll have to unlock
	 * and re-lock, to avoid holding the buffer lock across an I/O.  That's a
	 * bit unfortunate, especially since we'll now have to recheck whether
	 * the tuple has been locked or updated under us, but hopefully it won't
	 * happen very often.
	 */
	if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
	{
		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
		visibilitymap_pin(relation, block, &vmbuffer);
		LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
		goto l2;
	}

	/*
	 * We're about to do the actual update -- check for conflict first, to
	 * avoid possibly having to roll back work we've just done.
	 */
	CheckForSerializableConflictIn(relation, &oldtup, buffer);

	/* Fill in transaction status data */

	/*
	 * If the tuple we're updating is locked, we need to preserve the locking
	 * info in the old tuple's Xmax.  Prepare a new Xmax value for this.
	 */
	compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(oldtup.t_data),
							  oldtup.t_data->t_infomask,
							  oldtup.t_data->t_infomask2,
							  xid, *lockmode, true,
							  &xmax_old_tuple, &infomask_old_tuple,
							  &infomask2_old_tuple);

	/*
	 * And also prepare an Xmax value for the new copy of the tuple.  If there
	 * was no xmax previously, or there was one but all lockers are now gone,
	 * then use InvalidXid; otherwise, get the xmax from the old tuple.  (In
	 * rare cases that might also be InvalidXid and yet not have the
	 * HEAP_XMAX_INVALID bit set; that's fine.)
	 */
	if ((oldtup.t_data->t_infomask & HEAP_XMAX_INVALID) ||
		(checked_lockers && !locker_remains))
		xmax_new_tuple = InvalidTransactionId;
	else
		xmax_new_tuple = HeapTupleHeaderGetRawXmax(oldtup.t_data);

	if (!TransactionIdIsValid(xmax_new_tuple))
	{
		infomask_new_tuple = HEAP_XMAX_INVALID;
		infomask2_new_tuple = 0;
	}
	else
	{
		/*
		 * If we found a valid Xmax for the new tuple, then the infomask bits
		 * to use on the new tuple depend on what was there on the old one.
		 * Note that since we're doing an update, the only possibility is that
		 * the lockers had FOR KEY SHARE lock.
		 */
		if (oldtup.t_data->t_infomask & HEAP_XMAX_IS_MULTI)
		{
			GetMultiXactIdHintBits(xmax_new_tuple, &infomask_new_tuple,
								   &infomask2_new_tuple);
		}
		else
		{
			infomask_new_tuple = HEAP_XMAX_KEYSHR_LOCK | HEAP_XMAX_LOCK_ONLY;
			infomask2_new_tuple = 0;
		}
	}

	/*
	 * Prepare the new tuple with the appropriate initial values of Xmin and
	 * Xmax, as well as initial infomask bits as computed above.
	 */
	newtup->t_data->t_infomask &= ~(HEAP_XACT_MASK);
	newtup->t_data->t_infomask2 &= ~(HEAP2_XACT_MASK);
	HeapTupleHeaderSetXmin(newtup->t_data, xid);
	HeapTupleHeaderSetCmin(newtup->t_data, cid);
	newtup->t_data->t_infomask |= HEAP_UPDATED | infomask_new_tuple;
	newtup->t_data->t_infomask2 |= infomask2_new_tuple;
	HeapTupleHeaderSetXmax(newtup->t_data, xmax_new_tuple);

	/*
	 * Replace cid with a combo cid if necessary.  Note that we already put
	 * the plain cid into the new tuple.
	 */
	HeapTupleHeaderAdjustCmax(oldtup.t_data, &cid, &iscombo);

	/*
	 * If the toaster needs to be activated, OR if the new tuple will not fit
	 * on the same page as the old, then we need to release the content lock
	 * (but not the pin!) on the old tuple's buffer while we are off doing
	 * TOAST and/or table-file-extension work.	We must mark the old tuple to
	 * show that it's already being updated, else other processes may try to
	 * update it themselves.
	 *
	 * We need to invoke the toaster if there are already any out-of-line
	 * toasted values present, or if the new tuple is over-threshold.
	 */
	if (relation->rd_rel->relkind != RELKIND_RELATION &&
		relation->rd_rel->relkind != RELKIND_MATVIEW)
	{
		/* toast table entries should never be recursively toasted */
		Assert(!HeapTupleHasExternal(&oldtup));
		Assert(!HeapTupleHasExternal(newtup));
		need_toast = false;
	}
	else
		need_toast = (HeapTupleHasExternal(&oldtup) ||
					  HeapTupleHasExternal(newtup) ||
					  newtup->t_len > TOAST_TUPLE_THRESHOLD);

	pagefree = PageGetHeapFreeSpace(page);

	newtupsize = MAXALIGN(newtup->t_len);

	if (need_toast || newtupsize > pagefree)
	{
		/* Clear obsolete visibility flags ... */
		oldtup.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
		oldtup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
		HeapTupleClearHotUpdated(&oldtup);
		/* ... and store info about transaction updating this tuple */
		Assert(TransactionIdIsValid(xmax_old_tuple));
		HeapTupleHeaderSetXmax(oldtup.t_data, xmax_old_tuple);
		oldtup.t_data->t_infomask |= infomask_old_tuple;
		oldtup.t_data->t_infomask2 |= infomask2_old_tuple;
		HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
		/* temporarily make it look not-updated */
		oldtup.t_data->t_ctid = oldtup.t_self;
		already_marked = true;
		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

		/*
		 * Let the toaster do its thing, if needed.
		 *
		 * Note: below this point, heaptup is the data we actually intend to
		 * store into the relation; newtup is the caller's original untoasted
		 * data.
		 */
		if (need_toast)
		{
			/* Note we always use WAL and FSM during updates */
			heaptup = toast_insert_or_update(relation, newtup, &oldtup, 0);
			newtupsize = MAXALIGN(heaptup->t_len);
		}
		else
			heaptup = newtup;

		/*
		 * Now, do we need a new page for the tuple, or not?  This is a bit
		 * tricky since someone else could have added tuples to the page while
		 * we weren't looking.  We have to recheck the available space after
		 * reacquiring the buffer lock.  But don't bother to do that if the
		 * former amount of free space is still not enough; it's unlikely
		 * there's more free now than before.
		 *
		 * What's more, if we need to get a new page, we will need to acquire
		 * buffer locks on both old and new pages.	To avoid deadlock against
		 * some other backend trying to get the same two locks in the other
		 * order, we must be consistent about the order we get the locks in.
		 * We use the rule "lock the lower-numbered page of the relation
		 * first".  To implement this, we must do RelationGetBufferForTuple
		 * while not holding the lock on the old page, and we must rely on it
		 * to get the locks on both pages in the correct order.
		 */
		if (newtupsize > pagefree)
		{
			/* Assume there's no chance to put heaptup on same page. */
			newbuf = RelationGetBufferForTuple(relation, heaptup->t_len,
											   buffer, 0, NULL,
											   &vmbuffer_new, &vmbuffer);
		}
		else
		{
			/* Re-acquire the lock on the old tuple's page. */
			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
			/* Re-check using the up-to-date free space */
			pagefree = PageGetHeapFreeSpace(page);
			if (newtupsize > pagefree)
			{
				/*
				 * Rats, it doesn't fit anymore.  We must now unlock and
				 * relock to avoid deadlock.  Fortunately, this path should
				 * seldom be taken.
				 */
				LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
				newbuf = RelationGetBufferForTuple(relation, heaptup->t_len,
												   buffer, 0, NULL,
												   &vmbuffer_new, &vmbuffer);
			}
			else
			{
				/* OK, it fits here, so we're done. */
				newbuf = buffer;
			}
		}
	}
	else
	{
		/* No TOAST work needed, and it'll fit on same page */
		already_marked = false;
		newbuf = buffer;
		heaptup = newtup;
	}

	/*
	 * We're about to create the new tuple -- check for conflict first, to
	 * avoid possibly having to roll back work we've just done.
	 *
	 * NOTE: For a tuple insert, we only need to check for table locks, since
	 * predicate locking at the index level will cover ranges for anything
	 * except a table scan.  Therefore, only provide the relation.
	 */
	CheckForSerializableConflictIn(relation, NULL, InvalidBuffer);

	/*
	 * At this point newbuf and buffer are both pinned and locked, and newbuf
	 * has enough space for the new tuple.	If they are the same buffer, only
	 * one pin is held.
	 */

	if (newbuf == buffer)
	{
		/*
		 * Since the new tuple is going into the same page, we might be able
		 * to do a HOT update.	Check if any of the index columns have been
		 * changed.  If not, then HOT update is possible.
		 */
		if (satisfies_hot)
			use_hot_update = true;
	}
	else
	{
		/* Set a hint that the old page could use prune/defrag */
		PageSetFull(page);
	}

	/* NO EREPORT(ERROR) from here till changes are logged */
	START_CRIT_SECTION();

	/*
	 * If this transaction commits, the old tuple will become DEAD sooner or
	 * later.  Set flag that this page is a candidate for pruning once our xid
	 * falls below the OldestXmin horizon.	If the transaction finally aborts,
	 * the subsequent page pruning will be a no-op and the hint will be
	 * cleared.
	 *
	 * XXX Should we set hint on newbuf as well?  If the transaction aborts,
	 * there would be a prunable tuple in the newbuf; but for now we choose
	 * not to optimize for aborts.	Note that heap_xlog_update must be kept in
	 * sync if this decision changes.
	 */
	PageSetPrunable(page, xid);

	if (use_hot_update)
	{
		/* Mark the old tuple as HOT-updated */
		HeapTupleSetHotUpdated(&oldtup);
		/* And mark the new tuple as heap-only */
		HeapTupleSetHeapOnly(heaptup);
		/* Mark the caller's copy too, in case different from heaptup */
		HeapTupleSetHeapOnly(newtup);
	}
	else
	{
		/* Make sure tuples are correctly marked as not-HOT */
		HeapTupleClearHotUpdated(&oldtup);
		HeapTupleClearHeapOnly(heaptup);
		HeapTupleClearHeapOnly(newtup);
	}

	RelationPutHeapTuple(relation, newbuf, heaptup);	/* insert new tuple */

	if (!already_marked)
	{
		/* Clear obsolete visibility flags ... */
		oldtup.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
		oldtup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
		/* ... and store info about transaction updating this tuple */
		Assert(TransactionIdIsValid(xmax_old_tuple));
		HeapTupleHeaderSetXmax(oldtup.t_data, xmax_old_tuple);
		oldtup.t_data->t_infomask |= infomask_old_tuple;
		oldtup.t_data->t_infomask2 |= infomask2_old_tuple;
		HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
	}

	/* record address of new tuple in t_ctid of old one */
	oldtup.t_data->t_ctid = heaptup->t_self;

	/* clear PD_ALL_VISIBLE flags */
	if (PageIsAllVisible(BufferGetPage(buffer)))
	{
		all_visible_cleared = true;
		PageClearAllVisible(BufferGetPage(buffer));
		visibilitymap_clear(relation, BufferGetBlockNumber(buffer),
							vmbuffer);
	}
	if (newbuf != buffer && PageIsAllVisible(BufferGetPage(newbuf)))
	{
		all_visible_cleared_new = true;
		PageClearAllVisible(BufferGetPage(newbuf));
		visibilitymap_clear(relation, BufferGetBlockNumber(newbuf),
							vmbuffer_new);
	}

	if (newbuf != buffer)
		MarkBufferDirty(newbuf);
	MarkBufferDirty(buffer);

	/* XLOG stuff */
	if (RelationNeedsWAL(relation))
	{
		XLogRecPtr	recptr = log_heap_update(relation, buffer,
											 newbuf, &oldtup, heaptup,
											 all_visible_cleared,
											 all_visible_cleared_new);

		if (newbuf != buffer)
		{
			PageSetLSN(BufferGetPage(newbuf), recptr);
		}
		PageSetLSN(BufferGetPage(buffer), recptr);
	}

	END_CRIT_SECTION();

	if (newbuf != buffer)
		LockBuffer(newbuf, BUFFER_LOCK_UNLOCK);
	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

	/*
	 * Mark old tuple for invalidation from system caches at next command
	 * boundary, and mark the new tuple for invalidation in case we abort. We
	 * have to do this before releasing the buffer because oldtup is in the
	 * buffer.	(heaptup is all in local memory, but it's necessary to process
	 * both tuple versions in one call to inval.c so we can avoid redundant
	 * sinval messages.)
	 */
	CacheInvalidateHeapTuple(relation, &oldtup, heaptup);

	/* Now we can release the buffer(s) */
	if (newbuf != buffer)
		ReleaseBuffer(newbuf);
	ReleaseBuffer(buffer);
	if (BufferIsValid(vmbuffer_new))
		ReleaseBuffer(vmbuffer_new);
	if (BufferIsValid(vmbuffer))
		ReleaseBuffer(vmbuffer);

	/*
	 * Release the lmgr tuple lock, if we had it.
	 */
	if (have_tuple_lock)
		UnlockTupleTuplock(relation, &(oldtup.t_self), *lockmode);

	pgstat_count_heap_update(relation, use_hot_update);

	/*
	 * If heaptup is a private copy, release it.  Don't forget to copy t_self
	 * back to the caller's image, too.
	 */
	if (heaptup != newtup)
	{
		newtup->t_self = heaptup->t_self;
		heap_freetuple(heaptup);
	}

	bms_free(hot_attrs);
	bms_free(key_attrs);

	return HeapTupleMayBeUpdated;
}

/*
 * Check if the specified attribute's value is same in both given tuples.
 * Subroutine for HeapSatisfiesHOTandKeyUpdate.
 */
static bool
heap_tuple_attr_equals(TupleDesc tupdesc, int attrnum,
					   HeapTuple tup1, HeapTuple tup2)
{
	Datum		value1,
				value2;
	bool		isnull1,
				isnull2;
	Form_pg_attribute att;

	/*
	 * If it's a whole-tuple reference, say "not equal".  It's not really
	 * worth supporting this case, since it could only succeed after a no-op
	 * update, which is hardly a case worth optimizing for.
	 */
	if (attrnum == 0)
		return false;

	/*
	 * Likewise, automatically say "not equal" for any system attribute other
	 * than OID and tableOID; we cannot expect these to be consistent in a HOT
	 * chain, or even to be set correctly yet in the new tuple.
	 */
	if (attrnum < 0)
	{
		if (attrnum != ObjectIdAttributeNumber &&
			attrnum != TableOidAttributeNumber)
			return false;
	}

	/*
	 * Extract the corresponding values.  XXX this is pretty inefficient if
	 * there are many indexed columns.	Should HeapSatisfiesHOTandKeyUpdate do a
	 * single heap_deform_tuple call on each tuple, instead?  But that doesn't
	 * work for system columns ...
	 */
	value1 = heap_getattr(tup1, attrnum, tupdesc, &isnull1);
	value2 = heap_getattr(tup2, attrnum, tupdesc, &isnull2);

	/*
	 * If one value is NULL and other is not, then they are certainly not
	 * equal
	 */
	if (isnull1 != isnull2)
		return false;

	/*
	 * If both are NULL, they can be considered equal.
	 */
	if (isnull1)
		return true;

	/*
	 * We do simple binary comparison of the two datums.  This may be overly
	 * strict because there can be multiple binary representations for the
	 * same logical value.	But we should be OK as long as there are no false
	 * positives.  Using a type-specific equality operator is messy because
	 * there could be multiple notions of equality in different operator
	 * classes; furthermore, we cannot safely invoke user-defined functions
	 * while holding exclusive buffer lock.
	 */
	if (attrnum <= 0)
	{
		/* The only allowed system columns are OIDs, so do this */
		return (DatumGetObjectId(value1) == DatumGetObjectId(value2));
	}
	else
	{
		Assert(attrnum <= tupdesc->natts);
		att = tupdesc->attrs[attrnum - 1];
		return datumIsEqual(value1, value2, att->attbyval, att->attlen);
	}
}

/*
 * Check which columns are being updated.
 *
 * This simultaneously checks conditions for HOT updates and for FOR KEY
 * SHARE updates.  Since much of the time they will be checking very similar
 * sets of columns, and doing the same tests on them, it makes sense to
 * optimize and do them together.
 *
 * We receive two bitmapsets comprising the two sets of columns we're
 * interested in.  Note these are destructively modified; that is OK since
 * this is invoked at most once in heap_update.
 *
 * hot_result is set to TRUE if it's okay to do a HOT update (i.e. it does not
 * modified indexed columns); key_result is set to TRUE if the update does not
 * modify columns used in the key.
 */
static void
HeapSatisfiesHOTandKeyUpdate(Relation relation,
							 Bitmapset *hot_attrs, Bitmapset *key_attrs,
							 bool *satisfies_hot, bool *satisfies_key,
							 HeapTuple oldtup, HeapTuple newtup)
{
	int		next_hot_attnum;
	int		next_key_attnum;
	bool	hot_result = true;
	bool	key_result = true;
	bool	key_done = false;
	bool	hot_done = false;

	next_hot_attnum = bms_first_member(hot_attrs);
	if (next_hot_attnum == -1)
		hot_done = true;
	else
		/* Adjust for system attributes */
		next_hot_attnum += FirstLowInvalidHeapAttributeNumber;

	next_key_attnum = bms_first_member(key_attrs);
	if (next_key_attnum == -1)
		key_done = true;
	else
		/* Adjust for system attributes */
		next_key_attnum += FirstLowInvalidHeapAttributeNumber;

	for (;;)
	{
		int		check_now;
		bool	changed;

		/* both bitmapsets are now empty */
		if (key_done && hot_done)
			break;

		/* XXX there's probably an easier way ... */
		if (hot_done)
			check_now = next_key_attnum;
		if (key_done)
			check_now = next_hot_attnum;
		else
			check_now = Min(next_hot_attnum, next_key_attnum);

		changed = !heap_tuple_attr_equals(RelationGetDescr(relation),
										  check_now, oldtup, newtup);
		if (changed)
		{
			if (check_now == next_hot_attnum)
				hot_result = false;
			if (check_now == next_key_attnum)
				key_result = false;
		}

		/* if both are false now, we can stop checking */
		if (!hot_result && !key_result)
			break;

		if (check_now == next_hot_attnum)
		{
			next_hot_attnum = bms_first_member(hot_attrs);
			if (next_hot_attnum == -1)
				hot_done = true;
			else
				/* Adjust for system attributes */
				next_hot_attnum += FirstLowInvalidHeapAttributeNumber;
		}
		if (check_now == next_key_attnum)
		{
			next_key_attnum = bms_first_member(key_attrs);
			if (next_key_attnum == -1)
				key_done = true;
			else
				/* Adjust for system attributes */
				next_key_attnum += FirstLowInvalidHeapAttributeNumber;
		}
	}

	*satisfies_hot = hot_result;
	*satisfies_key = key_result;
}

/*
 *	simple_heap_update - replace a tuple
 *
 * This routine may be used to update a tuple when concurrent updates of
 * the target tuple are not expected (for example, because we have a lock
 * on the relation associated with the tuple).	Any failure is reported
 * via ereport().
 */
void
simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
{
	HTSU_Result result;
	HeapUpdateFailureData hufd;
	LockTupleMode lockmode;

	result = heap_update(relation, otid, tup,
						 GetCurrentCommandId(true), InvalidSnapshot,
						 true /* wait for commit */,
						 &hufd, &lockmode);
	switch (result)
	{
		case HeapTupleSelfUpdated:
			/* Tuple was already updated in current command? */
			elog(ERROR, "tuple already updated by self");
			break;

		case HeapTupleMayBeUpdated:
			/* done successfully */
			break;

		case HeapTupleUpdated:
			elog(ERROR, "tuple concurrently updated");
			break;

		default:
			elog(ERROR, "unrecognized heap_update status: %u", result);
			break;
	}
}


/*
 * Return the MultiXactStatus corresponding to the given tuple lock mode.
 */
static MultiXactStatus
get_mxact_status_for_lock(LockTupleMode mode, bool is_update)
{
	MultiXactStatus		retval;

	if (is_update)
		retval = tupleLockExtraInfo[mode].updstatus;
	else
		retval = tupleLockExtraInfo[mode].lockstatus;

	if (retval == -1)
		elog(ERROR, "invalid lock tuple mode %d/%s", mode,
			 is_update ? "true" : "false");

	return retval;
}


/*
 *	heap_lock_tuple - lock a tuple in shared or exclusive mode
 *
 * Note that this acquires a buffer pin, which the caller must release.
 *
 * Input parameters:
 *	relation: relation containing tuple (caller must hold suitable lock)
 *	tuple->t_self: TID of tuple to lock (rest of struct need not be valid)
 *	cid: current command ID (used for visibility test, and stored into
 *		tuple's cmax if lock is successful)
 *	mode: indicates if shared or exclusive tuple lock is desired
 *	nowait: if true, ereport rather than blocking if lock not available
 *	follow_updates: if true, follow the update chain to also lock descendant
 *		tuples.
 *
 * Output parameters:
 *	*tuple: all fields filled in
 *	*buffer: set to buffer holding tuple (pinned but not locked at exit)
 *	*hufd: filled in failure cases (see below)
 *
 * Function result may be:
 *	HeapTupleMayBeUpdated: lock was successfully acquired
 *	HeapTupleSelfUpdated: lock failed because tuple updated by self
 *	HeapTupleUpdated: lock failed because tuple updated by other xact
 *
 * In the failure cases, the routine fills *hufd with the tuple's t_ctid,
 * t_xmax (resolving a possible MultiXact, if necessary), and t_cmax
 * (the last only for HeapTupleSelfUpdated, since we
 * cannot obtain cmax from a combocid generated by another transaction).
 * See comments for struct HeapUpdateFailureData for additional info.
 *
 * See README.tuplock for a thorough explanation of this mechanism.
 */
HTSU_Result
heap_lock_tuple(Relation relation, HeapTuple tuple,
				CommandId cid, LockTupleMode mode, bool nowait,
				bool follow_updates,
				Buffer *buffer, HeapUpdateFailureData *hufd)
{
	HTSU_Result result;
	ItemPointer tid = &(tuple->t_self);
	ItemId		lp;
	Page		page;
	TransactionId xid,
				xmax;
	uint16		old_infomask,
				new_infomask,
				new_infomask2;
	bool		have_tuple_lock = false;

	*buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
	LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);

	page = BufferGetPage(*buffer);
	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
	Assert(ItemIdIsNormal(lp));

	tuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
	tuple->t_len = ItemIdGetLength(lp);
	tuple->t_tableOid = RelationGetRelid(relation);

l3:
	result = HeapTupleSatisfiesUpdate(tuple->t_data, cid, *buffer);

	if (result == HeapTupleInvisible)
	{
		UnlockReleaseBuffer(*buffer);
		elog(ERROR, "attempted to lock invisible tuple");
	}
	else if (result == HeapTupleBeingUpdated)
	{
		TransactionId xwait;
		uint16		infomask;
		uint16		infomask2;
		bool		require_sleep;
		ItemPointerData	t_ctid;

		/* must copy state data before unlocking buffer */
		xwait = HeapTupleHeaderGetRawXmax(tuple->t_data);
		infomask = tuple->t_data->t_infomask;
		infomask2 = tuple->t_data->t_infomask2;
		ItemPointerCopy(&tuple->t_data->t_ctid, &t_ctid);

		LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);

		/*
		 * If any subtransaction of the current top transaction already holds a
		 * lock as strong or stronger than what we're requesting, we
		 * effectively hold the desired lock already.  We *must* succeed
		 * without trying to take the tuple lock, else we will deadlock against
		 * anyone wanting to acquire a stronger lock.
		 */
		if (infomask & HEAP_XMAX_IS_MULTI)
		{
			int		i;
			int		nmembers;
			MultiXactMember *members;

			/*
			 * We don't need to allow old multixacts here; if that had been the
			 * case, HeapTupleSatisfiesUpdate would have returned MayBeUpdated
			 * and we wouldn't be here.
			 */
			nmembers = GetMultiXactIdMembers(xwait, &members, false);

			for (i = 0; i < nmembers; i++)
			{
				if (TransactionIdIsCurrentTransactionId(members[i].xid))
				{
					LockTupleMode	membermode;

					membermode = TUPLOCK_from_mxstatus(members[i].status);

					if (membermode >= mode)
					{
						if (have_tuple_lock)
							UnlockTupleTuplock(relation, tid, mode);

						pfree(members);
						return HeapTupleMayBeUpdated;
					}
				}
			}

			pfree(members);
		}

		/*
		 * Acquire tuple lock to establish our priority for the tuple.
		 * LockTuple will release us when we are next-in-line for the tuple.
		 * We must do this even if we are share-locking.
		 *
		 * If we are forced to "start over" below, we keep the tuple lock;
		 * this arranges that we stay at the head of the line while rechecking
		 * tuple state.
		 */
		if (!have_tuple_lock)
		{
			if (nowait)
			{
				if (!ConditionalLockTupleTuplock(relation, tid, mode))
					ereport(ERROR,
							(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
							 errmsg("could not obtain lock on row in relation \"%s\"",
									RelationGetRelationName(relation))));
			}
			else
				LockTupleTuplock(relation, tid, mode);
			have_tuple_lock = true;
		}

		/*
		 * Initially assume that we will have to wait for the locking
		 * transaction(s) to finish.  We check various cases below in which
		 * this can be turned off.
		 */
		require_sleep = true;
		if (mode == LockTupleKeyShare)
		{
			/*
			 * If we're requesting KeyShare, and there's no update present, we
			 * don't need to wait.  Even if there is an update, we can still
			 * continue if the key hasn't been modified.
			 *
			 * However, if there are updates, we need to walk the update chain
			 * to mark future versions of the row as locked, too.  That way, if
			 * somebody deletes that future version, we're protected against
			 * the key going away.  This locking of future versions could block
			 * momentarily, if a concurrent transaction is deleting a key; or
			 * it could return a value to the effect that the transaction
			 * deleting the key has already committed.  So we do this before
			 * re-locking the buffer; otherwise this would be prone to
			 * deadlocks.
			 *
			 * Note that the TID we're locking was grabbed before we unlocked
			 * the buffer.  For it to change while we're not looking, the other
			 * properties we're testing for below after re-locking the buffer
			 * would also change, in which case we would restart this loop
			 * above.
			 */
			if (!(infomask2 & HEAP_KEYS_UPDATED))
			{
				bool	updated;

				updated = !HEAP_XMAX_IS_LOCKED_ONLY(infomask);

				/*
				 * If there are updates, follow the update chain; bail out
				 * if that cannot be done.
				 */
				if (follow_updates && updated)
				{
					HTSU_Result		res;

					res = heap_lock_updated_tuple(relation, tuple, &t_ctid,
												  GetCurrentTransactionId(),
												  mode);
					if (res != HeapTupleMayBeUpdated)
					{
						result = res;
						/* recovery code expects to have buffer lock held */
						LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
						goto failed;
					}
				}

				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);

				/*
				 * Make sure it's still an appropriate lock, else start over.
				 * Also, if it wasn't updated before we released the lock, but
				 * is updated now, we start over too; the reason is that we now
				 * need to follow the update chain to lock the new versions.
				 */
				if (!HeapTupleHeaderIsOnlyLocked(tuple->t_data) &&
					((tuple->t_data->t_infomask2 & HEAP_KEYS_UPDATED) ||
					 !updated))
					goto l3;

				/* Things look okay, so we can skip sleeping */
				require_sleep = false;

				/*
				 * Note we allow Xmax to change here; other updaters/lockers
				 * could have modified it before we grabbed the buffer lock.
				 * However, this is not a problem, because with the recheck we
				 * just did we ensure that they still don't conflict with the
				 * lock we want.
				 */
			}
		}
		else if (mode == LockTupleShare)
		{
			/*
			 * If we're requesting Share, we can similarly avoid sleeping if
			 * there's no update and no exclusive lock present.
			 */
			if (HEAP_XMAX_IS_LOCKED_ONLY(infomask) &&
				!HEAP_XMAX_IS_EXCL_LOCKED(infomask))
			{
				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);

				/*
				 * Make sure it's still an appropriate lock, else start over.
				 * See above about allowing xmax to change.
				 */
				if (!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_data->t_infomask) ||
					HEAP_XMAX_IS_EXCL_LOCKED(tuple->t_data->t_infomask))
					goto l3;
				require_sleep = false;
			}
		}
		else if (mode == LockTupleNoKeyExclusive)
		{
			/*
			 * If we're requesting NoKeyExclusive, we might also be able to
			 * avoid sleeping; just ensure that there's no other lock type than
			 * KeyShare.  Note that this is a bit more involved than just
			 * checking hint bits -- we need to expand the multixact to figure
			 * out lock modes for each one (unless there was only one such
			 * locker).
			 */
			if (infomask & HEAP_XMAX_IS_MULTI)
			{
				int		nmembers;
				MultiXactMember *members;

				/*
				 * We don't need to allow old multixacts here; if that had been
				 * the case, HeapTupleSatisfiesUpdate would have returned
				 * MayBeUpdated and we wouldn't be here.
				 */
				nmembers = GetMultiXactIdMembers(xwait, &members, false);

				if (nmembers <= 0)
				{
					/*
					 * No need to keep the previous xmax here. This is unlikely
					 * to happen.
					 */
					require_sleep = false;
				}
				else
				{
					int		i;
					bool	allowed = true;

					for (i = 0; i < nmembers; i++)
					{
						if (members[i].status != MultiXactStatusForKeyShare)
						{
							allowed = false;
							break;
						}
					}
					if (allowed)
					{
						/*
						 * if the xmax changed under us in the meantime, start
						 * over.
						 */
						LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
						if (!(tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
							!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
												 xwait))
						{
							pfree(members);
							goto l3;
						}
						/* otherwise, we're good */
						require_sleep = false;
					}

					pfree(members);
				}
			}
			else if (HEAP_XMAX_IS_KEYSHR_LOCKED(infomask))
			{
				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);

				/* if the xmax changed in the meantime, start over */
				if ((tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
					!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
										 xwait))
					goto l3;
				/* otherwise, we're good */
				require_sleep = false;
			}
		}

		/*
		 * By here, we either have already acquired the buffer exclusive lock,
		 * or we must wait for the locking transaction or multixact; so below
		 * we ensure that we grab buffer lock after the sleep.
		 */

		if (require_sleep)
		{
			if (infomask & HEAP_XMAX_IS_MULTI)
			{
				MultiXactStatus status = get_mxact_status_for_lock(mode, false);

				/* We only ever lock tuples, never update them */
				if (status >= MultiXactStatusNoKeyUpdate)
					elog(ERROR, "invalid lock mode in heap_lock_tuple");

				/* wait for multixact to end */
				if (nowait)
				{
					if (!ConditionalMultiXactIdWait((MultiXactId) xwait,
													status, NULL, infomask))
						ereport(ERROR,
								(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
								 errmsg("could not obtain lock on row in relation \"%s\"",
										RelationGetRelationName(relation))));
				}
				else
					MultiXactIdWait((MultiXactId) xwait, status, NULL, infomask);

				/* if there are updates, follow the update chain */
				if (follow_updates &&
					!HEAP_XMAX_IS_LOCKED_ONLY(infomask))
				{
					HTSU_Result		res;

					res = heap_lock_updated_tuple(relation, tuple, &t_ctid,
												  GetCurrentTransactionId(),
												  mode);
					if (res != HeapTupleMayBeUpdated)
					{
						result = res;
						/* recovery code expects to have buffer lock held */
						LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
						goto failed;
					}
				}

				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);

				/*
				 * If xwait had just locked the tuple then some other xact
				 * could update this tuple before we get to this point. Check
				 * for xmax change, and start over if so.
				 */
				if (!(tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
					!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
										 xwait))
					goto l3;

				/*
				 * Of course, the multixact might not be done here: if we're
				 * requesting a light lock mode, other transactions with light
				 * locks could still be alive, as well as locks owned by our
				 * own xact or other subxacts of this backend.  We need to
				 * preserve the surviving MultiXact members.  Note that it
				 * isn't absolutely necessary in the latter case, but doing so
				 * is simpler.
				 */
			}
			else
			{
				/* wait for regular transaction to end */
				if (nowait)
				{
					if (!ConditionalXactLockTableWait(xwait))
						ereport(ERROR,
								(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
								 errmsg("could not obtain lock on row in relation \"%s\"",
										RelationGetRelationName(relation))));
				}
				else
					XactLockTableWait(xwait);

				/* if there are updates, follow the update chain */
				if (follow_updates &&
					!HEAP_XMAX_IS_LOCKED_ONLY(infomask))
				{
					HTSU_Result		res;

					res = heap_lock_updated_tuple(relation, tuple, &t_ctid,
												  GetCurrentTransactionId(),
												  mode);
					if (res != HeapTupleMayBeUpdated)
					{
						result = res;
						/* recovery code expects to have buffer lock held */
						LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
						goto failed;
					}
				}

				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);

				/*
				 * xwait is done, but if xwait had just locked the tuple then
				 * some other xact could update this tuple before we get to
				 * this point.  Check for xmax change, and start over if so.
				 */
				if ((tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
					!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
										 xwait))
					goto l3;

				/*
				 * Otherwise check if it committed or aborted.  Note we cannot
				 * be here if the tuple was only locked by somebody who didn't
				 * conflict with us; that should have been handled above.  So
				 * that transaction must necessarily be gone by now.
				 */
				UpdateXmaxHintBits(tuple->t_data, *buffer, xwait);
			}
		}

		/* By here, we're certain that we hold buffer exclusive lock again */

		/*
		 * We may lock if previous xmax aborted, or if it committed but only
		 * locked the tuple without updating it; or if we didn't have to wait
		 * at all for whatever reason.
		 */
		if (!require_sleep ||
			(tuple->t_data->t_infomask & HEAP_XMAX_INVALID) ||
			HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_data->t_infomask) ||
			HeapTupleHeaderIsOnlyLocked(tuple->t_data))
			result = HeapTupleMayBeUpdated;
		else
			result = HeapTupleUpdated;
	}

failed:
	if (result != HeapTupleMayBeUpdated)
	{
		Assert(result == HeapTupleSelfUpdated || result == HeapTupleUpdated);
		Assert(!(tuple->t_data->t_infomask & HEAP_XMAX_INVALID));
		hufd->ctid = tuple->t_data->t_ctid;
		hufd->xmax = HeapTupleHeaderGetUpdateXid(tuple->t_data);
		if (result == HeapTupleSelfUpdated)
			hufd->cmax = HeapTupleHeaderGetCmax(tuple->t_data);
		else
			hufd->cmax = 0;		/* for lack of an InvalidCommandId value */
		LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
		if (have_tuple_lock)
			UnlockTupleTuplock(relation, tid, mode);
		return result;
	}

	xmax = HeapTupleHeaderGetRawXmax(tuple->t_data);
	old_infomask = tuple->t_data->t_infomask;

	/*
	 * We might already hold the desired lock (or stronger), possibly under a
	 * different subtransaction of the current top transaction.  If so, there
	 * is no need to change state or issue a WAL record.  We already handled
	 * the case where this is true for xmax being a MultiXactId, so now check
	 * for cases where it is a plain TransactionId.
	 *
	 * Note in particular that this covers the case where we already hold
	 * exclusive lock on the tuple and the caller only wants key share or share
	 * lock. It would certainly not do to give up the exclusive lock.
	 */
	if (!(old_infomask & (HEAP_XMAX_INVALID |
						  HEAP_XMAX_COMMITTED |
						  HEAP_XMAX_IS_MULTI)) &&
		(mode == LockTupleKeyShare ?
		 (HEAP_XMAX_IS_KEYSHR_LOCKED(old_infomask) ||
		  HEAP_XMAX_IS_SHR_LOCKED(old_infomask) ||
		  HEAP_XMAX_IS_EXCL_LOCKED(old_infomask)) :
		 mode == LockTupleShare ?
		 (HEAP_XMAX_IS_SHR_LOCKED(old_infomask) ||
		  HEAP_XMAX_IS_EXCL_LOCKED(old_infomask)) :
		 (HEAP_XMAX_IS_EXCL_LOCKED(old_infomask))) &&
		TransactionIdIsCurrentTransactionId(xmax))
	{
		LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
		/* Probably can't hold tuple lock here, but may as well check */
		if (have_tuple_lock)
			UnlockTupleTuplock(relation, tid, mode);
		return HeapTupleMayBeUpdated;
	}

	/*
	 * If this is the first possibly-multixact-able operation in the
	 * current transaction, set my per-backend OldestMemberMXactId setting.
	 * We can be certain that the transaction will never become a member of
	 * any older MultiXactIds than that.  (We have to do this even if we
	 * end up just using our own TransactionId below, since some other
	 * backend could incorporate our XID into a MultiXact immediately
	 * afterwards.)
	 */
	MultiXactIdSetOldestMember();

	/*
	 * Compute the new xmax and infomask to store into the tuple.  Note we do
	 * not modify the tuple just yet, because that would leave it in the wrong
	 * state if multixact.c elogs.
	 */
	compute_new_xmax_infomask(xmax, old_infomask, tuple->t_data->t_infomask2,
							  GetCurrentTransactionId(), mode, false,
							  &xid, &new_infomask, &new_infomask2);

	START_CRIT_SECTION();

	/*
	 * Store transaction information of xact locking the tuple.
	 *
	 * Note: Cmax is meaningless in this context, so don't set it; this avoids
	 * possibly generating a useless combo CID.  Moreover, if we're locking a
	 * previously updated tuple, it's important to preserve the Cmax.
	 *
	 * Also reset the HOT UPDATE bit, but only if there's no update; otherwise
	 * we would break the HOT chain.
	 */
	tuple->t_data->t_infomask &= ~HEAP_XMAX_BITS;
	tuple->t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
	tuple->t_data->t_infomask |= new_infomask;
	tuple->t_data->t_infomask2 |= new_infomask2;
	if (HEAP_XMAX_IS_LOCKED_ONLY(new_infomask))
		HeapTupleHeaderClearHotUpdated(tuple->t_data);
	HeapTupleHeaderSetXmax(tuple->t_data, xid);

	/*
	 * Make sure there is no forward chain link in t_ctid.  Note that in the
	 * cases where the tuple has been updated, we must not overwrite t_ctid,
	 * because it was set by the updater.  Moreover, if the tuple has been
	 * updated, we need to follow the update chain to lock the new versions
	 * of the tuple as well.
	 */
	if (HEAP_XMAX_IS_LOCKED_ONLY(new_infomask))
		tuple->t_data->t_ctid = *tid;

	MarkBufferDirty(*buffer);

	/*
	 * XLOG stuff.	You might think that we don't need an XLOG record because
	 * there is no state change worth restoring after a crash.	You would be
	 * wrong however: we have just written either a TransactionId or a
	 * MultiXactId that may never have been seen on disk before, and we need
	 * to make sure that there are XLOG entries covering those ID numbers.
	 * Else the same IDs might be re-used after a crash, which would be
	 * disastrous if this page made it to disk before the crash.  Essentially
	 * we have to enforce the WAL log-before-data rule even in this case.
	 * (Also, in a PITR log-shipping or 2PC environment, we have to have XLOG
	 * entries for everything anyway.)
	 */
	if (RelationNeedsWAL(relation))
	{
		xl_heap_lock xlrec;
		XLogRecPtr	recptr;
		XLogRecData rdata[2];

		xlrec.target.node = relation->rd_node;
		xlrec.target.tid = tuple->t_self;
		xlrec.locking_xid = xid;
		xlrec.infobits_set = compute_infobits(new_infomask,
											  tuple->t_data->t_infomask2);
		rdata[0].data = (char *) &xlrec;
		rdata[0].len = SizeOfHeapLock;
		rdata[0].buffer = InvalidBuffer;
		rdata[0].next = &(rdata[1]);

		rdata[1].data = NULL;
		rdata[1].len = 0;
		rdata[1].buffer = *buffer;
		rdata[1].buffer_std = true;
		rdata[1].next = NULL;

		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_LOCK, rdata);

		PageSetLSN(page, recptr);
	}

	END_CRIT_SECTION();

	LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);

	/*
	 * Don't update the visibility map here. Locking a tuple doesn't change
	 * visibility info.
	 */

	/*
	 * Now that we have successfully marked the tuple as locked, we can
	 * release the lmgr tuple lock, if we had it.
	 */
	if (have_tuple_lock)
		UnlockTupleTuplock(relation, tid, mode);

	return HeapTupleMayBeUpdated;
}


/*
 * Given an original set of Xmax and infomask, and a transaction (identified by
 * add_to_xmax) acquiring a new lock of some mode, compute the new Xmax and
 * corresponding infomasks to use on the tuple.
 *
 * Note that this might have side effects such as creating a new MultiXactId.
 *
 * Most callers will have called HeapTupleSatisfiesUpdate before this function;
 * that will have set the HEAP_XMAX_INVALID bit if the xmax was a MultiXactId
 * but it was not running anymore. There is a race condition, which is that the
 * MultiXactId may have finished since then, but that uncommon case is handled
 * either here, or within MultiXactIdExpand.
 *
 * There is a similar race condition possible when the old xmax was a regular
 * TransactionId.  We test TransactionIdIsInProgress again just to narrow the
 * window, but it's still possible to end up creating an unnecessary
 * MultiXactId.  Fortunately this is harmless.
 */
static void
compute_new_xmax_infomask(TransactionId xmax, uint16 old_infomask,
						  uint16 old_infomask2, TransactionId add_to_xmax,
						  LockTupleMode mode, bool is_update,
						  TransactionId *result_xmax, uint16 *result_infomask,
						  uint16 *result_infomask2)
{
	TransactionId	new_xmax;
	uint16			new_infomask,
					new_infomask2;

l5:
	new_infomask = 0;
	new_infomask2 = 0;
	if (old_infomask & HEAP_XMAX_INVALID)
	{
		/*
		 * No previous locker; we just insert our own TransactionId.
		 */
		if (is_update)
		{
			new_xmax = add_to_xmax;
			if (mode == LockTupleExclusive)
				new_infomask2 |= HEAP_KEYS_UPDATED;
		}
		else
		{
			new_infomask |= HEAP_XMAX_LOCK_ONLY;
			switch (mode)
			{
				case LockTupleKeyShare:
					new_xmax = add_to_xmax;
					new_infomask |= HEAP_XMAX_KEYSHR_LOCK;
					break;
				case LockTupleShare:
					new_xmax = add_to_xmax;
					new_infomask |= HEAP_XMAX_SHR_LOCK;
					break;
				case LockTupleNoKeyExclusive:
					new_xmax = add_to_xmax;
					new_infomask |= HEAP_XMAX_EXCL_LOCK;
					break;
				case LockTupleExclusive:
					new_xmax = add_to_xmax;
					new_infomask |= HEAP_XMAX_EXCL_LOCK;
					new_infomask2 |= HEAP_KEYS_UPDATED;
					break;
				default:
					new_xmax = InvalidTransactionId;	/* silence compiler */
					elog(ERROR, "invalid lock mode");
			}
		}
	}
	else if (old_infomask & HEAP_XMAX_IS_MULTI)
	{
		MultiXactStatus		new_status;

		/*
		 * Currently we don't allow XMAX_COMMITTED to be set for multis,
		 * so cross-check.
		 */
		Assert(!(old_infomask & HEAP_XMAX_COMMITTED));

		/*
		 * A multixact together with LOCK_ONLY set but neither lock bit set
		 * (i.e. a pg_upgraded share locked tuple) cannot possibly be running
		 * anymore.  This check is critical for databases upgraded by
		 * pg_upgrade; both MultiXactIdIsRunning and MultiXactIdExpand assume
		 * that such multis are never passed.
		 */
		if (!(old_infomask & HEAP_LOCK_MASK) &&
			HEAP_XMAX_IS_LOCKED_ONLY(old_infomask))
		{
			old_infomask &= ~HEAP_XMAX_IS_MULTI;
			old_infomask |= HEAP_XMAX_INVALID;
			goto l5;
		}

		/*
		 * If the XMAX is already a MultiXactId, then we need to expand it to
		 * include add_to_xmax; but if all the members were lockers and are all
		 * gone, we can do away with the IS_MULTI bit and just set add_to_xmax
		 * as the only locker/updater.  If all lockers are gone and we have an
		 * updater that aborted, we can also do without a multi.
		 *
		 * The cost of doing GetMultiXactIdMembers would be paid by
		 * MultiXactIdExpand if we weren't to do this, so this check is not
		 * incurring extra work anyhow.
		 */
		if (!MultiXactIdIsRunning(xmax))
		{
			if (HEAP_XMAX_IS_LOCKED_ONLY(old_infomask) ||
				TransactionIdDidAbort(MultiXactIdGetUpdateXid(xmax,
															  old_infomask)))
			{
				/*
				 * Reset these bits and restart; otherwise fall through to
				 * create a new multi below.
				 */
				old_infomask &= ~HEAP_XMAX_IS_MULTI;
				old_infomask |= HEAP_XMAX_INVALID;
				goto l5;
			}
		}

		new_status = get_mxact_status_for_lock(mode, is_update);

		new_xmax = MultiXactIdExpand((MultiXactId) xmax, add_to_xmax,
									 new_status);
		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
	}
	else if (old_infomask & HEAP_XMAX_COMMITTED)
	{
		/*
		 * It's a committed update, so we need to preserve him as updater of
		 * the tuple.
		 */
		MultiXactStatus		status;
		MultiXactStatus		new_status;

		if (old_infomask2 & HEAP_KEYS_UPDATED)
			status = MultiXactStatusUpdate;
		else
			status = MultiXactStatusNoKeyUpdate;

		new_status = get_mxact_status_for_lock(mode, is_update);
		/*
		 * since it's not running, it's obviously impossible for the old
		 * updater to be identical to the current one, so we need not check
		 * for that case as we do in the block above.
		 */
		new_xmax = MultiXactIdCreate(xmax, status, add_to_xmax, new_status);
		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
	}
	else if (TransactionIdIsInProgress(xmax))
	{
		/*
		 * If the XMAX is a valid, in-progress TransactionId, then we need to
		 * create a new MultiXactId that includes both the old locker or
		 * updater and our own TransactionId.
		 */
		MultiXactStatus		status;
		MultiXactStatus		new_status;

		if (HEAP_XMAX_IS_LOCKED_ONLY(old_infomask))
		{
			if (HEAP_XMAX_IS_KEYSHR_LOCKED(old_infomask))
				status = MultiXactStatusForKeyShare;
			else if (HEAP_XMAX_IS_SHR_LOCKED(old_infomask))
				status = MultiXactStatusForShare;
			else if (HEAP_XMAX_IS_EXCL_LOCKED(old_infomask))
			{
				if (old_infomask2 & HEAP_KEYS_UPDATED)
					status = MultiXactStatusForUpdate;
				else
					status = MultiXactStatusForNoKeyUpdate;
			}
			else
			{
				/*
				 * LOCK_ONLY can be present alone only when a page has been
				 * upgraded by pg_upgrade.  But in that case,
				 * TransactionIdIsInProgress() should have returned false.  We
				 * assume it's no longer locked in this case.
				 */
				elog(WARNING, "LOCK_ONLY found for Xid in progress %u", xmax);
				old_infomask |= HEAP_XMAX_INVALID;
				old_infomask &= ~HEAP_XMAX_LOCK_ONLY;
				goto l5;
			}
		}
		else
		{
			/* it's an update, but which kind? */
			if (old_infomask2 & HEAP_KEYS_UPDATED)
				status = MultiXactStatusUpdate;
			else
				status = MultiXactStatusNoKeyUpdate;
		}

		new_status = get_mxact_status_for_lock(mode, is_update);

		/*
		 * If the existing lock mode is identical to or weaker than the new
		 * one, we can act as though there is no existing lock, so set
		 * XMAX_INVALID and restart.
		 */
		if (xmax == add_to_xmax)
		{
			LockTupleMode	old_mode = TUPLOCK_from_mxstatus(status);
			bool			old_isupd = ISUPDATE_from_mxstatus(status);

			/*
			 * We can do this if the new LockTupleMode is higher or equal than
			 * the old one; and if there was previously an update, we need an
			 * update, but if there wasn't, then we can accept there not being
			 * one.
			 */
			if ((mode >= old_mode) && (is_update || !old_isupd))
			{
				/*
				 * Note that the infomask might contain some other dirty bits.
				 * However, since the new infomask is reset to zero, we only
				 * set what's minimally necessary, and that the case that
				 * checks HEAP_XMAX_INVALID is the very first above, there is
				 * no need for extra cleanup of the infomask here.
				 */
				old_infomask |= HEAP_XMAX_INVALID;
				goto l5;
			}
		}
		new_xmax = MultiXactIdCreate(xmax, status, add_to_xmax, new_status);
		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
	}
	else if (!HEAP_XMAX_IS_LOCKED_ONLY(old_infomask) &&
			 TransactionIdDidCommit(xmax))
	{
		/*
		 * It's a committed update, so we gotta preserve him as updater of the
		 * tuple.
		 */
		MultiXactStatus		status;
		MultiXactStatus		new_status;

		if (old_infomask2 & HEAP_KEYS_UPDATED)
			status = MultiXactStatusUpdate;
		else
			status = MultiXactStatusNoKeyUpdate;

		new_status = get_mxact_status_for_lock(mode, is_update);
		/*
		 * since it's not running, it's obviously impossible for the old
		 * updater to be identical to the current one, so we need not check
		 * for that case as we do in the block above.
		 */
		new_xmax = MultiXactIdCreate(xmax, status, add_to_xmax, new_status);
		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
	}
	else
	{
		/*
		 * Can get here iff the locking/updating transaction was running when
		 * the infomask was extracted from the tuple, but finished before
		 * TransactionIdIsInProgress got to run.  Deal with it as if there was
		 * no locker at all in the first place.
		 */
		old_infomask |= HEAP_XMAX_INVALID;
		goto l5;
	}

	*result_infomask = new_infomask;
	*result_infomask2 = new_infomask2;
	*result_xmax = new_xmax;
}


/*
 * Recursive part of heap_lock_updated_tuple
 *
 * Fetch the tuple pointed to by tid in rel, and mark it as locked by the given
 * xid with the given mode; if this tuple is updated, recurse to lock the new
 * version as well.
 */
static HTSU_Result
heap_lock_updated_tuple_rec(Relation rel, ItemPointer tid, TransactionId xid,
							LockTupleMode mode)
{
	ItemPointerData	tupid;
	HeapTupleData	mytup;
	Buffer			buf;
	uint16			new_infomask,
					new_infomask2,
					old_infomask;
	TransactionId	xmax,
					new_xmax;

	ItemPointerCopy(tid, &tupid);

	for (;;)
	{
		new_infomask = 0;
		new_xmax = InvalidTransactionId;
		ItemPointerCopy(&tupid, &(mytup.t_self));

		if (!heap_fetch(rel, SnapshotAny, &mytup, &buf, false, NULL))
			elog(ERROR, "unable to fetch updated version of tuple");

l4:
		CHECK_FOR_INTERRUPTS();
		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);

		old_infomask = mytup.t_data->t_infomask;
		xmax = HeapTupleHeaderGetRawXmax(mytup.t_data);

		/*
		 * If this tuple is updated and the key has been modified (or deleted),
		 * what we do depends on the status of the updating transaction: if
		 * it's live, we sleep until it finishes; if it has committed, we have
		 * to fail (i.e. return HeapTupleUpdated); if it aborted, we ignore it.
		 * For updates that didn't touch the key, we can just plough ahead.
		 */
		if (!(old_infomask & HEAP_XMAX_INVALID) &&
			(mytup.t_data->t_infomask2 & HEAP_KEYS_UPDATED))
		{
			TransactionId	update_xid;

			/*
			 * Note: we *must* check TransactionIdIsInProgress before
			 * TransactionIdDidAbort/Commit; see comment at top of tqual.c for
			 * an explanation.
			 */
			update_xid = HeapTupleHeaderGetUpdateXid(mytup.t_data);
			if (TransactionIdIsCurrentTransactionId(update_xid))
			{
				UnlockReleaseBuffer(buf);
				return HeapTupleSelfUpdated;
			}
			else if (TransactionIdIsInProgress(update_xid))
			{
				LockBuffer(buf, BUFFER_LOCK_UNLOCK);
				/* No LockTupleTuplock here -- see heap_lock_updated_tuple */
				XactLockTableWait(update_xid);
				goto l4;
			}
			else if (TransactionIdDidAbort(update_xid))
				;	/* okay to proceed */
			else if (TransactionIdDidCommit(update_xid))
			{
				UnlockReleaseBuffer(buf);
				return HeapTupleUpdated;
			}
		}

		/* compute the new Xmax and infomask values for the tuple ... */
		compute_new_xmax_infomask(xmax, old_infomask, mytup.t_data->t_infomask2,
								  xid, mode, false,
								  &new_xmax, &new_infomask, &new_infomask2);

		START_CRIT_SECTION();

		/* ... and set them */
		HeapTupleHeaderSetXmax(mytup.t_data, new_xmax);
		mytup.t_data->t_infomask &= ~HEAP_XMAX_BITS;
		mytup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
		mytup.t_data->t_infomask |= new_infomask;
		mytup.t_data->t_infomask2 |= new_infomask2;

		MarkBufferDirty(buf);

		/* XLOG stuff */
		if (RelationNeedsWAL(rel))
		{
			xl_heap_lock_updated xlrec;
			XLogRecPtr	recptr;
			XLogRecData	rdata[2];
			Page		page = BufferGetPage(buf);

			xlrec.target.node = rel->rd_node;
			xlrec.target.tid = mytup.t_self;
			xlrec.xmax = new_xmax;
			xlrec.infobits_set = compute_infobits(new_infomask, new_infomask2);

			rdata[0].data = (char *) &xlrec;
			rdata[0].len = SizeOfHeapLockUpdated;
			rdata[0].buffer = InvalidBuffer;
			rdata[0].next = &(rdata[1]);

			rdata[1].data = NULL;
			rdata[1].len = 0;
			rdata[1].buffer = buf;
			rdata[1].buffer_std = true;
			rdata[1].next = NULL;

			recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_LOCK_UPDATED, rdata);

			PageSetLSN(page, recptr);
		}

		END_CRIT_SECTION();

		/* if we find the end of update chain, we're done. */
		if (mytup.t_data->t_infomask & HEAP_XMAX_INVALID ||
			ItemPointerEquals(&mytup.t_self, &mytup.t_data->t_ctid)  ||
			HeapTupleHeaderIsOnlyLocked(mytup.t_data))
		{
			UnlockReleaseBuffer(buf);
			return HeapTupleMayBeUpdated;
		}

		/* tail recursion */
		ItemPointerCopy(&(mytup.t_data->t_ctid), &tupid);
		UnlockReleaseBuffer(buf);
	}
}

/*
 * heap_lock_updated_tuple
 * 		Follow update chain when locking an updated tuple, acquiring locks (row
 * 		marks) on the updated versions.
 *
 * The initial tuple is assumed to be already locked.
 *
 * This function doesn't check visibility, it just inconditionally marks the
 * tuple(s) as locked.  If any tuple in the updated chain is being deleted
 * concurrently (or updated with the key being modified), sleep until the
 * transaction doing it is finished.
 *
 * Note that we don't acquire heavyweight tuple locks on the tuples we walk
 * when we have to wait for other transactions to release them, as opposed to
 * what heap_lock_tuple does.  The reason is that having more than one
 * transaction walking the chain is probably uncommon enough that risk of
 * starvation is not likely: one of the preconditions for being here is that
 * the snapshot in use predates the update that created this tuple (because we
 * started at an earlier version of the tuple), but at the same time such a
 * transaction cannot be using repeatable read or serializable isolation
 * levels, because that would lead to a serializability failure.
 */
static HTSU_Result
heap_lock_updated_tuple(Relation rel, HeapTuple tuple, ItemPointer ctid,
						TransactionId xid, LockTupleMode mode)
{
	if (!ItemPointerEquals(&tuple->t_self, ctid))
	{
		/*
		 * If this is the first possibly-multixact-able operation in the
		 * current transaction, set my per-backend OldestMemberMXactId setting.
		 * We can be certain that the transaction will never become a member of
		 * any older MultiXactIds than that.  (We have to do this even if we
		 * end up just using our own TransactionId below, since some other
		 * backend could incorporate our XID into a MultiXact immediately
		 * afterwards.)
		 */
		MultiXactIdSetOldestMember();

		return heap_lock_updated_tuple_rec(rel, ctid, xid, mode);
	}

	/* nothing to lock */
	return HeapTupleMayBeUpdated;
}


/*
 * heap_inplace_update - update a tuple "in place" (ie, overwrite it)
 *
 * Overwriting violates both MVCC and transactional safety, so the uses
 * of this function in Postgres are extremely limited.	Nonetheless we
 * find some places to use it.
 *
 * The tuple cannot change size, and therefore it's reasonable to assume
 * that its null bitmap (if any) doesn't change either.  So we just
 * overwrite the data portion of the tuple without touching the null
 * bitmap or any of the header fields.
 *
 * tuple is an in-memory tuple structure containing the data to be written
 * over the target tuple.  Also, tuple->t_self identifies the target tuple.
 */
void
heap_inplace_update(Relation relation, HeapTuple tuple)
{
	Buffer		buffer;
	Page		page;
	OffsetNumber offnum;
	ItemId		lp = NULL;
	HeapTupleHeader htup;
	uint32		oldlen;
	uint32		newlen;

	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&(tuple->t_self)));
	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
	page = (Page) BufferGetPage(buffer);

	offnum = ItemPointerGetOffsetNumber(&(tuple->t_self));
	if (PageGetMaxOffsetNumber(page) >= offnum)
		lp = PageGetItemId(page, offnum);

	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
		elog(ERROR, "heap_inplace_update: invalid lp");

	htup = (HeapTupleHeader) PageGetItem(page, lp);

	oldlen = ItemIdGetLength(lp) - htup->t_hoff;
	newlen = tuple->t_len - tuple->t_data->t_hoff;
	if (oldlen != newlen || htup->t_hoff != tuple->t_data->t_hoff)
		elog(ERROR, "heap_inplace_update: wrong tuple length");

	/* NO EREPORT(ERROR) from here till changes are logged */
	START_CRIT_SECTION();

	memcpy((char *) htup + htup->t_hoff,
		   (char *) tuple->t_data + tuple->t_data->t_hoff,
		   newlen);

	MarkBufferDirty(buffer);

	/* XLOG stuff */
	if (RelationNeedsWAL(relation))
	{
		xl_heap_inplace xlrec;
		XLogRecPtr	recptr;
		XLogRecData rdata[2];

		xlrec.target.node = relation->rd_node;
		xlrec.target.tid = tuple->t_self;

		rdata[0].data = (char *) &xlrec;
		rdata[0].len = SizeOfHeapInplace;
		rdata[0].buffer = InvalidBuffer;
		rdata[0].next = &(rdata[1]);

		rdata[1].data = (char *) htup + htup->t_hoff;
		rdata[1].len = newlen;
		rdata[1].buffer = buffer;
		rdata[1].buffer_std = true;
		rdata[1].next = NULL;

		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_INPLACE, rdata);

		PageSetLSN(page, recptr);
	}

	END_CRIT_SECTION();

	UnlockReleaseBuffer(buffer);

	/*
	 * Send out shared cache inval if necessary.  Note that because we only
	 * pass the new version of the tuple, this mustn't be used for any
	 * operations that could change catcache lookup keys.  But we aren't
	 * bothering with index updates either, so that's true a fortiori.
	 */
	if (!IsBootstrapProcessingMode())
		CacheInvalidateHeapTuple(relation, tuple, NULL);
}


/*
 * heap_freeze_tuple
 *
 * Check to see whether any of the XID fields of a tuple (xmin, xmax, xvac)
 * are older than the specified cutoff XID.  If so, replace them with
 * FrozenTransactionId or InvalidTransactionId as appropriate, and return
 * TRUE.  Return FALSE if nothing was changed.
 *
 * It is assumed that the caller has checked the tuple with
 * HeapTupleSatisfiesVacuum() and determined that it is not HEAPTUPLE_DEAD
 * (else we should be removing the tuple, not freezing it).
 *
 * NB: cutoff_xid *must* be <= the current global xmin, to ensure that any
 * XID older than it could neither be running nor seen as running by any
 * open transaction.  This ensures that the replacement will not change
 * anyone's idea of the tuple state.  Also, since we assume the tuple is
 * not HEAPTUPLE_DEAD, the fact that an XID is not still running allows us
 * to assume that it is either committed good or aborted, as appropriate;
 * so we need no external state checks to decide what to do.  (This is good
 * because this function is applied during WAL recovery, when we don't have
 * access to any such state, and can't depend on the hint bits to be set.)
 *
 * Similarly, cutoff_multi must be less than or equal to the smallest
 * MultiXactId used by any transaction currently open.
 *
 * If the tuple is in a shared buffer, caller must hold an exclusive lock on
 * that buffer.
 *
 * Note: it might seem we could make the changes without exclusive lock, since
 * TransactionId read/write is assumed atomic anyway.  However there is a race
 * condition: someone who just fetched an old XID that we overwrite here could
 * conceivably not finish checking the XID against pg_clog before we finish
 * the VACUUM and perhaps truncate off the part of pg_clog he needs.  Getting
 * exclusive lock ensures no other backend is in process of checking the
 * tuple status.  Also, getting exclusive lock makes it safe to adjust the
 * infomask bits.
 */
bool
heap_freeze_tuple(HeapTupleHeader tuple, TransactionId cutoff_xid,
				  MultiXactId cutoff_multi)
{
	bool		changed = false;
	TransactionId xid;

	xid = HeapTupleHeaderGetXmin(tuple);
	if (TransactionIdIsNormal(xid) &&
		TransactionIdPrecedes(xid, cutoff_xid))
	{
		HeapTupleHeaderSetXmin(tuple, FrozenTransactionId);

		/*
		 * Might as well fix the hint bits too; usually XMIN_COMMITTED will
		 * already be set here, but there's a small chance not.
		 */
		Assert(!(tuple->t_infomask & HEAP_XMIN_INVALID));
		tuple->t_infomask |= HEAP_XMIN_COMMITTED;
		changed = true;
	}

	/*
	 * Note that this code handles IS_MULTI Xmax values, too, but only to mark
	 * the tuple frozen if the updating Xid in the mxact is below the freeze
	 * cutoff; it doesn't remove dead members of a very old multixact.
	 */
	xid = HeapTupleHeaderGetRawXmax(tuple);
	if ((tuple->t_infomask & HEAP_XMAX_IS_MULTI) ?
		(MultiXactIdIsValid(xid) &&
		 MultiXactIdPrecedes(xid, cutoff_multi)) :
		(TransactionIdIsNormal(xid) &&
		 TransactionIdPrecedes(xid, cutoff_xid)))
	{
		HeapTupleHeaderSetXmax(tuple, InvalidTransactionId);

		/*
		 * The tuple might be marked either XMAX_INVALID or XMAX_COMMITTED
		 * + LOCKED.  Normalize to INVALID just to be sure no one gets
		 * confused.  Also get rid of the HEAP_KEYS_UPDATED bit.
		 */
		tuple->t_infomask &= ~HEAP_XMAX_BITS;
		tuple->t_infomask |= HEAP_XMAX_INVALID;
		HeapTupleHeaderClearHotUpdated(tuple);
		tuple->t_infomask2 &= ~HEAP_KEYS_UPDATED;
		changed = true;
	}

	/*
	 * Old-style VACUUM FULL is gone, but we have to keep this code as long as
	 * we support having MOVED_OFF/MOVED_IN tuples in the database.
	 */
	if (tuple->t_infomask & HEAP_MOVED)
	{
		xid = HeapTupleHeaderGetXvac(tuple);
		if (TransactionIdIsNormal(xid) &&
			TransactionIdPrecedes(xid, cutoff_xid))
		{
			/*
			 * If a MOVED_OFF tuple is not dead, the xvac transaction must
			 * have failed; whereas a non-dead MOVED_IN tuple must mean the
			 * xvac transaction succeeded.
			 */
			if (tuple->t_infomask & HEAP_MOVED_OFF)
				HeapTupleHeaderSetXvac(tuple, InvalidTransactionId);
			else
				HeapTupleHeaderSetXvac(tuple, FrozenTransactionId);

			/*
			 * Might as well fix the hint bits too; usually XMIN_COMMITTED
			 * will already be set here, but there's a small chance not.
			 */
			Assert(!(tuple->t_infomask & HEAP_XMIN_INVALID));
			tuple->t_infomask |= HEAP_XMIN_COMMITTED;
			changed = true;
		}
	}

	return changed;
}

/*
 * For a given MultiXactId, return the hint bits that should be set in the
 * tuple's infomask.
 *
 * Normally this should be called for a multixact that was just created, and
 * so is on our local cache, so the GetMembers call is fast.
 */
static void
GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
					   uint16 *new_infomask2)
{
	int		nmembers;
	MultiXactMember	*members;
	int		i;
	uint16	bits = HEAP_XMAX_IS_MULTI;
	uint16	bits2 = 0;
	bool	has_update = false;
	LockTupleMode	strongest = LockTupleKeyShare;

	/*
	 * We only use this in multis we just created, so they cannot be values
	 * pre-pg_upgrade.
	 */
	nmembers = GetMultiXactIdMembers(multi, &members, false);

	for (i = 0; i < nmembers; i++)
	{
		LockTupleMode	mode;

		/*
		 * Remember the strongest lock mode held by any member of the
		 * multixact.
		 */
		mode = TUPLOCK_from_mxstatus(members[i].status);
		if (mode > strongest)
			strongest = mode;

		/* See what other bits we need */
		switch (members[i].status)
		{
			case MultiXactStatusForKeyShare:
			case MultiXactStatusForShare:
			case MultiXactStatusForNoKeyUpdate:
				break;

			case MultiXactStatusForUpdate:
				bits2 |= HEAP_KEYS_UPDATED;
				break;

			case MultiXactStatusNoKeyUpdate:
				has_update = true;
				break;

			case MultiXactStatusUpdate:
				bits2 |= HEAP_KEYS_UPDATED;
				has_update = true;
				break;
		}
	}

	if (strongest == LockTupleExclusive ||
		strongest == LockTupleNoKeyExclusive)
		bits |= HEAP_XMAX_EXCL_LOCK;
	else if (strongest == LockTupleShare)
		bits |= HEAP_XMAX_SHR_LOCK;
	else if (strongest == LockTupleKeyShare)
		bits |= HEAP_XMAX_KEYSHR_LOCK;

	if (!has_update)
		bits |= HEAP_XMAX_LOCK_ONLY;

	if (nmembers > 0)
		pfree(members);

	*new_infomask = bits;
	*new_infomask2 = bits2;
}

/*
 * MultiXactIdGetUpdateXid
 *
 * Given a multixact Xmax and corresponding infomask, which does not have the
 * HEAP_XMAX_LOCK_ONLY bit set, obtain and return the Xid of the updating
 * transaction.
 */
static TransactionId
MultiXactIdGetUpdateXid(TransactionId xmax, uint16 t_infomask)
{
	TransactionId	update_xact = InvalidTransactionId;
	MultiXactMember	*members;
	int				nmembers;

	Assert(!(t_infomask & HEAP_XMAX_LOCK_ONLY));
	Assert(t_infomask & HEAP_XMAX_IS_MULTI);

	/*
	 * Since we know the LOCK_ONLY bit is not set, this cannot be a
	 * multi from pre-pg_upgrade.
	 */
	nmembers = GetMultiXactIdMembers(xmax, &members, false);

	if (nmembers > 0)
	{
		int		i;

		for (i = 0; i < nmembers; i++)
		{
			/* Ignore lockers */
			if (members[i].status == MultiXactStatusForKeyShare ||
				members[i].status == MultiXactStatusForShare ||
				members[i].status == MultiXactStatusForNoKeyUpdate ||
				members[i].status == MultiXactStatusForUpdate)
				continue;

			/* ignore aborted transactions */
			if (TransactionIdDidAbort(members[i].xid))
				continue;
			/* there should be at most one non-aborted updater */
			Assert(update_xact == InvalidTransactionId);
			Assert(members[i].status == MultiXactStatusNoKeyUpdate ||
				   members[i].status == MultiXactStatusUpdate);
			update_xact = members[i].xid;
#ifndef USE_ASSERT_CHECKING
			/*
			 * in an assert-enabled build, walk the whole array to ensure
			 * there's no other updater.
			 */
			break;
#endif
		}

		pfree(members);
	}

	return update_xact;
}

/*
 * HeapTupleGetUpdateXid
 * 		As above, but use a HeapTupleHeader
 *
 * See also HeapTupleHeaderGetUpdateXid, which can be used without previously
 * checking the hint bits.
 */
TransactionId
HeapTupleGetUpdateXid(HeapTupleHeader tuple)
{
	return MultiXactIdGetUpdateXid(HeapTupleHeaderGetRawXmax(tuple),
								   tuple->t_infomask);
}

/*
 * Do_MultiXactIdWait
 * 		Actual implementation for the two functions below.
 *
 * We do this by sleeping on each member using XactLockTableWait.  Any
 * members that belong to the current backend are *not* waited for, however;
 * this would not merely be useless but would lead to Assert failure inside
 * XactLockTableWait.  By the time this returns, it is certain that all
 * transactions *of other backends* that were members of the MultiXactId
 * that conflict with the requested status are dead (and no new ones can have
 * been added, since it is not legal to add members to an existing
 * MultiXactId).
 *
 * But by the time we finish sleeping, someone else may have changed the Xmax
 * of the containing tuple, so the caller needs to iterate on us somehow.
 *
 * Note that in case we return false, the number of remaining members is
 * not to be trusted.
 */
static bool
Do_MultiXactIdWait(MultiXactId multi, MultiXactStatus status,
				   int *remaining, uint16 infomask, bool nowait)
{
	bool		allow_old;
	bool		result = true;
	MultiXactMember *members;
	int			nmembers;
	int			remain = 0;

	allow_old = !(infomask & HEAP_LOCK_MASK) && HEAP_XMAX_IS_LOCKED_ONLY(infomask);
	nmembers = GetMultiXactIdMembers(multi, &members, allow_old);

	if (nmembers >= 0)
	{
		int			i;

		for (i = 0; i < nmembers; i++)
		{
			TransactionId memxid = members[i].xid;
			MultiXactStatus memstatus = members[i].status;

			if (TransactionIdIsCurrentTransactionId(memxid))
			{
				remain++;
				continue;
			}

			if (!DoLockModesConflict(LOCKMODE_from_mxstatus(memstatus),
									 LOCKMODE_from_mxstatus(status)))
			{
				if (remaining && TransactionIdIsInProgress(memxid))
					remain++;
				continue;
			}

			/*
			 * This member conflicts with our multi, so we have to sleep (or
			 * return failure, if asked to avoid waiting.)
			 */
			if (nowait)
			{
				result = ConditionalXactLockTableWait(memxid);
				if (!result)
					break;
			}
			else
				XactLockTableWait(memxid);
		}

		pfree(members);
	}

	if (remaining)
		*remaining = remain;

	return result;
}

/*
 * MultiXactIdWait
 *		Sleep on a MultiXactId.
 *
 * By the time we finish sleeping, someone else may have changed the Xmax
 * of the containing tuple, so the caller needs to iterate on us somehow.
 *
 * We return (in *remaining, if not NULL) the number of members that are still
 * running, including any (non-aborted) subtransactions of our own transaction.
 *
 */
static void
MultiXactIdWait(MultiXactId multi, MultiXactStatus status,
				int *remaining, uint16 infomask)
{
	Do_MultiXactIdWait(multi, status, remaining, infomask, false);
}

/*
 * ConditionalMultiXactIdWait
 *		As above, but only lock if we can get the lock without blocking.
 *
 * By the time we finish sleeping, someone else may have changed the Xmax
 * of the containing tuple, so the caller needs to iterate on us somehow.
 *
 * If the multixact is now all gone, return true.  Returns false if some
 * transactions might still be running.
 *
 * We return (in *remaining, if not NULL) the number of members that are still
 * running, including any (non-aborted) subtransactions of our own transaction.
 */
static bool
ConditionalMultiXactIdWait(MultiXactId multi, MultiXactStatus status,
						   int *remaining, uint16 infomask)
{
	return Do_MultiXactIdWait(multi, status, remaining, infomask, true);
}

/*
 * heap_tuple_needs_freeze
 *
 * Check to see whether any of the XID fields of a tuple (xmin, xmax, xvac)
 * are older than the specified cutoff XID or MultiXactId.  If so, return TRUE.
 *
 * It doesn't matter whether the tuple is alive or dead, we are checking
 * to see if a tuple needs to be removed or frozen to avoid wraparound.
 */
bool
heap_tuple_needs_freeze(HeapTupleHeader tuple, TransactionId cutoff_xid,
						MultiXactId cutoff_multi, Buffer buf)
{
	TransactionId xid;

	xid = HeapTupleHeaderGetXmin(tuple);
	if (TransactionIdIsNormal(xid) &&
		TransactionIdPrecedes(xid, cutoff_xid))
		return true;

	if (!(tuple->t_infomask & HEAP_XMAX_INVALID))
	{
		if (!(tuple->t_infomask & HEAP_XMAX_IS_MULTI))
		{
			xid = HeapTupleHeaderGetRawXmax(tuple);
			if (TransactionIdIsNormal(xid) &&
				TransactionIdPrecedes(xid, cutoff_xid))
				return true;
		}
		else
		{
			MultiXactId multi;

			multi = HeapTupleHeaderGetRawXmax(tuple);
			if (MultiXactIdPrecedes(multi, cutoff_multi))
				return true;
		}
	}

	if (tuple->t_infomask & HEAP_MOVED)
	{
		xid = HeapTupleHeaderGetXvac(tuple);
		if (TransactionIdIsNormal(xid) &&
			TransactionIdPrecedes(xid, cutoff_xid))
			return true;
	}

	return false;
}

/* ----------------
 *		heap_markpos	- mark scan position
 * ----------------
 */
void
heap_markpos(HeapScanDesc scan)
{
	/* Note: no locking manipulations needed */

	if (scan->rs_ctup.t_data != NULL)
	{
		scan->rs_mctid = scan->rs_ctup.t_self;
		if (scan->rs_pageatatime)
			scan->rs_mindex = scan->rs_cindex;
	}
	else
		ItemPointerSetInvalid(&scan->rs_mctid);
}

/* ----------------
 *		heap_restrpos	- restore position to marked location
 * ----------------
 */
void
heap_restrpos(HeapScanDesc scan)
{
	/* XXX no amrestrpos checking that ammarkpos called */

	if (!ItemPointerIsValid(&scan->rs_mctid))
	{
		scan->rs_ctup.t_data = NULL;

		/*
		 * unpin scan buffers
		 */
		if (BufferIsValid(scan->rs_cbuf))
			ReleaseBuffer(scan->rs_cbuf);
		scan->rs_cbuf = InvalidBuffer;
		scan->rs_cblock = InvalidBlockNumber;
		scan->rs_inited = false;
	}
	else
	{
		/*
		 * If we reached end of scan, rs_inited will now be false.	We must
		 * reset it to true to keep heapgettup from doing the wrong thing.
		 */
		scan->rs_inited = true;
		scan->rs_ctup.t_self = scan->rs_mctid;
		if (scan->rs_pageatatime)
		{
			scan->rs_cindex = scan->rs_mindex;
			heapgettup_pagemode(scan,
								NoMovementScanDirection,
								0,		/* needn't recheck scan keys */
								NULL);
		}
		else
			heapgettup(scan,
					   NoMovementScanDirection,
					   0,		/* needn't recheck scan keys */
					   NULL);
	}
}

/*
 * If 'tuple' contains any visible XID greater than latestRemovedXid,
 * ratchet forwards latestRemovedXid to the greatest one found.
 * This is used as the basis for generating Hot Standby conflicts, so
 * if a tuple was never visible then removing it should not conflict
 * with queries.
 */
void
HeapTupleHeaderAdvanceLatestRemovedXid(HeapTupleHeader tuple,
									   TransactionId *latestRemovedXid)
{
	TransactionId xmin = HeapTupleHeaderGetXmin(tuple);
	TransactionId xmax = HeapTupleHeaderGetUpdateXid(tuple);
	TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

	if (tuple->t_infomask & HEAP_MOVED)
	{
		if (TransactionIdPrecedes(*latestRemovedXid, xvac))
			*latestRemovedXid = xvac;
	}

	/*
	 * Ignore tuples inserted by an aborted transaction or if the tuple was
	 * updated/deleted by the inserting transaction.
	 *
	 * Look for a committed hint bit, or if no xmin bit is set, check clog.
	 * This needs to work on both master and standby, where it is used to
	 * assess btree delete records.
	 */
	if ((tuple->t_infomask & HEAP_XMIN_COMMITTED) ||
		(!(tuple->t_infomask & HEAP_XMIN_COMMITTED) &&
		 !(tuple->t_infomask & HEAP_XMIN_INVALID) &&
		 TransactionIdDidCommit(xmin)))
	{
		if (xmax != xmin &&
			TransactionIdFollows(xmax, *latestRemovedXid))
			*latestRemovedXid = xmax;
	}

	/* *latestRemovedXid may still be invalid at end */
}

/*
 * Perform XLogInsert to register a heap cleanup info message. These
 * messages are sent once per VACUUM and are required because
 * of the phasing of removal operations during a lazy VACUUM.
 * see comments for vacuum_log_cleanup_info().
 */
XLogRecPtr
log_heap_cleanup_info(RelFileNode rnode, TransactionId latestRemovedXid)
{
	xl_heap_cleanup_info xlrec;
	XLogRecPtr	recptr;
	XLogRecData rdata;

	xlrec.node = rnode;
	xlrec.latestRemovedXid = latestRemovedXid;

	rdata.data = (char *) &xlrec;
	rdata.len = SizeOfHeapCleanupInfo;
	rdata.buffer = InvalidBuffer;
	rdata.next = NULL;

	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_CLEANUP_INFO, &rdata);

	return recptr;
}

/*
 * Perform XLogInsert for a heap-clean operation.  Caller must already
 * have modified the buffer and marked it dirty.
 *
 * Note: prior to Postgres 8.3, the entries in the nowunused[] array were
 * zero-based tuple indexes.  Now they are one-based like other uses
 * of OffsetNumber.
 *
 * We also include latestRemovedXid, which is the greatest XID present in
 * the removed tuples. That allows recovery processing to cancel or wait
 * for long standby queries that can still see these tuples.
 */
XLogRecPtr
log_heap_clean(Relation reln, Buffer buffer,
			   OffsetNumber *redirected, int nredirected,
			   OffsetNumber *nowdead, int ndead,
			   OffsetNumber *nowunused, int nunused,
			   TransactionId latestRemovedXid)
{
	xl_heap_clean xlrec;
	uint8		info;
	XLogRecPtr	recptr;
	XLogRecData rdata[4];

	/* Caller should not call me on a non-WAL-logged relation */
	Assert(RelationNeedsWAL(reln));

	xlrec.node = reln->rd_node;
	xlrec.block = BufferGetBlockNumber(buffer);
	xlrec.latestRemovedXid = latestRemovedXid;
	xlrec.nredirected = nredirected;
	xlrec.ndead = ndead;

	rdata[0].data = (char *) &xlrec;
	rdata[0].len = SizeOfHeapClean;
	rdata[0].buffer = InvalidBuffer;
	rdata[0].next = &(rdata[1]);

	/*
	 * The OffsetNumber arrays are not actually in the buffer, but we pretend
	 * that they are.  When XLogInsert stores the whole buffer, the offset
	 * arrays need not be stored too.  Note that even if all three arrays are
	 * empty, we want to expose the buffer as a candidate for whole-page
	 * storage, since this record type implies a defragmentation operation
	 * even if no item pointers changed state.
	 */
	if (nredirected > 0)
	{
		rdata[1].data = (char *) redirected;
		rdata[1].len = nredirected * sizeof(OffsetNumber) * 2;
	}
	else
	{
		rdata[1].data = NULL;
		rdata[1].len = 0;
	}
	rdata[1].buffer = buffer;
	rdata[1].buffer_std = true;
	rdata[1].next = &(rdata[2]);

	if (ndead > 0)
	{
		rdata[2].data = (char *) nowdead;
		rdata[2].len = ndead * sizeof(OffsetNumber);
	}
	else
	{
		rdata[2].data = NULL;
		rdata[2].len = 0;
	}
	rdata[2].buffer = buffer;
	rdata[2].buffer_std = true;
	rdata[2].next = &(rdata[3]);

	if (nunused > 0)
	{
		rdata[3].data = (char *) nowunused;
		rdata[3].len = nunused * sizeof(OffsetNumber);
	}
	else
	{
		rdata[3].data = NULL;
		rdata[3].len = 0;
	}
	rdata[3].buffer = buffer;
	rdata[3].buffer_std = true;
	rdata[3].next = NULL;

	info = XLOG_HEAP2_CLEAN;
	recptr = XLogInsert(RM_HEAP2_ID, info, rdata);

	return recptr;
}

/*
 * Perform XLogInsert for a heap-freeze operation.	Caller must already
 * have modified the buffer and marked it dirty.
 */
XLogRecPtr
log_heap_freeze(Relation reln, Buffer buffer,
				TransactionId cutoff_xid, MultiXactId cutoff_multi,
				OffsetNumber *offsets, int offcnt)
{
	xl_heap_freeze xlrec;
	XLogRecPtr	recptr;
	XLogRecData rdata[2];

	/* Caller should not call me on a non-WAL-logged relation */
	Assert(RelationNeedsWAL(reln));
	/* nor when there are no tuples to freeze */
	Assert(offcnt > 0);

	xlrec.node = reln->rd_node;
	xlrec.block = BufferGetBlockNumber(buffer);
	xlrec.cutoff_xid = cutoff_xid;
	xlrec.cutoff_multi = cutoff_multi;

	rdata[0].data = (char *) &xlrec;
	rdata[0].len = SizeOfHeapFreeze;
	rdata[0].buffer = InvalidBuffer;
	rdata[0].next = &(rdata[1]);

	/*
	 * The tuple-offsets array is not actually in the buffer, but pretend that
	 * it is.  When XLogInsert stores the whole buffer, the offsets array need
	 * not be stored too.
	 */
	rdata[1].data = (char *) offsets;
	rdata[1].len = offcnt * sizeof(OffsetNumber);
	rdata[1].buffer = buffer;
	rdata[1].buffer_std = true;
	rdata[1].next = NULL;

	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_FREEZE, rdata);

	return recptr;
}

/*
 * Perform XLogInsert for a heap-visible operation.  'block' is the block
 * being marked all-visible, and vm_buffer is the buffer containing the
 * corresponding visibility map block.	Both should have already been modified
 * and dirtied.
 *
 * If checksums are enabled, we also add the heap_buffer to the chain to
 * protect it from being torn.
 */
XLogRecPtr
log_heap_visible(RelFileNode rnode, Buffer heap_buffer, Buffer vm_buffer,
				 TransactionId cutoff_xid)
{
	xl_heap_visible xlrec;
	XLogRecPtr	recptr;
	XLogRecData rdata[3];

	Assert(BufferIsValid(heap_buffer));
	Assert(BufferIsValid(vm_buffer));

	xlrec.node = rnode;
	xlrec.block = BufferGetBlockNumber(heap_buffer);
	xlrec.cutoff_xid = cutoff_xid;

	rdata[0].data = (char *) &xlrec;
	rdata[0].len = SizeOfHeapVisible;
	rdata[0].buffer = InvalidBuffer;
	rdata[0].next = &(rdata[1]);

	rdata[1].data = NULL;
	rdata[1].len = 0;
	rdata[1].buffer = vm_buffer;
	rdata[1].buffer_std = false;
	rdata[1].next = NULL;

	if (DataChecksumsEnabled())
	{
		rdata[1].next = &(rdata[2]);

		rdata[2].data = NULL;
		rdata[2].len = 0;
		rdata[2].buffer = heap_buffer;
		rdata[2].buffer_std = true;
		rdata[2].next = NULL;
	}

	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_VISIBLE, rdata);

	return recptr;
}

/*
 * Perform XLogInsert for a heap-update operation.	Caller must already
 * have modified the buffer(s) and marked them dirty.
 */
static XLogRecPtr
log_heap_update(Relation reln, Buffer oldbuf,
				Buffer newbuf, HeapTuple oldtup, HeapTuple newtup,
				bool all_visible_cleared, bool new_all_visible_cleared)
{
	xl_heap_update xlrec;
	xl_heap_header xlhdr;
	uint8		info;
	XLogRecPtr	recptr;
	XLogRecData rdata[4];
	Page		page = BufferGetPage(newbuf);

	/* Caller should not call me on a non-WAL-logged relation */
	Assert(RelationNeedsWAL(reln));

	if (HeapTupleIsHeapOnly(newtup))
		info = XLOG_HEAP_HOT_UPDATE;
	else
		info = XLOG_HEAP_UPDATE;

	xlrec.target.node = reln->rd_node;
	xlrec.target.tid = oldtup->t_self;
	xlrec.old_xmax = HeapTupleHeaderGetRawXmax(oldtup->t_data);
	xlrec.old_infobits_set = compute_infobits(oldtup->t_data->t_infomask,
											  oldtup->t_data->t_infomask2);
	xlrec.new_xmax = HeapTupleHeaderGetRawXmax(newtup->t_data);
	xlrec.all_visible_cleared = all_visible_cleared;
	xlrec.newtid = newtup->t_self;
	xlrec.new_all_visible_cleared = new_all_visible_cleared;

	rdata[0].data = (char *) &xlrec;
	rdata[0].len = SizeOfHeapUpdate;
	rdata[0].buffer = InvalidBuffer;
	rdata[0].next = &(rdata[1]);

	rdata[1].data = NULL;
	rdata[1].len = 0;
	rdata[1].buffer = oldbuf;
	rdata[1].buffer_std = true;
	rdata[1].next = &(rdata[2]);

	xlhdr.t_infomask2 = newtup->t_data->t_infomask2;
	xlhdr.t_infomask = newtup->t_data->t_infomask;
	xlhdr.t_hoff = newtup->t_data->t_hoff;

	/*
	 * As with insert records, we need not store the rdata[2] segment if we
	 * decide to store the whole buffer instead.
	 */
	rdata[2].data = (char *) &xlhdr;
	rdata[2].len = SizeOfHeapHeader;
	rdata[2].buffer = newbuf;
	rdata[2].buffer_std = true;
	rdata[2].next = &(rdata[3]);

	/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
	rdata[3].data = (char *) newtup->t_data + offsetof(HeapTupleHeaderData, t_bits);
	rdata[3].len = newtup->t_len - offsetof(HeapTupleHeaderData, t_bits);
	rdata[3].buffer = newbuf;
	rdata[3].buffer_std = true;
	rdata[3].next = NULL;

	/* If new tuple is the single and first tuple on page... */
	if (ItemPointerGetOffsetNumber(&(newtup->t_self)) == FirstOffsetNumber &&
		PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
	{
		info |= XLOG_HEAP_INIT_PAGE;
		rdata[2].buffer = rdata[3].buffer = InvalidBuffer;
	}

	recptr = XLogInsert(RM_HEAP_ID, info, rdata);

	return recptr;
}

/*
 * Perform XLogInsert of a HEAP_NEWPAGE record to WAL. Caller is responsible
 * for writing the page to disk after calling this routine.
 *
 * Note: If you're using this function, you should be building pages in private
 * memory and writing them directly to smgr.  If you're using buffers, call
 * log_newpage_buffer instead.
 *
 * Note: the NEWPAGE log record is used for both heaps and indexes, so do
 * not do anything that assumes we are touching a heap.
 */
XLogRecPtr
log_newpage(RelFileNode *rnode, ForkNumber forkNum, BlockNumber blkno,
			Page page)
{
	xl_heap_newpage xlrec;
	XLogRecPtr	recptr;
	XLogRecData rdata[2];

	/* NO ELOG(ERROR) from here till newpage op is logged */
	START_CRIT_SECTION();

	xlrec.node = *rnode;
	xlrec.forknum = forkNum;
	xlrec.blkno = blkno;

	rdata[0].data = (char *) &xlrec;
	rdata[0].len = SizeOfHeapNewpage;
	rdata[0].buffer = InvalidBuffer;
	rdata[0].next = &(rdata[1]);

	rdata[1].data = (char *) page;
	rdata[1].len = BLCKSZ;
	rdata[1].buffer = InvalidBuffer;
	rdata[1].next = NULL;

	recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_NEWPAGE, rdata);

	/*
	 * The page may be uninitialized. If so, we can't set the LSN and TLI
	 * because that would corrupt the page.
	 */
	if (!PageIsNew(page))
	{
		PageSetLSN(page, recptr);
	}

	END_CRIT_SECTION();

	return recptr;
}

/*
 * Perform XLogInsert of a HEAP_NEWPAGE record to WAL.
 *
 * Caller should initialize the buffer and mark it dirty before calling this
 * function.  This function will set the page LSN and TLI.
 *
 * Note: the NEWPAGE log record is used for both heaps and indexes, so do
 * not do anything that assumes we are touching a heap.
 */
XLogRecPtr
log_newpage_buffer(Buffer buffer)
{
	xl_heap_newpage xlrec;
	XLogRecPtr	recptr;
	XLogRecData rdata[2];
	Page		page = BufferGetPage(buffer);

	/* We should be in a critical section. */
	Assert(CritSectionCount > 0);

	BufferGetTag(buffer, &xlrec.node, &xlrec.forknum, &xlrec.blkno);

	rdata[0].data = (char *) &xlrec;
	rdata[0].len = SizeOfHeapNewpage;
	rdata[0].buffer = InvalidBuffer;
	rdata[0].next = &(rdata[1]);

	rdata[1].data = page;
	rdata[1].len = BLCKSZ;
	rdata[1].buffer = InvalidBuffer;
	rdata[1].next = NULL;

	recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_NEWPAGE, rdata);

	/*
	 * The page may be uninitialized. If so, we can't set the LSN and TLI
	 * because that would corrupt the page.
	 */
	if (!PageIsNew(page))
	{
		PageSetLSN(page, recptr);
	}

	return recptr;
}

/*
 * Handles CLEANUP_INFO
 */
static void
heap_xlog_cleanup_info(XLogRecPtr lsn, XLogRecord *record)
{
	xl_heap_cleanup_info *xlrec = (xl_heap_cleanup_info *) XLogRecGetData(record);

	if (InHotStandby)
		ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid, xlrec->node);

	/*
	 * Actual operation is a no-op. Record type exists to provide a means for
	 * conflict processing to occur before we begin index vacuum actions. see
	 * vacuumlazy.c and also comments in btvacuumpage()
	 */

	/* Backup blocks are not used in cleanup_info records */
	Assert(!(record->xl_info & XLR_BKP_BLOCK_MASK));
}

/*
 * Handles HEAP2_CLEAN record type
 */
static void
heap_xlog_clean(XLogRecPtr lsn, XLogRecord *record)
{
	xl_heap_clean *xlrec = (xl_heap_clean *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;
	OffsetNumber *end;
	OffsetNumber *redirected;
	OffsetNumber *nowdead;
	OffsetNumber *nowunused;
	int			nredirected;
	int			ndead;
	int			nunused;
	Size		freespace;

	/*
	 * We're about to remove tuples. In Hot Standby mode, ensure that there's
	 * no queries running for which the removed tuples are still visible.
	 *
	 * Not all HEAP2_CLEAN records remove tuples with xids, so we only want to
	 * conflict on the records that cause MVCC failures for user queries. If
	 * latestRemovedXid is invalid, skip conflict processing.
	 */
	if (InHotStandby && TransactionIdIsValid(xlrec->latestRemovedXid))
		ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid,
											xlrec->node);

	/*
	 * If we have a full-page image, restore it (using a cleanup lock) and
	 * we're done.
	 */
	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		(void) RestoreBackupBlock(lsn, record, 0, true, false);
		return;
	}

	buffer = XLogReadBufferExtended(xlrec->node, MAIN_FORKNUM, xlrec->block, RBM_NORMAL);
	if (!BufferIsValid(buffer))
		return;
	LockBufferForCleanup(buffer);
	page = (Page) BufferGetPage(buffer);

	if (lsn <= PageGetLSN(page))
	{
		UnlockReleaseBuffer(buffer);
		return;
	}

	nredirected = xlrec->nredirected;
	ndead = xlrec->ndead;
	end = (OffsetNumber *) ((char *) xlrec + record->xl_len);
	redirected = (OffsetNumber *) ((char *) xlrec + SizeOfHeapClean);
	nowdead = redirected + (nredirected * 2);
	nowunused = nowdead + ndead;
	nunused = (end - nowunused);
	Assert(nunused >= 0);

	/* Update all item pointers per the record, and repair fragmentation */
	heap_page_prune_execute(buffer,
							redirected, nredirected,
							nowdead, ndead,
							nowunused, nunused);

	freespace = PageGetHeapFreeSpace(page);		/* needed to update FSM below */

	/*
	 * Note: we don't worry about updating the page's prunability hints. At
	 * worst this will cause an extra prune cycle to occur soon.
	 */

	PageSetLSN(page, lsn);
	MarkBufferDirty(buffer);
	UnlockReleaseBuffer(buffer);

	/*
	 * Update the FSM as well.
	 *
	 * XXX: We don't get here if the page was restored from full page image.
	 * We don't bother to update the FSM in that case, it doesn't need to be
	 * totally accurate anyway.
	 */
	XLogRecordPageWithFreeSpace(xlrec->node, xlrec->block, freespace);
}

static void
heap_xlog_freeze(XLogRecPtr lsn, XLogRecord *record)
{
	xl_heap_freeze *xlrec = (xl_heap_freeze *) XLogRecGetData(record);
	TransactionId cutoff_xid = xlrec->cutoff_xid;
	MultiXactId	cutoff_multi = xlrec->cutoff_multi;
	Buffer		buffer;
	Page		page;

	/*
	 * In Hot Standby mode, ensure that there's no queries running which still
	 * consider the frozen xids as running.
	 */
	if (InHotStandby)
		ResolveRecoveryConflictWithSnapshot(cutoff_xid, xlrec->node);

	/* If we have a full-page image, restore it and we're done */
	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
		return;
	}

	buffer = XLogReadBuffer(xlrec->node, xlrec->block, false);
	if (!BufferIsValid(buffer))
		return;
	page = (Page) BufferGetPage(buffer);

	if (lsn <= PageGetLSN(page))
	{
		UnlockReleaseBuffer(buffer);
		return;
	}

	if (record->xl_len > SizeOfHeapFreeze)
	{
		OffsetNumber *offsets;
		OffsetNumber *offsets_end;

		offsets = (OffsetNumber *) ((char *) xlrec + SizeOfHeapFreeze);
		offsets_end = (OffsetNumber *) ((char *) xlrec + record->xl_len);

		while (offsets < offsets_end)
		{
			/* offsets[] entries are one-based */
			ItemId		lp = PageGetItemId(page, *offsets);
			HeapTupleHeader tuple = (HeapTupleHeader) PageGetItem(page, lp);

			(void) heap_freeze_tuple(tuple, cutoff_xid, cutoff_multi);
			offsets++;
		}
	}

	PageSetLSN(page, lsn);
	MarkBufferDirty(buffer);
	UnlockReleaseBuffer(buffer);
}

/*
 * Replay XLOG_HEAP2_VISIBLE record.
 *
 * The critical integrity requirement here is that we must never end up with
 * a situation where the visibility map bit is set, and the page-level
 * PD_ALL_VISIBLE bit is clear.  If that were to occur, then a subsequent
 * page modification would fail to clear the visibility map bit.
 */
static void
heap_xlog_visible(XLogRecPtr lsn, XLogRecord *record)
{
	xl_heap_visible *xlrec = (xl_heap_visible *) XLogRecGetData(record);

	/*
	 * If there are any Hot Standby transactions running that have an xmin
	 * horizon old enough that this page isn't all-visible for them, they
	 * might incorrectly decide that an index-only scan can skip a heap fetch.
	 *
	 * NB: It might be better to throw some kind of "soft" conflict here that
	 * forces any index-only scan that is in flight to perform heap fetches,
	 * rather than killing the transaction outright.
	 */
	if (InHotStandby)
		ResolveRecoveryConflictWithSnapshot(xlrec->cutoff_xid, xlrec->node);

	/*
	 * If heap block was backed up, restore it. This can only happen with
	 * checksums enabled.
	 */
	if (record->xl_info & XLR_BKP_BLOCK(1))
	{
		Assert(DataChecksumsEnabled());
		(void) RestoreBackupBlock(lsn, record, 1, false, false);
	}
	else
	{
		Buffer		buffer;
		Page		page;

		/*
		 * Read the heap page, if it still exists. If the heap file has been
		 * dropped or truncated later in recovery, we don't need to update the
		 * page, but we'd better still update the visibility map.
		 */
		buffer = XLogReadBufferExtended(xlrec->node, MAIN_FORKNUM,
										xlrec->block, RBM_NORMAL);
		if (BufferIsValid(buffer))
		{
			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

			page = (Page) BufferGetPage(buffer);

			/*
			 * We don't bump the LSN of the heap page when setting the
			 * visibility map bit (unless checksums are enabled, in which case
			 * we must), because that would generate an unworkable volume of
			 * full-page writes.  This exposes us to torn page hazards, but
			 * since we're not inspecting the existing page contents in any
			 * way, we don't care.
			 *
			 * However, all operations that clear the visibility map bit *do*
			 * bump the LSN, and those operations will only be replayed if the
			 * XLOG LSN follows the page LSN.  Thus, if the page LSN has
			 * advanced past our XLOG record's LSN, we mustn't mark the page
			 * all-visible, because the subsequent update won't be replayed to
			 * clear the flag.
			 */
			if (lsn > PageGetLSN(page))
			{
				PageSetAllVisible(page);
				MarkBufferDirty(buffer);
			}

			/* Done with heap page. */
			UnlockReleaseBuffer(buffer);
		}
	}

	/*
	 * Even if we skipped the heap page update due to the LSN interlock, it's
	 * still safe to update the visibility map.  Any WAL record that clears
	 * the visibility map bit does so before checking the page LSN, so any
	 * bits that need to be cleared will still be cleared.
	 */
	if (record->xl_info & XLR_BKP_BLOCK(0))
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
	else
	{
		Relation	reln;
		Buffer		vmbuffer = InvalidBuffer;

		reln = CreateFakeRelcacheEntry(xlrec->node);
		visibilitymap_pin(reln, xlrec->block, &vmbuffer);

		/*
		 * Don't set the bit if replay has already passed this point.
		 *
		 * It might be safe to do this unconditionally; if replay has passed
		 * this point, we'll replay at least as far this time as we did
		 * before, and if this bit needs to be cleared, the record responsible
		 * for doing so should be again replayed, and clear it.  For right
		 * now, out of an abundance of conservatism, we use the same test here
		 * we did for the heap page.  If this results in a dropped bit, no
		 * real harm is done; and the next VACUUM will fix it.
		 */
		if (lsn > PageGetLSN(BufferGetPage(vmbuffer)))
			visibilitymap_set(reln, xlrec->block, InvalidBuffer, lsn, vmbuffer,
							  xlrec->cutoff_xid);

		ReleaseBuffer(vmbuffer);
		FreeFakeRelcacheEntry(reln);
	}
}

static void
heap_xlog_newpage(XLogRecPtr lsn, XLogRecord *record)
{
	xl_heap_newpage *xlrec = (xl_heap_newpage *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;

	/* Backup blocks are not used in newpage records */
	Assert(!(record->xl_info & XLR_BKP_BLOCK_MASK));

	/*
	 * Note: the NEWPAGE log record is used for both heaps and indexes, so do
	 * not do anything that assumes we are touching a heap.
	 */
	buffer = XLogReadBufferExtended(xlrec->node, xlrec->forknum, xlrec->blkno,
									RBM_ZERO);
	Assert(BufferIsValid(buffer));
	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
	page = (Page) BufferGetPage(buffer);

	Assert(record->xl_len == SizeOfHeapNewpage + BLCKSZ);
	memcpy(page, (char *) xlrec + SizeOfHeapNewpage, BLCKSZ);

	/*
	 * The page may be uninitialized. If so, we can't set the LSN because that
	 * would corrupt the page.
	 */
	if (!PageIsNew(page))
	{
		PageSetLSN(page, lsn);
	}

	MarkBufferDirty(buffer);
	UnlockReleaseBuffer(buffer);
}

/*
 * Given an "infobits" field from an XLog record, set the correct bits in the
 * given infomask and infomask2 for the tuple touched by the record.
 *
 * (This is the reverse of compute_infobits).
 */
static void
fix_infomask_from_infobits(uint8 infobits, uint16 *infomask, uint16 *infomask2)
{
	*infomask &= ~(HEAP_XMAX_IS_MULTI | HEAP_XMAX_LOCK_ONLY |
				   HEAP_XMAX_KEYSHR_LOCK | HEAP_XMAX_EXCL_LOCK);
	*infomask2 &= ~HEAP_KEYS_UPDATED;

	if (infobits & XLHL_XMAX_IS_MULTI)
		*infomask |= HEAP_XMAX_IS_MULTI;
	if (infobits & XLHL_XMAX_LOCK_ONLY)
		*infomask |= HEAP_XMAX_LOCK_ONLY;
	if (infobits & XLHL_XMAX_EXCL_LOCK)
		*infomask |= HEAP_XMAX_EXCL_LOCK;
	/* note HEAP_XMAX_SHR_LOCK isn't considered here */
	if (infobits & XLHL_XMAX_KEYSHR_LOCK)
		*infomask |= HEAP_XMAX_KEYSHR_LOCK;

	if (infobits & XLHL_KEYS_UPDATED)
		*infomask2 |= HEAP_KEYS_UPDATED;
}

static void
heap_xlog_delete(XLogRecPtr lsn, XLogRecord *record)
{
	xl_heap_delete *xlrec = (xl_heap_delete *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;
	OffsetNumber offnum;
	ItemId		lp = NULL;
	HeapTupleHeader htup;
	BlockNumber blkno;

	blkno = ItemPointerGetBlockNumber(&(xlrec->target.tid));

	/*
	 * The visibility map may need to be fixed even if the heap page is
	 * already up-to-date.
	 */
	if (xlrec->all_visible_cleared)
	{
		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
		Buffer		vmbuffer = InvalidBuffer;

		visibilitymap_pin(reln, blkno, &vmbuffer);
		visibilitymap_clear(reln, blkno, vmbuffer);
		ReleaseBuffer(vmbuffer);
		FreeFakeRelcacheEntry(reln);
	}

	/* If we have a full-page image, restore it and we're done */
	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
		return;
	}

	buffer = XLogReadBuffer(xlrec->target.node, blkno, false);
	if (!BufferIsValid(buffer))
		return;
	page = (Page) BufferGetPage(buffer);

	if (lsn <= PageGetLSN(page))		/* changes are applied */
	{
		UnlockReleaseBuffer(buffer);
		return;
	}

	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
	if (PageGetMaxOffsetNumber(page) >= offnum)
		lp = PageGetItemId(page, offnum);

	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
		elog(PANIC, "heap_delete_redo: invalid lp");

	htup = (HeapTupleHeader) PageGetItem(page, lp);

	htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
	htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
	HeapTupleHeaderClearHotUpdated(htup);
	fix_infomask_from_infobits(xlrec->infobits_set,
							   &htup->t_infomask, &htup->t_infomask2);
	HeapTupleHeaderSetXmax(htup, xlrec->xmax);
	HeapTupleHeaderSetCmax(htup, FirstCommandId, false);

	/* Mark the page as a candidate for pruning */
	PageSetPrunable(page, record->xl_xid);

	if (xlrec->all_visible_cleared)
		PageClearAllVisible(page);

	/* Make sure there is no forward chain link in t_ctid */
	htup->t_ctid = xlrec->target.tid;
	PageSetLSN(page, lsn);
	MarkBufferDirty(buffer);
	UnlockReleaseBuffer(buffer);
}

static void
heap_xlog_insert(XLogRecPtr lsn, XLogRecord *record)
{
	xl_heap_insert *xlrec = (xl_heap_insert *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;
	OffsetNumber offnum;
	struct
	{
		HeapTupleHeaderData hdr;
		char		data[MaxHeapTupleSize];
	}			tbuf;
	HeapTupleHeader htup;
	xl_heap_header xlhdr;
	uint32		newlen;
	Size		freespace;
	BlockNumber blkno;

	blkno = ItemPointerGetBlockNumber(&(xlrec->target.tid));

	/*
	 * The visibility map may need to be fixed even if the heap page is
	 * already up-to-date.
	 */
	if (xlrec->all_visible_cleared)
	{
		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
		Buffer		vmbuffer = InvalidBuffer;

		visibilitymap_pin(reln, blkno, &vmbuffer);
		visibilitymap_clear(reln, blkno, vmbuffer);
		ReleaseBuffer(vmbuffer);
		FreeFakeRelcacheEntry(reln);
	}

	/* If we have a full-page image, restore it and we're done */
	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
		return;
	}

	if (record->xl_info & XLOG_HEAP_INIT_PAGE)
	{
		buffer = XLogReadBuffer(xlrec->target.node, blkno, true);
		Assert(BufferIsValid(buffer));
		page = (Page) BufferGetPage(buffer);

		PageInit(page, BufferGetPageSize(buffer), 0);
	}
	else
	{
		buffer = XLogReadBuffer(xlrec->target.node, blkno, false);
		if (!BufferIsValid(buffer))
			return;
		page = (Page) BufferGetPage(buffer);

		if (lsn <= PageGetLSN(page))	/* changes are applied */
		{
			UnlockReleaseBuffer(buffer);
			return;
		}
	}

	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
	if (PageGetMaxOffsetNumber(page) + 1 < offnum)
		elog(PANIC, "heap_insert_redo: invalid max offset number");

	newlen = record->xl_len - SizeOfHeapInsert - SizeOfHeapHeader;
	Assert(newlen <= MaxHeapTupleSize);
	memcpy((char *) &xlhdr,
		   (char *) xlrec + SizeOfHeapInsert,
		   SizeOfHeapHeader);
	htup = &tbuf.hdr;
	MemSet((char *) htup, 0, sizeof(HeapTupleHeaderData));
	/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
	memcpy((char *) htup + offsetof(HeapTupleHeaderData, t_bits),
		   (char *) xlrec + SizeOfHeapInsert + SizeOfHeapHeader,
		   newlen);
	newlen += offsetof(HeapTupleHeaderData, t_bits);
	htup->t_infomask2 = xlhdr.t_infomask2;
	htup->t_infomask = xlhdr.t_infomask;
	htup->t_hoff = xlhdr.t_hoff;
	HeapTupleHeaderSetXmin(htup, record->xl_xid);
	HeapTupleHeaderSetCmin(htup, FirstCommandId);
	htup->t_ctid = xlrec->target.tid;

	offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
	if (offnum == InvalidOffsetNumber)
		elog(PANIC, "heap_insert_redo: failed to add tuple");

	freespace = PageGetHeapFreeSpace(page);		/* needed to update FSM below */

	PageSetLSN(page, lsn);

	if (xlrec->all_visible_cleared)
		PageClearAllVisible(page);

	MarkBufferDirty(buffer);
	UnlockReleaseBuffer(buffer);

	/*
	 * If the page is running low on free space, update the FSM as well.
	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
	 * better than that without knowing the fill-factor for the table.
	 *
	 * XXX: We don't get here if the page was restored from full page image.
	 * We don't bother to update the FSM in that case, it doesn't need to be
	 * totally accurate anyway.
	 */
	if (freespace < BLCKSZ / 5)
		XLogRecordPageWithFreeSpace(xlrec->target.node, blkno, freespace);
}

/*
 * Handles MULTI_INSERT record type.
 */
static void
heap_xlog_multi_insert(XLogRecPtr lsn, XLogRecord *record)
{
	char	   *recdata = XLogRecGetData(record);
	xl_heap_multi_insert *xlrec;
	Buffer		buffer;
	Page		page;
	struct
	{
		HeapTupleHeaderData hdr;
		char		data[MaxHeapTupleSize];
	}			tbuf;
	HeapTupleHeader htup;
	uint32		newlen;
	Size		freespace;
	BlockNumber blkno;
	int			i;
	bool		isinit = (record->xl_info & XLOG_HEAP_INIT_PAGE) != 0;

	/*
	 * Insertion doesn't overwrite MVCC data, so no conflict processing is
	 * required.
	 */

	xlrec = (xl_heap_multi_insert *) recdata;
	recdata += SizeOfHeapMultiInsert;

	/*
	 * If we're reinitializing the page, the tuples are stored in order from
	 * FirstOffsetNumber. Otherwise there's an array of offsets in the WAL
	 * record.
	 */
	if (!isinit)
		recdata += sizeof(OffsetNumber) * xlrec->ntuples;

	blkno = xlrec->blkno;

	/*
	 * The visibility map may need to be fixed even if the heap page is
	 * already up-to-date.
	 */
	if (xlrec->all_visible_cleared)
	{
		Relation	reln = CreateFakeRelcacheEntry(xlrec->node);
		Buffer		vmbuffer = InvalidBuffer;

		visibilitymap_pin(reln, blkno, &vmbuffer);
		visibilitymap_clear(reln, blkno, vmbuffer);
		ReleaseBuffer(vmbuffer);
		FreeFakeRelcacheEntry(reln);
	}

	/* If we have a full-page image, restore it and we're done */
	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
		return;
	}

	if (isinit)
	{
		buffer = XLogReadBuffer(xlrec->node, blkno, true);
		Assert(BufferIsValid(buffer));
		page = (Page) BufferGetPage(buffer);

		PageInit(page, BufferGetPageSize(buffer), 0);
	}
	else
	{
		buffer = XLogReadBuffer(xlrec->node, blkno, false);
		if (!BufferIsValid(buffer))
			return;
		page = (Page) BufferGetPage(buffer);

		if (lsn <= PageGetLSN(page))	/* changes are applied */
		{
			UnlockReleaseBuffer(buffer);
			return;
		}
	}

	for (i = 0; i < xlrec->ntuples; i++)
	{
		OffsetNumber offnum;
		xl_multi_insert_tuple *xlhdr;

		if (isinit)
			offnum = FirstOffsetNumber + i;
		else
			offnum = xlrec->offsets[i];
		if (PageGetMaxOffsetNumber(page) + 1 < offnum)
			elog(PANIC, "heap_multi_insert_redo: invalid max offset number");

		xlhdr = (xl_multi_insert_tuple *) SHORTALIGN(recdata);
		recdata = ((char *) xlhdr) + SizeOfMultiInsertTuple;

		newlen = xlhdr->datalen;
		Assert(newlen <= MaxHeapTupleSize);
		htup = &tbuf.hdr;
		MemSet((char *) htup, 0, sizeof(HeapTupleHeaderData));
		/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
		memcpy((char *) htup + offsetof(HeapTupleHeaderData, t_bits),
			   (char *) recdata,
			   newlen);
		recdata += newlen;

		newlen += offsetof(HeapTupleHeaderData, t_bits);
		htup->t_infomask2 = xlhdr->t_infomask2;
		htup->t_infomask = xlhdr->t_infomask;
		htup->t_hoff = xlhdr->t_hoff;
		HeapTupleHeaderSetXmin(htup, record->xl_xid);
		HeapTupleHeaderSetCmin(htup, FirstCommandId);
		ItemPointerSetBlockNumber(&htup->t_ctid, blkno);
		ItemPointerSetOffsetNumber(&htup->t_ctid, offnum);

		offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
		if (offnum == InvalidOffsetNumber)
			elog(PANIC, "heap_multi_insert_redo: failed to add tuple");
	}

	freespace = PageGetHeapFreeSpace(page);		/* needed to update FSM below */

	PageSetLSN(page, lsn);

	if (xlrec->all_visible_cleared)
		PageClearAllVisible(page);

	MarkBufferDirty(buffer);
	UnlockReleaseBuffer(buffer);

	/*
	 * If the page is running low on free space, update the FSM as well.
	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
	 * better than that without knowing the fill-factor for the table.
	 *
	 * XXX: We don't get here if the page was restored from full page image.
	 * We don't bother to update the FSM in that case, it doesn't need to be
	 * totally accurate anyway.
	 */
	if (freespace < BLCKSZ / 5)
		XLogRecordPageWithFreeSpace(xlrec->node, blkno, freespace);
}

/*
 * Handles UPDATE and HOT_UPDATE
 */
static void
heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool hot_update)
{
	xl_heap_update *xlrec = (xl_heap_update *) XLogRecGetData(record);
	bool		samepage = (ItemPointerGetBlockNumber(&(xlrec->newtid)) ==
							ItemPointerGetBlockNumber(&(xlrec->target.tid)));
	Buffer		obuffer,
				nbuffer;
	Page		page;
	OffsetNumber offnum;
	ItemId		lp = NULL;
	HeapTupleHeader htup;
	struct
	{
		HeapTupleHeaderData hdr;
		char		data[MaxHeapTupleSize];
	}			tbuf;
	xl_heap_header xlhdr;
	int			hsize;
	uint32		newlen;
	Size		freespace;

	/*
	 * The visibility map may need to be fixed even if the heap page is
	 * already up-to-date.
	 */
	if (xlrec->all_visible_cleared)
	{
		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
		BlockNumber block = ItemPointerGetBlockNumber(&xlrec->target.tid);
		Buffer		vmbuffer = InvalidBuffer;

		visibilitymap_pin(reln, block, &vmbuffer);
		visibilitymap_clear(reln, block, vmbuffer);
		ReleaseBuffer(vmbuffer);
		FreeFakeRelcacheEntry(reln);
	}

	/*
	 * In normal operation, it is important to lock the two pages in
	 * page-number order, to avoid possible deadlocks against other update
	 * operations going the other way.	However, during WAL replay there can
	 * be no other update happening, so we don't need to worry about that. But
	 * we *do* need to worry that we don't expose an inconsistent state to Hot
	 * Standby queries --- so the original page can't be unlocked before we've
	 * added the new tuple to the new page.
	 */

	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		obuffer = RestoreBackupBlock(lsn, record, 0, false, true);
		if (samepage)
		{
			/* backup block covered both changes, so we're done */
			UnlockReleaseBuffer(obuffer);
			return;
		}
		goto newt;
	}

	/* Deal with old tuple version */

	obuffer = XLogReadBuffer(xlrec->target.node,
							 ItemPointerGetBlockNumber(&(xlrec->target.tid)),
							 false);
	if (!BufferIsValid(obuffer))
		goto newt;
	page = (Page) BufferGetPage(obuffer);

	if (lsn <= PageGetLSN(page))		/* changes are applied */
	{
		if (samepage)
		{
			UnlockReleaseBuffer(obuffer);
			return;
		}
		goto newt;
	}

	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
	if (PageGetMaxOffsetNumber(page) >= offnum)
		lp = PageGetItemId(page, offnum);

	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
		elog(PANIC, "heap_update_redo: invalid lp");

	htup = (HeapTupleHeader) PageGetItem(page, lp);

	htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
	htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
	if (hot_update)
		HeapTupleHeaderSetHotUpdated(htup);
	else
		HeapTupleHeaderClearHotUpdated(htup);
	fix_infomask_from_infobits(xlrec->old_infobits_set, &htup->t_infomask,
							   &htup->t_infomask2);
	HeapTupleHeaderSetXmax(htup, xlrec->old_xmax);
	HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
	/* Set forward chain link in t_ctid */
	htup->t_ctid = xlrec->newtid;

	/* Mark the page as a candidate for pruning */
	PageSetPrunable(page, record->xl_xid);

	if (xlrec->all_visible_cleared)
		PageClearAllVisible(page);

	/*
	 * this test is ugly, but necessary to avoid thinking that insert change
	 * is already applied
	 */
	if (samepage)
	{
		nbuffer = obuffer;
		goto newsame;
	}

	PageSetLSN(page, lsn);
	MarkBufferDirty(obuffer);

	/* Deal with new tuple */

newt:;

	/*
	 * The visibility map may need to be fixed even if the heap page is
	 * already up-to-date.
	 */
	if (xlrec->new_all_visible_cleared)
	{
		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
		BlockNumber block = ItemPointerGetBlockNumber(&xlrec->newtid);
		Buffer		vmbuffer = InvalidBuffer;

		visibilitymap_pin(reln, block, &vmbuffer);
		visibilitymap_clear(reln, block, vmbuffer);
		ReleaseBuffer(vmbuffer);
		FreeFakeRelcacheEntry(reln);
	}

	if (record->xl_info & XLR_BKP_BLOCK(1))
	{
		(void) RestoreBackupBlock(lsn, record, 1, false, false);
		if (BufferIsValid(obuffer))
			UnlockReleaseBuffer(obuffer);
		return;
	}

	if (record->xl_info & XLOG_HEAP_INIT_PAGE)
	{
		nbuffer = XLogReadBuffer(xlrec->target.node,
								 ItemPointerGetBlockNumber(&(xlrec->newtid)),
								 true);
		Assert(BufferIsValid(nbuffer));
		page = (Page) BufferGetPage(nbuffer);

		PageInit(page, BufferGetPageSize(nbuffer), 0);
	}
	else
	{
		nbuffer = XLogReadBuffer(xlrec->target.node,
								 ItemPointerGetBlockNumber(&(xlrec->newtid)),
								 false);
		if (!BufferIsValid(nbuffer))
		{
			if (BufferIsValid(obuffer))
				UnlockReleaseBuffer(obuffer);
			return;
		}
		page = (Page) BufferGetPage(nbuffer);

		if (lsn <= PageGetLSN(page))	/* changes are applied */
		{
			UnlockReleaseBuffer(nbuffer);
			if (BufferIsValid(obuffer))
				UnlockReleaseBuffer(obuffer);
			return;
		}
	}

newsame:;

	offnum = ItemPointerGetOffsetNumber(&(xlrec->newtid));
	if (PageGetMaxOffsetNumber(page) + 1 < offnum)
		elog(PANIC, "heap_update_redo: invalid max offset number");

	hsize = SizeOfHeapUpdate + SizeOfHeapHeader;

	newlen = record->xl_len - hsize;
	Assert(newlen <= MaxHeapTupleSize);
	memcpy((char *) &xlhdr,
		   (char *) xlrec + SizeOfHeapUpdate,
		   SizeOfHeapHeader);
	htup = &tbuf.hdr;
	MemSet((char *) htup, 0, sizeof(HeapTupleHeaderData));
	/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
	memcpy((char *) htup + offsetof(HeapTupleHeaderData, t_bits),
		   (char *) xlrec + hsize,
		   newlen);
	newlen += offsetof(HeapTupleHeaderData, t_bits);
	htup->t_infomask2 = xlhdr.t_infomask2;
	htup->t_infomask = xlhdr.t_infomask;
	htup->t_hoff = xlhdr.t_hoff;

	HeapTupleHeaderSetXmin(htup, record->xl_xid);
	HeapTupleHeaderSetCmin(htup, FirstCommandId);
	HeapTupleHeaderSetXmax(htup, xlrec->new_xmax);
	/* Make sure there is no forward chain link in t_ctid */
	htup->t_ctid = xlrec->newtid;

	offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
	if (offnum == InvalidOffsetNumber)
		elog(PANIC, "heap_update_redo: failed to add tuple");

	if (xlrec->new_all_visible_cleared)
		PageClearAllVisible(page);

	freespace = PageGetHeapFreeSpace(page);		/* needed to update FSM below */

	PageSetLSN(page, lsn);
	MarkBufferDirty(nbuffer);
	UnlockReleaseBuffer(nbuffer);

	if (BufferIsValid(obuffer) && obuffer != nbuffer)
		UnlockReleaseBuffer(obuffer);

	/*
	 * If the new page is running low on free space, update the FSM as well.
	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
	 * better than that without knowing the fill-factor for the table.
	 *
	 * However, don't update the FSM on HOT updates, because after crash
	 * recovery, either the old or the new tuple will certainly be dead and
	 * prunable. After pruning, the page will have roughly as much free space
	 * as it did before the update, assuming the new tuple is about the same
	 * size as the old one.
	 *
	 * XXX: We don't get here if the page was restored from full page image.
	 * We don't bother to update the FSM in that case, it doesn't need to be
	 * totally accurate anyway.
	 */
	if (!hot_update && freespace < BLCKSZ / 5)
		XLogRecordPageWithFreeSpace(xlrec->target.node,
								 ItemPointerGetBlockNumber(&(xlrec->newtid)),
									freespace);
}

static void
heap_xlog_lock(XLogRecPtr lsn, XLogRecord *record)
{
	xl_heap_lock *xlrec = (xl_heap_lock *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;
	OffsetNumber offnum;
	ItemId		lp = NULL;
	HeapTupleHeader htup;

	/* If we have a full-page image, restore it and we're done */
	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
		return;
	}

	buffer = XLogReadBuffer(xlrec->target.node,
							ItemPointerGetBlockNumber(&(xlrec->target.tid)),
							false);
	if (!BufferIsValid(buffer))
		return;
	page = (Page) BufferGetPage(buffer);

	if (lsn <= PageGetLSN(page))		/* changes are applied */
	{
		UnlockReleaseBuffer(buffer);
		return;
	}

	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
	if (PageGetMaxOffsetNumber(page) >= offnum)
		lp = PageGetItemId(page, offnum);

	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
		elog(PANIC, "heap_lock_redo: invalid lp");

	htup = (HeapTupleHeader) PageGetItem(page, lp);

	fix_infomask_from_infobits(xlrec->infobits_set, &htup->t_infomask,
							   &htup->t_infomask2);
	HeapTupleHeaderClearHotUpdated(htup);
	HeapTupleHeaderSetXmax(htup, xlrec->locking_xid);
	HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
	/* Make sure there is no forward chain link in t_ctid */
	htup->t_ctid = xlrec->target.tid;
	PageSetLSN(page, lsn);
	MarkBufferDirty(buffer);
	UnlockReleaseBuffer(buffer);
}

static void
heap_xlog_lock_updated(XLogRecPtr lsn, XLogRecord *record)
{
	xl_heap_lock_updated *xlrec =
		(xl_heap_lock_updated *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;
	OffsetNumber offnum;
	ItemId		lp = NULL;
	HeapTupleHeader htup;

	/* If we have a full-page image, restore it and we're done */
	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
		return;
	}

	buffer = XLogReadBuffer(xlrec->target.node,
							ItemPointerGetBlockNumber(&(xlrec->target.tid)),
							false);
	if (!BufferIsValid(buffer))
		return;
	page = (Page) BufferGetPage(buffer);

	if (lsn <= PageGetLSN(page))		/* changes are applied */
	{
		UnlockReleaseBuffer(buffer);
		return;
	}

	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
	if (PageGetMaxOffsetNumber(page) >= offnum)
		lp = PageGetItemId(page, offnum);

	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
		elog(PANIC, "heap_xlog_lock_updated: invalid lp");

	htup = (HeapTupleHeader) PageGetItem(page, lp);

	fix_infomask_from_infobits(xlrec->infobits_set, &htup->t_infomask,
							   &htup->t_infomask2);
	HeapTupleHeaderSetXmax(htup, xlrec->xmax);

	PageSetLSN(page, lsn);
	MarkBufferDirty(buffer);
	UnlockReleaseBuffer(buffer);
}

static void
heap_xlog_inplace(XLogRecPtr lsn, XLogRecord *record)
{
	xl_heap_inplace *xlrec = (xl_heap_inplace *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;
	OffsetNumber offnum;
	ItemId		lp = NULL;
	HeapTupleHeader htup;
	uint32		oldlen;
	uint32		newlen;

	/* If we have a full-page image, restore it and we're done */
	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
		return;
	}

	buffer = XLogReadBuffer(xlrec->target.node,
							ItemPointerGetBlockNumber(&(xlrec->target.tid)),
							false);
	if (!BufferIsValid(buffer))
		return;
	page = (Page) BufferGetPage(buffer);

	if (lsn <= PageGetLSN(page))		/* changes are applied */
	{
		UnlockReleaseBuffer(buffer);
		return;
	}

	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
	if (PageGetMaxOffsetNumber(page) >= offnum)
		lp = PageGetItemId(page, offnum);

	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
		elog(PANIC, "heap_inplace_redo: invalid lp");

	htup = (HeapTupleHeader) PageGetItem(page, lp);

	oldlen = ItemIdGetLength(lp) - htup->t_hoff;
	newlen = record->xl_len - SizeOfHeapInplace;
	if (oldlen != newlen)
		elog(PANIC, "heap_inplace_redo: wrong tuple length");

	memcpy((char *) htup + htup->t_hoff,
		   (char *) xlrec + SizeOfHeapInplace,
		   newlen);

	PageSetLSN(page, lsn);
	MarkBufferDirty(buffer);
	UnlockReleaseBuffer(buffer);
}

void
heap_redo(XLogRecPtr lsn, XLogRecord *record)
{
	uint8		info = record->xl_info & ~XLR_INFO_MASK;

	/*
	 * These operations don't overwrite MVCC data so no conflict processing is
	 * required. The ones in heap2 rmgr do.
	 */

	switch (info & XLOG_HEAP_OPMASK)
	{
		case XLOG_HEAP_INSERT:
			heap_xlog_insert(lsn, record);
			break;
		case XLOG_HEAP_DELETE:
			heap_xlog_delete(lsn, record);
			break;
		case XLOG_HEAP_UPDATE:
			heap_xlog_update(lsn, record, false);
			break;
		case XLOG_HEAP_HOT_UPDATE:
			heap_xlog_update(lsn, record, true);
			break;
		case XLOG_HEAP_NEWPAGE:
			heap_xlog_newpage(lsn, record);
			break;
		case XLOG_HEAP_LOCK:
			heap_xlog_lock(lsn, record);
			break;
		case XLOG_HEAP_INPLACE:
			heap_xlog_inplace(lsn, record);
			break;
		default:
			elog(PANIC, "heap_redo: unknown op code %u", info);
	}
}

void
heap2_redo(XLogRecPtr lsn, XLogRecord *record)
{
	uint8		info = record->xl_info & ~XLR_INFO_MASK;

	switch (info & XLOG_HEAP_OPMASK)
	{
		case XLOG_HEAP2_FREEZE:
			heap_xlog_freeze(lsn, record);
			break;
		case XLOG_HEAP2_CLEAN:
			heap_xlog_clean(lsn, record);
			break;
		case XLOG_HEAP2_CLEANUP_INFO:
			heap_xlog_cleanup_info(lsn, record);
			break;
		case XLOG_HEAP2_VISIBLE:
			heap_xlog_visible(lsn, record);
			break;
		case XLOG_HEAP2_MULTI_INSERT:
			heap_xlog_multi_insert(lsn, record);
			break;
		case XLOG_HEAP2_LOCK_UPDATED:
			heap_xlog_lock_updated(lsn, record);
			break;
		default:
			elog(PANIC, "heap2_redo: unknown op code %u", info);
	}
}

/*
 *	heap_sync		- sync a heap, for use when no WAL has been written
 *
 * This forces the heap contents (including TOAST heap if any) down to disk.
 * If we skipped using WAL, and WAL is otherwise needed, we must force the
 * relation down to disk before it's safe to commit the transaction.  This
 * requires writing out any dirty buffers and then doing a forced fsync.
 *
 * Indexes are not touched.  (Currently, index operations associated with
 * the commands that use this are WAL-logged and so do not need fsync.
 * That behavior might change someday, but in any case it's likely that
 * any fsync decisions required would be per-index and hence not appropriate
 * to be done here.)
 */
void
heap_sync(Relation rel)
{
	/* non-WAL-logged tables never need fsync */
	if (!RelationNeedsWAL(rel))
		return;

	/* main heap */
	FlushRelationBuffers(rel);
	/* FlushRelationBuffers will have opened rd_smgr */
	smgrimmedsync(rel->rd_smgr, MAIN_FORKNUM);

	/* FSM is not critical, don't bother syncing it */

	/* toast heap, if any */
	if (OidIsValid(rel->rd_rel->reltoastrelid))
	{
		Relation	toastrel;

		toastrel = heap_open(rel->rd_rel->reltoastrelid, AccessShareLock);
		FlushRelationBuffers(toastrel);
		smgrimmedsync(toastrel->rd_smgr, MAIN_FORKNUM);
		heap_close(toastrel, AccessShareLock);
	}
}