text: /*-------------------------------------------------------------------------
   *
   * heapam.c
   *	  heap access method code
   *
   * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   *
   * IDENTIFICATION
   *	  src/backend/access/heap/heapam.c
   *
   *
   * INTERFACE ROUTINES
   *		heap_beginscan	- begin relation scan
   *		heap_rescan		- restart a relation scan
   *		heap_endscan	- end relation scan
   *		heap_getnext	- retrieve next tuple in scan
   *		heap_fetch		- retrieve tuple with given tid
   *		heap_insert		- insert tuple into a relation
   *		heap_multi_insert - insert multiple tuples into a relation
   *		heap_delete		- delete a tuple from a relation
   *		heap_update		- replace a tuple in a relation with another tuple
   *		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/bufmask.h"
  #include "access/genam.h"
  #include "access/heapam.h"
  #include "access/heapam_xlog.h"
  #include "access/hio.h"
  #include "access/multixact.h"
  #include "access/parallel.h"
  #include "access/relscan.h"
  #include "access/sysattr.h"
  #include "access/tableam.h"
  #include "access/transam.h"
  #include "access/tuptoaster.h"
  #include "access/valid.h"
  #include "access/visibilitymap.h"
  #include "access/xact.h"
  #include "access/xlog.h"
  #include "access/xloginsert.h"
  #include "access/xlogutils.h"
  #include "catalog/catalog.h"
  #include "miscadmin.h"
  #include "pgstat.h"
  #include "port/atomics.h"
  #include "storage/bufmgr.h"
  #include "storage/freespace.h"
  #include "storage/lmgr.h"
  #include "storage/predicate.h"
  #include "storage/procarray.h"
  #include "storage/smgr.h"
  #include "storage/spin.h"
  #include "storage/standby.h"
  #include "utils/datum.h"
  #include "utils/gpexpand.h"
  #include "utils/inval.h"
  #include "utils/lsyscache.h"
  #include "utils/relcache.h"
  #include "utils/snapmgr.h"
  #include "utils/spccache.h"
  
  #include "catalog/oid_dispatch.h"
  #include "cdb/cdbvars.h"
  #include "utils/guc.h"
  #include "utils/faultinjector.h"
  
  
  static TM_Result heap_update_internal(Relation relation, ItemPointer otid, HeapTuple newtup,
  									  CommandId cid, Snapshot crosscheck, bool wait,
  									  TM_FailureData *tmfd, LockTupleMode *lockmode, bool simple);
  
  static HeapTuple heap_prepare_insert(Relation relation, HeapTuple tup,
  									 TransactionId xid, CommandId cid, int options, bool isFrozen);
  static XLogRecPtr log_heap_update(Relation reln, Buffer oldbuf,
  								  Buffer newbuf, HeapTuple oldtup,
  								  HeapTuple newtup, HeapTuple old_key_tup,
  								  bool all_visible_cleared, bool new_all_visible_cleared);
  static Bitmapset *HeapDetermineModifiedColumns(Relation relation,
  											   Bitmapset *interesting_cols,
  											   HeapTuple oldtup, HeapTuple newtup);
  static bool heap_acquire_tuplock(Relation relation, ItemPointer tid,
  								 LockTupleMode mode, LockWaitPolicy wait_policy,
  								 bool *have_tuple_lock);
  static void compute_new_xmax_infomask(TransactionId xmax, uint16 old_infomask,
  									  uint16 old_infomask2, TransactionId add_to_xmax,
  									  LockTupleMode mode, bool is_update,
  									  TransactionId *result_xmax, uint16 *result_infomask,
  									  uint16 *result_infomask2);
  static TM_Result heap_lock_updated_tuple(Relation rel, HeapTuple tuple,
  										 ItemPointer ctid, TransactionId xid,
  										 LockTupleMode mode);
  static void GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
  								   uint16 *new_infomask2);
  static TransactionId MultiXactIdGetUpdateXid(TransactionId xmax,
  											 uint16 t_infomask);
  static bool DoesMultiXactIdConflict(MultiXactId multi, uint16 infomask,
  									LockTupleMode lockmode, bool *current_is_member);
  static void MultiXactIdWait(MultiXactId multi, MultiXactStatus status, uint16 infomask,
  							Relation rel, ItemPointer ctid, XLTW_Oper oper,
  							int *remaining);
  static bool ConditionalMultiXactIdWait(MultiXactId multi, MultiXactStatus status,
  									   uint16 infomask, Relation rel, int *remaining);
  static XLogRecPtr log_heap_new_cid(Relation relation, HeapTuple tup);
  static HeapTuple ExtractReplicaIdentity(Relation rel, HeapTuple tup, bool key_modified,
  										bool *copy);
  
  
  /*
   * Each tuple lock mode has a corresponding heavyweight lock, and one or two
   * corresponding MultiXactStatuses (one to merely lock tuples, another one to
   * update them).  This table (and the macros below) helps us determine the
   * heavyweight lock mode and MultiXactStatus values to use for any particular
   * tuple lock strength.
   *
   * Don't look at lockstatus/updstatus directly!  Use get_mxact_status_for_lock
   * instead.
   */
  static const struct
  {
  	LOCKMODE	hwlock;
  	int			lockstatus;
  	int			updstatus;
  }
  
  			tupleLockExtraInfo[MaxLockTupleMode + 1] =
  {
  	{							/* LockTupleKeyShare */
  		AccessShareLock,
  		MultiXactStatusForKeyShare,
  		-1						/* KeyShare does not allow updating tuples */
  	},
  	{							/* LockTupleShare */
  		RowShareLock,
  		MultiXactStatusForShare,
  		-1						/* Share does not allow updating tuples */
  	},
  	{							/* LockTupleNoKeyExclusive */
  		ExclusiveLock,
  		MultiXactStatusForNoKeyUpdate,
  		MultiXactStatusNoKeyUpdate
  	},
  	{							/* LockTupleExclusive */
  		AccessExclusiveLock,
  		MultiXactStatusForUpdate,
  		MultiXactStatusUpdate
  	}
  };
  
  /* Get the LOCKMODE for a given MultiXactStatus */
  #define LOCKMODE_from_mxstatus(status) \
  			(tupleLockExtraInfo[TUPLOCK_from_mxstatus((status))].hwlock)
  
  /*
   * Acquire heavyweight locks on tuples, using a LockTupleMode strength value.
   * This is more readable than having every caller translate it to lock.h's
   * LOCKMODE.
   */
  #define LockTupleTuplock(rel, tup, mode) \
  	LockTuple((rel), (tup), tupleLockExtraInfo[mode].hwlock)
  #define UnlockTupleTuplock(rel, tup, mode) \
  	UnlockTuple((rel), (tup), tupleLockExtraInfo[mode].hwlock)
  #define ConditionalLockTupleTuplock(rel, tup, mode) \
  	ConditionalLockTuple((rel), (tup), tupleLockExtraInfo[mode].hwlock)
  
  #ifdef USE_PREFETCH
  /*
   * heap_compute_xid_horizon_for_tuples and xid_horizon_prefetch_buffer use
   * this structure to coordinate prefetching activity.
   */
  typedef struct
  {
  	BlockNumber cur_hblkno;
  	int			next_item;
  	int			nitems;
  	ItemPointerData *tids;
  } XidHorizonPrefetchState;
  #endif
  
  /*
   * This table maps tuple lock strength values for each particular
   * MultiXactStatus value.
   */
  static const int MultiXactStatusLock[MaxMultiXactStatus + 1] =
  {
  	LockTupleKeyShare,			/* ForKeyShare */
  	LockTupleShare,				/* ForShare */
  	LockTupleNoKeyExclusive,	/* ForNoKeyUpdate */
  	LockTupleExclusive,			/* ForUpdate */
  	LockTupleNoKeyExclusive,	/* NoKeyUpdate */
  	LockTupleExclusive			/* Update */
  };
  
  /* Get the LockTupleMode for a given MultiXactStatus */
  #define TUPLOCK_from_mxstatus(status) \
  			(MultiXactStatusLock[(status)])
  
  /* ----------------------------------------------------------------
   *						 heap support routines
   * ----------------------------------------------------------------
   */
  
  /* ----------------
   *		initscan - scan code common to heap_beginscan and heap_rescan
   * ----------------
   */
  static void
  initscan(HeapScanDesc scan, ScanKey key, bool keep_startblock)
  {
  	ParallelBlockTableScanDesc bpscan = NULL;
  	bool		allow_strat;
  	bool		allow_sync;
  
  	/*
  	 * Determine the number of blocks we have to scan.
  	 *
  	 * It is sufficient to do this once at scan start, since any tuples added
  	 * while the scan is in progress will be invisible to my snapshot anyway.
  	 * (That is not true when using a non-MVCC snapshot.  However, we couldn't
  	 * guarantee to return tuples added after scan start anyway, since they
  	 * might go into pages we already scanned.  To guarantee consistent
  	 * results for a non-MVCC snapshot, the caller must hold some higher-level
  	 * lock that ensures the interesting tuple(s) won't change.)
  	 */
  	if (scan->rs_base.rs_parallel != NULL)
  	{
  		bpscan = (ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
  		scan->rs_nblocks = bpscan->phs_nblocks;
  	}
  	else
  		scan->rs_nblocks = RelationGetNumberOfBlocks(scan->rs_base.rs_rd);
  
  	/*
  	 * If the table is large relative to NBuffers, use a bulk-read access
  	 * strategy and enable synchronized scanning (see syncscan.c).  Although
  	 * the thresholds for these features could be different, we make them the
  	 * same so that there are only two behaviors to tune rather than four.
  	 * (However, some callers need to be able to disable one or both of these
  	 * behaviors, independently of the size of the table; also there is a GUC
  	 * variable that can disable synchronized scanning.)
  	 *
  	 * Note that table_block_parallelscan_initialize has a very similar test;
  	 * if you change this, consider changing that one, too.
  	 */
  	if (!RelationUsesLocalBuffers(scan->rs_base.rs_rd) &&
  		scan->rs_nblocks > NBuffers / 4)
  	{
  		allow_strat = (scan->rs_base.rs_flags & SO_ALLOW_STRAT) != 0;
  		allow_sync = (scan->rs_base.rs_flags & SO_ALLOW_SYNC) != 0;
  	}
  	else
  		allow_strat = allow_sync = false;
  
  	if (allow_strat)
  	{
  		/* During a rescan, keep the previous strategy object. */
  		if (scan->rs_strategy == NULL)
  			scan->rs_strategy = GetAccessStrategy(BAS_BULKREAD);
  	}
  	else
  	{
  		if (scan->rs_strategy != NULL)
  			FreeAccessStrategy(scan->rs_strategy);
  		scan->rs_strategy = NULL;
  	}
  
  	if (scan->rs_base.rs_parallel != NULL)
  	{
  		/* For parallel scan, believe whatever ParallelTableScanDesc says. */
  		if (scan->rs_base.rs_parallel->phs_syncscan)
  			scan->rs_base.rs_flags |= SO_ALLOW_SYNC;
  		else
  			scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
  	}
  	else if (keep_startblock)
  	{
  		/*
  		 * When rescanning, we want to keep the previous startblock setting,
  		 * so that rewinding a cursor doesn't generate surprising results.
  		 * Reset the active syncscan setting, though.
  		 */
  		if (allow_sync && synchronize_seqscans)
  			scan->rs_base.rs_flags |= SO_ALLOW_SYNC;
  		else
  			scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
  	}
  	else if (allow_sync && synchronize_seqscans)
  	{
  		scan->rs_base.rs_flags |= SO_ALLOW_SYNC;
  		scan->rs_startblock = ss_get_location(scan->rs_base.rs_rd, scan->rs_nblocks);
  	}
  	else
  	{
  		scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
  		scan->rs_startblock = 0;
  	}
  
  	scan->rs_numblocks = InvalidBlockNumber;
  	scan->rs_inited = false;
  	scan->rs_ctup.t_data = NULL;
  	ItemPointerSetInvalid(&scan->rs_ctup.t_self);
  	scan->rs_cbuf = InvalidBuffer;
  	scan->rs_cblock = InvalidBlockNumber;
  
  	/* page-at-a-time fields are always invalid when not rs_inited */
  
  	/*
  	 * copy the scan key, if appropriate
  	 */
  	if (key != NULL)
  		memcpy(scan->rs_base.rs_key, key, scan->rs_base.rs_nkeys * sizeof(ScanKeyData));
  
  	/*
  	 * Currently, we only have a stats counter for sequential heap scans (but
  	 * e.g for bitmap scans the underlying bitmap index scans will be counted,
  	 * and for sample scans we update stats for tuple fetches).
  	 */
  	if (scan->rs_base.rs_flags & SO_TYPE_SEQSCAN)
  		pgstat_count_heap_scan(scan->rs_base.rs_rd);
  }
  
  /*
   * heap_setscanlimits - restrict range of a heapscan
   *
   * startBlk is the page to start at
   * numBlks is number of pages to scan (InvalidBlockNumber means "all")
   */
  void
  heap_setscanlimits(TableScanDesc sscan, BlockNumber startBlk, BlockNumber numBlks)
  {
  	HeapScanDesc scan = (HeapScanDesc) sscan;
  
  	Assert(!scan->rs_inited);	/* else too late to change */
  	/* else rs_startblock is significant */
  	Assert(!(scan->rs_base.rs_flags & SO_ALLOW_SYNC));
  
  	/* Check startBlk is valid (but allow case of zero blocks...) */
  	Assert(startBlk == 0 || startBlk < scan->rs_nblocks);
  
  	scan->rs_startblock = startBlk;
  	scan->rs_numblocks = numBlks;
  }
  
  /*
   * heapgetpage - subroutine for heapgettup()
   *
   * This routine reads and pins the specified page of the relation.
   * In page-at-a-time mode it performs additional work, namely determining
   * which tuples on the page are visible.
   */
  void
  heapgetpage(TableScanDesc sscan, BlockNumber page)
  {
  	HeapScanDesc scan = (HeapScanDesc) sscan;
  	Buffer		buffer;
  	Snapshot	snapshot;
  	Page		dp;
  	int			lines;
  	int			ntup;
  	OffsetNumber lineoff;
  	ItemId		lpp;
  	bool		all_visible;
  	TransactionId t_xmin;
  	CommandId	t_cid;
  
  	Assert(page < scan->rs_nblocks);
  
  	/* release previous scan buffer, if any */
  	if (BufferIsValid(scan->rs_cbuf))
  	{
  		ReleaseBuffer(scan->rs_cbuf);
  		scan->rs_cbuf = InvalidBuffer;
  	}
  
  	/*
  	 * Be sure to check for interrupts at least once per page.  Checks at
  	 * higher code levels won't be able to stop a seqscan that encounters many
  	 * pages' worth of consecutive dead tuples.
  	 */
  	CHECK_FOR_INTERRUPTS();
  
  	/* read page using selected strategy */
  	scan->rs_cbuf = ReadBufferExtended(scan->rs_base.rs_rd, MAIN_FORKNUM, page,
  									   RBM_NORMAL, scan->rs_strategy);
  	scan->rs_cblock = page;
  
  	if (!(scan->rs_base.rs_flags & SO_ALLOW_PAGEMODE))
  		return;
  
  	buffer = scan->rs_cbuf;
  	snapshot = scan->rs_base.rs_snapshot;
  
  	/*
  	 * Prune and repair fragmentation for the whole page, if possible.
  	 */
  	heap_page_prune_opt(scan->rs_base.rs_rd, buffer);
  
  	/*
  	 * We must hold share lock on the buffer content while examining tuple
  	 * visibility.  Afterwards, however, the tuples we have found to be
  	 * visible are guaranteed good as long as we hold the buffer pin.
  	 */
  	LockBuffer(buffer, BUFFER_LOCK_SHARE);
  
  	dp = BufferGetPage(buffer);
  	TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, dp);
  	lines = PageGetMaxOffsetNumber(dp);
  	ntup = 0;
  
  	t_xmin = 0;
  	t_cid = 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;
  			HeapTupleHeader theader = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
  
  			loctup.t_tableOid = RelationGetRelid(scan->rs_base.rs_rd);
  			loctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
  			loctup.t_len = ItemIdGetLength(lpp);
  			ItemPointerSet(&(loctup.t_self), page, lineoff);
  
  			if (all_visible)
  			{
  				valid = true;
  			}
  			else
  			{
  				/*
  				 * GPDB: We have a one-item cache for the common case that a
  				 * lot of tuples have the same visibility info. Don't use the
  				 * cache, if the tuple was ever deleted, though (i.e. if xmax
  				 * is valid, and not just for tuple-locking). We could cache
  				 * the xmax too, but the visibility rules get more complicated
  				 * with locked-only tuples and multi-XIDs, so it seems better
  				 * to just give up early.
  				 */
  				bool		use_cache;
  
  				if ((theader->t_infomask & HEAP_XMAX_INVALID) != 0 ||
  					HEAP_XMAX_IS_LOCKED_ONLY(theader->t_infomask))
  					use_cache = true;
  				else
  					use_cache = false;
  
  				if (use_cache &&
  					t_xmin == HeapTupleHeaderGetXmin(theader) &&
  					t_cid == HeapTupleHeaderGetRawCommandId(theader))
  				{
  					valid = true;
  				}
  				else
  				{
  					valid = HeapTupleSatisfiesVisibility(scan->rs_base.rs_rd,
  														 &loctup, snapshot, buffer);
  
  					if (valid && use_cache)
  					{
  						t_xmin = HeapTupleHeaderGetXmin(loctup.t_data);
  						t_cid = HeapTupleHeaderGetRawCommandId(loctup.t_data);
  					}
  				}
  			}
  
  			CheckForSerializableConflictOut(valid, scan->rs_base.rs_rd,
  											&loctup, buffer, snapshot);
  
  			if (valid)
  				scan->rs_vistuples[ntup++] = lineoff;
  		}
  	}
  
  	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  	Assert(ntup <= MaxHeapTuplesPerPage);
  	scan->rs_ntuples = ntup;
  }
  
  /* ----------------
   *		heapgettup - fetch next heap tuple
   *
   *		Initialize the scan if not already done; then advance to the next
   *		tuple as indicated by "dir"; return the next tuple in scan->rs_ctup,
   *		or set scan->rs_ctup.t_data = NULL if no more tuples.
   *
   * dir == NoMovementScanDirection means "re-fetch the tuple indicated
   * by scan->rs_ctup".
   *
   * Note: the reason nkeys/key are passed separately, even though they are
   * kept in the scan descriptor, is that the caller may not want us to check
   * the scankeys.
   *
   * Note: when we fall off the end of the scan in either direction, we
   * reset rs_inited.  This means that a further request with the same
   * scan direction will restart the scan, which is a bit odd, but a
   * request with the opposite scan direction will start a fresh scan
   * in the proper direction.  The latter is required behavior for cursors,
   * while the former case is generally undefined behavior in Postgres
   * so we don't care too much.
   * ----------------
   */
  static void
  heapgettup(HeapScanDesc scan,
  		   ScanDirection dir,
  		   int nkeys,
  		   ScanKey key)
  {
  	HeapTuple	tuple = &(scan->rs_ctup);
  	Snapshot	snapshot = scan->rs_base.rs_snapshot;
  	bool		backward = ScanDirectionIsBackward(dir);
  	BlockNumber page;
  	bool		finished;
  	Page		dp;
  	int			lines;
  	OffsetNumber lineoff;
  	int			linesleft;
  	ItemId		lpp;
  
  	/*
  	 * calculate next starting lineoff, given scan direction
  	 */
  	if (ScanDirectionIsForward(dir))
  	{
  		if (!scan->rs_inited)
  		{
  			/*
  			 * return null immediately if relation is empty
  			 */
  			if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
  			{
  				Assert(!BufferIsValid(scan->rs_cbuf));
  				tuple->t_data = NULL;
  				return;
  			}
  			if (scan->rs_base.rs_parallel != NULL)
  			{
  				ParallelBlockTableScanDesc pbscan =
  				(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
  
  				table_block_parallelscan_startblock_init(scan->rs_base.rs_rd,
  														 pbscan);
  
  				page = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
  														 pbscan);
  
  				/* Other processes might have already finished the scan. */
  				if (page == InvalidBlockNumber)
  				{
  					Assert(!BufferIsValid(scan->rs_cbuf));
  					tuple->t_data = NULL;
  					return;
  				}
  			}
  			else
  				page = scan->rs_startblock; /* first page */
  			heapgetpage((TableScanDesc) scan, page);
  			lineoff = FirstOffsetNumber;	/* first offnum */
  			scan->rs_inited = true;
  		}
  		else
  		{
  			/* continue from previously returned page/tuple */
  			page = scan->rs_cblock; /* current page */
  			lineoff =			/* next offnum */
  				OffsetNumberNext(ItemPointerGetOffsetNumber(&(tuple->t_self)));
  		}
  
  		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
  
  		dp = BufferGetPage(scan->rs_cbuf);
  		TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, dp);
  		lines = PageGetMaxOffsetNumber(dp);
  		/* page and lineoff now reference the physically next tid */
  
  		linesleft = lines - lineoff + 1;
  	}
  	else if (backward)
  	{
  		/* backward parallel scan not supported */
  		Assert(scan->rs_base.rs_parallel == NULL);
  
  		if (!scan->rs_inited)
  		{
  			/*
  			 * return null immediately if relation is empty
  			 */
  			if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
  			{
  				Assert(!BufferIsValid(scan->rs_cbuf));
  				tuple->t_data = NULL;
  				return;
  			}
  
  			/*
  			 * Disable reporting to syncscan logic in a backwards scan; it's
  			 * not very likely anyone else is doing the same thing at the same
  			 * time, and much more likely that we'll just bollix things for
  			 * forward scanners.
  			 */
  			scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
  			/* start from last page of the scan */
  			if (scan->rs_startblock > 0)
  				page = scan->rs_startblock - 1;
  			else
  				page = scan->rs_nblocks - 1;
  			heapgetpage((TableScanDesc) scan, page);
  		}
  		else
  		{
  			/* continue from previously returned page/tuple */
  			page = scan->rs_cblock; /* current page */
  		}
  
  		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
  
  		dp = BufferGetPage(scan->rs_cbuf);
  		TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, dp);
  		lines = PageGetMaxOffsetNumber(dp);
  
  		if (!scan->rs_inited)
  		{
  			lineoff = lines;	/* final offnum */
  			scan->rs_inited = true;
  		}
  		else
  		{
  			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((TableScanDesc) scan, page);
  
  		/* Since the tuple was previously fetched, needn't lock page here */
  		dp = BufferGetPage(scan->rs_cbuf);
  		TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, dp);
  		lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
  		lpp = PageGetItemId(dp, lineoff);
  		Assert(ItemIdIsNormal(lpp));
  
  		tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
  		tuple->t_len = ItemIdGetLength(lpp);
  
  		return;
  	}
  
  	/*
  	 * advance the scan until we find a qualifying tuple or run out of stuff
  	 * to scan
  	 */
  	lpp = PageGetItemId(dp, lineoff);
  	for (;;)
  	{
          CHECK_FOR_INTERRUPTS();
  
  		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(scan->rs_base.rs_rd,
  													 tuple,
  													 snapshot,
  													 scan->rs_cbuf);
  
  				CheckForSerializableConflictOut(valid, scan->rs_base.rs_rd,
  												tuple, scan->rs_cbuf,
  												snapshot);
  
  				if (valid && key != NULL)
  					HeapKeyTest(tuple, RelationGetDescr(scan->rs_base.rs_rd),
  								nkeys, key, valid);
  
  				if (valid)
  				{
  					LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
  					return;
  				}
  			}
  
  			/*
  			 * otherwise move to the next item on the page
  			 */
  			--linesleft;
  			if (backward)
  			{
  				--lpp;			/* move back in this page's ItemId array */
  				--lineoff;
  			}
  			else
  			{
  				++lpp;			/* move forward in this page's ItemId array */
  				++lineoff;
  			}
  		}
  
  		/*
  		 * if we get here, it means we've exhausted the items on this page and
  		 * it's time to move to the next.
  		 */
  		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
  
  		/*
  		 * advance to next/prior page and detect end of scan
  		 */
  		if (backward)
  		{
  			finished = (page == scan->rs_startblock) ||
  				(scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
  			if (page == 0)
  				page = scan->rs_nblocks;
  			page--;
  		}
  		else if (scan->rs_base.rs_parallel != NULL)
  		{
  			ParallelBlockTableScanDesc pbscan =
  			(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
  
  			page = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
  													 pbscan);
  			finished = (page == InvalidBlockNumber);
  		}
  		else
  		{
  			page++;
  			if (page >= scan->rs_nblocks)
  				page = 0;
  			finished = (page == scan->rs_startblock) ||
  				(scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
  
  			/*
  			 * Report our new scan position for synchronization purposes. We
  			 * don't do that when moving backwards, however. That would just
  			 * mess up any other forward-moving scanners.
  			 *
  			 * Note: we do this before checking for end of scan so that the
  			 * final state of the position hint is back at the start of the
  			 * rel.  That's not strictly necessary, but otherwise when you run
  			 * the same query multiple times the starting position would shift
  			 * a little bit backwards on every invocation, which is confusing.
  			 * We don't guarantee any specific ordering in general, though.
  			 */
  			if (scan->rs_base.rs_flags & SO_ALLOW_SYNC)
  				ss_report_location(scan->rs_base.rs_rd, page);
  		}
  
  		/*
  		 * return NULL if we've exhausted all the pages
  		 */
  		if (finished)
  		{
  			if (BufferIsValid(scan->rs_cbuf))
  				ReleaseBuffer(scan->rs_cbuf);
  			scan->rs_cbuf = InvalidBuffer;
  			scan->rs_cblock = InvalidBlockNumber;
  			tuple->t_data = NULL;
  			scan->rs_inited = false;
  			return;
  		}
  
  		heapgetpage((TableScanDesc) scan, page);
  
  		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
  
  		dp = BufferGetPage(scan->rs_cbuf);
  		TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, dp);
  		lines = PageGetMaxOffsetNumber((Page) dp);
  		linesleft = lines;
  		if (backward)
  		{
  			lineoff = lines;
  			lpp = PageGetItemId(dp, lines);
  		}
  		else
  		{
  			lineoff = FirstOffsetNumber;
  			lpp = PageGetItemId(dp, FirstOffsetNumber);
  		}
  	}
  }
  
  /* ----------------
   *		heapgettup_pagemode - fetch next heap tuple in page-at-a-time mode
   *
   *		Same API as heapgettup, but used in page-at-a-time mode
   *
   * The internal logic is much the same as heapgettup's too, but there are some
   * differences: we do not take the buffer content lock (that only needs to
   * happen inside heapgetpage), and we iterate through just the tuples listed
   * in rs_vistuples[] rather than all tuples on the page.  Notice that
   * lineindex is 0-based, where the corresponding loop variable lineoff in
   * heapgettup is 1-based.
   * ----------------
   */
  static void
  heapgettup_pagemode(HeapScanDesc scan,
  					ScanDirection dir,
  					int nkeys,
  					ScanKey key)
  {
  	HeapTuple	tuple = &(scan->rs_ctup);
  	bool		backward = ScanDirectionIsBackward(dir);
  	BlockNumber page;
  	bool		finished;
  	Page		dp;
  	int			lines;
  	int			lineindex;
  	OffsetNumber lineoff;
  	int			linesleft;
  	ItemId		lpp;
  
  	/*
  	 * calculate next starting lineindex, given scan direction
  	 */
  	if (ScanDirectionIsForward(dir))
  	{
  		if (!scan->rs_inited)
  		{
  			/*
  			 * return null immediately if relation is empty
  			 */
  			if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
  			{
  				Assert(!BufferIsValid(scan->rs_cbuf));
  				tuple->t_data = NULL;
  				return;
  			}
  			if (scan->rs_base.rs_parallel != NULL)
  			{
  				ParallelBlockTableScanDesc pbscan =
  				(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
  
  				table_block_parallelscan_startblock_init(scan->rs_base.rs_rd,
  														 pbscan);
  
  				page = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
  														 pbscan);
  
  				/* Other processes might have already finished the scan. */
  				if (page == InvalidBlockNumber)
  				{
  					Assert(!BufferIsValid(scan->rs_cbuf));
  					tuple->t_data = NULL;
  					return;
  				}
  			}
  			else
  				page = scan->rs_startblock; /* first page */
  			heapgetpage((TableScanDesc) scan, page);
  			lineindex = 0;
  			scan->rs_inited = true;
  		}
  		else
  		{
  			/* continue from previously returned page/tuple */
  			page = scan->rs_cblock; /* current page */
  			lineindex = scan->rs_cindex + 1;
  		}
  
  		dp = BufferGetPage(scan->rs_cbuf);
  		TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, dp);
  		lines = scan->rs_ntuples;
  		/* page and lineindex now reference the next visible tid */
  
  		linesleft = lines - lineindex;
  	}
  	else if (backward)
  	{
  		/* backward parallel scan not supported */
  		Assert(scan->rs_base.rs_parallel == NULL);
  
  		if (!scan->rs_inited)
  		{
  			/*
  			 * return null immediately if relation is empty
  			 */
  			if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
  			{
  				Assert(!BufferIsValid(scan->rs_cbuf));
  				tuple->t_data = NULL;
  				return;
  			}
  
  			/*
  			 * Disable reporting to syncscan logic in a backwards scan; it's
  			 * not very likely anyone else is doing the same thing at the same
  			 * time, and much more likely that we'll just bollix things for
  			 * forward scanners.
  			 */
  			scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
  			/* start from last page of the scan */
  			if (scan->rs_startblock > 0)
  				page = scan->rs_startblock - 1;
  			else
  				page = scan->rs_nblocks - 1;
  			heapgetpage((TableScanDesc) scan, page);
  		}
  		else
  		{
  			/* continue from previously returned page/tuple */
  			page = scan->rs_cblock; /* current page */
  		}
  
  		dp = BufferGetPage(scan->rs_cbuf);
  		TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, dp);
  		lines = scan->rs_ntuples;
  
  		if (!scan->rs_inited)
  		{
  			lineindex = lines - 1;
  			scan->rs_inited = true;
  		}
  		else
  		{
  			lineindex = scan->rs_cindex - 1;
  		}
  		/* page and lineindex now reference the previous visible tid */
  
  		linesleft = lineindex + 1;
  	}
  	else
  	{
  		/*
  		 * ``no movement'' scan direction: refetch prior tuple
  		 */
  		if (!scan->rs_inited)
  		{
  			Assert(!BufferIsValid(scan->rs_cbuf));
  			tuple->t_data = NULL;
  			return;
  		}
  
  		page = ItemPointerGetBlockNumber(&(tuple->t_self));
  		if (page != scan->rs_cblock)
  			heapgetpage((TableScanDesc) scan, page);
  
  		/* Since the tuple was previously fetched, needn't lock page here */
  		dp = BufferGetPage(scan->rs_cbuf);
  		TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, dp);
  		lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
  		lpp = PageGetItemId(dp, lineoff);
  		Assert(ItemIdIsNormal(lpp));
  
  		tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
  		tuple->t_len = ItemIdGetLength(lpp);
  
  		/* check that rs_cindex is in sync */
  		Assert(scan->rs_cindex < scan->rs_ntuples);
  		Assert(lineoff == scan->rs_vistuples[scan->rs_cindex]);
  
  		return;
  	}
  
  	/*
  	 * advance the scan until we find a qualifying tuple or run out of stuff
  	 * to scan
  	 */
  	for (;;)
  	{
          CHECK_FOR_INTERRUPTS();
  
  		while (linesleft > 0)
  		{
  			lineoff = scan->rs_vistuples[lineindex];
  			lpp = PageGetItemId(dp, lineoff);
  			Assert(ItemIdIsNormal(lpp));
  
  			tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
  			tuple->t_len = ItemIdGetLength(lpp);
  			ItemPointerSet(&(tuple->t_self), page, lineoff);
  
  			/*
  			 * if current tuple qualifies, return it.
  			 */
  			if (key != NULL)
  			{
  				bool		valid;
  
  				HeapKeyTest(tuple, RelationGetDescr(scan->rs_base.rs_rd),
  							nkeys, key, valid);
  				if (valid)
  				{
  					scan->rs_cindex = lineindex;
  					return;
  				}
  			}
  			else
  			{
  				scan->rs_cindex = lineindex;
  				return;
  			}
  
  			/*
  			 * otherwise move to the next item on the page
  			 */
  			--linesleft;
  			if (backward)
  				--lineindex;
  			else
  				++lineindex;
  		}
  
  		/*
  		 * if we get here, it means we've exhausted the items on this page and
  		 * it's time to move to the next.
  		 */
  		if (backward)
  		{
  			finished = (page == scan->rs_startblock) ||
  				(scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
  			if (page == 0)
  				page = scan->rs_nblocks;
  			page--;
  		}
  		else if (scan->rs_base.rs_parallel != NULL)
  		{
  			ParallelBlockTableScanDesc pbscan =
  			(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
  
  			page = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
  													 pbscan);
  			finished = (page == InvalidBlockNumber);
  		}
  		else
  		{
  			page++;
  			if (page >= scan->rs_nblocks)
  				page = 0;
  			finished = (page == scan->rs_startblock) ||
  				(scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
  
  			/*
  			 * Report our new scan position for synchronization purposes. We
  			 * don't do that when moving backwards, however. That would just
  			 * mess up any other forward-moving scanners.
  			 *
  			 * Note: we do this before checking for end of scan so that the
  			 * final state of the position hint is back at the start of the
  			 * rel.  That's not strictly necessary, but otherwise when you run
  			 * the same query multiple times the starting position would shift
  			 * a little bit backwards on every invocation, which is confusing.
  			 * We don't guarantee any specific ordering in general, though.
  			 */
  			if (scan->rs_base.rs_flags & SO_ALLOW_SYNC)
  				ss_report_location(scan->rs_base.rs_rd, page);
  		}
  
  		/*
  		 * return NULL if we've exhausted all the pages
  		 */
  		if (finished)
  		{
  			if (BufferIsValid(scan->rs_cbuf))
  				ReleaseBuffer(scan->rs_cbuf);
  			scan->rs_cbuf = InvalidBuffer;
  			scan->rs_cblock = InvalidBlockNumber;
  			tuple->t_data = NULL;
  			scan->rs_inited = false;
  			return;
  		}
  
  		heapgetpage((TableScanDesc) scan, page);
  
  		dp = BufferGetPage(scan->rs_cbuf);
  		TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, dp);
  		lines = scan->rs_ntuples;
  		linesleft = lines;
  		if (backward)
  			lineindex = lines - 1;
  		else
  			lineindex = 0;
  	}
  }
  
  
  #if defined(DISABLE_COMPLEX_MACRO)
  /*
   * This is formatted so oddly so that the correspondence to the macro
   * definition in access/htup_details.h is maintained.
   */
  Datum
  fastgetattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
  			bool *isnull)
  {
  	return (
  			(attnum) > 0 ?
  			(
  			 (*(isnull) = false),
  			 HeapTupleNoNulls(tup) ?
  			 (
  			  TupleDescAttr((tupleDesc), (attnum) - 1)->attcacheoff >= 0 ?
  			  (
  			   fetchatt(TupleDescAttr((tupleDesc), (attnum) - 1),
  						(char *) (tup)->t_data + (tup)->t_data->t_hoff +
  						TupleDescAttr((tupleDesc), (attnum) - 1)->attcacheoff)
  			   )
  			  :
  			  nocachegetattr((tup), (attnum), (tupleDesc))
  			  )
  			 :
  			 (
  			  att_isnull((attnum) - 1, (tup)->t_data->t_bits) ?
  			  (
  			   (*(isnull) = true),
  			   (Datum) NULL
  			   )
  			  :
  			  (
  			   nocachegetattr((tup), (attnum), (tupleDesc))
  			   )
  			  )
  			 )
  			:
  			(
  			 (Datum) NULL
  			 )
  		);
  }
  #endif							/* defined(DISABLE_COMPLEX_MACRO) */
  
  
  /* ----------------------------------------------------------------
   *					 heap access method interface
   * ----------------------------------------------------------------
   */
  TableScanDesc
  heap_beginscan(Relation relation, Snapshot snapshot,
  			   int nkeys, ScanKey key,
  			   ParallelTableScanDesc parallel_scan,
  			   uint32 flags)
  {
  	HeapScanDesc scan;
  
  	/*
  	 * increment relation ref count while scanning relation
  	 *
  	 * This is just to make really sure the relcache entry won't go away while
  	 * the scan has a pointer to it.  Caller should be holding the rel open
  	 * anyway, so this is redundant in all normal scenarios...
  	 */
  	RelationIncrementReferenceCount(relation);
  
  	/*
  	 * allocate and initialize scan descriptor
  	 */
  	scan = (HeapScanDesc) palloc(sizeof(HeapScanDescData));
  
  	scan->rs_base.rs_rd = relation;
  	scan->rs_base.rs_snapshot = snapshot;
  	scan->rs_base.rs_nkeys = nkeys;
  	scan->rs_base.rs_flags = flags;
  	scan->rs_base.rs_parallel = parallel_scan;
  	scan->rs_strategy = NULL;	/* set in initscan */
  
  	/*
  	 * Disable page-at-a-time mode if it's not a MVCC-safe snapshot.
  	 */
  	if (!(snapshot && IsMVCCSnapshot(snapshot)))
  		scan->rs_base.rs_flags &= ~SO_ALLOW_PAGEMODE;
  
  	/*
  	 * For seqscan and sample scans in a serializable transaction, acquire a
  	 * predicate lock on the entire relation. This is required not only to
  	 * lock all the matching tuples, but also to conflict with new insertions
  	 * into the table. In an indexscan, we take page locks on the index pages
  	 * covering the range specified in the scan qual, but in a heap scan there
  	 * is nothing more fine-grained to lock. A bitmap scan is a different
  	 * story, there we have already scanned the index and locked the index
  	 * pages covering the predicate. But in that case we still have to lock
  	 * any matching heap tuples. For sample scan we could optimize the locking
  	 * to be at least page-level granularity, but we'd need to add per-tuple
  	 * locking for that.
  	 */
  	if (scan->rs_base.rs_flags & (SO_TYPE_SEQSCAN | SO_TYPE_SAMPLESCAN))
  	{
  		/*
  		 * Ensure a missing snapshot is noticed reliably, even if the
  		 * isolation mode means predicate locking isn't performed (and
  		 * therefore the snapshot isn't used here).
  		 */
  		Assert(snapshot);
  		PredicateLockRelation(relation, snapshot);
  	}
  
  	/* we only need to set this up once */
  	scan->rs_ctup.t_tableOid = RelationGetRelid(relation);
  
  	/*
  	 * we do this here instead of in initscan() because heap_rescan also calls
  	 * initscan() and we don't want to allocate memory again
  	 */
  	if (nkeys > 0)
  		scan->rs_base.rs_key = (ScanKey) palloc(sizeof(ScanKeyData) * nkeys);
  	else
  		scan->rs_base.rs_key = NULL;
  
  	initscan(scan, key, false);
  
  	return (TableScanDesc) scan;
  }
  
  void
  heap_rescan(TableScanDesc sscan, ScanKey key, bool set_params,
  			bool allow_strat, bool allow_sync, bool allow_pagemode)
  {
  	HeapScanDesc scan = (HeapScanDesc) sscan;
  
  	if (set_params)
  	{
  		if (allow_strat)
  			scan->rs_base.rs_flags |= SO_ALLOW_STRAT;
  		else
  			scan->rs_base.rs_flags &= ~SO_ALLOW_STRAT;
  
  		if (allow_sync)
  			scan->rs_base.rs_flags |= SO_ALLOW_SYNC;
  		else
  			scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
  
  		if (allow_pagemode && scan->rs_base.rs_snapshot &&
  			IsMVCCSnapshot(scan->rs_base.rs_snapshot))
  			scan->rs_base.rs_flags |= SO_ALLOW_PAGEMODE;
  		else
  			scan->rs_base.rs_flags &= ~SO_ALLOW_PAGEMODE;
  	}
  
  	/*
  	 * unpin scan buffers
  	 */
  	if (BufferIsValid(scan->rs_cbuf))
  		ReleaseBuffer(scan->rs_cbuf);
  
  	/*
  	 * reinitialize scan descriptor
  	 */
  	initscan(scan, key, true);
  }
  
  void
  heap_endscan(TableScanDesc sscan)
  {
  	HeapScanDesc scan = (HeapScanDesc) sscan;
  
  	/* Note: no locking manipulations needed */
  
  	/*
  	 * unpin scan buffers
  	 */
  	if (BufferIsValid(scan->rs_cbuf))
  		ReleaseBuffer(scan->rs_cbuf);
  
  	/*
  	 * decrement relation reference count and free scan descriptor storage
  	 */
  	RelationDecrementReferenceCount(scan->rs_base.rs_rd);
  
  	if (scan->rs_base.rs_key)
  		pfree(scan->rs_base.rs_key);
  
  	if (scan->rs_strategy != NULL)
  		FreeAccessStrategy(scan->rs_strategy);
  
  	if (scan->rs_base.rs_flags & SO_TEMP_SNAPSHOT)
  		UnregisterSnapshot(scan->rs_base.rs_snapshot);
  
  	pfree(scan);
  }
  
  #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(TableScanDesc sscan, ScanDirection direction)
  {
  	HeapScanDesc scan = (HeapScanDesc) sscan;
  
  	/*
  	 * This is still widely used directly, without going through table AM, so
  	 * add a safety check.  It's possible we should, at a later point,
  	 * downgrade this to an assert. The reason for checking the AM routine,
  	 * rather than the AM oid, is that this allows to write regression tests
  	 * that create another AM reusing the heap handler.
  	 */
  	if (unlikely(sscan->rs_rd->rd_tableam != GetHeapamTableAmRoutine()))
  		ereport(ERROR,
  				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
  				 errmsg_internal("only heap AM is supported")));
  
  	/* Note: no locking manipulations needed */
  
  	HEAPDEBUG_1;				/* heap_getnext( info ) */
  
  	if (scan->rs_base.rs_flags & SO_ALLOW_PAGEMODE)
  		heapgettup_pagemode(scan, direction,
  							scan->rs_base.rs_nkeys, scan->rs_base.rs_key);
  	else
  		heapgettup(scan, direction,
  				   scan->rs_base.rs_nkeys, scan->rs_base.rs_key);
  
  	if (scan->rs_ctup.t_data == NULL)
  	{
  		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_base.rs_rd);
  
  	return &scan->rs_ctup;
  }
  
  #ifdef HEAPAMSLOTDEBUGALL
  #define HEAPAMSLOTDEBUG_1 \
  	elog(DEBUG2, "heapam_getnextslot([%s,nkeys=%d],dir=%d) called", \
  		 RelationGetRelationName(scan->rs_base.rs_rd), scan->rs_base.rs_nkeys, (int) direction)
  #define HEAPAMSLOTDEBUG_2 \
  	elog(DEBUG2, "heapam_getnextslot returning EOS")
  #define HEAPAMSLOTDEBUG_3 \
  	elog(DEBUG2, "heapam_getnextslot returning tuple")
  #else
  #define HEAPAMSLOTDEBUG_1
  #define HEAPAMSLOTDEBUG_2
  #define HEAPAMSLOTDEBUG_3
  #endif
  
  bool
  heap_getnextslot(TableScanDesc sscan, ScanDirection direction, TupleTableSlot *slot)
  {
  	HeapScanDesc scan = (HeapScanDesc) sscan;
  
  	/* Note: no locking manipulations needed */
  
  	HEAPAMSLOTDEBUG_1;			/* heap_getnextslot( info ) */
  
  	if (sscan->rs_flags & SO_ALLOW_PAGEMODE)
  		heapgettup_pagemode(scan, direction, sscan->rs_nkeys, sscan->rs_key);
  	else
  		heapgettup(scan, direction, sscan->rs_nkeys, sscan->rs_key);
  
  	if (scan->rs_ctup.t_data == NULL)
  	{
  		HEAPAMSLOTDEBUG_2;		/* heap_getnextslot returning EOS */
  		ExecClearTuple(slot);
  		return false;
  	}
  
  	/*
  	 * if we get here it means we have a new current scan tuple, so point to
  	 * the proper return buffer and return the tuple.
  	 */
  	HEAPAMSLOTDEBUG_3;			/* heap_getnextslot returning tuple */
  
  	pgstat_count_heap_getnext(scan->rs_base.rs_rd);
  
  	ExecStoreBufferHeapTuple(&scan->rs_ctup, slot,
  							 scan->rs_cbuf);
  	return true;
  }
  
  /*
   *	heap_fetch		- retrieve tuple with given tid
   *
   * On entry, tuple->t_self is the TID to fetch.  We pin the buffer holding
   * the tuple, fill in the remaining fields of *tuple, and check the tuple
   * against the specified snapshot.
   *
   * If successful (tuple found and passes snapshot time qual), then *userbuf
   * is set to the buffer holding the tuple and true is returned.  The caller
   * must unpin the buffer when done with the tuple.
   *
   * If the tuple is not found (ie, item number references a deleted slot),
   * then tuple->t_data is set to NULL 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.
   *
   * 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)
  {
  	ItemPointer tid = &(tuple->t_self);
  	ItemId		lp;
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	bool		valid;
  
  	/*
  	 * Fetch and pin the appropriate page of the relation.
  	 */
  	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
  
  	/*
  	 * Need share lock on buffer to examine tuple commit status.
  	 */
  	LockBuffer(buffer, BUFFER_LOCK_SHARE);
  	page = BufferGetPage(buffer);
  	TestForOldSnapshot(snapshot, relation, page);
  
  	/*
  	 * We'd better check for out-of-range offnum in case of VACUUM since the
  	 * TID was obtained.
  	 */
  	offnum = ItemPointerGetOffsetNumber(tid);
  	if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(page))
  	{
  		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  		ReleaseBuffer(buffer);
  		*userbuf = InvalidBuffer;
  		tuple->t_data = NULL;
  		return false;
  	}
  
  	/*
  	 * get the item line pointer corresponding to the requested tid
  	 */
  	lp = PageGetItemId(page, offnum);
  
  	/*
  	 * Must check for deleted tuple.
  	 */
  	if (!ItemIdIsNormal(lp))
  	{
  		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  		ReleaseBuffer(buffer);
  		*userbuf = InvalidBuffer;
  		tuple->t_data = NULL;
  		return false;
  	}
  
  	/*
  	 * fill in *tuple fields
  	 */
  	tuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
  	tuple->t_len = ItemIdGetLength(lp);
  	tuple->t_tableOid = RelationGetRelid(relation);
  
  	/*
  	 * check tuple visibility, then release lock
  	 */
  	valid = HeapTupleSatisfiesVisibility(relation, 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;
  
  		return true;
  	}
  
  	/* Tuple failed time qual */
  	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;
  
  	heapTuple->t_self = *tid;
  
  	/* 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 = RelationGetRelid(relation);
  		ItemPointerSetOffsetNumber(&heapTuple->t_self, offnum);
  
  		/*
  		 * Shouldn't see a HEAP_ONLY tuple at chain start.
  		 */
  		if (at_chain_start && HeapTupleIsHeapOnly(heapTuple))
  			break;
  
  		/*
  		 * The xmin should match the previous xmax value, else chain is
  		 * broken.
  		 */
  		if (TransactionIdIsValid(prev_xmax) &&
  			!TransactionIdEquals(prev_xmax,
  								 HeapTupleHeaderGetXmin(heapTuple->t_data)))
  			break;
  
  		/*
  		 * When first_call is true (and thus, skip is initially false) we'll
  		 * return the first tuple we find.  But on later passes, heapTuple
  		 * will initially be pointing to the tuple we returned last time.
  		 * Returning it again would be incorrect (and would loop forever), so
  		 * we skip it and return the next match we find.
  		 */
  		if (!skip)
  		{
  			/*
  			 * For the benefit of logical decoding, have t_self point at the
  			 * element of the HOT chain we're currently investigating instead
  			 * of the root tuple of the HOT chain. This is important because
  			 * the *Satisfies routine for historical mvcc snapshots needs the
  			 * correct tid to decide about the visibility in some cases.
  			 */
  			ItemPointerSet(&(heapTuple->t_self), BufferGetBlockNumber(buffer), offnum);
  
  			/* If it's visible per the snapshot, we must return it */
  			valid = HeapTupleSatisfiesVisibility(relation, heapTuple, snapshot, buffer);
  			CheckForSerializableConflictOut(valid, relation, heapTuple,
  											buffer, snapshot);
  			/* reset to original, non-redirected, tid */
  			heapTuple->t_self = *tid;
  
  			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.
  		 *
  		 * Note: if you change the criterion here for what is "dead", fix the
  		 * planner's get_actual_variable_range() function to match.
  		 */
  		if (all_dead && *all_dead &&
  			!HeapTupleIsSurelyDead(heapTuple, 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_get_latest_tid -  get the latest tid of a specified tuple
   *
   * Actually, this gets the latest version that is visible according to the
   * scan's snapshot.  Create a scan using SnapshotDirty to get the very latest,
   * possibly uncommitted version.
   *
   * *tid is both an input and an output parameter: it is updated to
   * show the latest version of the row.  Note that it will not be changed
   * if no version of the row passes the snapshot test.
   */
  void
  heap_get_latest_tid(TableScanDesc sscan,
  					ItemPointer tid)
  {
  	Relation	relation = sscan->rs_rd;
  	Snapshot	snapshot = sscan->rs_snapshot;
  	ItemPointerData ctid;
  	TransactionId priorXmax;
  
  	/*
  	 * table_get_latest_tid verified that the passed in tid is valid.  Assume
  	 * that t_ctid links are valid however - there shouldn't be invalid ones
  	 * in the table.
  	 */
  	Assert(ItemPointerIsValid(tid));
  
  	/*
  	 * Loop to chase down t_ctid links.  At top of loop, ctid is the tuple we
  	 * need to examine, and *tid is the TID we will return if ctid turns out
  	 * to be bogus.
  	 *
  	 * Note that we will loop until we reach the end of the t_ctid chain.
  	 * Depending on the snapshot passed, there might be at most one visible
  	 * version of the row, but we don't try to optimize for that.
  	 */
  	ctid = *tid;
  	priorXmax = InvalidTransactionId;	/* cannot check first XMIN */
  	for (;;)
  	{
  		Buffer		buffer;
  		Page		page;
  		OffsetNumber offnum;
  		ItemId		lp;
  		HeapTupleData tp;
  		bool		valid;
  
  		/*
  		 * Read, pin, and lock the page.
  		 */
  		buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&ctid));
  		LockBuffer(buffer, BUFFER_LOCK_SHARE);
  		page = BufferGetPage(buffer);
  		TestForOldSnapshot(snapshot, relation, page);
  
  		/*
  		 * Check for bogus item number.  This is not treated as an error
  		 * condition because it can happen while following a t_ctid link. We
  		 * just assume that the prior tid is OK and return it unchanged.
  		 */
  		offnum = ItemPointerGetOffsetNumber(&ctid);
  		if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(page))
  		{
  			UnlockReleaseBuffer(buffer);
  			break;
  		}
  		lp = PageGetItemId(page, offnum);
  		if (!ItemIdIsNormal(lp))
  		{
  			UnlockReleaseBuffer(buffer);
  			break;
  		}
  
  		/* OK to access the tuple */
  		tp.t_self = ctid;
  		tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
  		tp.t_len = ItemIdGetLength(lp);
  		tp.t_tableOid = RelationGetRelid(relation);
  
  		/*
  		 * After following a t_ctid link, we might arrive at an unrelated
  		 * tuple.  Check for XMIN match.
  		 */
  		if (TransactionIdIsValid(priorXmax) &&
  			!TransactionIdEquals(priorXmax, HeapTupleHeaderGetXmin(tp.t_data)))
  		{
  			UnlockReleaseBuffer(buffer);
  			break;
  		}
  
  		/*
  		 * Check tuple visibility; if visible, set it as the new result
  		 * candidate.
  		 */
  		valid = HeapTupleSatisfiesVisibility(relation, &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) ||
  			HeapTupleHeaderIndicatesMovedPartitions(tp.t_data) ||
  			ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid))
  		{
  			UnlockReleaseBuffer(buffer);
  			break;
  		}
  
  		ctid = tp.t_data->t_ctid;
  		priorXmax = HeapTupleHeaderGetUpdateXid(tp.t_data);
  		UnlockReleaseBuffer(buffer);
  	}							/* end of loop */
  }
  
  
  /*
   * UpdateXmaxHintBits - update tuple hint bits after xmax transaction ends
   *
   * This is called after we have waited for the XMAX transaction to terminate.
   * If the transaction aborted, we guarantee the XMAX_INVALID hint bit will
   * be set on exit.  If the transaction committed, we set the XMAX_COMMITTED
   * hint bit if possible --- but beware that that may not yet be possible,
   * if the transaction committed asynchronously.
   *
   * Note that if the transaction was a locker only, we set HEAP_XMAX_INVALID
   * even if it commits.
   *
   * Hence callers should look only at XMAX_INVALID.
   *
   * Note this is not allowed for tuples whose xmax is a multixact.
   */
  static void
  UpdateXmaxHintBits(HeapTupleHeader tuple, Buffer buffer, TransactionId xid, Relation rel)
  {
  	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, rel, HEAP_XMAX_COMMITTED,
  								 xid);
  		else
  			HeapTupleSetHintBits(tuple, buffer, rel, HEAP_XMAX_INVALID,
  								 InvalidTransactionId);
  	}
  }
  
  
  /*
   * GetBulkInsertState - prepare status object for a bulk insert
   */
  BulkInsertState
  GetBulkInsertState(void)
  {
  	BulkInsertState bistate;
  
  	bistate = (BulkInsertState) palloc(sizeof(BulkInsertStateData));
  	bistate->strategy = GetAccessStrategy(BAS_BULKWRITE);
  	bistate->current_buf = InvalidBuffer;
  	return bistate;
  }
  
  /*
   * FreeBulkInsertState - clean up after finishing a bulk insert
   */
  void
  FreeBulkInsertState(BulkInsertState bistate)
  {
  	if (bistate->current_buf != InvalidBuffer)
  		ReleaseBuffer(bistate->current_buf);
  	FreeAccessStrategy(bistate->strategy);
  	pfree(bistate);
  }
  
  /*
   * ReleaseBulkInsertStatePin - release a buffer currently held in bistate
   */
  void
  ReleaseBulkInsertStatePin(BulkInsertState bistate)
  {
  	if (bistate->current_buf != InvalidBuffer)
  		ReleaseBuffer(bistate->current_buf);
  	bistate->current_buf = InvalidBuffer;
  }
  
  
  /*
   *	heap_insert		- insert tuple into a heap
   *
   * The new tuple is stamped with current transaction ID and the specified
   * command ID.
   *
   * See table_tuple_insert for comments about most of the input flags, except
   * that this routine directly takes a tuple rather than a slot.
   *
   * There's corresponding HEAP_INSERT_ options to all the TABLE_INSERT_
   * options, and there additionally is HEAP_INSERT_SPECULATIVE which is used to
   * implement table_tuple_insert_speculative().
   *
   * On return the header fields of *tup are updated to match the stored tuple;
   * in particular tup->t_self receives the actual TID where the tuple was
   * stored.  But note that any toasting of fields within the tuple data is NOT
   * reflected into *tup.
   */
  void
  heap_insert(Relation relation, HeapTuple tup, CommandId cid,
  			int options, BulkInsertState bistate, TransactionId xid)
  {
  	bool		isFrozen = (xid == FrozenTransactionId);
  	HeapTuple	heaptup;
  	Buffer		buffer;
  	Buffer		vmbuffer = InvalidBuffer;
  	bool		all_visible_cleared = false;
  	bool		needwal;
  
  	needwal = !(options & HEAP_INSERT_SKIP_WAL) && RelationNeedsWAL(relation);
  	gp_expand_protect_catalog_changes(relation);
  
  #ifdef FAULT_INJECTOR
  	FaultInjector_InjectFaultIfSet("heap_insert", DDLNotSpecified, "",
  								   RelationGetRelationName(relation));
  #endif
  
  	/*
  	 * Fill in tuple header fields and toast the tuple if necessary.
  	 *
  	 * Note: below this point, heaptup is the data we actually intend to store
  	 * into the relation; tup is the caller's original untoasted data.
  	 */
  	heaptup = heap_prepare_insert(relation, tup, xid, cid, options, isFrozen);
  
  	/*
  	 * Find buffer to insert this tuple into.  If the page is all visible,
  	 * this will also pin the requisite visibility map page.
  	 */
  	buffer = RelationGetBufferForTuple(relation, heaptup->t_len,
  									   InvalidBuffer, options, bistate,
  									   &vmbuffer, NULL);
  
  	/*
  	 * We're about to do the actual insert -- but check for conflict first, to
  	 * avoid possibly having to roll back work we've just done.
  	 *
  	 * This is safe without a recheck as long as there is no possibility of
  	 * another process scanning the page between this check and the insert
  	 * being visible to the scan (i.e., an exclusive buffer content lock is
  	 * continuously held from this point until the tuple insert is visible).
  	 *
  	 * For a heap insert, we only need to check for table-level SSI locks. Our
  	 * new tuple can't possibly conflict with existing tuple locks, and heap
  	 * page locks are only consolidated versions of tuple locks; they do not
  	 * lock "gaps" as index page locks do.  So we don't need to specify a
  	 * buffer when making the call, which makes for a faster check.
  	 */
  	CheckForSerializableConflictIn(relation, NULL, InvalidBuffer);
  
  	/* NO EREPORT(ERROR) from here till changes are logged */
  	START_CRIT_SECTION();
  
  	RelationPutHeapTuple(relation, buffer, heaptup,
  						 (options & HEAP_INSERT_SPECULATIVE) != 0);
  
  	if (PageIsAllVisible(BufferGetPage(buffer)))
  	{
  		all_visible_cleared = true;
  		PageClearAllVisible(BufferGetPage(buffer));
  		visibilitymap_clear(relation,
  							ItemPointerGetBlockNumber(&(heaptup->t_self)),
  							vmbuffer, VISIBILITYMAP_VALID_BITS);
  	}
  
  	/*
  	 * XXX Should we set PageSetPrunable on this page ?
  	 *
  	 * The inserting transaction may eventually abort thus making this tuple
  	 * DEAD and hence available for pruning. Though we don't want to optimize
  	 * for aborts, if no other tuple in this page is UPDATEd/DELETEd, the
  	 * aborted tuple will never be pruned until next vacuum is triggered.
  	 *
  	 * If you do add PageSetPrunable here, add it in heap_xlog_insert too.
  	 */
  
  	MarkBufferDirty(buffer);
  
  	/* XLOG stuff */
  	if (needwal)
  	{
  		xl_heap_insert xlrec;
  		xl_heap_header xlhdr;
  		XLogRecPtr	recptr;
  		Page		page = BufferGetPage(buffer);
  		uint8		info = XLOG_HEAP_INSERT;
  		int			bufflags = 0;
  
  		/*
  		 * If this is a catalog, we need to transmit combocids to properly
  		 * decode, so log that as well.
  		 */
  		if (RelationIsAccessibleInLogicalDecoding(relation))
  			log_heap_new_cid(relation, heaptup);
  
  		/*
  		 * If this is the single and first tuple on page, we can reinit the
  		 * page instead of restoring the whole thing.  Set flag, and hide
  		 * buffer references from XLogInsert.
  		 */
  		if (ItemPointerGetOffsetNumber(&(heaptup->t_self)) == FirstOffsetNumber &&
  			PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
  		{
  			info |= XLOG_HEAP_INIT_PAGE;
  			bufflags |= REGBUF_WILL_INIT;
  		}
  
  		xlrec.offnum = ItemPointerGetOffsetNumber(&heaptup->t_self);
  		xlrec.flags = 0;
  		if (all_visible_cleared)
  			xlrec.flags |= XLH_INSERT_ALL_VISIBLE_CLEARED;
  		if (options & HEAP_INSERT_SPECULATIVE)
  			xlrec.flags |= XLH_INSERT_IS_SPECULATIVE;
  		Assert(ItemPointerGetBlockNumber(&heaptup->t_self) == BufferGetBlockNumber(buffer));
  
  		/*
  		 * For logical decoding, we need the tuple even if we're doing a full
  		 * page write, so make sure it's included even if we take a full-page
  		 * image. (XXX We could alternatively store a pointer into the FPW).
  		 */
  		if (RelationIsLogicallyLogged(relation) &&
  			!(options & HEAP_INSERT_NO_LOGICAL))
  		{
  			xlrec.flags |= XLH_INSERT_CONTAINS_NEW_TUPLE;
  			bufflags |= REGBUF_KEEP_DATA;
  		}
  
  		XLogBeginInsert();
  		XLogRegisterData((char *) &xlrec, SizeOfHeapInsert);
  
  		xlhdr.t_infomask2 = heaptup->t_data->t_infomask2;
  		xlhdr.t_infomask = heaptup->t_data->t_infomask;
  		xlhdr.t_hoff = heaptup->t_data->t_hoff;
  
  		/*
  		 * note we mark xlhdr as belonging to buffer; if XLogInsert decides to
  		 * write the whole page to the xlog, we don't need to store
  		 * xl_heap_header in the xlog.
  		 */
  		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD | bufflags);
  		XLogRegisterBufData(0, (char *) &xlhdr, SizeOfHeapHeader);
  		/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
  		XLogRegisterBufData(0,
  							(char *) heaptup->t_data + SizeofHeapTupleHeader,
  							heaptup->t_len - SizeofHeapTupleHeader);
  
  		/* filtering by origin on a row level is much more efficient */
  		XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
  
  		if (!isFrozen)
  			recptr = XLogInsert(RM_HEAP_ID, info);
  		else
  			recptr = XLogInsert_OverrideXid(RM_HEAP_ID, info, FrozenTransactionId);
  
  		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.
  	 */
  	if (IsSystemRelation(relation))
  		CacheInvalidateHeapTuple(relation, heaptup, NULL);
  
  	/* Note: speculative insertions are counted too, even if aborted later */
  	pgstat_count_heap_insert(relation, 1);
  
  	/*
  	 * If heaptup is a private copy, release it.  Don't forget to copy t_self
  	 * back to the caller's image, too.
  	 */
  	if (heaptup != tup)
  	{
  		tup->t_self = heaptup->t_self;
  		heap_freetuple(heaptup);
  	}
  
  	if (needwal)
  		wait_to_avoid_large_repl_lag();
  }
  
  /*
   * Subroutine for heap_insert(). Prepares a tuple for insertion. This sets the
   * tuple header fields and toasts the tuple if necessary.  Returns a toasted
   * version of the tuple if it was toasted, or the original tuple if not. Note
   * that in any case, the header fields are also set in the original tuple.
   */
  static HeapTuple
  heap_prepare_insert(Relation relation, HeapTuple tup, TransactionId xid,
  					CommandId cid, int options, bool isFrozen)
  {
  	/*
  	 * Parallel operations are required to be strictly read-only in a parallel
  	 * worker.  Parallel inserts are not safe even in the leader in the
  	 * general case, because group locking means that heavyweight locks for
  	 * relation extension or GIN page locks will not conflict between members
  	 * of a lock group, but we don't prohibit that case here because there are
  	 * useful special cases that we can safely allow, such as CREATE TABLE AS.
  	 */
  	if (IsParallelWorker())
  		ereport(ERROR,
  				(errcode(ERRCODE_INVALID_TRANSACTION_STATE),
  				 errmsg("cannot insert tuples in a parallel worker")));
  
  	tup->t_data->t_infomask &= ~(HEAP_XACT_MASK);
  	if (isFrozen)
  		tup->t_data->t_infomask |= HEAP_XMIN_COMMITTED;
  	tup->t_data->t_infomask2 &= ~(HEAP2_XACT_MASK);
  	tup->t_data->t_infomask |= HEAP_XMAX_INVALID;
  	HeapTupleHeaderSetXmin(tup->t_data, xid);
  	if (options & HEAP_INSERT_FROZEN)
  		HeapTupleHeaderSetXminFrozen(tup->t_data);
  
  	HeapTupleHeaderSetCmin(tup->t_data, cid);
  	HeapTupleHeaderSetXmax(tup->t_data, 0); /* for cleanliness */
  	tup->t_tableOid = RelationGetRelid(relation);
  
  	/*
  	 * If the new tuple is too big for storage or contains already toasted
  	 * out-of-line attributes from some other relation, invoke the toaster.
  	 */
  	if (relation->rd_rel->relkind != RELKIND_RELATION &&
  		relation->rd_rel->relkind != RELKIND_MATVIEW)
  	{
  		/* toast table entries should never be recursively toasted */
  		Assert(!HeapTupleHasExternal(tup));
  		return tup;
  	}
  	else if (HeapTupleHasExternal(tup) || tup->t_len > TOAST_TUPLE_THRESHOLD)
  		return toast_insert_or_update(relation, tup, NULL,
  									  TOAST_TUPLE_TARGET, isFrozen,
  									  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, TupleTableSlot **slots, int ntuples,
  				  CommandId cid, int options, BulkInsertState bistate)
  {
  	TransactionId xid = GetCurrentTransactionId();
  	bool        isFrozen = false;
  	HeapTuple  *heaptuples;
  	int			i;
  	int			ndone;
  	PGAlignedBlock scratch;
  	Page		page;
  	bool		needwal;
  	Size		saveFreeSpace;
  	bool		need_tuple_data = RelationIsLogicallyLogged(relation);
  	bool		need_cids = RelationIsAccessibleInLogicalDecoding(relation);
  
  	/* currently not needed (thus unsupported) for heap_multi_insert() */
  	AssertArg(!(options & HEAP_INSERT_NO_LOGICAL));
  
  	needwal = !(options & HEAP_INSERT_SKIP_WAL) && RelationNeedsWAL(relation);
  	saveFreeSpace = RelationGetTargetPageFreeSpace(relation,
  												   HEAP_DEFAULT_FILLFACTOR);
  
  	/* Toast and set header data in all the slots */
  	heaptuples = palloc(ntuples * sizeof(HeapTuple));
  	for (i = 0; i < ntuples; i++)
  	{
  		HeapTuple	tuple;
  
  		tuple = ExecFetchSlotHeapTuple(slots[i], true, NULL);
  		slots[i]->tts_tableOid = RelationGetRelid(relation);
  		tuple->t_tableOid = slots[i]->tts_tableOid;
  		heaptuples[i] = heap_prepare_insert(relation, tuple, xid, cid,
  											options, isFrozen);
  	}
  
  	/*
  	 * We're about to do the actual inserts -- but check for conflict first,
  	 * to minimize the possibility of having to roll back work we've just
  	 * done.
  	 *
  	 * A check here does not definitively prevent a serialization anomaly;
  	 * that check MUST be done at least past the point of acquiring an
  	 * exclusive buffer content lock on every buffer that will be affected,
  	 * and MAY be done after all inserts are reflected in the buffers and
  	 * those locks are released; otherwise there race condition.  Since
  	 * multiple buffers can be locked and unlocked in the loop below, and it
  	 * would not be feasible to identify and lock all of those buffers before
  	 * the loop, we must do a final check at the end.
  	 *
  	 * The check here could be omitted with no loss of correctness; it is
  	 * present strictly as an optimization.
  	 *
  	 * For heap inserts, we only need to check for table-level SSI locks. Our
  	 * new tuples can't possibly conflict with existing tuple locks, and heap
  	 * page locks are only consolidated versions of tuple locks; they do not
  	 * lock "gaps" as index page locks do.  So we don't need to specify a
  	 * buffer when making the call, which makes for a faster check.
  	 */
  	CheckForSerializableConflictIn(relation, NULL, InvalidBuffer);
  
  	ndone = 0;
  	while (ndone < ntuples)
  	{
  		Buffer		buffer;
  		Buffer		vmbuffer = InvalidBuffer;
  		bool		all_visible_cleared = false;
  		int			nthispage;
  
  		CHECK_FOR_INTERRUPTS();
  
  		/*
  		 * Find buffer where at least the next tuple will fit.  If the page is
  		 * all-visible, this will also pin the requisite visibility map page.
  		 */
  		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], false);
  		for (nthispage = 1; ndone + nthispage < ntuples; nthispage++)
  		{
  			HeapTuple	heaptup = heaptuples[ndone + nthispage];
  
  			if (PageGetHeapFreeSpace(page) < MAXALIGN(heaptup->t_len) + saveFreeSpace)
  				break;
  
  			RelationPutHeapTuple(relation, buffer, heaptup, false);
  
  			/*
  			 * We don't use heap_multi_insert for catalog tuples yet, but
  			 * better be prepared...
  			 */
  			if (needwal && need_cids)
  				log_heap_new_cid(relation, heaptup);
  		}
  
  		if (PageIsAllVisible(page))
  		{
  			all_visible_cleared = true;
  			PageClearAllVisible(page);
  			visibilitymap_clear(relation,
  								BufferGetBlockNumber(buffer),
  								vmbuffer, VISIBILITYMAP_VALID_BITS);
  		}
  
  		/*
  		 * XXX Should we set PageSetPrunable on this page ? See heap_insert()
  		 */
  
  		MarkBufferDirty(buffer);
  
  		/* XLOG stuff */
  		if (needwal)
  		{
  			XLogRecPtr	recptr;
  			xl_heap_multi_insert *xlrec;
  			uint8		info = XLOG_HEAP2_MULTI_INSERT;
  			char	   *tupledata;
  			int			totaldatalen;
  			char	   *scratchptr = scratch.data;
  			bool		init;
  			int			bufflags = 0;
  
  			/*
  			 * If the page was previously empty, we can reinit the page
  			 * instead of restoring the whole thing.
  			 */
  			init = (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->flags = all_visible_cleared ? XLH_INSERT_ALL_VISIBLE_CLEARED : 0;
  			xlrec->ntuples = nthispage;
  
  			/*
  			 * Write out an xl_multi_insert_tuple and the tuple data itself
  			 * for each tuple.
  			 */
  			for (i = 0; i < nthispage; i++)
  			{
  				HeapTuple	heaptup = heaptuples[ndone + i];
  				xl_multi_insert_tuple *tuphdr;
  				int			datalen;
  
  				if (!init)
  					xlrec->offsets[i] = ItemPointerGetOffsetNumber(&heaptup->t_self);
  				/* xl_multi_insert_tuple needs two-byte alignment. */
  				tuphdr = (xl_multi_insert_tuple *) SHORTALIGN(scratchptr);
  				scratchptr = ((char *) tuphdr) + SizeOfMultiInsertTuple;
  
  				tuphdr->t_infomask2 = heaptup->t_data->t_infomask2;
  				tuphdr->t_infomask = heaptup->t_data->t_infomask;
  				tuphdr->t_hoff = heaptup->t_data->t_hoff;
  
  				/* write bitmap [+ padding] [+ oid] + data */
  				datalen = heaptup->t_len - SizeofHeapTupleHeader;
  				memcpy(scratchptr,
  					   (char *) heaptup->t_data + SizeofHeapTupleHeader,
  					   datalen);
  				tuphdr->datalen = datalen;
  				scratchptr += datalen;
  			}
  			totaldatalen = scratchptr - tupledata;
  			Assert((scratchptr - scratch.data) < BLCKSZ);
  
  			if (need_tuple_data)
  				xlrec->flags |= XLH_INSERT_CONTAINS_NEW_TUPLE;
  
  			/*
  			 * Signal that this is the last xl_heap_multi_insert record
  			 * emitted by this call to heap_multi_insert(). Needed for logical
  			 * decoding so it knows when to cleanup temporary data.
  			 */
  			if (ndone + nthispage == ntuples)
  				xlrec->flags |= XLH_INSERT_LAST_IN_MULTI;
  
  			if (init)
  			{
  				info |= XLOG_HEAP_INIT_PAGE;
  				bufflags |= REGBUF_WILL_INIT;
  			}
  
  			/*
  			 * If we're doing logical decoding, include the new tuple data
  			 * even if we take a full-page image of the page.
  			 */
  			if (need_tuple_data)
  				bufflags |= REGBUF_KEEP_DATA;
  
  			XLogBeginInsert();
  			XLogRegisterData((char *) xlrec, tupledata - scratch.data);
  			XLogRegisterBuffer(0, buffer, REGBUF_STANDARD | bufflags);
  
  			XLogRegisterBufData(0, tupledata, totaldatalen);
  
  			/* filtering by origin on a row level is much more efficient */
  			XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
  
  			recptr = XLogInsert(RM_HEAP2_ID, info);
  
  			PageSetLSN(page, recptr);
  		}
  
  		END_CRIT_SECTION();
  
  		UnlockReleaseBuffer(buffer);
  		if (vmbuffer != InvalidBuffer)
  			ReleaseBuffer(vmbuffer);
  
  		ndone += nthispage;
  	}
  
  	/*
  	 * We're done with the actual inserts.  Check for conflicts again, to
  	 * ensure that all rw-conflicts in to these inserts are detected.  Without
  	 * this final check, a sequential scan of the heap may have locked the
  	 * table after the "before" check, missing one opportunity to detect the
  	 * conflict, and then scanned the table before the new tuples were there,
  	 * missing the other chance to detect the conflict.
  	 *
  	 * For heap inserts, we only need to check for table-level SSI locks. Our
  	 * new tuples can't possibly conflict with existing tuple locks, and heap
  	 * page locks are only consolidated versions of tuple locks; they do not
  	 * lock "gaps" as index page locks do.  So we don't need to specify a
  	 * buffer when making the call.
  	 */
  	CheckForSerializableConflictIn(relation, NULL, InvalidBuffer);
  
  	/*
  	 * If tuples are cachable, mark them for invalidation from the caches in
  	 * case we abort.  Note it is OK to do this after releasing the buffer,
  	 * because the heaptuples data structure is all in local memory, not in
  	 * the shared buffer.
  	 */
  	if (IsCatalogRelation(relation))
  	{
  		for (i = 0; i < ntuples; i++)
  			CacheInvalidateHeapTuple(relation, heaptuples[i], NULL);
  	}
  
  	/* copy t_self fields back to the caller's slots */
  	for (i = 0; i < ntuples; i++)
  		slots[i]->tts_tid = heaptuples[i]->t_self;
  
  	pgstat_count_heap_insert(relation, ntuples);
  
  	if (needwal)
  		wait_to_avoid_large_repl_lag();
  }
  
  /*
   *	simple_heap_insert - insert a tuple
   *
   * Currently, this routine differs from heap_insert only in supplying
   * a default command ID and not allowing access to the speedup options.
   *
   * This should be used rather than using heap_insert directly in most places
   * where we are modifying system catalogs.
   */
  void
  simple_heap_insert(Relation relation, HeapTuple tup)
  {
  	heap_insert(relation, tup, GetCurrentCommandId(true), 0, NULL,
  				GetCurrentTransactionId());
  }
  
  /*
   *	frozen_heap_insert - insert a tuple and freeze it (always visible).
   *
   * Currently, this routine differs from heap_insert in supplying
   * a default command ID and a frozen transaction id. Also, the committed
   * bit of the tuple is set. This function is currently used for data that
   * goes into error tables and need to stay there even if transaction
   * aborts.
   */
  void
  frozen_heap_insert(Relation relation, HeapTuple tup)
  {
  	return heap_insert(relation, tup, GetCurrentCommandId(true),
  					   0, NULL, FrozenTransactionId);
  }
  
  /*
   * Given infomask/infomask2, compute the bits that must be saved in the
   * "infobits" field of xl_heap_delete, xl_heap_update, xl_heap_lock,
   * xl_heap_lock_updated WAL records.
   *
   * See fix_infomask_from_infobits.
   */
  static uint8
  compute_infobits(uint16 infomask, uint16 infomask2)
  {
  	return
  		((infomask & HEAP_XMAX_IS_MULTI) != 0 ? XLHL_XMAX_IS_MULTI : 0) |
  		((infomask & HEAP_XMAX_LOCK_ONLY) != 0 ? XLHL_XMAX_LOCK_ONLY : 0) |
  		((infomask & HEAP_XMAX_EXCL_LOCK) != 0 ? XLHL_XMAX_EXCL_LOCK : 0) |
  	/* note we ignore HEAP_XMAX_SHR_LOCK here */
  		((infomask & HEAP_XMAX_KEYSHR_LOCK) != 0 ? XLHL_XMAX_KEYSHR_LOCK : 0) |
  		((infomask2 & HEAP_KEYS_UPDATED) != 0 ?
  		 XLHL_KEYS_UPDATED : 0);
  }
  
  /*
   * Given two versions of the same t_infomask for a tuple, compare them and
   * return whether the relevant status for a tuple Xmax has changed.  This is
   * used after a buffer lock has been released and reacquired: we want to ensure
   * that the tuple state continues to be the same it was when we previously
   * examined it.
   *
   * Note the Xmax field itself must be compared separately.
   */
  static inline bool
  xmax_infomask_changed(uint16 new_infomask, uint16 old_infomask)
  {
  	const uint16 interesting =
  	HEAP_XMAX_IS_MULTI | HEAP_XMAX_LOCK_ONLY | HEAP_LOCK_MASK;
  
  	if ((new_infomask & interesting) != (old_infomask & interesting))
  		return true;
  
  	return false;
  }
  
  /*
   *	heap_delete - delete a tuple
   *
   * See table_tuple_delete() for an explanation of the parameters, except that
   * this routine directly takes a tuple rather than a slot.
   *
   * In the failure cases, the routine fills *tmfd with the tuple's t_ctid,
   * t_xmax (resolving a possible MultiXact, if necessary), and t_cmax (the last
   * only for TM_SelfModified, since we cannot obtain cmax from a combocid
   * generated by another transaction).
   */
  TM_Result
  heap_delete(Relation relation, ItemPointer tid,
  			CommandId cid, Snapshot crosscheck, bool wait,
  			TM_FailureData *tmfd, bool changingPart)
  {
  	TM_Result	result;
  	TransactionId xid = GetCurrentTransactionId();
  	ItemId		lp;
  	HeapTupleData tp;
  	Page		page;
  	BlockNumber block;
  	Buffer		buffer;
  	Buffer		vmbuffer = InvalidBuffer;
  	TransactionId new_xmax;
  	uint16		new_infomask,
  				new_infomask2;
  	bool		have_tuple_lock = false;
  	bool		iscombo;
  	bool		all_visible_cleared = false;
  	HeapTuple	old_key_tuple = NULL;	/* replica identity of the tuple */
  	bool		old_key_copied = false;
  
  	Assert(ItemPointerIsValid(tid));
  
  	gp_expand_protect_catalog_changes(relation);
  
  	/*
  	 * Forbid this during a parallel operation, lest it allocate a combocid.
  	 * Other workers might need that combocid for visibility checks, and we
  	 * have no provision for broadcasting it to them.
  	 */
  	if (IsInParallelMode())
  		ereport(ERROR,
  				(errcode(ERRCODE_INVALID_TRANSACTION_STATE),
  				 errmsg("cannot delete tuples during a parallel operation")));
  
  	block = ItemPointerGetBlockNumber(tid);
  	buffer = ReadBuffer(relation, block);
  	page = BufferGetPage(buffer);
  
  	/*
  	 * Before locking the buffer, pin the visibility map page if it appears to
  	 * be necessary.  Since we haven't got the lock yet, someone else might be
  	 * in the middle of changing this, so we'll need to recheck after we have
  	 * the lock.
  	 */
  	if (PageIsAllVisible(page))
  		visibilitymap_pin(relation, block, &vmbuffer);
  
  	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  	/*
  	 * If we didn't pin the visibility map page and the page has become all
  	 * visible while we were busy locking the buffer, we'll have to unlock and
  	 * re-lock, to avoid holding the buffer lock across an I/O.  That's a bit
  	 * unfortunate, but hopefully shouldn't happen often.
  	 */
  	if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
  	{
  		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  		visibilitymap_pin(relation, block, &vmbuffer);
  		LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  	}
  
  	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
  	Assert(ItemIdIsNormal(lp));
  
  	tp.t_tableOid = RelationGetRelid(relation);
  	tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
  	tp.t_len = ItemIdGetLength(lp);
  	tp.t_self = *tid;
  
  l1:
  	result = HeapTupleSatisfiesUpdate(relation, &tp, cid, buffer);
  
  	if (result == TM_Invisible)
  	{
  		UnlockReleaseBuffer(buffer);
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("attempted to delete invisible tuple")));
  	}
  	else if (result == TM_BeingModified && wait)
  	{
  		TransactionId xwait;
  		uint16		infomask;
  
  		/* must copy state data before unlocking buffer */
  		xwait = HeapTupleHeaderGetRawXmax(tp.t_data);
  		infomask = tp.t_data->t_infomask;
  
  		/*
  		 * Sleep until concurrent transaction ends -- except when there's a
  		 * single locker and it's our own transaction.  Note we don't care
  		 * which lock mode the locker has, because we need the strongest one.
  		 *
  		 * Before sleeping, we need to acquire tuple lock to establish our
  		 * priority for the tuple (see heap_lock_tuple).  LockTuple will
  		 * release us when we are next-in-line for the tuple.
  		 *
  		 * If we are forced to "start over" below, we keep the tuple lock;
  		 * this arranges that we stay at the head of the line while rechecking
  		 * tuple state.
  		 */
  		if (infomask & HEAP_XMAX_IS_MULTI)
  		{
  			bool		current_is_member = false;
  
  			if (DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
  										LockTupleExclusive, &current_is_member))
  			{
  				LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  				/*
  				 * Acquire the lock, if necessary (but skip it when we're
  				 * requesting a lock and already have one; avoids deadlock).
  				 */
  				if (!current_is_member)
  					heap_acquire_tuplock(relation, &(tp.t_self), LockTupleExclusive,
  										 LockWaitBlock, &have_tuple_lock);
  
  				/* wait for multixact */
  				MultiXactIdWait((MultiXactId) xwait, MultiXactStatusUpdate, infomask,
  								relation, &(tp.t_self), XLTW_Delete,
  								NULL);
  				LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  				/*
  				 * If xwait had just locked the tuple then some other xact
  				 * could update this tuple before we get to this point.  Check
  				 * for xmax change, and start over if so.
  				 */
  				if (xmax_infomask_changed(tp.t_data->t_infomask, infomask) ||
  					!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tp.t_data),
  										 xwait))
  					goto l1;
  			}
  
  			/*
  			 * You might think the multixact is necessarily done here, but not
  			 * so: it could have surviving members, namely our own xact or
  			 * other subxacts of this backend.  It is legal for us to delete
  			 * the tuple in either case, however (the latter case is
  			 * essentially a situation of upgrading our former shared lock to
  			 * exclusive).  We don't bother changing the on-disk hint bits
  			 * since we are about to overwrite the xmax altogether.
  			 */
  		}
  		else if (!TransactionIdIsCurrentTransactionId(xwait))
  		{
  			/*
  			 * Wait for regular transaction to end; but first, acquire tuple
  			 * lock.
  			 */
  			LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  			heap_acquire_tuplock(relation, &(tp.t_self), LockTupleExclusive,
  								 LockWaitBlock, &have_tuple_lock);
  			XactLockTableWait(xwait, relation, &(tp.t_self), XLTW_Delete);
  			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  			/*
  			 * xwait is done, but if xwait had just locked the tuple then some
  			 * other xact could update this tuple before we get to this point.
  			 * Check for xmax change, and start over if so.
  			 */
  			if (xmax_infomask_changed(tp.t_data->t_infomask, infomask) ||
  				!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tp.t_data),
  									 xwait))
  				goto l1;
  
  			/* Otherwise check if it committed or aborted */
  			UpdateXmaxHintBits(tp.t_data, buffer, xwait, relation);
  		}
  
  		/*
  		 * We may overwrite if previous xmax aborted, or if it committed but
  		 * only locked the tuple without updating it.
  		 */
  		if ((tp.t_data->t_infomask & HEAP_XMAX_INVALID) ||
  			HEAP_XMAX_IS_LOCKED_ONLY(tp.t_data->t_infomask) ||
  			HeapTupleHeaderIsOnlyLocked(tp.t_data))
  			result = TM_Ok;
  		else if (!ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid) ||
  				 HeapTupleHeaderIndicatesMovedPartitions(tp.t_data))
  			result = TM_Updated;
  		else
  			result = TM_Deleted;
  	}
  
  	if (crosscheck != InvalidSnapshot && result == TM_Ok)
  	{
  		/* Perform additional check for transaction-snapshot mode RI updates */
  		if (!HeapTupleSatisfiesVisibility(relation, &tp, crosscheck, buffer))
  			result = TM_Updated;
  	}
  
  	if (result != TM_Ok)
  	{
  		Assert(result == TM_SelfModified ||
  			   result == TM_Updated ||
  			   result == TM_Deleted ||
  			   result == TM_BeingModified);
  		Assert(!(tp.t_data->t_infomask & HEAP_XMAX_INVALID));
  		Assert(result != TM_Updated ||
  			   !ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid));
  		tmfd->ctid = tp.t_data->t_ctid;
  		tmfd->xmax = HeapTupleHeaderGetUpdateXid(tp.t_data);
  		if (result == TM_SelfModified)
  			tmfd->cmax = HeapTupleHeaderGetCmax(tp.t_data);
  		else
  			tmfd->cmax = InvalidCommandId;
  		UnlockReleaseBuffer(buffer);
  		if (have_tuple_lock)
  			UnlockTupleTuplock(relation, &(tp.t_self), LockTupleExclusive);
  		if (vmbuffer != InvalidBuffer)
  			ReleaseBuffer(vmbuffer);
  		return result;
  	}
  
  	/*
  	 * We're about to do the actual delete -- check for conflict first, to
  	 * avoid possibly having to roll back work we've just done.
  	 *
  	 * This is safe without a recheck as long as there is no possibility of
  	 * another process scanning the page between this check and the delete
  	 * being visible to the scan (i.e., an exclusive buffer content lock is
  	 * continuously held from this point until the tuple delete is visible).
  	 */
  	CheckForSerializableConflictIn(relation, &tp, buffer);
  
  	/* replace cid with a combo cid if necessary */
  	HeapTupleHeaderAdjustCmax(tp.t_data, &cid, &iscombo);
  
  	/*
  	 * Compute replica identity tuple before entering the critical section so
  	 * we don't PANIC upon a memory allocation failure.
  	 */
  	old_key_tuple = ExtractReplicaIdentity(relation, &tp, true, &old_key_copied);
  
  	/*
  	 * If this is the first possibly-multixact-able operation in the current
  	 * transaction, set my per-backend OldestMemberMXactId setting. We can be
  	 * certain that the transaction will never become a member of any older
  	 * MultiXactIds than that.  (We have to do this even if we end up just
  	 * using our own TransactionId below, since some other backend could
  	 * incorporate our XID into a MultiXact immediately afterwards.)
  	 */
  	MultiXactIdSetOldestMember();
  
  	compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(tp.t_data),
  							  tp.t_data->t_infomask, tp.t_data->t_infomask2,
  							  xid, LockTupleExclusive, true,
  							  &new_xmax, &new_infomask, &new_infomask2);
  
  	START_CRIT_SECTION();
  
  	/*
  	 * If this transaction commits, the tuple will become DEAD sooner or
  	 * later.  Set flag that this page is a candidate for pruning once our xid
  	 * falls below the OldestXmin horizon.  If the transaction finally aborts,
  	 * the subsequent page pruning will be a no-op and the hint will be
  	 * cleared.
  	 */
  	PageSetPrunable(page, xid);
  
  	if (PageIsAllVisible(page))
  	{
  		all_visible_cleared = true;
  		PageClearAllVisible(page);
  		visibilitymap_clear(relation, BufferGetBlockNumber(buffer),
  							vmbuffer, VISIBILITYMAP_VALID_BITS);
  	}
  
  	/* store transaction information of xact deleting the tuple */
  	tp.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
  	tp.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  	tp.t_data->t_infomask |= new_infomask;
  	tp.t_data->t_infomask2 |= new_infomask2;
  	HeapTupleHeaderClearHotUpdated(tp.t_data);
  	HeapTupleHeaderSetXmax(tp.t_data, new_xmax);
  	HeapTupleHeaderSetCmax(tp.t_data, cid, iscombo);
  	/* Make sure there is no forward chain link in t_ctid */
  	tp.t_data->t_ctid = tp.t_self;
  
  	/* Signal that this is actually a move into another partition */
  	if (changingPart)
  		HeapTupleHeaderSetMovedPartitions(tp.t_data);
  
  	MarkBufferDirty(buffer);
  
  	/*
  	 * XLOG stuff
  	 *
  	 * NB: heap_abort_speculative() uses the same xlog record and replay
  	 * routines.
  	 */
  	if (RelationNeedsWAL(relation))
  	{
  		xl_heap_delete xlrec;
  		xl_heap_header xlhdr;
  		XLogRecPtr	recptr;
  
  		/* For logical decode we need combocids to properly decode the catalog */
  		if (RelationIsAccessibleInLogicalDecoding(relation))
  			log_heap_new_cid(relation, &tp);
  
  		xlrec.flags = 0;
  		if (all_visible_cleared)
  			xlrec.flags |= XLH_DELETE_ALL_VISIBLE_CLEARED;
  		if (changingPart)
  			xlrec.flags |= XLH_DELETE_IS_PARTITION_MOVE;
  		xlrec.infobits_set = compute_infobits(tp.t_data->t_infomask,
  											  tp.t_data->t_infomask2);
  		xlrec.offnum = ItemPointerGetOffsetNumber(&tp.t_self);
  		xlrec.xmax = new_xmax;
  
  		if (old_key_tuple != NULL)
  		{
  			if (relation->rd_rel->relreplident == REPLICA_IDENTITY_FULL)
  				xlrec.flags |= XLH_DELETE_CONTAINS_OLD_TUPLE;
  			else
  				xlrec.flags |= XLH_DELETE_CONTAINS_OLD_KEY;
  		}
  
  		XLogBeginInsert();
  		XLogRegisterData((char *) &xlrec, SizeOfHeapDelete);
  
  		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
  
  		/*
  		 * Log replica identity of the deleted tuple if there is one
  		 */
  		if (old_key_tuple != NULL)
  		{
  			xlhdr.t_infomask2 = old_key_tuple->t_data->t_infomask2;
  			xlhdr.t_infomask = old_key_tuple->t_data->t_infomask;
  			xlhdr.t_hoff = old_key_tuple->t_data->t_hoff;
  
  			XLogRegisterData((char *) &xlhdr, SizeOfHeapHeader);
  			XLogRegisterData((char *) old_key_tuple->t_data
  							 + SizeofHeapTupleHeader,
  							 old_key_tuple->t_len
  							 - SizeofHeapTupleHeader);
  		}
  
  		/* filtering by origin on a row level is much more efficient */
  		XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
  
  		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_DELETE);
  
  		PageSetLSN(page, recptr);
  	}
  
  	END_CRIT_SECTION();
  
  	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  	if (vmbuffer != InvalidBuffer)
  		ReleaseBuffer(vmbuffer);
  
  	/*
  	 * If the tuple has toasted out-of-line attributes, we need to delete
  	 * those items too.  We have to do this before releasing the buffer
  	 * because we need to look at the contents of the tuple, but it's OK to
  	 * release the content lock on the buffer first.
  	 */
  	if (relation->rd_rel->relkind != RELKIND_RELATION &&
  		relation->rd_rel->relkind != RELKIND_MATVIEW)
  	{
  		/* toast table entries should never be recursively toasted */
  		Assert(!HeapTupleHasExternal(&tp));
  	}
  	else if (HeapTupleHasExternal(&tp))
  		toast_delete(relation, &tp, false);
  
  	/*
  	 * Mark tuple for invalidation from system caches at next command
  	 * boundary. We have to do this before releasing the buffer because we
  	 * need to look at the contents of the tuple.
  	 */
  	CacheInvalidateHeapTuple(relation, &tp, NULL);
  
  	/* Now we can release the buffer */
  	ReleaseBuffer(buffer);
  
  	/*
  	 * Release the lmgr tuple lock, if we had it.
  	 */
  	if (have_tuple_lock)
  		UnlockTupleTuplock(relation, &(tp.t_self), LockTupleExclusive);
  
  	pgstat_count_heap_delete(relation);
  
  	if (old_key_tuple != NULL && old_key_copied)
  		heap_freetuple(old_key_tuple);
  
  	return TM_Ok;
  }
  
  /*
   *	simple_heap_delete - delete a tuple
   *
   * This routine may be used to delete a tuple when concurrent updates of
   * the target tuple are not expected (for example, because we have a lock
   * on the relation associated with the tuple).  Any failure is reported
   * via ereport().
   */
  void
  simple_heap_delete(Relation relation, ItemPointer tid)
  {
  	TM_Result	result;
  	TM_FailureData tmfd;
  
  	result = heap_delete(relation, tid,
  						 GetCurrentCommandId(true), InvalidSnapshot,
  						 true /* wait for commit */ ,
  						 &tmfd, false /* changingPart */ );
  	switch (result)
  	{
  		case TM_SelfModified:
  			/* Tuple was already updated in current command? */
  			elog(ERROR, "tuple already updated by self");
  			break;
  
  		case TM_Ok:
  			/* done successfully */
  			break;
  
  		case TM_Updated:
  			elog(ERROR, "tuple concurrently updated");
  			break;
  
  		case TM_Deleted:
  			elog(ERROR, "tuple concurrently deleted");
  			break;
  
  		default:
  			elog(ERROR, "unrecognized heap_delete status: %u", result);
  			break;
  	}
  }
  
  /*
   *	heap_update - replace a tuple
   *
   * See table_tuple_update() for an explanation of the parameters, except that
   * this routine directly takes a tuple rather than a slot.
   *
   * In the failure cases, the routine fills *tmfd with the tuple's t_ctid,
   * t_xmax (resolving a possible MultiXact, if necessary), and t_cmax (the last
   * only for TM_SelfModified, since we cannot obtain cmax from a combocid
   * generated by another transaction).
   */
  static TM_Result
  heap_update_internal(Relation relation, ItemPointer otid, HeapTuple newtup,
  			CommandId cid, Snapshot crosscheck, bool wait,
  			TM_FailureData *tmfd, LockTupleMode *lockmode, bool simple)
  {
  	TM_Result	result;
  	TransactionId xid = GetCurrentTransactionId();
  	Bitmapset  *hot_attrs;
  	Bitmapset  *key_attrs;
  	Bitmapset  *id_attrs;
  	Bitmapset  *interesting_attrs;
  	Bitmapset  *modified_attrs;
  	ItemId		lp;
  	HeapTupleData oldtup;
  	HeapTuple	heaptup;
  	HeapTuple	old_key_tuple = NULL;
  	bool		old_key_copied = false;
  	Page		page;
  	BlockNumber block;
  	MultiXactStatus mxact_status;
  	Buffer		buffer,
  				newbuf,
  				vmbuffer = InvalidBuffer,
  				vmbuffer_new = InvalidBuffer;
  	bool		need_toast;
  	Size		newtupsize,
  				pagefree;
  	bool		have_tuple_lock = false;
  	bool		iscombo;
  	bool		use_hot_update = false;
  	bool		hot_attrs_checked = false;
  	bool		key_intact;
  	bool		all_visible_cleared = false;
  	bool		all_visible_cleared_new = false;
  	bool		checked_lockers;
  	bool		locker_remains;
  	TransactionId xmax_new_tuple,
  				xmax_old_tuple;
  	uint16		infomask_old_tuple,
  				infomask2_old_tuple,
  				infomask_new_tuple,
  				infomask2_new_tuple;
  
  	Assert(ItemPointerIsValid(otid));
  
  	gp_expand_protect_catalog_changes(relation);
  
  	/*
  	 * Forbid this during a parallel operation, lest it allocate a combocid.
  	 * Other workers might need that combocid for visibility checks, and we
  	 * have no provision for broadcasting it to them.
  	 */
  	if (IsInParallelMode())
  		ereport(ERROR,
  				(errcode(ERRCODE_INVALID_TRANSACTION_STATE),
  				 errmsg("cannot update tuples during a parallel operation")));
  
  	/*
  	 * Fetch the list of attributes to be checked for various operations.
  	 *
  	 * For HOT considerations, this is wasted effort if we fail to update or
  	 * have to put the new tuple on a different page.  But we must compute the
  	 * list before obtaining buffer lock --- in the worst case, if we are
  	 * doing an update on one of the relevant system catalogs, we could
  	 * deadlock if we try to fetch the list later.  In any case, the relcache
  	 * caches the data so this is usually pretty cheap.
  	 *
  	 * We also need columns used by the replica identity and columns that are
  	 * considered the "key" of rows in the table.
  	 *
  	 * Note that we get copies of each bitmap, so we need not worry about
  	 * relcache flush happening midway through.
  	 */
  	hot_attrs = RelationGetIndexAttrBitmap(relation, INDEX_ATTR_BITMAP_ALL);
  	key_attrs = RelationGetIndexAttrBitmap(relation, INDEX_ATTR_BITMAP_KEY);
  	id_attrs = RelationGetIndexAttrBitmap(relation,
  										  INDEX_ATTR_BITMAP_IDENTITY_KEY);
  
  
  	block = ItemPointerGetBlockNumber(otid);
  	buffer = ReadBuffer(relation, block);
  	page = BufferGetPage(buffer);
  
  	interesting_attrs = NULL;
  
  	/*
  	 * If the page is already full, there is hardly any chance of doing a HOT
  	 * update on this page. It might be wasteful effort to look for index
  	 * column updates only to later reject HOT updates for lack of space in
  	 * the same page. So we be conservative and only fetch hot_attrs if the
  	 * page is not already full. Since we are already holding a pin on the
  	 * buffer, there is no chance that the buffer can get cleaned up
  	 * concurrently and even if that was possible, in the worst case we lose a
  	 * chance to do a HOT update.
  	 */
  	if (!PageIsFull(page))
  	{
  		interesting_attrs = bms_add_members(interesting_attrs, hot_attrs);
  		hot_attrs_checked = true;
  	}
  	interesting_attrs = bms_add_members(interesting_attrs, key_attrs);
  	interesting_attrs = bms_add_members(interesting_attrs, id_attrs);
  
  	/*
  	 * Before locking the buffer, pin the visibility map page if it appears to
  	 * be necessary.  Since we haven't got the lock yet, someone else might be
  	 * in the middle of changing this, so we'll need to recheck after we have
  	 * the lock.
  	 */
  	if (PageIsAllVisible(page))
  		visibilitymap_pin(relation, block, &vmbuffer);
  
  	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(otid));
  	Assert(ItemIdIsNormal(lp));
  
  	/*
  	 * Fill in enough data in oldtup for HeapDetermineModifiedColumns to work
  	 * properly.
  	 */
  	oldtup.t_tableOid = RelationGetRelid(relation);
  	oldtup.t_data = (HeapTupleHeader) PageGetItem(page, lp);
  	oldtup.t_len = ItemIdGetLength(lp);
  	oldtup.t_self = *otid;
  
  	/* the new tuple is ready, except for this: */
  	newtup->t_tableOid = RelationGetRelid(relation);
  
  	/* Determine columns modified by the update. */
  	modified_attrs = HeapDetermineModifiedColumns(relation, interesting_attrs,
  												  &oldtup, newtup);
  
  	/*
  	 * 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.
  	 */
  	if (!bms_overlap(modified_attrs, key_attrs))
  	{
  		*lockmode = LockTupleNoKeyExclusive;
  		mxact_status = MultiXactStatusNoKeyUpdate;
  		key_intact = true;
  
  		/*
  		 * If this is the first possibly-multixact-able operation in the
  		 * current transaction, set my per-backend OldestMemberMXactId
  		 * setting. We can be certain that the transaction will never become a
  		 * member of any older MultiXactIds than that.  (We have to do this
  		 * even if we end up just using our own TransactionId below, since
  		 * some other backend could incorporate our XID into a MultiXact
  		 * immediately afterwards.)
  		 */
  		MultiXactIdSetOldestMember();
  	}
  	else
  	{
  		*lockmode = LockTupleExclusive;
  		mxact_status = MultiXactStatusUpdate;
  		key_intact = false;
  	}
  
  	/*
  	 * Note: beyond this point, use oldtup not otid to refer to old tuple.
  	 * otid may very well point at newtup->t_self, which we will overwrite
  	 * with the new tuple's location, so there's great risk of confusion if we
  	 * use otid anymore.
  	 */
  
  l2:
  	checked_lockers = false;
  	locker_remains = false;
  	result = HeapTupleSatisfiesUpdate(relation, &oldtup, cid, buffer);
  
  	/* see below about the "no wait" case */
  	Assert(result != TM_BeingModified || wait);
  
  	if (result == TM_Invisible)
  	{
  		UnlockReleaseBuffer(buffer);
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("attempted to update invisible tuple")));
  	}
  	else if (result == TM_BeingModified && wait)
  	{
  		TransactionId xwait;
  		uint16		infomask;
  		bool		can_continue = false;
  
  		/*
  		 * XXX note that we don't consider the "no wait" case here.  This
  		 * isn't a problem currently because no caller uses that case, but it
  		 * should be fixed if such a caller is introduced.  It wasn't a
  		 * problem previously because this code would always wait, but now
  		 * that some tuple locks do not conflict with one of the lock modes we
  		 * use, it is possible that this case is interesting to handle
  		 * specially.
  		 *
  		 * This may cause failures with third-party code that calls
  		 * heap_update directly.
  		 */
  
  		/* must copy state data before unlocking buffer */
  		xwait = HeapTupleHeaderGetRawXmax(oldtup.t_data);
  		infomask = oldtup.t_data->t_infomask;
  
  		/*
  		 * Now we have to do something about the existing locker.  If it's a
  		 * multi, sleep on it; we might be awakened before it is completely
  		 * gone (or even not sleep at all in some cases); we need to preserve
  		 * it as locker, unless it is gone completely.
  		 *
  		 * If it's not a multi, we need to check for sleeping conditions
  		 * before actually going to sleep.  If the update doesn't conflict
  		 * with the locks, we just continue without sleeping (but making sure
  		 * it is preserved).
  		 *
  		 * Before sleeping, we need to acquire tuple lock to establish our
  		 * priority for the tuple (see heap_lock_tuple).  LockTuple will
  		 * release us when we are next-in-line for the tuple.  Note we must
  		 * not acquire the tuple lock until we're sure we're going to sleep;
  		 * otherwise we're open for race conditions with other transactions
  		 * holding the tuple lock which sleep on us.
  		 *
  		 * If we are forced to "start over" below, we keep the tuple lock;
  		 * this arranges that we stay at the head of the line while rechecking
  		 * tuple state.
  		 */
  		if (infomask & HEAP_XMAX_IS_MULTI)
  		{
  			TransactionId update_xact;
  			int			remain;
  			bool		current_is_member = false;
  
  			if (DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
  										*lockmode, &current_is_member))
  			{
  				LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  				/*
  				 * Acquire the lock, if necessary (but skip it when we're
  				 * requesting a lock and already have one; avoids deadlock).
  				 */
  				if (!current_is_member)
  					heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
  										 LockWaitBlock, &have_tuple_lock);
  
  				/* wait for multixact */
  				MultiXactIdWait((MultiXactId) xwait, mxact_status, infomask,
  								relation, &oldtup.t_self, XLTW_Update,
  								&remain);
  				checked_lockers = true;
  				locker_remains = remain != 0;
  				LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  				/*
  				 * If xwait had just locked the tuple then some other xact
  				 * could update this tuple before we get to this point.  Check
  				 * for xmax change, and start over if so.
  				 */
  				if (xmax_infomask_changed(oldtup.t_data->t_infomask,
  										  infomask) ||
  					!TransactionIdEquals(HeapTupleHeaderGetRawXmax(oldtup.t_data),
  										 xwait))
  					goto l2;
  			}
  
  			/*
  			 * Note that the multixact may not be done by now.  It could have
  			 * surviving members; our own xact or other subxacts of this
  			 * backend, and also any other concurrent transaction that locked
  			 * the tuple with 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
  			 * TableTuple{Deleted, Updated} below.
  			 *
  			 * In the LockTupleExclusive case, we still need to preserve the
  			 * surviving members: those would include the tuple locks we had
  			 * before this one, which are important to keep in case this
  			 * subxact aborts.
  			 */
  			if (!HEAP_XMAX_IS_LOCKED_ONLY(oldtup.t_data->t_infomask))
  				update_xact = HeapTupleGetUpdateXid(oldtup.t_data);
  			else
  				update_xact = InvalidTransactionId;
  
  			/*
  			 * There was no UPDATE in the MultiXact; or it aborted. No
  			 * TransactionIdIsInProgress() call needed here, since we called
  			 * MultiXactIdWait() above.
  			 */
  			if (!TransactionIdIsValid(update_xact) ||
  				TransactionIdDidAbort(update_xact))
  				can_continue = true;
  		}
  		else if (TransactionIdIsCurrentTransactionId(xwait))
  		{
  			/*
  			 * The only locker is ourselves; we can avoid grabbing the tuple
  			 * lock here, but must preserve our locking information.
  			 */
  			checked_lockers = true;
  			locker_remains = true;
  			can_continue = true;
  		}
  		else if (HEAP_XMAX_IS_KEYSHR_LOCKED(infomask) && key_intact)
  		{
  			/*
  			 * If it's just a key-share locker, and we're not changing the key
  			 * columns, we don't need to wait for it to end; but we need to
  			 * preserve it as locker.
  			 */
  			checked_lockers = true;
  			locker_remains = true;
  			can_continue = true;
  		}
  		else
  		{
  			/*
  			 * Wait for regular transaction to end; but first, acquire tuple
  			 * lock.
  			 */
  			LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  			heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
  								 LockWaitBlock, &have_tuple_lock);
  			XactLockTableWait(xwait, relation, &oldtup.t_self,
  							  XLTW_Update);
  			checked_lockers = true;
  			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  			/*
  			 * xwait is done, but if xwait had just locked the tuple then some
  			 * other xact could update this tuple before we get to this point.
  			 * Check for xmax change, and start over if so.
  			 */
  			if (xmax_infomask_changed(oldtup.t_data->t_infomask, infomask) ||
  				!TransactionIdEquals(xwait,
  									 HeapTupleHeaderGetRawXmax(oldtup.t_data)))
  				goto l2;
  
  			/* Otherwise check if it committed or aborted */
  			UpdateXmaxHintBits(oldtup.t_data, buffer, xwait, relation);
  			if (oldtup.t_data->t_infomask & HEAP_XMAX_INVALID)
  				can_continue = true;
  		}
  
  		if (can_continue)
  			result = TM_Ok;
  		else if (!ItemPointerEquals(&oldtup.t_self, &oldtup.t_data->t_ctid) ||
  				 HeapTupleHeaderIndicatesMovedPartitions(oldtup.t_data))
  			result = TM_Updated;
  		else
  			result = TM_Deleted;
  	}
  
  	if (crosscheck != InvalidSnapshot && result == TM_Ok)
  	{
  		/* Perform additional check for transaction-snapshot mode RI updates */
  		if (!HeapTupleSatisfiesVisibility(relation, &oldtup, crosscheck, buffer))
  		{
  			result = TM_Updated;
  			Assert(!ItemPointerEquals(&oldtup.t_self, &oldtup.t_data->t_ctid));
  		}
  	}
  
  	if (result != TM_Ok)
  	{
  		Assert(result == TM_SelfModified ||
  			   result == TM_Updated ||
  			   result == TM_Deleted ||
  			   result == TM_BeingModified);
  		Assert(!(oldtup.t_data->t_infomask & HEAP_XMAX_INVALID));
  		Assert(result != TM_Updated ||
  			   !ItemPointerEquals(&oldtup.t_self, &oldtup.t_data->t_ctid));
  		tmfd->ctid = oldtup.t_data->t_ctid;
  		tmfd->xmax = HeapTupleHeaderGetUpdateXid(oldtup.t_data);
  		if (result == TM_SelfModified)
  			tmfd->cmax = HeapTupleHeaderGetCmax(oldtup.t_data);
  		else
  			tmfd->cmax = InvalidCommandId;
  
  		UnlockReleaseBuffer(buffer);
  		if (have_tuple_lock)
  			UnlockTupleTuplock(relation, &(oldtup.t_self), *lockmode);
  		if (vmbuffer != InvalidBuffer)
  			ReleaseBuffer(vmbuffer);
  		bms_free(hot_attrs);
  		bms_free(key_attrs);
  		bms_free(id_attrs);
  		bms_free(modified_attrs);
  		bms_free(interesting_attrs);
  		return result;
  	}
  
  	/*
  	 * If we didn't pin the visibility map page and the page has become all
  	 * visible while we were busy locking the buffer, or during some
  	 * subsequent window during which we had it unlocked, we'll have to unlock
  	 * and re-lock, to avoid holding the buffer lock across an I/O.  That's a
  	 * bit unfortunate, especially since we'll now have to recheck whether the
  	 * tuple has been locked or updated under us, but hopefully it won't
  	 * happen very often.
  	 */
  	if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
  	{
  		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  		visibilitymap_pin(relation, block, &vmbuffer);
  		LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  		goto l2;
  	}
  
  	/* Fill in transaction status data */
  
  	/*
  	 * If the tuple we're updating is locked, we need to preserve the locking
  	 * info in the old tuple's Xmax.  Prepare a new Xmax value for this.
  	 */
  	compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(oldtup.t_data),
  							  oldtup.t_data->t_infomask,
  							  oldtup.t_data->t_infomask2,
  							  xid, *lockmode, true,
  							  &xmax_old_tuple, &infomask_old_tuple,
  							  &infomask2_old_tuple);
  
  	/*
  	 * And also prepare an Xmax value for the new copy of the tuple.  If there
  	 * was no xmax previously, or there was one but all lockers are now gone,
  	 * then use InvalidXid; otherwise, get the xmax from the old tuple.  (In
  	 * rare cases that might also be InvalidXid and yet not have the
  	 * HEAP_XMAX_INVALID bit set; that's fine.)
  	 */
  	if ((oldtup.t_data->t_infomask & HEAP_XMAX_INVALID) ||
  		HEAP_LOCKED_UPGRADED(oldtup.t_data->t_infomask) ||
  		(checked_lockers && !locker_remains))
  		xmax_new_tuple = InvalidTransactionId;
  	else
  		xmax_new_tuple = HeapTupleHeaderGetRawXmax(oldtup.t_data);
  
  	if (!TransactionIdIsValid(xmax_new_tuple))
  	{
  		infomask_new_tuple = HEAP_XMAX_INVALID;
  		infomask2_new_tuple = 0;
  	}
  	else
  	{
  		/*
  		 * If we found a valid Xmax for the new tuple, then the infomask bits
  		 * to use on the new tuple depend on what was there on the old one.
  		 * Note that since we're doing an update, the only possibility is that
  		 * the lockers had FOR KEY SHARE lock.
  		 */
  		if (oldtup.t_data->t_infomask & HEAP_XMAX_IS_MULTI)
  		{
  			GetMultiXactIdHintBits(xmax_new_tuple, &infomask_new_tuple,
  								   &infomask2_new_tuple);
  		}
  		else
  		{
  			infomask_new_tuple = HEAP_XMAX_KEYSHR_LOCK | HEAP_XMAX_LOCK_ONLY;
  			infomask2_new_tuple = 0;
  		}
  	}
  
  	/*
  	 * Prepare the new tuple with the appropriate initial values of Xmin and
  	 * Xmax, as well as initial infomask bits as computed above.
  	 */
  	newtup->t_data->t_infomask &= ~(HEAP_XACT_MASK);
  	newtup->t_data->t_infomask2 &= ~(HEAP2_XACT_MASK);
  	HeapTupleHeaderSetXmin(newtup->t_data, xid);
  	HeapTupleHeaderSetCmin(newtup->t_data, cid);
  	newtup->t_data->t_infomask |= HEAP_UPDATED | infomask_new_tuple;
  	newtup->t_data->t_infomask2 |= infomask2_new_tuple;
  	HeapTupleHeaderSetXmax(newtup->t_data, xmax_new_tuple);
  
  	/*
  	 * Replace cid with a combo cid if necessary.  Note that we already put
  	 * the plain cid into the new tuple.
  	 */
  	HeapTupleHeaderAdjustCmax(oldtup.t_data, &cid, &iscombo);
  
  	/*
  	 * If the toaster needs to be activated, OR if the new tuple will not fit
  	 * on the same page as the old, then we need to release the content lock
  	 * (but not the pin!) on the old tuple's buffer while we are off doing
  	 * TOAST and/or table-file-extension work.  We must mark the old tuple to
  	 * show that it's locked, else other processes may try to update it
  	 * themselves.
  	 *
  	 * We need to invoke the toaster if there are already any out-of-line
  	 * toasted values present, or if the new tuple is over-threshold.
  	 */
  	if (relation->rd_rel->relkind != RELKIND_RELATION &&
  		relation->rd_rel->relkind != RELKIND_MATVIEW)
  	{
  		/* toast table entries should never be recursively toasted */
  		Assert(!HeapTupleHasExternal(&oldtup));
  		Assert(!HeapTupleHasExternal(newtup));
  		need_toast = false;
  	}
  	else
  		need_toast = (HeapTupleHasExternal(&oldtup) ||
  					  HeapTupleHasExternal(newtup) ||
  					  newtup->t_len > TOAST_TUPLE_THRESHOLD);
  
  	pagefree = PageGetHeapFreeSpace(page);
  
  	newtupsize = MAXALIGN(newtup->t_len);
  
  	if (need_toast || newtupsize > pagefree)
  	{
  		TransactionId xmax_lock_old_tuple;
  		uint16		infomask_lock_old_tuple,
  					infomask2_lock_old_tuple;
  		bool		cleared_all_frozen = false;
  
  		/*
  		 * To prevent concurrent sessions from updating the tuple, we have to
  		 * temporarily mark it locked, while we release the page-level lock.
  		 *
  		 * To satisfy the rule that any xid potentially appearing in a buffer
  		 * written out to disk, we unfortunately have to WAL log this
  		 * temporary modification.  We can reuse xl_heap_lock for this
  		 * purpose.  If we crash/error before following through with the
  		 * actual update, xmax will be of an aborted transaction, allowing
  		 * other sessions to proceed.
  		 */
  
  		/*
  		 * Compute xmax / infomask appropriate for locking the tuple. This has
  		 * to be done separately from the combo that's going to be used for
  		 * updating, because the potentially created multixact would otherwise
  		 * be wrong.
  		 */
  		compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(oldtup.t_data),
  								  oldtup.t_data->t_infomask,
  								  oldtup.t_data->t_infomask2,
  								  xid, *lockmode, false,
  								  &xmax_lock_old_tuple, &infomask_lock_old_tuple,
  								  &infomask2_lock_old_tuple);
  
  		Assert(HEAP_XMAX_IS_LOCKED_ONLY(infomask_lock_old_tuple));
  
  		START_CRIT_SECTION();
  
  		/* Clear obsolete visibility flags ... */
  		oldtup.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
  		oldtup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  		HeapTupleClearHotUpdated(&oldtup);
  		/* ... and store info about transaction updating this tuple */
  		Assert(TransactionIdIsValid(xmax_lock_old_tuple));
  		HeapTupleHeaderSetXmax(oldtup.t_data, xmax_lock_old_tuple);
  		oldtup.t_data->t_infomask |= infomask_lock_old_tuple;
  		oldtup.t_data->t_infomask2 |= infomask2_lock_old_tuple;
  		HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
  
  		/* temporarily make it look not-updated, but locked */
  		oldtup.t_data->t_ctid = oldtup.t_self;
  
  		/*
  		 * Clear all-frozen bit on visibility map if needed. We could
  		 * immediately reset ALL_VISIBLE, but given that the WAL logging
  		 * overhead would be unchanged, that doesn't seem necessarily
  		 * worthwhile.
  		 */
  		if (PageIsAllVisible(BufferGetPage(buffer)) &&
  			visibilitymap_clear(relation, block, vmbuffer,
  								VISIBILITYMAP_ALL_FROZEN))
  			cleared_all_frozen = true;
  
  		MarkBufferDirty(buffer);
  
  		if (RelationNeedsWAL(relation))
  		{
  			xl_heap_lock xlrec;
  			XLogRecPtr	recptr;
  
  			XLogBeginInsert();
  			XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
  
  			xlrec.offnum = ItemPointerGetOffsetNumber(&oldtup.t_self);
  			xlrec.locking_xid = xmax_lock_old_tuple;
  			xlrec.infobits_set = compute_infobits(oldtup.t_data->t_infomask,
  												  oldtup.t_data->t_infomask2);
  			xlrec.flags =
  				cleared_all_frozen ? XLH_LOCK_ALL_FROZEN_CLEARED : 0;
  			XLogRegisterData((char *) &xlrec, SizeOfHeapLock);
  			recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_LOCK);
  			PageSetLSN(page, recptr);
  		}
  
  		END_CRIT_SECTION();
  
  		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  		/*
  		 * Let the toaster do its thing, if needed.
  		 *
  		 * Note: below this point, heaptup is the data we actually intend to
  		 * store into the relation; newtup is the caller's original untoasted
  		 * data.
  		 */
  		if (need_toast)
  		{
  			/* Note we always use WAL and FSM during updates */
  			heaptup = toast_insert_or_update(relation, newtup, &oldtup,
  											 TOAST_TUPLE_TARGET, false, 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 */
  		newbuf = buffer;
  		heaptup = newtup;
  	}
  
  	/*
  	 * We're about to do the actual update -- check for conflict first, to
  	 * avoid possibly having to roll back work we've just done.
  	 *
  	 * This is safe without a recheck as long as there is no possibility of
  	 * another process scanning the pages between this check and the update
  	 * being visible to the scan (i.e., exclusive buffer content lock(s) are
  	 * continuously held from this point until the tuple update is visible).
  	 *
  	 * For the new tuple the only check needed is at the relation level, but
  	 * since both tuples are in the same relation and the check for oldtup
  	 * will include checking the relation level, there is no benefit to a
  	 * separate check for the new tuple.
  	 */
  	CheckForSerializableConflictIn(relation, &oldtup, buffer);
  
  	/*
  	 * At this point newbuf and buffer are both pinned and locked, and newbuf
  	 * has enough space for the new tuple.  If they are the same buffer, only
  	 * one pin is held.
  	 */
  
  	if (newbuf == buffer)
  	{
  		/*
  		 * Since the new tuple is going into the same page, we might be able
  		 * to do a HOT update.  Check if any of the index columns have been
  		 * changed. If the page was already full, we may have skipped checking
  		 * for index columns, and also can't do a HOT update.
  		 */
  		if (hot_attrs_checked && !bms_overlap(modified_attrs, hot_attrs))
  			use_hot_update = true;
  	}
  	else
  	{
  		/* Set a hint that the old page could use prune/defrag */
  		PageSetFull(page);
  	}
  
  	/*
  	 * Compute replica identity tuple before entering the critical section so
  	 * we don't PANIC upon a memory allocation failure.
  	 * ExtractReplicaIdentity() will return NULL if nothing needs to be
  	 * logged.
  	 */
  	old_key_tuple = ExtractReplicaIdentity(relation, &oldtup,
  										   bms_overlap(modified_attrs, id_attrs),
  										   &old_key_copied);
  
  	/* NO EREPORT(ERROR) from here till changes are logged */
  	START_CRIT_SECTION();
  
  	/*
  	 * If this transaction commits, the old tuple will become DEAD sooner or
  	 * later.  Set flag that this page is a candidate for pruning once our xid
  	 * falls below the OldestXmin horizon.  If the transaction finally aborts,
  	 * the subsequent page pruning will be a no-op and the hint will be
  	 * cleared.
  	 *
  	 * XXX Should we set hint on newbuf as well?  If the transaction aborts,
  	 * there would be a prunable tuple in the newbuf; but for now we choose
  	 * not to optimize for aborts.  Note that heap_xlog_update must be kept in
  	 * sync if this decision changes.
  	 */
  	PageSetPrunable(page, xid);
  
  	if (use_hot_update)
  	{
  		/* Mark the old tuple as HOT-updated */
  		HeapTupleSetHotUpdated(&oldtup);
  		/* And mark the new tuple as heap-only */
  		HeapTupleSetHeapOnly(heaptup);
  		/* Mark the caller's copy too, in case different from heaptup */
  		HeapTupleSetHeapOnly(newtup);
  	}
  	else
  	{
  		/* Make sure tuples are correctly marked as not-HOT */
  		HeapTupleClearHotUpdated(&oldtup);
  		HeapTupleClearHeapOnly(heaptup);
  		HeapTupleClearHeapOnly(newtup);
  	}
  
  	RelationPutHeapTuple(relation, newbuf, heaptup, false); /* insert new tuple */
  
  
  	/* Clear obsolete visibility flags, possibly set by ourselves above... */
  	oldtup.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
  	oldtup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  	/* ... and store info about transaction updating this tuple */
  	Assert(TransactionIdIsValid(xmax_old_tuple));
  	HeapTupleHeaderSetXmax(oldtup.t_data, xmax_old_tuple);
  	oldtup.t_data->t_infomask |= infomask_old_tuple;
  	oldtup.t_data->t_infomask2 |= infomask2_old_tuple;
  	HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
  
  	/* record address of new tuple in t_ctid of old one */
  	oldtup.t_data->t_ctid = heaptup->t_self;
  
  	/* clear PD_ALL_VISIBLE flags, reset all visibilitymap bits */
  	if (PageIsAllVisible(BufferGetPage(buffer)))
  	{
  		all_visible_cleared = true;
  		PageClearAllVisible(BufferGetPage(buffer));
  		visibilitymap_clear(relation, BufferGetBlockNumber(buffer),
  							vmbuffer, VISIBILITYMAP_VALID_BITS);
  	}
  	if (newbuf != buffer && PageIsAllVisible(BufferGetPage(newbuf)))
  	{
  		all_visible_cleared_new = true;
  		PageClearAllVisible(BufferGetPage(newbuf));
  		visibilitymap_clear(relation, BufferGetBlockNumber(newbuf),
  							vmbuffer_new, VISIBILITYMAP_VALID_BITS);
  	}
  
  	if (newbuf != buffer)
  		MarkBufferDirty(newbuf);
  	MarkBufferDirty(buffer);
  
  	/* XLOG stuff */
  	if (RelationNeedsWAL(relation))
  	{
  		XLogRecPtr	recptr;
  
  		/*
  		 * For logical decoding we need combocids to properly decode the
  		 * catalog.
  		 */
  		if (RelationIsAccessibleInLogicalDecoding(relation))
  		{
  			log_heap_new_cid(relation, &oldtup);
  			log_heap_new_cid(relation, heaptup);
  		}
  
  		recptr = log_heap_update(relation, buffer,
  								 newbuf, &oldtup, heaptup,
  								 old_key_tuple,
  								 all_visible_cleared,
  								 all_visible_cleared_new);
  		if (newbuf != buffer)
  		{
  			PageSetLSN(BufferGetPage(newbuf), recptr);
  		}
  		PageSetLSN(BufferGetPage(buffer), recptr);
  	}
  
  	END_CRIT_SECTION();
  
  	if (newbuf != buffer)
  		LockBuffer(newbuf, BUFFER_LOCK_UNLOCK);
  	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  	/*
  	 * Mark old tuple for invalidation from system caches at next command
  	 * boundary, and mark the new tuple for invalidation in case we abort. We
  	 * have to do this before releasing the buffer because oldtup is in the
  	 * buffer.  (heaptup is all in local memory, but it's necessary to process
  	 * both tuple versions in one call to inval.c so we can avoid redundant
  	 * sinval messages.)
  	 */
  	CacheInvalidateHeapTuple(relation, &oldtup, heaptup);
  
  	/* Now we can release the buffer(s) */
  	if (newbuf != buffer)
  		ReleaseBuffer(newbuf);
  	ReleaseBuffer(buffer);
  	if (BufferIsValid(vmbuffer_new))
  		ReleaseBuffer(vmbuffer_new);
  	if (BufferIsValid(vmbuffer))
  		ReleaseBuffer(vmbuffer);
  
  	/*
  	 * Release the lmgr tuple lock, if we had it.
  	 */
  	if (have_tuple_lock)
  		UnlockTupleTuplock(relation, &(oldtup.t_self), *lockmode);
  
  	pgstat_count_heap_update(relation, false);
  
  	/*
  	 * If heaptup is a private copy, release it.  Don't forget to copy t_self
  	 * back to the caller's image, too.
  	 */
  	if (heaptup != newtup)
  	{
  		newtup->t_self = heaptup->t_self;
  		heap_freetuple(heaptup);
  	}
  
  	if (old_key_tuple != NULL && old_key_copied)
  		heap_freetuple(old_key_tuple);
  
  	bms_free(hot_attrs);
  	bms_free(key_attrs);
  	bms_free(id_attrs);
  	bms_free(modified_attrs);
  	bms_free(interesting_attrs);
  
  	return TM_Ok;
  }
  
  TM_Result
  heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
  			CommandId cid, Snapshot crosscheck, bool wait,
  			TM_FailureData *tmfd, LockTupleMode *lockmode)
  {
  	return heap_update_internal(relation, otid, newtup,
  								cid, crosscheck, wait,
  								tmfd, lockmode,
  								/* simple */ false);
  }
  
  /*
   * Check if the specified attribute's value is same in both given tuples.
   * Subroutine for HeapDetermineModifiedColumns.
   */
  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 tableOID; we cannot expect these to be consistent in a HOT chain,
  	 * or even to be set correctly yet in the new tuple.
  	 */
  	if (attrnum < 0)
  	{
  		if (attrnum != TableOidAttributeNumber)
  			return false;
  	}
  
  	/*
  	 * Extract the corresponding values.  XXX this is pretty inefficient if
  	 * there are many indexed columns.  Should HeapDetermineModifiedColumns 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 = TupleDescAttr(tupdesc, attrnum - 1);
  		return datumIsEqual(value1, value2, att->attbyval, att->attlen);
  	}
  }
  
  /*
   * Check which columns are being updated.
   *
   * Given an updated tuple, determine (and return into the output bitmapset),
   * from those listed as interesting, the set of columns that changed.
   *
   * The input bitmapset is destructively modified; that is OK since this is
   * invoked at most once in heap_update.
   */
  static Bitmapset *
  HeapDetermineModifiedColumns(Relation relation, Bitmapset *interesting_cols,
  							 HeapTuple oldtup, HeapTuple newtup)
  {
  	int			attnum;
  	Bitmapset  *modified = NULL;
  
  	while ((attnum = bms_first_member(interesting_cols)) >= 0)
  	{
  		attnum += FirstLowInvalidHeapAttributeNumber;
  
  		if (!heap_tuple_attr_equals(RelationGetDescr(relation),
  									attnum, oldtup, newtup))
  			modified = bms_add_member(modified,
  									  attnum - FirstLowInvalidHeapAttributeNumber);
  	}
  
  	return modified;
  }
  
  /*
   *	simple_heap_update - replace a tuple
   *
   * This routine may be used to update a tuple when concurrent updates of
   * the target tuple are not expected (for example, because we have a lock
   * on the relation associated with the tuple).  Any failure is reported
   * via ereport().
   */
  void
  simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
  {
  	TM_Result	result;
  	TM_FailureData tmfd;
  	LockTupleMode lockmode;
  
  	result = heap_update_internal(relation, otid, tup,
  						 GetCurrentCommandId(true), InvalidSnapshot,
  						 true /* wait for commit */ ,
  						 &tmfd, &lockmode,
  						 /* simple */ true);
  	switch (result)
  	{
  		case TM_SelfModified:
  			/* Tuple was already updated in current command? */
  			elog(ERROR, "tuple already updated by self");
  			break;
  
  		case TM_Ok:
  			/* done successfully */
  			break;
  
  		case TM_Updated:
  			elog(ERROR, "tuple concurrently updated");
  			break;
  
  		case TM_Deleted:
  			elog(ERROR, "tuple concurrently deleted");
  			break;
  
  		default:
  			elog(ERROR, "unrecognized heap_update status: %u", result);
  			break;
  	}
  }
  
  
  /*
   * Return the MultiXactStatus corresponding to the given tuple lock mode.
   */
  static MultiXactStatus
  get_mxact_status_for_lock(LockTupleMode mode, bool is_update)
  {
  	int			retval;
  
  	if (is_update)
  		retval = tupleLockExtraInfo[mode].updstatus;
  	else
  		retval = tupleLockExtraInfo[mode].lockstatus;
  
  	if (retval == -1)
  		elog(ERROR, "invalid lock tuple mode %d/%s", mode,
  			 is_update ? "true" : "false");
  
  	return (MultiXactStatus) retval;
  }
  
  /*
   *	heap_lock_tuple - lock a tuple in shared or exclusive mode
   *
   * Note that this acquires a buffer pin, which the caller must release.
   *
   * Input parameters:
   *	relation: relation containing tuple (caller must hold suitable lock)
   *	tid: TID of tuple to lock
   *	cid: current command ID (used for visibility test, and stored into
   *		tuple's cmax if lock is successful)
   *	mode: indicates if shared or exclusive tuple lock is desired
   *	wait_policy: what to do if tuple lock is not available
   *	follow_updates: if true, follow the update chain to also lock descendant
   *		tuples.
   *
   * Output parameters:
   *	*tuple: all fields filled in
   *	*buffer: set to buffer holding tuple (pinned but not locked at exit)
   *	*tmfd: filled in failure cases (see below)
   *
   * Function results are the same as the ones for table_tuple_lock().
   *
   * In the failure cases other than TM_Invisible, the routine fills
   * *tmfd with the tuple's t_ctid, t_xmax (resolving a possible MultiXact,
   * if necessary), and t_cmax (the last only for TM_SelfModified,
   * since we cannot obtain cmax from a combocid generated by another
   * transaction).
   * See comments for struct TM_FailureData for additional info.
   *
   * See README.tuplock for a thorough explanation of this mechanism.
   */
  TM_Result
  heap_lock_tuple(Relation relation, HeapTuple tuple,
  				CommandId cid, LockTupleMode mode, LockWaitPolicy wait_policy,
  				bool follow_updates,
  				Buffer *buffer, TM_FailureData *tmfd)
  {
  	TM_Result	result;
  	ItemPointer tid = &(tuple->t_self);
  	ItemId		lp;
  	Page		page;
  	Buffer		vmbuffer = InvalidBuffer;
  	BlockNumber block;
  	TransactionId xid,
  				xmax;
  	uint16		old_infomask,
  				new_infomask,
  				new_infomask2;
  	bool		first_time = true;
  	bool		skip_tuple_lock = false;
  	bool		have_tuple_lock = false;
  	bool		cleared_all_frozen = false;
  
  	*buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
  	block = ItemPointerGetBlockNumber(tid);
  
  	/*
  	 * Before locking the buffer, pin the visibility map page if it appears to
  	 * be necessary.  Since we haven't got the lock yet, someone else might be
  	 * in the middle of changing this, so we'll need to recheck after we have
  	 * the lock.
  	 */
  	if (PageIsAllVisible(BufferGetPage(*buffer)))
  		visibilitymap_pin(relation, block, &vmbuffer);
  
  	LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  
  	page = BufferGetPage(*buffer);
  	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
  	Assert(ItemIdIsNormal(lp));
  
  	tuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
  	tuple->t_len = ItemIdGetLength(lp);
  	tuple->t_tableOid = RelationGetRelid(relation);
  
  l3:
  	result = HeapTupleSatisfiesUpdate(relation, tuple, cid, *buffer);
  
  	if (result == TM_Invisible)
  	{
  		/*
  		 * This is possible, but only when locking a tuple for ON CONFLICT
  		 * UPDATE.  We return this value here rather than throwing an error in
  		 * order to give that case the opportunity to throw a more specific
  		 * error.
  		 */
  		result = TM_Invisible;
  		goto out_locked;
  	}
  	else if (result == TM_BeingModified ||
  			 result == TM_Updated ||
  			 result == TM_Deleted)
  	{
  		TransactionId xwait;
  		uint16		infomask;
  		uint16		infomask2;
  		bool		require_sleep;
  		ItemPointerData t_ctid;
  
  		/* must copy state data before unlocking buffer */
  		xwait = HeapTupleHeaderGetRawXmax(tuple->t_data);
  		infomask = tuple->t_data->t_infomask;
  		infomask2 = tuple->t_data->t_infomask2;
  		ItemPointerCopy(&tuple->t_data->t_ctid, &t_ctid);
  
  		LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
  
  		/*
  		 * If any subtransaction of the current top transaction already holds
  		 * a lock as strong as or stronger than what we're requesting, we
  		 * effectively hold the desired lock already.  We *must* succeed
  		 * without trying to take the tuple lock, else we will deadlock
  		 * against anyone wanting to acquire a stronger lock.
  		 *
  		 * Note we only do this the first time we loop on the HTSU result;
  		 * there is no point in testing in subsequent passes, because
  		 * evidently our own transaction cannot have acquired a new lock after
  		 * the first time we checked.
  		 */
  		if (first_time)
  		{
  			first_time = false;
  
  			if (infomask & HEAP_XMAX_IS_MULTI)
  			{
  				int			i;
  				int			nmembers;
  				MultiXactMember *members;
  
  				/*
  				 * We don't need to allow old multixacts here; if that had
  				 * been the case, HeapTupleSatisfiesUpdate would have returned
  				 * MayBeUpdated and we wouldn't be here.
  				 */
  				nmembers =
  					GetMultiXactIdMembers(xwait, &members, false,
  										  HEAP_XMAX_IS_LOCKED_ONLY(infomask));
  
  				for (i = 0; i < nmembers; i++)
  				{
  					/* only consider members of our own transaction */
  					if (!TransactionIdIsCurrentTransactionId(members[i].xid))
  						continue;
  
  					if (TUPLOCK_from_mxstatus(members[i].status) >= mode)
  					{
  						pfree(members);
  						result = TM_Ok;
  						goto out_unlocked;
  					}
  					else
  					{
  						/*
  						 * Disable acquisition of the heavyweight tuple lock.
  						 * Otherwise, when promoting a weaker lock, we might
  						 * deadlock with another locker that has acquired the
  						 * heavyweight tuple lock and is waiting for our
  						 * transaction to finish.
  						 *
  						 * Note that in this case we still need to wait for
  						 * the multixact if required, to avoid acquiring
  						 * conflicting locks.
  						 */
  						skip_tuple_lock = true;
  					}
  				}
  
  				if (members)
  					pfree(members);
  			}
  			else if (TransactionIdIsCurrentTransactionId(xwait))
  			{
  				switch (mode)
  				{
  					case LockTupleKeyShare:
  						Assert(HEAP_XMAX_IS_KEYSHR_LOCKED(infomask) ||
  							   HEAP_XMAX_IS_SHR_LOCKED(infomask) ||
  							   HEAP_XMAX_IS_EXCL_LOCKED(infomask));
  						result = TM_Ok;
  						goto out_unlocked;
  					case LockTupleShare:
  						if (HEAP_XMAX_IS_SHR_LOCKED(infomask) ||
  							HEAP_XMAX_IS_EXCL_LOCKED(infomask))
  						{
  							result = TM_Ok;
  							goto out_unlocked;
  						}
  						break;
  					case LockTupleNoKeyExclusive:
  						if (HEAP_XMAX_IS_EXCL_LOCKED(infomask))
  						{
  							result = TM_Ok;
  							goto out_unlocked;
  						}
  						break;
  					case LockTupleExclusive:
  						if (HEAP_XMAX_IS_EXCL_LOCKED(infomask) &&
  							infomask2 & HEAP_KEYS_UPDATED)
  						{
  							result = TM_Ok;
  							goto out_unlocked;
  						}
  						break;
  				}
  			}
  		}
  
  		/*
  		 * Initially assume that we will have to wait for the locking
  		 * transaction(s) to finish.  We check various cases below in which
  		 * this can be turned off.
  		 */
  		require_sleep = true;
  		if (mode == LockTupleKeyShare)
  		{
  			/*
  			 * If we're requesting KeyShare, and there's no update present, we
  			 * don't need to wait.  Even if there is an update, we can still
  			 * continue if the key hasn't been modified.
  			 *
  			 * However, if there are updates, we need to walk the update chain
  			 * to mark future versions of the row as locked, too.  That way,
  			 * if somebody deletes that future version, we're protected
  			 * against the key going away.  This locking of future versions
  			 * could block momentarily, if a concurrent transaction is
  			 * deleting a key; or it could return a value to the effect that
  			 * the transaction deleting the key has already committed.  So we
  			 * do this before re-locking the buffer; otherwise this would be
  			 * prone to deadlocks.
  			 *
  			 * Note that the TID we're locking was grabbed before we unlocked
  			 * the buffer.  For it to change while we're not looking, the
  			 * other properties we're testing for below after re-locking the
  			 * buffer would also change, in which case we would restart this
  			 * loop above.
  			 */
  			if (!(infomask2 & HEAP_KEYS_UPDATED))
  			{
  				bool		updated;
  
  				updated = !HEAP_XMAX_IS_LOCKED_ONLY(infomask);
  
  				/*
  				 * If there are updates, follow the update chain; bail out if
  				 * that cannot be done.
  				 */
  				if (follow_updates && updated)
  				{
  					TM_Result	res;
  
  					res = heap_lock_updated_tuple(relation, tuple, &t_ctid,
  												  GetCurrentTransactionId(),
  												  mode);
  					if (res != TM_Ok)
  					{
  						result = res;
  						/* recovery code expects to have buffer lock held */
  						LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  						goto failed;
  					}
  				}
  
  				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  
  				/*
  				 * Make sure it's still an appropriate lock, else start over.
  				 * Also, if it wasn't updated before we released the lock, but
  				 * is updated now, we start over too; the reason is that we
  				 * now need to follow the update chain to lock the new
  				 * versions.
  				 */
  				if (!HeapTupleHeaderIsOnlyLocked(tuple->t_data) &&
  					((tuple->t_data->t_infomask2 & HEAP_KEYS_UPDATED) ||
  					 !updated))
  					goto l3;
  
  				/* Things look okay, so we can skip sleeping */
  				require_sleep = false;
  
  				/*
  				 * Note we allow Xmax to change here; other updaters/lockers
  				 * could have modified it before we grabbed the buffer lock.
  				 * However, this is not a problem, because with the recheck we
  				 * just did we ensure that they still don't conflict with the
  				 * lock we want.
  				 */
  			}
  		}
  		else if (mode == LockTupleShare)
  		{
  			/*
  			 * If we're requesting Share, we can similarly avoid sleeping if
  			 * there's no update and no exclusive lock present.
  			 */
  			if (HEAP_XMAX_IS_LOCKED_ONLY(infomask) &&
  				!HEAP_XMAX_IS_EXCL_LOCKED(infomask))
  			{
  				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  
  				/*
  				 * Make sure it's still an appropriate lock, else start over.
  				 * See above about allowing xmax to change.
  				 */
  				if (!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_data->t_infomask) ||
  					HEAP_XMAX_IS_EXCL_LOCKED(tuple->t_data->t_infomask))
  					goto l3;
  				require_sleep = false;
  			}
  		}
  		else if (mode == LockTupleNoKeyExclusive)
  		{
  			/*
  			 * If we're requesting NoKeyExclusive, we might also be able to
  			 * avoid sleeping; just ensure that there no conflicting lock
  			 * already acquired.
  			 */
  			if (infomask & HEAP_XMAX_IS_MULTI)
  			{
  				if (!DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
  											 mode, NULL))
  				{
  					/*
  					 * No conflict, but if the xmax changed under us in the
  					 * meantime, start over.
  					 */
  					LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  					if (xmax_infomask_changed(tuple->t_data->t_infomask, infomask) ||
  						!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
  											 xwait))
  						goto l3;
  
  					/* otherwise, we're good */
  					require_sleep = false;
  				}
  			}
  			else if (HEAP_XMAX_IS_KEYSHR_LOCKED(infomask))
  			{
  				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  
  				/* if the xmax changed in the meantime, start over */
  				if (xmax_infomask_changed(tuple->t_data->t_infomask, infomask) ||
  					!TransactionIdEquals(
  										 HeapTupleHeaderGetRawXmax(tuple->t_data),
  										 xwait))
  					goto l3;
  				/* otherwise, we're good */
  				require_sleep = false;
  			}
  		}
  
  		/*
  		 * As a check independent from those above, we can also avoid sleeping
  		 * if the current transaction is the sole locker of the tuple.  Note
  		 * that the strength of the lock already held is irrelevant; this is
  		 * not about recording the lock in Xmax (which will be done regardless
  		 * of this optimization, below).  Also, note that the cases where we
  		 * hold a lock stronger than we are requesting are already handled
  		 * above by not doing anything.
  		 *
  		 * Note we only deal with the non-multixact case here; MultiXactIdWait
  		 * is well equipped to deal with this situation on its own.
  		 */
  		if (require_sleep && !(infomask & HEAP_XMAX_IS_MULTI) &&
  			TransactionIdIsCurrentTransactionId(xwait))
  		{
  			/* ... but if the xmax changed in the meantime, start over */
  			LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  			if (xmax_infomask_changed(tuple->t_data->t_infomask, infomask) ||
  				!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
  									 xwait))
  				goto l3;
  			Assert(HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_data->t_infomask));
  			require_sleep = false;
  		}
  
  		/*
  		 * Time to sleep on the other transaction/multixact, if necessary.
  		 *
  		 * If the other transaction is an update/delete that's already
  		 * committed, then sleeping cannot possibly do any good: if we're
  		 * required to sleep, get out to raise an error instead.
  		 *
  		 * By here, we either have already acquired the buffer exclusive lock,
  		 * or we must wait for the locking transaction or multixact; so below
  		 * we ensure that we grab buffer lock after the sleep.
  		 */
  		if (require_sleep && (result == TM_Updated || result == TM_Deleted))
  		{
  			LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  			goto failed;
  		}
  		else if (require_sleep)
  		{
  			/*
  			 * Acquire tuple lock to establish our priority for the tuple, or
  			 * die trying.  LockTuple will release us when we are next-in-line
  			 * for the tuple.  We must do this even if we are share-locking,
  			 * but not if we already have a weaker lock on the tuple.
  			 *
  			 * If we are forced to "start over" below, we keep the tuple lock;
  			 * this arranges that we stay at the head of the line while
  			 * rechecking tuple state.
  			 */
  			if (!skip_tuple_lock &&
  				!heap_acquire_tuplock(relation, tid, mode, wait_policy,
  									  &have_tuple_lock))
  			{
  				/*
  				 * This can only happen if wait_policy is Skip and the lock
  				 * couldn't be obtained.
  				 */
  				result = TM_WouldBlock;
  				/* recovery code expects to have buffer lock held */
  				LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  				goto failed;
  			}
  
  			if (infomask & HEAP_XMAX_IS_MULTI)
  			{
  				MultiXactStatus status = get_mxact_status_for_lock(mode, false);
  
  				/* We only ever lock tuples, never update them */
  				if (status >= MultiXactStatusNoKeyUpdate)
  					elog(ERROR, "invalid lock mode in heap_lock_tuple");
  
  				/* wait for multixact to end, or die trying  */
  				switch (wait_policy)
  				{
  					case LockWaitBlock:
  						MultiXactIdWait((MultiXactId) xwait, status, infomask,
  										relation, &tuple->t_self, XLTW_Lock, NULL);
  						break;
  					case LockWaitSkip:
  						if (!ConditionalMultiXactIdWait((MultiXactId) xwait,
  														status, infomask, relation,
  														NULL))
  						{
  							result = TM_WouldBlock;
  							/* recovery code expects to have buffer lock held */
  							LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  							goto failed;
  						}
  						break;
  					case LockWaitError:
  						if (!ConditionalMultiXactIdWait((MultiXactId) xwait,
  														status, infomask, relation,
  														NULL))
  							ereport(ERROR,
  									(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
  									 errmsg("could not obtain lock on row in relation \"%s\"",
  											RelationGetRelationName(relation))));
  
  						break;
  				}
  
  				/*
  				 * Of course, the multixact might not be done here: if we're
  				 * requesting a light lock mode, other transactions with light
  				 * locks could still be alive, as well as locks owned by our
  				 * own xact or other subxacts of this backend.  We need to
  				 * preserve the surviving MultiXact members.  Note that it
  				 * isn't absolutely necessary in the latter case, but doing so
  				 * is simpler.
  				 */
  			}
  			else
  			{
  				/* wait for regular transaction to end, or die trying */
  				switch (wait_policy)
  				{
  					case LockWaitBlock:
  						XactLockTableWait(xwait, relation, &tuple->t_self,
  										  XLTW_Lock);
  						break;
  					case LockWaitSkip:
  						if (!ConditionalXactLockTableWait(xwait))
  						{
  							result = TM_WouldBlock;
  							/* recovery code expects to have buffer lock held */
  							LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  							goto failed;
  						}
  						break;
  					case LockWaitError:
  						if (!ConditionalXactLockTableWait(xwait))
  							ereport(ERROR,
  									(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
  									 errmsg("could not obtain lock on row in relation \"%s\"",
  											RelationGetRelationName(relation))));
  						break;
  				}
  			}
  
  			/* if there are updates, follow the update chain */
  			if (follow_updates && !HEAP_XMAX_IS_LOCKED_ONLY(infomask))
  			{
  				TM_Result	res;
  
  				res = heap_lock_updated_tuple(relation, tuple, &t_ctid,
  											  GetCurrentTransactionId(),
  											  mode);
  				if (res != TM_Ok)
  				{
  					result = res;
  					/* recovery code expects to have buffer lock held */
  					LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  					goto failed;
  				}
  			}
  
  			LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  
  			/*
  			 * xwait is done, but if xwait had just locked the tuple then some
  			 * other xact could update this tuple before we get to this point.
  			 * Check for xmax change, and start over if so.
  			 */
  			if (xmax_infomask_changed(tuple->t_data->t_infomask, infomask) ||
  				!TransactionIdEquals(HeapTupleHeaderGetRawXmax(tuple->t_data),
  									 xwait))
  				goto l3;
  
  			if (!(infomask & HEAP_XMAX_IS_MULTI))
  			{
  				/*
  				 * Otherwise check if it committed or aborted.  Note we cannot
  				 * be here if the tuple was only locked by somebody who didn't
  				 * conflict with us; that would have been handled above.  So
  				 * that transaction must necessarily be gone by now.  But
  				 * don't check for this in the multixact case, because some
  				 * locker transactions might still be running.
  				 */
  				UpdateXmaxHintBits(tuple->t_data, *buffer, xwait, relation);
  			}
  		}
  
  		/* By here, we're certain that we hold buffer exclusive lock again */
  
  		/*
  		 * We may lock if previous xmax aborted, or if it committed but only
  		 * locked the tuple without updating it; or if we didn't have to wait
  		 * at all for whatever reason.
  		 */
  		if (!require_sleep ||
  			(tuple->t_data->t_infomask & HEAP_XMAX_INVALID) ||
  			HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_data->t_infomask) ||
  			HeapTupleHeaderIsOnlyLocked(tuple->t_data))
  			result = TM_Ok;
  		else if (!ItemPointerEquals(&tuple->t_self, &tuple->t_data->t_ctid) ||
  				 HeapTupleHeaderIndicatesMovedPartitions(tuple->t_data))
  			result = TM_Updated;
  		else
  			result = TM_Deleted;
  	}
  
  failed:
  	if (result != TM_Ok)
  	{
  		Assert(result == TM_SelfModified || result == TM_Updated ||
  			   result == TM_Deleted || result == TM_WouldBlock);
  		Assert(!(tuple->t_data->t_infomask & HEAP_XMAX_INVALID));
  		Assert(result != TM_Updated ||
  			   !ItemPointerEquals(&tuple->t_self, &tuple->t_data->t_ctid));
  		tmfd->ctid = tuple->t_data->t_ctid;
  		tmfd->xmax = HeapTupleHeaderGetUpdateXid(tuple->t_data);
  		if (result == TM_SelfModified)
  			tmfd->cmax = HeapTupleHeaderGetCmax(tuple->t_data);
  		else
  			tmfd->cmax = InvalidCommandId;
  		goto out_locked;
  	}
  
  	/*
  	 * If we didn't pin the visibility map page and the page has become all
  	 * visible while we were busy locking the buffer, or during some
  	 * subsequent window during which we had it unlocked, we'll have to unlock
  	 * and re-lock, to avoid holding the buffer lock across I/O.  That's a bit
  	 * unfortunate, especially since we'll now have to recheck whether the
  	 * tuple has been locked or updated under us, but hopefully it won't
  	 * happen very often.
  	 */
  	if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
  	{
  		LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
  		visibilitymap_pin(relation, block, &vmbuffer);
  		LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  		goto l3;
  	}
  
  	xmax = HeapTupleHeaderGetRawXmax(tuple->t_data);
  	old_infomask = tuple->t_data->t_infomask;
  
  	/*
  	 * If this is the first possibly-multixact-able operation in the current
  	 * transaction, set my per-backend OldestMemberMXactId setting. We can be
  	 * certain that the transaction will never become a member of any older
  	 * MultiXactIds than that.  (We have to do this even if we end up just
  	 * using our own TransactionId below, since some other backend could
  	 * incorporate our XID into a MultiXact immediately afterwards.)
  	 */
  	MultiXactIdSetOldestMember();
  
  	/*
  	 * Compute the new xmax and infomask to store into the tuple.  Note we do
  	 * not modify the tuple just yet, because that would leave it in the wrong
  	 * state if multixact.c elogs.
  	 */
  	compute_new_xmax_infomask(xmax, old_infomask, tuple->t_data->t_infomask2,
  							  GetCurrentTransactionId(), mode, false,
  							  &xid, &new_infomask, &new_infomask2);
  
  	START_CRIT_SECTION();
  
  	/*
  	 * Store transaction information of xact locking the tuple.
  	 *
  	 * Note: Cmax is meaningless in this context, so don't set it; this avoids
  	 * possibly generating a useless combo CID.  Moreover, if we're locking a
  	 * previously updated tuple, it's important to preserve the Cmax.
  	 *
  	 * Also reset the HOT UPDATE bit, but only if there's no update; otherwise
  	 * we would break the HOT chain.
  	 */
  	tuple->t_data->t_infomask &= ~HEAP_XMAX_BITS;
  	tuple->t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  	tuple->t_data->t_infomask |= new_infomask;
  	tuple->t_data->t_infomask2 |= new_infomask2;
  	if (HEAP_XMAX_IS_LOCKED_ONLY(new_infomask))
  		HeapTupleHeaderClearHotUpdated(tuple->t_data);
  	HeapTupleHeaderSetXmax(tuple->t_data, xid);
  
  	/*
  	 * Make sure there is no forward chain link in t_ctid.  Note that in the
  	 * cases where the tuple has been updated, we must not overwrite t_ctid,
  	 * because it was set by the updater.  Moreover, if the tuple has been
  	 * updated, we need to follow the update chain to lock the new versions of
  	 * the tuple as well.
  	 */
  	if (HEAP_XMAX_IS_LOCKED_ONLY(new_infomask))
  		tuple->t_data->t_ctid = *tid;
  
  	/* Clear only the all-frozen bit on visibility map if needed */
  	if (PageIsAllVisible(page) &&
  		visibilitymap_clear(relation, block, vmbuffer,
  							VISIBILITYMAP_ALL_FROZEN))
  		cleared_all_frozen = true;
  
  
  	MarkBufferDirty(*buffer);
  
  	/*
  	 * XLOG stuff.  You might think that we don't need an XLOG record because
  	 * there is no state change worth restoring after a crash.  You would be
  	 * wrong however: we have just written either a TransactionId or a
  	 * MultiXactId that may never have been seen on disk before, and we need
  	 * to make sure that there are XLOG entries covering those ID numbers.
  	 * Else the same IDs might be re-used after a crash, which would be
  	 * disastrous if this page made it to disk before the crash.  Essentially
  	 * we have to enforce the WAL log-before-data rule even in this case.
  	 * (Also, in a PITR log-shipping or 2PC environment, we have to have XLOG
  	 * entries for everything anyway.)
  	 */
  	if (RelationNeedsWAL(relation))
  	{
  		xl_heap_lock xlrec;
  		XLogRecPtr	recptr;
  
  		XLogBeginInsert();
  		XLogRegisterBuffer(0, *buffer, REGBUF_STANDARD);
  
  		xlrec.offnum = ItemPointerGetOffsetNumber(&tuple->t_self);
  		xlrec.locking_xid = xid;
  		xlrec.infobits_set = compute_infobits(new_infomask,
  											  tuple->t_data->t_infomask2);
  		xlrec.flags = cleared_all_frozen ? XLH_LOCK_ALL_FROZEN_CLEARED : 0;
  		XLogRegisterData((char *) &xlrec, SizeOfHeapLock);
  
  		/* we don't decode row locks atm, so no need to log the origin */
  
  		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_LOCK);
  
  		PageSetLSN(page, recptr);
  	}
  
  	END_CRIT_SECTION();
  
  	result = TM_Ok;
  
  out_locked:
  	LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
  
  out_unlocked:
  	if (BufferIsValid(vmbuffer))
  		ReleaseBuffer(vmbuffer);
  
  	/*
  	 * Don't update the visibility map here. Locking a tuple doesn't change
  	 * visibility info.
  	 */
  
  	/*
  	 * Now that we have successfully marked the tuple as locked, we can
  	 * release the lmgr tuple lock, if we had it.
  	 */
  	if (have_tuple_lock)
  		UnlockTupleTuplock(relation, tid, mode);
  
  	return result;
  }
  
  /*
   * Acquire heavyweight lock on the given tuple, in preparation for acquiring
   * its normal, Xmax-based tuple lock.
   *
   * have_tuple_lock is an input and output parameter: on input, it indicates
   * whether the lock has previously been acquired (and this function does
   * nothing in that case).  If this function returns success, have_tuple_lock
   * has been flipped to true.
   *
   * Returns false if it was unable to obtain the lock; this can only happen if
   * wait_policy is Skip.
   */
  static bool
  heap_acquire_tuplock(Relation relation, ItemPointer tid, LockTupleMode mode,
  					 LockWaitPolicy wait_policy, bool *have_tuple_lock)
  {
  	if (*have_tuple_lock)
  		return true;
  
  	switch (wait_policy)
  	{
  		case LockWaitBlock:
  			LockTupleTuplock(relation, tid, mode);
  			break;
  
  		case LockWaitSkip:
  			if (!ConditionalLockTupleTuplock(relation, tid, mode))
  				return false;
  			break;
  
  		case LockWaitError:
  			if (!ConditionalLockTupleTuplock(relation, tid, mode))
  				ereport(ERROR,
  						(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
  						 errmsg("could not obtain lock on row in relation \"%s\"",
  								RelationGetRelationName(relation))));
  			break;
  	}
  	*have_tuple_lock = true;
  
  	return true;
  }
  
  /*
   * Given an original set of Xmax and infomask, and a transaction (identified by
   * add_to_xmax) acquiring a new lock of some mode, compute the new Xmax and
   * corresponding infomasks to use on the tuple.
   *
   * Note that this might have side effects such as creating a new MultiXactId.
   *
   * Most callers will have called HeapTupleSatisfiesUpdate before this function;
   * that will have set the HEAP_XMAX_INVALID bit if the xmax was a MultiXactId
   * but it was not running anymore. There is a race condition, which is that the
   * MultiXactId may have finished since then, but that uncommon case is handled
   * either here, or within MultiXactIdExpand.
   *
   * There is a similar race condition possible when the old xmax was a regular
   * TransactionId.  We test TransactionIdIsInProgress again just to narrow the
   * window, but it's still possible to end up creating an unnecessary
   * MultiXactId.  Fortunately this is harmless.
   */
  static void
  compute_new_xmax_infomask(TransactionId xmax, uint16 old_infomask,
  						  uint16 old_infomask2, TransactionId add_to_xmax,
  						  LockTupleMode mode, bool is_update,
  						  TransactionId *result_xmax, uint16 *result_infomask,
  						  uint16 *result_infomask2)
  {
  	TransactionId new_xmax;
  	uint16		new_infomask,
  				new_infomask2;
  
  	Assert(TransactionIdIsCurrentTransactionId(add_to_xmax));
  
  l5:
  	new_infomask = 0;
  	new_infomask2 = 0;
  	if (old_infomask & HEAP_XMAX_INVALID)
  	{
  		/*
  		 * No previous locker; we just insert our own TransactionId.
  		 *
  		 * Note that it's critical that this case be the first one checked,
  		 * because there are several blocks below that come back to this one
  		 * to implement certain optimizations; old_infomask might contain
  		 * other dirty bits in those cases, but we don't really care.
  		 */
  		if (is_update)
  		{
  			new_xmax = add_to_xmax;
  			if (mode == LockTupleExclusive)
  				new_infomask2 |= HEAP_KEYS_UPDATED;
  		}
  		else
  		{
  			new_infomask |= HEAP_XMAX_LOCK_ONLY;
  			switch (mode)
  			{
  				case LockTupleKeyShare:
  					new_xmax = add_to_xmax;
  					new_infomask |= HEAP_XMAX_KEYSHR_LOCK;
  					break;
  				case LockTupleShare:
  					new_xmax = add_to_xmax;
  					new_infomask |= HEAP_XMAX_SHR_LOCK;
  					break;
  				case LockTupleNoKeyExclusive:
  					new_xmax = add_to_xmax;
  					new_infomask |= HEAP_XMAX_EXCL_LOCK;
  					break;
  				case LockTupleExclusive:
  					new_xmax = add_to_xmax;
  					new_infomask |= HEAP_XMAX_EXCL_LOCK;
  					new_infomask2 |= HEAP_KEYS_UPDATED;
  					break;
  				default:
  					new_xmax = InvalidTransactionId;	/* silence compiler */
  					elog(ERROR, "invalid lock mode");
  			}
  		}
  	}
  	else if (old_infomask & HEAP_XMAX_IS_MULTI)
  	{
  		MultiXactStatus new_status;
  
  		/*
  		 * Currently we don't allow XMAX_COMMITTED to be set for multis, so
  		 * cross-check.
  		 */
  		Assert(!(old_infomask & HEAP_XMAX_COMMITTED));
  
  		/*
  		 * A multixact together with LOCK_ONLY set but neither lock bit set
  		 * (i.e. a pg_upgraded share locked tuple) cannot possibly be running
  		 * anymore.  This check is critical for databases upgraded by
  		 * pg_upgrade; both MultiXactIdIsRunning and MultiXactIdExpand assume
  		 * that such multis are never passed.
  		 */
  		if (HEAP_LOCKED_UPGRADED(old_infomask))
  		{
  			old_infomask &= ~HEAP_XMAX_IS_MULTI;
  			old_infomask |= HEAP_XMAX_INVALID;
  			goto l5;
  		}
  
  		/*
  		 * If the XMAX is already a MultiXactId, then we need to expand it to
  		 * include add_to_xmax; but if all the members were lockers and are
  		 * all gone, we can do away with the IS_MULTI bit and just set
  		 * add_to_xmax as the only locker/updater.  If all lockers are gone
  		 * and we have an updater that aborted, we can also do without a
  		 * multi.
  		 *
  		 * The cost of doing GetMultiXactIdMembers would be paid by
  		 * MultiXactIdExpand if we weren't to do this, so this check is not
  		 * incurring extra work anyhow.
  		 */
  		if (!MultiXactIdIsRunning(xmax, HEAP_XMAX_IS_LOCKED_ONLY(old_infomask)))
  		{
  			if (HEAP_XMAX_IS_LOCKED_ONLY(old_infomask) ||
  				!TransactionIdDidCommit(MultiXactIdGetUpdateXid(xmax,
  																old_infomask)))
  			{
  				/*
  				 * Reset these bits and restart; otherwise fall through to
  				 * create a new multi below.
  				 */
  				old_infomask &= ~HEAP_XMAX_IS_MULTI;
  				old_infomask |= HEAP_XMAX_INVALID;
  				goto l5;
  			}
  		}
  
  		new_status = get_mxact_status_for_lock(mode, is_update);
  
  		new_xmax = MultiXactIdExpand((MultiXactId) xmax, add_to_xmax,
  									 new_status);
  		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
  	}
  	else if (old_infomask & HEAP_XMAX_COMMITTED)
  	{
  		/*
  		 * It's a committed update, so we need to preserve him as updater of
  		 * the tuple.
  		 */
  		MultiXactStatus status;
  		MultiXactStatus new_status;
  
  		if (old_infomask2 & HEAP_KEYS_UPDATED)
  			status = MultiXactStatusUpdate;
  		else
  			status = MultiXactStatusNoKeyUpdate;
  
  		new_status = get_mxact_status_for_lock(mode, is_update);
  
  		/*
  		 * since it's not running, it's obviously impossible for the old
  		 * updater to be identical to the current one, so we need not check
  		 * for that case as we do in the block above.
  		 */
  		new_xmax = MultiXactIdCreate(xmax, status, add_to_xmax, new_status);
  		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
  	}
  	else if (TransactionIdIsInProgress(xmax))
  	{
  		/*
  		 * If the XMAX is a valid, in-progress TransactionId, then we need to
  		 * create a new MultiXactId that includes both the old locker or
  		 * updater and our own TransactionId.
  		 */
  		MultiXactStatus new_status;
  		MultiXactStatus old_status;
  		LockTupleMode old_mode;
  
  		if (HEAP_XMAX_IS_LOCKED_ONLY(old_infomask))
  		{
  			if (HEAP_XMAX_IS_KEYSHR_LOCKED(old_infomask))
  				old_status = MultiXactStatusForKeyShare;
  			else if (HEAP_XMAX_IS_SHR_LOCKED(old_infomask))
  				old_status = MultiXactStatusForShare;
  			else if (HEAP_XMAX_IS_EXCL_LOCKED(old_infomask))
  			{
  				if (old_infomask2 & HEAP_KEYS_UPDATED)
  					old_status = MultiXactStatusForUpdate;
  				else
  					old_status = MultiXactStatusForNoKeyUpdate;
  			}
  			else
  			{
  				/*
  				 * LOCK_ONLY can be present alone only when a page has been
  				 * upgraded by pg_upgrade.  But in that case,
  				 * TransactionIdIsInProgress() should have returned false.  We
  				 * assume it's no longer locked in this case.
  				 */
  				elog(WARNING, "LOCK_ONLY found for Xid in progress %u", xmax);
  				old_infomask |= HEAP_XMAX_INVALID;
  				old_infomask &= ~HEAP_XMAX_LOCK_ONLY;
  				goto l5;
  			}
  		}
  		else
  		{
  			/* it's an update, but which kind? */
  			if (old_infomask2 & HEAP_KEYS_UPDATED)
  				old_status = MultiXactStatusUpdate;
  			else
  				old_status = MultiXactStatusNoKeyUpdate;
  		}
  
  		old_mode = TUPLOCK_from_mxstatus(old_status);
  
  		/*
  		 * If the lock to be acquired is for the same TransactionId as the
  		 * existing lock, there's an optimization possible: consider only the
  		 * strongest of both locks as the only one present, and restart.
  		 */
  		if (xmax == add_to_xmax)
  		{
  			/*
  			 * Note that it's not possible for the original tuple to be
  			 * updated: we wouldn't be here because the tuple would have been
  			 * invisible and we wouldn't try to update it.  As a subtlety,
  			 * this code can also run when traversing an update chain to lock
  			 * future versions of a tuple.  But we wouldn't be here either,
  			 * because the add_to_xmax would be different from the original
  			 * updater.
  			 */
  			Assert(HEAP_XMAX_IS_LOCKED_ONLY(old_infomask));
  
  			/* acquire the strongest of both */
  			if (mode < old_mode)
  				mode = old_mode;
  			/* mustn't touch is_update */
  
  			old_infomask |= HEAP_XMAX_INVALID;
  			goto l5;
  		}
  
  		/* otherwise, just fall back to creating a new multixact */
  		new_status = get_mxact_status_for_lock(mode, is_update);
  		new_xmax = MultiXactIdCreate(xmax, old_status,
  									 add_to_xmax, new_status);
  		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
  	}
  	else if (!HEAP_XMAX_IS_LOCKED_ONLY(old_infomask) &&
  			 TransactionIdDidCommit(xmax))
  	{
  		/*
  		 * It's a committed update, so we gotta preserve him as updater of the
  		 * tuple.
  		 */
  		MultiXactStatus status;
  		MultiXactStatus new_status;
  
  		if (old_infomask2 & HEAP_KEYS_UPDATED)
  			status = MultiXactStatusUpdate;
  		else
  			status = MultiXactStatusNoKeyUpdate;
  
  		new_status = get_mxact_status_for_lock(mode, is_update);
  
  		/*
  		 * since it's not running, it's obviously impossible for the old
  		 * updater to be identical to the current one, so we need not check
  		 * for that case as we do in the block above.
  		 */
  		new_xmax = MultiXactIdCreate(xmax, status, add_to_xmax, new_status);
  		GetMultiXactIdHintBits(new_xmax, &new_infomask, &new_infomask2);
  	}
  	else
  	{
  		/*
  		 * Can get here iff the locking/updating transaction was running when
  		 * the infomask was extracted from the tuple, but finished before
  		 * TransactionIdIsInProgress got to run.  Deal with it as if there was
  		 * no locker at all in the first place.
  		 */
  		old_infomask |= HEAP_XMAX_INVALID;
  		goto l5;
  	}
  
  	*result_infomask = new_infomask;
  	*result_infomask2 = new_infomask2;
  	*result_xmax = new_xmax;
  }
  
  /*
   * Subroutine for heap_lock_updated_tuple_rec.
   *
   * Given a hypothetical multixact status held by the transaction identified
   * with the given xid, does the current transaction need to wait, fail, or can
   * it continue if it wanted to acquire a lock of the given mode?  "needwait"
   * is set to true if waiting is necessary; if it can continue, then TM_Ok is
   * returned.  If the lock is already held by the current transaction, return
   * TM_SelfModified.  In case of a conflict with another transaction, a
   * different HeapTupleSatisfiesUpdate return code is returned.
   *
   * The held status is said to be hypothetical because it might correspond to a
   * lock held by a single Xid, i.e. not a real MultiXactId; we express it this
   * way for simplicity of API.
   */
  static TM_Result
  test_lockmode_for_conflict(MultiXactStatus status, TransactionId xid,
  						   LockTupleMode mode, HeapTuple tup,
  						   bool *needwait)
  {
  	MultiXactStatus wantedstatus;
  
  	*needwait = false;
  	wantedstatus = get_mxact_status_for_lock(mode, false);
  
  	/*
  	 * Note: we *must* check TransactionIdIsInProgress before
  	 * TransactionIdDidAbort/Commit; see comment at top of heapam_visibility.c
  	 * for an explanation.
  	 */
  	if (TransactionIdIsCurrentTransactionId(xid))
  	{
  		/*
  		 * The tuple has already been locked by our own transaction.  This is
  		 * very rare but can happen if multiple transactions are trying to
  		 * lock an ancient version of the same tuple.
  		 */
  		return TM_SelfModified;
  	}
  	else if (TransactionIdIsInProgress(xid))
  	{
  		/*
  		 * If the locking transaction is running, what we do depends on
  		 * whether the lock modes conflict: if they do, then we must wait for
  		 * it to finish; otherwise we can fall through to lock this tuple
  		 * version without waiting.
  		 */
  		if (DoLockModesConflict(LOCKMODE_from_mxstatus(status),
  								LOCKMODE_from_mxstatus(wantedstatus)))
  		{
  			*needwait = true;
  		}
  
  		/*
  		 * If we set needwait above, then this value doesn't matter;
  		 * otherwise, this value signals to caller that it's okay to proceed.
  		 */
  		return TM_Ok;
  	}
  	else if (TransactionIdDidAbort(xid))
  		return TM_Ok;
  	else if (TransactionIdDidCommit(xid))
  	{
  		/*
  		 * The other transaction committed.  If it was only a locker, then the
  		 * lock is completely gone now and we can return success; but if it
  		 * was an update, then what we do depends on whether the two lock
  		 * modes conflict.  If they conflict, then we must report error to
  		 * caller. But if they don't, we can fall through to allow the current
  		 * transaction to lock the tuple.
  		 *
  		 * Note: the reason we worry about ISUPDATE here is because as soon as
  		 * a transaction ends, all its locks are gone and meaningless, and
  		 * thus we can ignore them; whereas its updates persist.  In the
  		 * TransactionIdIsInProgress case, above, we don't need to check
  		 * because we know the lock is still "alive" and thus a conflict needs
  		 * always be checked.
  		 */
  		if (!ISUPDATE_from_mxstatus(status))
  			return TM_Ok;
  
  		if (DoLockModesConflict(LOCKMODE_from_mxstatus(status),
  								LOCKMODE_from_mxstatus(wantedstatus)))
  		{
  			/* bummer */
  			if (!ItemPointerEquals(&tup->t_self, &tup->t_data->t_ctid) ||
  				HeapTupleHeaderIndicatesMovedPartitions(tup->t_data))
  				return TM_Updated;
  			else
  				return TM_Deleted;
  		}
  
  		return TM_Ok;
  	}
  
  	/* Not in progress, not aborted, not committed -- must have crashed */
  	return TM_Ok;
  }
  
  
  /*
   * Recursive part of heap_lock_updated_tuple
   *
   * Fetch the tuple pointed to by tid in rel, and mark it as locked by the given
   * xid with the given mode; if this tuple is updated, recurse to lock the new
   * version as well.
   */
  static TM_Result
  heap_lock_updated_tuple_rec(Relation rel, ItemPointer tid, TransactionId xid,
  							LockTupleMode mode)
  {
  	TM_Result	result;
  	ItemPointerData tupid;
  	HeapTupleData mytup;
  	Buffer		buf;
  	uint16		new_infomask,
  				new_infomask2,
  				old_infomask,
  				old_infomask2;
  	TransactionId xmax,
  				new_xmax;
  	TransactionId priorXmax = InvalidTransactionId;
  	bool		cleared_all_frozen = false;
  	bool		pinned_desired_page;
  	Buffer		vmbuffer = InvalidBuffer;
  	BlockNumber block;
  
  	ItemPointerCopy(tid, &tupid);
  
  	for (;;)
  	{
  		new_infomask = 0;
  		new_xmax = InvalidTransactionId;
  		block = ItemPointerGetBlockNumber(&tupid);
  		ItemPointerCopy(&tupid, &(mytup.t_self));
  
  		if (!heap_fetch(rel, SnapshotAny, &mytup, &buf))
  		{
  			/*
  			 * if we fail to find the updated version of the tuple, it's
  			 * because it was vacuumed/pruned away after its creator
  			 * transaction aborted.  So behave as if we got to the end of the
  			 * chain, and there's no further tuple to lock: return success to
  			 * caller.
  			 */
  			result = TM_Ok;
  			goto out_unlocked;
  		}
  
  l4:
  		CHECK_FOR_INTERRUPTS();
  
  		/*
  		 * Before locking the buffer, pin the visibility map page if it
  		 * appears to be necessary.  Since we haven't got the lock yet,
  		 * someone else might be in the middle of changing this, so we'll need
  		 * to recheck after we have the lock.
  		 */
  		if (PageIsAllVisible(BufferGetPage(buf)))
  		{
  			visibilitymap_pin(rel, block, &vmbuffer);
  			pinned_desired_page = true;
  		}
  		else
  			pinned_desired_page = false;
  
  		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
  
  		/*
  		 * If we didn't pin the visibility map page and the page has become
  		 * all visible while we were busy locking the buffer, we'll have to
  		 * unlock and re-lock, to avoid holding the buffer lock across I/O.
  		 * That's a bit unfortunate, but hopefully shouldn't happen often.
  		 *
  		 * Note: in some paths through this function, we will reach here
  		 * holding a pin on a vm page that may or may not be the one matching
  		 * this page.  If this page isn't all-visible, we won't use the vm
  		 * page, but we hold onto such a pin till the end of the function.
  		 */
  		if (!pinned_desired_page && PageIsAllVisible(BufferGetPage(buf)))
  		{
  			LockBuffer(buf, BUFFER_LOCK_UNLOCK);
  			visibilitymap_pin(rel, block, &vmbuffer);
  			LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
  		}
  
  		/*
  		 * Check the tuple XMIN against prior XMAX, if any.  If we reached the
  		 * end of the chain, we're done, so return success.
  		 */
  		if (TransactionIdIsValid(priorXmax) &&
  			!TransactionIdEquals(HeapTupleHeaderGetXmin(mytup.t_data),
  								 priorXmax))
  		{
  			result = TM_Ok;
  			goto out_locked;
  		}
  
  		/*
  		 * Also check Xmin: if this tuple was created by an aborted
  		 * (sub)transaction, then we already locked the last live one in the
  		 * chain, thus we're done, so return success.
  		 */
  		if (TransactionIdDidAbort(HeapTupleHeaderGetXmin(mytup.t_data)))
  		{
  			result = TM_Ok;
  			goto out_locked;
  		}
  
  		old_infomask = mytup.t_data->t_infomask;
  		old_infomask2 = mytup.t_data->t_infomask2;
  		xmax = HeapTupleHeaderGetRawXmax(mytup.t_data);
  
  		/*
  		 * If this tuple version has been updated or locked by some concurrent
  		 * transaction(s), what we do depends on whether our lock mode
  		 * conflicts with what those other transactions hold, and also on the
  		 * status of them.
  		 */
  		if (!(old_infomask & HEAP_XMAX_INVALID))
  		{
  			TransactionId rawxmax;
  			bool		needwait;
  
  			rawxmax = HeapTupleHeaderGetRawXmax(mytup.t_data);
  			if (old_infomask & HEAP_XMAX_IS_MULTI)
  			{
  				int			nmembers;
  				int			i;
  				MultiXactMember *members;
  
  				/*
  				 * We don't need a test for pg_upgrade'd tuples: this is only
  				 * applied to tuples after the first in an update chain.  Said
  				 * first tuple in the chain may well be locked-in-9.2-and-
  				 * pg_upgraded, but that one was already locked by our caller,
  				 * not us; and any subsequent ones cannot be because our
  				 * caller must necessarily have obtained a snapshot later than
  				 * the pg_upgrade itself.
  				 */
  				Assert(!HEAP_LOCKED_UPGRADED(mytup.t_data->t_infomask));
  
  				nmembers = GetMultiXactIdMembers(rawxmax, &members, false,
  												 HEAP_XMAX_IS_LOCKED_ONLY(old_infomask));
  				for (i = 0; i < nmembers; i++)
  				{
  					result = test_lockmode_for_conflict(members[i].status,
  														members[i].xid,
  														mode,
  														&mytup,
  														&needwait);
  
  					/*
  					 * If the tuple was already locked by ourselves in a
  					 * previous iteration of this (say heap_lock_tuple was
  					 * forced to restart the locking loop because of a change
  					 * in xmax), then we hold the lock already on this tuple
  					 * version and we don't need to do anything; and this is
  					 * not an error condition either.  We just need to skip
  					 * this tuple and continue locking the next version in the
  					 * update chain.
  					 */
  					if (result == TM_SelfModified)
  					{
  						pfree(members);
  						goto next;
  					}
  
  					if (needwait)
  					{
  						LockBuffer(buf, BUFFER_LOCK_UNLOCK);
  						XactLockTableWait(members[i].xid, rel,
  										  &mytup.t_self,
  										  XLTW_LockUpdated);
  						pfree(members);
  						goto l4;
  					}
  					if (result != TM_Ok)
  					{
  						pfree(members);
  						goto out_locked;
  					}
  				}
  				if (members)
  					pfree(members);
  			}
  			else
  			{
  				MultiXactStatus status;
  
  				/*
  				 * For a non-multi Xmax, we first need to compute the
  				 * corresponding MultiXactStatus by using the infomask bits.
  				 */
  				if (HEAP_XMAX_IS_LOCKED_ONLY(old_infomask))
  				{
  					if (HEAP_XMAX_IS_KEYSHR_LOCKED(old_infomask))
  						status = MultiXactStatusForKeyShare;
  					else if (HEAP_XMAX_IS_SHR_LOCKED(old_infomask))
  						status = MultiXactStatusForShare;
  					else if (HEAP_XMAX_IS_EXCL_LOCKED(old_infomask))
  					{
  						if (old_infomask2 & HEAP_KEYS_UPDATED)
  							status = MultiXactStatusForUpdate;
  						else
  							status = MultiXactStatusForNoKeyUpdate;
  					}
  					else
  					{
  						/*
  						 * LOCK_ONLY present alone (a pg_upgraded tuple marked
  						 * as share-locked in the old cluster) shouldn't be
  						 * seen in the middle of an update chain.
  						 */
  						elog(ERROR, "invalid lock status in tuple");
  					}
  				}
  				else
  				{
  					/* it's an update, but which kind? */
  					if (old_infomask2 & HEAP_KEYS_UPDATED)
  						status = MultiXactStatusUpdate;
  					else
  						status = MultiXactStatusNoKeyUpdate;
  				}
  
  				result = test_lockmode_for_conflict(status, rawxmax, mode,
  													&mytup, &needwait);
  
  				/*
  				 * If the tuple was already locked by ourselves in a previous
  				 * iteration of this (say heap_lock_tuple was forced to
  				 * restart the locking loop because of a change in xmax), then
  				 * we hold the lock already on this tuple version and we don't
  				 * need to do anything; and this is not an error condition
  				 * either.  We just need to skip this tuple and continue
  				 * locking the next version in the update chain.
  				 */
  				if (result == TM_SelfModified)
  					goto next;
  
  				if (needwait)
  				{
  					LockBuffer(buf, BUFFER_LOCK_UNLOCK);
  					XactLockTableWait(rawxmax, rel, &mytup.t_self,
  									  XLTW_LockUpdated);
  					goto l4;
  				}
  				if (result != TM_Ok)
  				{
  					goto out_locked;
  				}
  			}
  		}
  
  		/* compute the new Xmax and infomask values for the tuple ... */
  		compute_new_xmax_infomask(xmax, old_infomask, mytup.t_data->t_infomask2,
  								  xid, mode, false,
  								  &new_xmax, &new_infomask, &new_infomask2);
  
  		if (PageIsAllVisible(BufferGetPage(buf)) &&
  			visibilitymap_clear(rel, block, vmbuffer,
  								VISIBILITYMAP_ALL_FROZEN))
  			cleared_all_frozen = true;
  
  		START_CRIT_SECTION();
  
  		/* ... and set them */
  		HeapTupleHeaderSetXmax(mytup.t_data, new_xmax);
  		mytup.t_data->t_infomask &= ~HEAP_XMAX_BITS;
  		mytup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  		mytup.t_data->t_infomask |= new_infomask;
  		mytup.t_data->t_infomask2 |= new_infomask2;
  
  		MarkBufferDirty(buf);
  
  		/* XLOG stuff */
  		if (RelationNeedsWAL(rel))
  		{
  			xl_heap_lock_updated xlrec;
  			XLogRecPtr	recptr;
  			Page		page = BufferGetPage(buf);
  
  			XLogBeginInsert();
  			XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
  
  			xlrec.offnum = ItemPointerGetOffsetNumber(&mytup.t_self);
  			xlrec.xmax = new_xmax;
  			xlrec.infobits_set = compute_infobits(new_infomask, new_infomask2);
  			xlrec.flags =
  				cleared_all_frozen ? XLH_LOCK_ALL_FROZEN_CLEARED : 0;
  
  			XLogRegisterData((char *) &xlrec, SizeOfHeapLockUpdated);
  
  			recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_LOCK_UPDATED);
  
  			PageSetLSN(page, recptr);
  		}
  
  		END_CRIT_SECTION();
  
  next:
  		/* if we find the end of update chain, we're done. */
  		if (mytup.t_data->t_infomask & HEAP_XMAX_INVALID ||
  			HeapTupleHeaderIndicatesMovedPartitions(mytup.t_data) ||
  			ItemPointerEquals(&mytup.t_self, &mytup.t_data->t_ctid) ||
  			HeapTupleHeaderIsOnlyLocked(mytup.t_data))
  		{
  			result = TM_Ok;
  			goto out_locked;
  		}
  
  		/* tail recursion */
  		priorXmax = HeapTupleHeaderGetUpdateXid(mytup.t_data);
  		ItemPointerCopy(&(mytup.t_data->t_ctid), &tupid);
  		UnlockReleaseBuffer(buf);
  	}
  
  	result = TM_Ok;
  
  out_locked:
  	UnlockReleaseBuffer(buf);
  
  out_unlocked:
  	if (vmbuffer != InvalidBuffer)
  		ReleaseBuffer(vmbuffer);
  
  	return result;
  }
  
  /*
   * heap_lock_updated_tuple
   *		Follow update chain when locking an updated tuple, acquiring locks (row
   *		marks) on the updated versions.
   *
   * The initial tuple is assumed to be already locked.
   *
   * This function doesn't check visibility, it just unconditionally marks the
   * tuple(s) as locked.  If any tuple in the updated chain is being deleted
   * concurrently (or updated with the key being modified), sleep until the
   * transaction doing it is finished.
   *
   * Note that we don't acquire heavyweight tuple locks on the tuples we walk
   * when we have to wait for other transactions to release them, as opposed to
   * what heap_lock_tuple does.  The reason is that having more than one
   * transaction walking the chain is probably uncommon enough that risk of
   * starvation is not likely: one of the preconditions for being here is that
   * the snapshot in use predates the update that created this tuple (because we
   * started at an earlier version of the tuple), but at the same time such a
   * transaction cannot be using repeatable read or serializable isolation
   * levels, because that would lead to a serializability failure.
   */
  static TM_Result
  heap_lock_updated_tuple(Relation rel, HeapTuple tuple, ItemPointer ctid,
  						TransactionId xid, LockTupleMode mode)
  {
  	/*
  	 * If the tuple has not been updated, or has moved into another partition
  	 * (effectively a delete) stop here.
  	 */
  	if (!HeapTupleHeaderIndicatesMovedPartitions(tuple->t_data) &&
  		!ItemPointerEquals(&tuple->t_self, ctid))
  	{
  		/*
  		 * If this is the first possibly-multixact-able operation in the
  		 * current transaction, set my per-backend OldestMemberMXactId
  		 * setting. We can be certain that the transaction will never become a
  		 * member of any older MultiXactIds than that.  (We have to do this
  		 * even if we end up just using our own TransactionId below, since
  		 * some other backend could incorporate our XID into a MultiXact
  		 * immediately afterwards.)
  		 */
  		MultiXactIdSetOldestMember();
  
  		return heap_lock_updated_tuple_rec(rel, ctid, xid, mode);
  	}
  
  	/* nothing to lock */
  	return TM_Ok;
  }
  
  /*
   *	heap_finish_speculative - mark speculative insertion as successful
   *
   * To successfully finish a speculative insertion we have to clear speculative
   * token from tuple.  To do so the t_ctid field, which will contain a
   * speculative token value, is modified in place to point to the tuple itself,
   * which is characteristic of a newly inserted ordinary tuple.
   *
   * NB: It is not ok to commit without either finishing or aborting a
   * speculative insertion.  We could treat speculative tuples of committed
   * transactions implicitly as completed, but then we would have to be prepared
   * to deal with speculative tokens on committed tuples.  That wouldn't be
   * difficult - no-one looks at the ctid field of a tuple with invalid xmax -
   * but clearing the token at completion isn't very expensive either.
   * An explicit confirmation WAL record also makes logical decoding simpler.
   */
  void
  heap_finish_speculative(Relation relation, ItemPointer tid)
  {
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  
  	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
  	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  	page = (Page) BufferGetPage(buffer);
  
  	offnum = ItemPointerGetOffsetNumber(tid);
  	if (PageGetMaxOffsetNumber(page) >= offnum)
  		lp = PageGetItemId(page, offnum);
  
  	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  		elog(ERROR, "invalid lp");
  
  	htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  	/* SpecTokenOffsetNumber should be distinguishable from any real offset */
  	StaticAssertStmt(MaxOffsetNumber < SpecTokenOffsetNumber,
  					 "invalid speculative token constant");
  
  	/* NO EREPORT(ERROR) from here till changes are logged */
  	START_CRIT_SECTION();
  
  	Assert(HeapTupleHeaderIsSpeculative(htup));
  
  	MarkBufferDirty(buffer);
  
  	/*
  	 * Replace the speculative insertion token with a real t_ctid, pointing to
  	 * itself like it does on regular tuples.
  	 */
  	htup->t_ctid = *tid;
  
  	/* XLOG stuff */
  	if (RelationNeedsWAL(relation))
  	{
  		xl_heap_confirm xlrec;
  		XLogRecPtr	recptr;
  
  		xlrec.offnum = ItemPointerGetOffsetNumber(tid);
  
  		XLogBeginInsert();
  
  		/* We want the same filtering on this as on a plain insert */
  		XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
  
  		XLogRegisterData((char *) &xlrec, SizeOfHeapConfirm);
  		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
  
  		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_CONFIRM);
  
  		PageSetLSN(page, recptr);
  	}
  
  	END_CRIT_SECTION();
  
  	UnlockReleaseBuffer(buffer);
  }
  
  /*
   *	heap_abort_speculative - kill a speculatively inserted tuple
   *
   * Marks a tuple that was speculatively inserted in the same command as dead,
   * by setting its xmin as invalid.  That makes it immediately appear as dead
   * to all transactions, including our own.  In particular, it makes
   * HeapTupleSatisfiesDirty() regard the tuple as dead, so that another backend
   * inserting a duplicate key value won't unnecessarily wait for our whole
   * transaction to finish (it'll just wait for our speculative insertion to
   * finish).
   *
   * Killing the tuple prevents "unprincipled deadlocks", which are deadlocks
   * that arise due to a mutual dependency that is not user visible.  By
   * definition, unprincipled deadlocks cannot be prevented by the user
   * reordering lock acquisition in client code, because the implementation level
   * lock acquisitions are not under the user's direct control.  If speculative
   * inserters did not take this precaution, then under high concurrency they
   * could deadlock with each other, which would not be acceptable.
   *
   * This is somewhat redundant with heap_delete, but we prefer to have a
   * dedicated routine with stripped down requirements.  Note that this is also
   * used to delete the TOAST tuples created during speculative insertion.
   *
   * This routine does not affect logical decoding as it only looks at
   * confirmation records.
   */
  void
  heap_abort_speculative(Relation relation, ItemPointer tid)
  {
  	TransactionId xid = GetCurrentTransactionId();
  	ItemId		lp;
  	HeapTupleData tp;
  	Page		page;
  	BlockNumber block;
  	Buffer		buffer;
  
  	Assert(ItemPointerIsValid(tid));
  
  	block = ItemPointerGetBlockNumber(tid);
  	buffer = ReadBuffer(relation, block);
  	page = BufferGetPage(buffer);
  
  	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  	/*
  	 * Page can't be all visible, we just inserted into it, and are still
  	 * running.
  	 */
  	Assert(!PageIsAllVisible(page));
  
  	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
  	Assert(ItemIdIsNormal(lp));
  
  	tp.t_tableOid = RelationGetRelid(relation);
  	tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
  	tp.t_len = ItemIdGetLength(lp);
  	tp.t_self = *tid;
  
  	/*
  	 * Sanity check that the tuple really is a speculatively inserted tuple,
  	 * inserted by us.
  	 */
  	if (tp.t_data->t_choice.t_heap.t_xmin != xid)
  		elog(ERROR, "attempted to kill a tuple inserted by another transaction");
  	if (!(IsToastRelation(relation) || HeapTupleHeaderIsSpeculative(tp.t_data)))
  		elog(ERROR, "attempted to kill a non-speculative tuple");
  	Assert(!HeapTupleHeaderIsHeapOnly(tp.t_data));
  
  	/*
  	 * No need to check for serializable conflicts here.  There is never a
  	 * need for a combocid, either.  No need to extract replica identity, or
  	 * do anything special with infomask bits.
  	 */
  
  	START_CRIT_SECTION();
  
  	/*
  	 * The tuple will become DEAD immediately.  Flag that this page
  	 * immediately is a candidate for pruning by setting xmin to
  	 * RecentGlobalXmin.  That's not pretty, but it doesn't seem worth
  	 * inventing a nicer API for this.
  	 */
  	Assert(TransactionIdIsValid(RecentGlobalXmin));
  	PageSetPrunable(page, RecentGlobalXmin);
  
  	/* store transaction information of xact deleting the tuple */
  	tp.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
  	tp.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  
  	/*
  	 * Set the tuple header xmin to InvalidTransactionId.  This makes the
  	 * tuple immediately invisible everyone.  (In particular, to any
  	 * transactions waiting on the speculative token, woken up later.)
  	 */
  	HeapTupleHeaderSetXmin(tp.t_data, InvalidTransactionId);
  
  	/* Clear the speculative insertion token too */
  	tp.t_data->t_ctid = tp.t_self;
  
  	MarkBufferDirty(buffer);
  
  	/*
  	 * XLOG stuff
  	 *
  	 * The WAL records generated here match heap_delete().  The same recovery
  	 * routines are used.
  	 */
  	if (RelationNeedsWAL(relation))
  	{
  		xl_heap_delete xlrec;
  		XLogRecPtr	recptr;
  
  		xlrec.flags = XLH_DELETE_IS_SUPER;
  		xlrec.infobits_set = compute_infobits(tp.t_data->t_infomask,
  											  tp.t_data->t_infomask2);
  		xlrec.offnum = ItemPointerGetOffsetNumber(&tp.t_self);
  		xlrec.xmax = xid;
  
  		XLogBeginInsert();
  		XLogRegisterData((char *) &xlrec, SizeOfHeapDelete);
  		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
  
  		/* No replica identity & replication origin logged */
  
  		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_DELETE);
  
  		PageSetLSN(page, recptr);
  	}
  
  	END_CRIT_SECTION();
  
  	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  	if (HeapTupleHasExternal(&tp))
  	{
  		Assert(!IsToastRelation(relation));
  		toast_delete(relation, &tp, true);
  	}
  
  	/*
  	 * Never need to mark tuple for invalidation, since catalogs don't support
  	 * speculative insertion
  	 */
  
  	/* Now we can release the buffer */
  	ReleaseBuffer(buffer);
  
  	/* count deletion, as we counted the insertion too */
  	pgstat_count_heap_delete(relation);
  }
  
  /*
   * heap_inplace_update - update a tuple "in place" (ie, overwrite it)
   *
   * Overwriting violates both MVCC and transactional safety, so the uses
   * of this function in Postgres are extremely limited.  Nonetheless we
   * find some places to use it.
   *
   * The tuple cannot change size, and therefore it's reasonable to assume
   * that its null bitmap (if any) doesn't change either.  So we just
   * overwrite the data portion of the tuple without touching the null
   * bitmap or any of the header fields.
   *
   * tuple is an in-memory tuple structure containing the data to be written
   * over the target tuple.  Also, tuple->t_self identifies the target tuple.
   */
  void
  heap_inplace_update(Relation relation, HeapTuple tuple)
  {
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  	uint32		oldlen;
  	uint32		newlen;
  
  	/*
  	 * For now, parallel operations are required to be strictly read-only.
  	 * Unlike a regular update, this should never create a combo CID, so it
  	 * might be possible to relax this restriction, but not without more
  	 * thought and testing.  It's not clear that it would be useful, anyway.
  	 */
  	if (IsInParallelMode())
  		ereport(ERROR,
  				(errcode(ERRCODE_INVALID_TRANSACTION_STATE),
  				 errmsg("cannot update tuples during a parallel operation")));
  
  	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&(tuple->t_self)));
  	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  	page = (Page) BufferGetPage(buffer);
  
  	offnum = ItemPointerGetOffsetNumber(&(tuple->t_self));
  	if (PageGetMaxOffsetNumber(page) >= offnum)
  		lp = PageGetItemId(page, offnum);
  
  	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  		elog(ERROR, "invalid lp");
  
  	htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  	oldlen = ItemIdGetLength(lp) - htup->t_hoff;
  	newlen = tuple->t_len - tuple->t_data->t_hoff;
  	if (oldlen != newlen || htup->t_hoff != tuple->t_data->t_hoff)
  		elog(ERROR, "wrong tuple length");
  
  	/* NO EREPORT(ERROR) from here till changes are logged */
  	START_CRIT_SECTION();
  
  	memcpy((char *) htup + htup->t_hoff,
  		   (char *) tuple->t_data + tuple->t_data->t_hoff,
  		   newlen);
  
  	MarkBufferDirty(buffer);
  
  	/* XLOG stuff */
  	if (RelationNeedsWAL(relation))
  	{
  		xl_heap_inplace xlrec;
  		XLogRecPtr	recptr;
  
  		xlrec.offnum = ItemPointerGetOffsetNumber(&tuple->t_self);
  
  		XLogBeginInsert();
  		XLogRegisterData((char *) &xlrec, SizeOfHeapInplace);
  
  		XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
  		XLogRegisterBufData(0, (char *) htup + htup->t_hoff, newlen);
  
  		/* inplace updates aren't decoded atm, don't log the origin */
  
  		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_INPLACE);
  
  		PageSetLSN(page, recptr);
  	}
  
  	END_CRIT_SECTION();
  
  	UnlockReleaseBuffer(buffer);
  
  	/*
  	 * Send out shared cache inval if necessary.  Note that because we only
  	 * pass the new version of the tuple, this mustn't be used for any
  	 * operations that could change catcache lookup keys.  But we aren't
  	 * bothering with index updates either, so that's true a fortiori.
  	 */
  	if (!IsBootstrapProcessingMode())
  		CacheInvalidateHeapTuple(relation, tuple, NULL);
  }
  
  #define		FRM_NOOP				0x0001
  #define		FRM_INVALIDATE_XMAX		0x0002
  #define		FRM_RETURN_IS_XID		0x0004
  #define		FRM_RETURN_IS_MULTI		0x0008
  #define		FRM_MARK_COMMITTED		0x0010
  
  /*
   * FreezeMultiXactId
   *		Determine what to do during freezing when a tuple is marked by a
   *		MultiXactId.
   *
   * NB -- this might have the side-effect of creating a new MultiXactId!
   *
   * "flags" is an output value; it's used to tell caller what to do on return.
   * Possible flags are:
   * FRM_NOOP
   *		don't do anything -- keep existing Xmax
   * FRM_INVALIDATE_XMAX
   *		mark Xmax as InvalidTransactionId and set XMAX_INVALID flag.
   * FRM_RETURN_IS_XID
   *		The Xid return value is a single update Xid to set as xmax.
   * FRM_MARK_COMMITTED
   *		Xmax can be marked as HEAP_XMAX_COMMITTED
   * FRM_RETURN_IS_MULTI
   *		The return value is a new MultiXactId to set as new Xmax.
   *		(caller must obtain proper infomask bits using GetMultiXactIdHintBits)
   */
  static TransactionId
  FreezeMultiXactId(MultiXactId multi, uint16 t_infomask,
  				  TransactionId relfrozenxid, TransactionId relminmxid,
  				  TransactionId cutoff_xid, MultiXactId cutoff_multi,
  				  uint16 *flags)
  {
  	TransactionId xid = InvalidTransactionId;
  	int			i;
  	MultiXactMember *members;
  	int			nmembers;
  	bool		need_replace;
  	int			nnewmembers;
  	MultiXactMember *newmembers;
  	bool		has_lockers;
  	TransactionId update_xid;
  	bool		update_committed;
  
  	*flags = 0;
  
  	/* We should only be called in Multis */
  	Assert(t_infomask & HEAP_XMAX_IS_MULTI);
  
  	if (!MultiXactIdIsValid(multi) ||
  		HEAP_LOCKED_UPGRADED(t_infomask))
  	{
  		/* Ensure infomask bits are appropriately set/reset */
  		*flags |= FRM_INVALIDATE_XMAX;
  		return InvalidTransactionId;
  	}
  	else if (MultiXactIdPrecedes(multi, relminmxid))
  		ereport(ERROR,
  				(errcode(ERRCODE_DATA_CORRUPTED),
  				 errmsg_internal("found multixact %u from before relminmxid %u",
  								 multi, relminmxid)));
  	else if (MultiXactIdPrecedes(multi, cutoff_multi))
  	{
  		/*
  		 * This old multi cannot possibly have members still running, but
  		 * verify just in case.  If it was a locker only, it can be removed
  		 * without any further consideration; but if it contained an update,
  		 * we might need to preserve it.
  		 */
  		if (MultiXactIdIsRunning(multi,
  								 HEAP_XMAX_IS_LOCKED_ONLY(t_infomask)))
  			ereport(ERROR,
  					(errcode(ERRCODE_DATA_CORRUPTED),
  					 errmsg_internal("multixact %u from before cutoff %u found to be still running",
  									 multi, cutoff_multi)));
  
  		if (HEAP_XMAX_IS_LOCKED_ONLY(t_infomask))
  		{
  			*flags |= FRM_INVALIDATE_XMAX;
  			xid = InvalidTransactionId; /* not strictly necessary */
  		}
  		else
  		{
  			/* replace multi by update xid */
  			xid = MultiXactIdGetUpdateXid(multi, t_infomask);
  
  			/* wasn't only a lock, xid needs to be valid */
  			Assert(TransactionIdIsValid(xid));
  
  			if (TransactionIdPrecedes(xid, relfrozenxid))
  				ereport(ERROR,
  						(errcode(ERRCODE_DATA_CORRUPTED),
  						 errmsg_internal("found update xid %u from before relfrozenxid %u",
  										 xid, relfrozenxid)));
  
  			/*
  			 * If the xid is older than the cutoff, it has to have aborted,
  			 * otherwise the tuple would have gotten pruned away.
  			 */
  			if (TransactionIdPrecedes(xid, cutoff_xid))
  			{
  				if (TransactionIdDidCommit(xid))
  					ereport(ERROR,
  							(errcode(ERRCODE_DATA_CORRUPTED),
  							 errmsg_internal("cannot freeze committed update xid %u", xid)));
  				*flags |= FRM_INVALIDATE_XMAX;
  				xid = InvalidTransactionId; /* not strictly necessary */
  			}
  			else
  			{
  				*flags |= FRM_RETURN_IS_XID;
  			}
  		}
  
  		return xid;
  	}
  
  	/*
  	 * This multixact might have or might not have members still running, but
  	 * we know it's valid and is newer than the cutoff point for multis.
  	 * However, some member(s) of it may be below the cutoff for Xids, so we
  	 * need to walk the whole members array to figure out what to do, if
  	 * anything.
  	 */
  
  	nmembers =
  		GetMultiXactIdMembers(multi, &members, false,
  							  HEAP_XMAX_IS_LOCKED_ONLY(t_infomask));
  	if (nmembers <= 0)
  	{
  		/* Nothing worth keeping */
  		*flags |= FRM_INVALIDATE_XMAX;
  		return InvalidTransactionId;
  	}
  
  	/* is there anything older than the cutoff? */
  	need_replace = false;
  	for (i = 0; i < nmembers; i++)
  	{
  		if (TransactionIdPrecedes(members[i].xid, cutoff_xid))
  		{
  			need_replace = true;
  			break;
  		}
  	}
  
  	/*
  	 * In the simplest case, there is no member older than the cutoff; we can
  	 * keep the existing MultiXactId as is.
  	 */
  	if (!need_replace)
  	{
  		*flags |= FRM_NOOP;
  		pfree(members);
  		return InvalidTransactionId;
  	}
  
  	/*
  	 * If the multi needs to be updated, figure out which members do we need
  	 * to keep.
  	 */
  	nnewmembers = 0;
  	newmembers = palloc(sizeof(MultiXactMember) * nmembers);
  	has_lockers = false;
  	update_xid = InvalidTransactionId;
  	update_committed = false;
  
  	for (i = 0; i < nmembers; i++)
  	{
  		/*
  		 * Determine whether to keep this member or ignore it.
  		 */
  		if (ISUPDATE_from_mxstatus(members[i].status))
  		{
  			TransactionId xid = members[i].xid;
  
  			Assert(TransactionIdIsValid(xid));
  			if (TransactionIdPrecedes(xid, relfrozenxid))
  				ereport(ERROR,
  						(errcode(ERRCODE_DATA_CORRUPTED),
  						 errmsg_internal("found update xid %u from before relfrozenxid %u",
  										 xid, relfrozenxid)));
  
  			/*
  			 * It's an update; should we keep it?  If the transaction is known
  			 * aborted or crashed then it's okay to ignore it, otherwise not.
  			 * Note that an updater older than cutoff_xid cannot possibly be
  			 * committed, because HeapTupleSatisfiesVacuum would have returned
  			 * HEAPTUPLE_DEAD and we would not be trying to freeze the tuple.
  			 *
  			 * As with all tuple visibility routines, it's critical to test
  			 * TransactionIdIsInProgress before TransactionIdDidCommit,
  			 * because of race conditions explained in detail in
  			 * heapam_visibility.c.
  			 */
  			if (TransactionIdIsCurrentTransactionId(xid) ||
  				TransactionIdIsInProgress(xid))
  			{
  				Assert(!TransactionIdIsValid(update_xid));
  				update_xid = xid;
  			}
  			else if (TransactionIdDidCommit(xid))
  			{
  				/*
  				 * The transaction committed, so we can tell caller to set
  				 * HEAP_XMAX_COMMITTED.  (We can only do this because we know
  				 * the transaction is not running.)
  				 */
  				Assert(!TransactionIdIsValid(update_xid));
  				update_committed = true;
  				update_xid = xid;
  			}
  			else
  			{
  				/*
  				 * Not in progress, not committed -- must be aborted or
  				 * crashed; we can ignore it.
  				 */
  			}
  
  			/*
  			 * Since the tuple wasn't marked HEAPTUPLE_DEAD by vacuum, the
  			 * update Xid cannot possibly be older than the xid cutoff. The
  			 * presence of such a tuple would cause corruption, so be paranoid
  			 * and check.
  			 */
  			if (TransactionIdIsValid(update_xid) &&
  				TransactionIdPrecedes(update_xid, cutoff_xid))
  				ereport(ERROR,
  						(errcode(ERRCODE_DATA_CORRUPTED),
  						 errmsg_internal("found update xid %u from before xid cutoff %u",
  										 update_xid, cutoff_xid)));
  
  			/*
  			 * If we determined that it's an Xid corresponding to an update
  			 * that must be retained, additionally add it to the list of
  			 * members of the new Multi, in case we end up using that.  (We
  			 * might still decide to use only an update Xid and not a multi,
  			 * but it's easier to maintain the list as we walk the old members
  			 * list.)
  			 */
  			if (TransactionIdIsValid(update_xid))
  				newmembers[nnewmembers++] = members[i];
  		}
  		else
  		{
  			/* We only keep lockers if they are still running */
  			if (TransactionIdIsCurrentTransactionId(members[i].xid) ||
  				TransactionIdIsInProgress(members[i].xid))
  			{
  				/* running locker cannot possibly be older than the cutoff */
  				Assert(!TransactionIdPrecedes(members[i].xid, cutoff_xid));
  				newmembers[nnewmembers++] = members[i];
  				has_lockers = true;
  			}
  		}
  	}
  
  	pfree(members);
  
  	if (nnewmembers == 0)
  	{
  		/* nothing worth keeping!? Tell caller to remove the whole thing */
  		*flags |= FRM_INVALIDATE_XMAX;
  		xid = InvalidTransactionId;
  	}
  	else if (TransactionIdIsValid(update_xid) && !has_lockers)
  	{
  		/*
  		 * If there's a single member and it's an update, pass it back alone
  		 * without creating a new Multi.  (XXX we could do this when there's a
  		 * single remaining locker, too, but that would complicate the API too
  		 * much; moreover, the case with the single updater is more
  		 * interesting, because those are longer-lived.)
  		 */
  		Assert(nnewmembers == 1);
  		*flags |= FRM_RETURN_IS_XID;
  		if (update_committed)
  			*flags |= FRM_MARK_COMMITTED;
  		xid = update_xid;
  	}
  	else
  	{
  		/*
  		 * Create a new multixact with the surviving members of the previous
  		 * one, to set as new Xmax in the tuple.
  		 */
  		xid = MultiXactIdCreateFromMembers(nnewmembers, newmembers);
  		*flags |= FRM_RETURN_IS_MULTI;
  	}
  
  	pfree(newmembers);
  
  	return xid;
  }
  
  /*
   * heap_prepare_freeze_tuple
   *
   * Check to see whether any of the XID fields of a tuple (xmin, xmax, xvac)
   * are older than the specified cutoff XID and cutoff MultiXactId.  If so,
   * setup enough state (in the *frz output argument) to later execute and
   * WAL-log what we would need to do, and return true.  Return false if nothing
   * is to be changed.  In addition, set *totally_frozen_p to true if the tuple
   * will be totally frozen after these operations are performed and false if
   * more freezing will eventually be required.
   *
   * Caller is responsible for setting the offset field, if appropriate.
   *
   * It is assumed that the caller has checked the tuple with
   * HeapTupleSatisfiesVacuum() and determined that it is not HEAPTUPLE_DEAD
   * (else we should be removing the tuple, not freezing it).
   *
   * NB: cutoff_xid *must* be <= the current global xmin, to ensure that any
   * XID older than it could neither be running nor seen as running by any
   * open transaction.  This ensures that the replacement will not change
   * anyone's idea of the tuple state.
   * Similarly, cutoff_multi must be less than or equal to the smallest
   * MultiXactId used by any transaction currently open.
   *
   * If the tuple is in a shared buffer, caller must hold an exclusive lock on
   * that buffer.
   *
   * NB: It is not enough to set hint bits to indicate something is
   * committed/invalid -- they might not be set on a standby, or after crash
   * recovery.  We really need to remove old xids.
   */
  bool
  heap_prepare_freeze_tuple(HeapTupleHeader tuple,
  						  TransactionId relfrozenxid, TransactionId relminmxid,
  						  TransactionId cutoff_xid, TransactionId cutoff_multi,
  						  xl_heap_freeze_tuple *frz, bool *totally_frozen_p)
  {
  	bool		changed = false;
  	bool		xmax_already_frozen = false;
  	bool		xmin_frozen;
  	bool		freeze_xmax;
  	TransactionId xid;
  
  	frz->frzflags = 0;
  	frz->t_infomask2 = tuple->t_infomask2;
  	frz->t_infomask = tuple->t_infomask;
  	frz->xmax = HeapTupleHeaderGetRawXmax(tuple);
  
  	/*
  	 * Process xmin.  xmin_frozen has two slightly different meanings: in the
  	 * !XidIsNormal case, it means "the xmin doesn't need any freezing" (it's
  	 * already a permanent value), while in the block below it is set true to
  	 * mean "xmin won't need freezing after what we do to it here" (false
  	 * otherwise).  In both cases we're allowed to set totally_frozen, as far
  	 * as xmin is concerned.
  	 */
  	xid = HeapTupleHeaderGetXmin(tuple);
  	if (!TransactionIdIsNormal(xid))
  		xmin_frozen = true;
  	else
  	{
  		if (TransactionIdPrecedes(xid, relfrozenxid))
  			ereport(ERROR,
  					(errcode(ERRCODE_DATA_CORRUPTED),
  					 errmsg_internal("found xmin %u from before relfrozenxid %u",
  									 xid, relfrozenxid)));
  
  		xmin_frozen = TransactionIdPrecedes(xid, cutoff_xid);
  		if (xmin_frozen)
  		{
  			if (!TransactionIdDidCommit(xid))
  				ereport(ERROR,
  						(errcode(ERRCODE_DATA_CORRUPTED),
  						 errmsg_internal("uncommitted xmin %u from before xid cutoff %u needs to be frozen",
  										 xid, cutoff_xid)));
  
  			frz->t_infomask |= HEAP_XMIN_FROZEN;
  			changed = true;
  			xmin_frozen = true;
  		}
  	}
  
  	/*
  	 * Process xmax.  To thoroughly examine the current Xmax value we need to
  	 * resolve a MultiXactId to its member Xids, in case some of them are
  	 * below the given cutoff for Xids.  In that case, those values might need
  	 * freezing, too.  Also, if a multi needs freezing, we cannot simply take
  	 * it out --- if there's a live updater Xid, it needs to be kept.
  	 *
  	 * Make sure to keep heap_tuple_needs_freeze in sync with this.
  	 */
  	xid = HeapTupleHeaderGetRawXmax(tuple);
  
  	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
  	{
  		TransactionId newxmax;
  		uint16		flags;
  
  		newxmax = FreezeMultiXactId(xid, tuple->t_infomask,
  									relfrozenxid, relminmxid,
  									cutoff_xid, cutoff_multi, &flags);
  
  		freeze_xmax = (flags & FRM_INVALIDATE_XMAX);
  
  		if (flags & FRM_RETURN_IS_XID)
  		{
  			/*
  			 * NB -- some of these transformations are only valid because we
  			 * know the return Xid is a tuple updater (i.e. not merely a
  			 * locker.) Also note that the only reason we don't explicitly
  			 * worry about HEAP_KEYS_UPDATED is because it lives in
  			 * t_infomask2 rather than t_infomask.
  			 */
  			frz->t_infomask &= ~HEAP_XMAX_BITS;
  			frz->xmax = newxmax;
  			if (flags & FRM_MARK_COMMITTED)
  				frz->t_infomask |= HEAP_XMAX_COMMITTED;
  			changed = true;
  		}
  		else if (flags & FRM_RETURN_IS_MULTI)
  		{
  			uint16		newbits;
  			uint16		newbits2;
  
  			/*
  			 * We can't use GetMultiXactIdHintBits directly on the new multi
  			 * here; that routine initializes the masks to all zeroes, which
  			 * would lose other bits we need.  Doing it this way ensures all
  			 * unrelated bits remain untouched.
  			 */
  			frz->t_infomask &= ~HEAP_XMAX_BITS;
  			frz->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  			GetMultiXactIdHintBits(newxmax, &newbits, &newbits2);
  			frz->t_infomask |= newbits;
  			frz->t_infomask2 |= newbits2;
  
  			frz->xmax = newxmax;
  
  			changed = true;
  		}
  	}
  	else if (TransactionIdIsNormal(xid))
  	{
  		if (TransactionIdPrecedes(xid, relfrozenxid))
  			ereport(ERROR,
  					(errcode(ERRCODE_DATA_CORRUPTED),
  					 errmsg_internal("found xmax %u from before relfrozenxid %u",
  									 xid, relfrozenxid)));
  
  		if (TransactionIdPrecedes(xid, cutoff_xid))
  		{
  			/*
  			 * If we freeze xmax, make absolutely sure that it's not an XID
  			 * that is important.  (Note, a lock-only xmax can be removed
  			 * independent of committedness, since a committed lock holder has
  			 * released the lock).
  			 */
  			if (!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask) &&
  				TransactionIdDidCommit(xid))
  				ereport(ERROR,
  						(errcode(ERRCODE_DATA_CORRUPTED),
  						 errmsg_internal("cannot freeze committed xmax %u",
  										 xid)));
  			freeze_xmax = true;
  		}
  		else
  			freeze_xmax = false;
  	}
  	else if ((tuple->t_infomask & HEAP_XMAX_INVALID) ||
  			 !TransactionIdIsValid(HeapTupleHeaderGetRawXmax(tuple)))
  	{
  		freeze_xmax = false;
  		xmax_already_frozen = true;
  	}
  	else
  		ereport(ERROR,
  				(errcode(ERRCODE_DATA_CORRUPTED),
  				 errmsg_internal("found xmax %u (infomask 0x%04x) not frozen, not multi, not normal",
  								 xid, tuple->t_infomask)));
  
  	if (freeze_xmax)
  	{
  		Assert(!xmax_already_frozen);
  
  		frz->xmax = InvalidTransactionId;
  
  		/*
  		 * The tuple might be marked either XMAX_INVALID or XMAX_COMMITTED +
  		 * LOCKED.  Normalize to INVALID just to be sure no one gets confused.
  		 * Also get rid of the HEAP_KEYS_UPDATED bit.
  		 */
  		frz->t_infomask &= ~HEAP_XMAX_BITS;
  		frz->t_infomask |= HEAP_XMAX_INVALID;
  		frz->t_infomask2 &= ~HEAP_HOT_UPDATED;
  		frz->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  		changed = true;
  	}
  
  	/*
  	 * Old-style VACUUM FULL is gone, but we have to keep this code as long as
  	 * we support having MOVED_OFF/MOVED_IN tuples in the database.
  	 */
  	if (tuple->t_infomask & HEAP_MOVED)
  	{
  		xid = HeapTupleHeaderGetXvac(tuple);
  
  		/*
  		 * For Xvac, we ignore the cutoff_xid and just always perform the
  		 * freeze operation.  The oldest release in which such a value can
  		 * actually be set is PostgreSQL 8.4, because old-style VACUUM FULL
  		 * was removed in PostgreSQL 9.0.  Note that if we were to respect
  		 * cutoff_xid here, we'd need to make surely to clear totally_frozen
  		 * when we skipped freezing on that basis.
  		 */
  		if (TransactionIdIsNormal(xid))
  		{
  			/*
  			 * If a MOVED_OFF tuple is not dead, the xvac transaction must
  			 * have failed; whereas a non-dead MOVED_IN tuple must mean the
  			 * xvac transaction succeeded.
  			 */
  			if (tuple->t_infomask & HEAP_MOVED_OFF)
  				frz->frzflags |= XLH_INVALID_XVAC;
  			else
  				frz->frzflags |= XLH_FREEZE_XVAC;
  
  			/*
  			 * Might as well fix the hint bits too; usually XMIN_COMMITTED
  			 * will already be set here, but there's a small chance not.
  			 */
  			Assert(!(tuple->t_infomask & HEAP_XMIN_INVALID));
  			frz->t_infomask |= HEAP_XMIN_COMMITTED;
  			changed = true;
  		}
  	}
  
  	*totally_frozen_p = (xmin_frozen &&
  						 (freeze_xmax || xmax_already_frozen));
  	return changed;
  }
  
  /*
   * heap_execute_freeze_tuple
   *		Execute the prepared freezing of a tuple.
   *
   * Caller is responsible for ensuring that no other backend can access the
   * storage underlying this tuple, either by holding an exclusive lock on the
   * buffer containing it (which is what lazy VACUUM does), or by having it be
   * in private storage (which is what CLUSTER and friends do).
   *
   * Note: it might seem we could make the changes without exclusive lock, since
   * TransactionId read/write is assumed atomic anyway.  However there is a race
   * condition: someone who just fetched an old XID that we overwrite here could
   * conceivably not finish checking the XID against pg_xact before we finish
   * the VACUUM and perhaps truncate off the part of pg_xact he needs.  Getting
   * exclusive lock ensures no other backend is in process of checking the
   * tuple status.  Also, getting exclusive lock makes it safe to adjust the
   * infomask bits.
   *
   * NB: All code in here must be safe to execute during crash recovery!
   */
  void
  heap_execute_freeze_tuple(HeapTupleHeader tuple, xl_heap_freeze_tuple *frz)
  {
  	HeapTupleHeaderSetXmax(tuple, frz->xmax);
  
  	if (frz->frzflags & XLH_FREEZE_XVAC)
  		HeapTupleHeaderSetXvac(tuple, FrozenTransactionId);
  
  	if (frz->frzflags & XLH_INVALID_XVAC)
  		HeapTupleHeaderSetXvac(tuple, InvalidTransactionId);
  
  	tuple->t_infomask = frz->t_infomask;
  	tuple->t_infomask2 = frz->t_infomask2;
  }
  
  /*
   * heap_freeze_tuple
   *		Freeze tuple in place, without WAL logging.
   *
   * Useful for callers like CLUSTER that perform their own WAL logging.
   */
  bool
  heap_freeze_tuple(HeapTupleHeader tuple,
  				  TransactionId relfrozenxid, TransactionId relminmxid,
  				  TransactionId cutoff_xid, TransactionId cutoff_multi)
  {
  	xl_heap_freeze_tuple frz;
  	bool		do_freeze;
  	bool		tuple_totally_frozen;
  
  	do_freeze = heap_prepare_freeze_tuple(tuple,
  										  relfrozenxid, relminmxid,
  										  cutoff_xid, cutoff_multi,
  										  &frz, &tuple_totally_frozen);
  
  	/*
  	 * Note that because this is not a WAL-logged operation, we don't need to
  	 * fill in the offset in the freeze record.
  	 */
  
  	if (do_freeze)
  		heap_execute_freeze_tuple(tuple, &frz);
  	return do_freeze;
  }
  
  /*
   * For a given MultiXactId, return the hint bits that should be set in the
   * tuple's infomask.
   *
   * Normally this should be called for a multixact that was just created, and
   * so is on our local cache, so the GetMembers call is fast.
   */
  static void
  GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
  					   uint16 *new_infomask2)
  {
  	int			nmembers;
  	MultiXactMember *members;
  	int			i;
  	uint16		bits = HEAP_XMAX_IS_MULTI;
  	uint16		bits2 = 0;
  	bool		has_update = false;
  	LockTupleMode strongest = LockTupleKeyShare;
  
  	/*
  	 * We only use this in multis we just created, so they cannot be values
  	 * pre-pg_upgrade.
  	 */
  	nmembers = GetMultiXactIdMembers(multi, &members, false, false);
  
  	for (i = 0; i < nmembers; i++)
  	{
  		LockTupleMode mode;
  
  		/*
  		 * Remember the strongest lock mode held by any member of the
  		 * multixact.
  		 */
  		mode = TUPLOCK_from_mxstatus(members[i].status);
  		if (mode > strongest)
  			strongest = mode;
  
  		/* See what other bits we need */
  		switch (members[i].status)
  		{
  			case MultiXactStatusForKeyShare:
  			case MultiXactStatusForShare:
  			case MultiXactStatusForNoKeyUpdate:
  				break;
  
  			case MultiXactStatusForUpdate:
  				bits2 |= HEAP_KEYS_UPDATED;
  				break;
  
  			case MultiXactStatusNoKeyUpdate:
  				has_update = true;
  				break;
  
  			case MultiXactStatusUpdate:
  				bits2 |= HEAP_KEYS_UPDATED;
  				has_update = true;
  				break;
  		}
  	}
  
  	if (strongest == LockTupleExclusive ||
  		strongest == LockTupleNoKeyExclusive)
  		bits |= HEAP_XMAX_EXCL_LOCK;
  	else if (strongest == LockTupleShare)
  		bits |= HEAP_XMAX_SHR_LOCK;
  	else if (strongest == LockTupleKeyShare)
  		bits |= HEAP_XMAX_KEYSHR_LOCK;
  
  	if (!has_update)
  		bits |= HEAP_XMAX_LOCK_ONLY;
  
  	if (nmembers > 0)
  		pfree(members);
  
  	*new_infomask = bits;
  	*new_infomask2 = bits2;
  }
  
  /*
   * MultiXactIdGetUpdateXid
   *
   * Given a multixact Xmax and corresponding infomask, which does not have the
   * HEAP_XMAX_LOCK_ONLY bit set, obtain and return the Xid of the updating
   * transaction.
   *
   * Caller is expected to check the status of the updating transaction, if
   * necessary.
   */
  static TransactionId
  MultiXactIdGetUpdateXid(TransactionId xmax, uint16 t_infomask)
  {
  	TransactionId update_xact = InvalidTransactionId;
  	MultiXactMember *members;
  	int			nmembers;
  
  	Assert(!(t_infomask & HEAP_XMAX_LOCK_ONLY));
  	Assert(t_infomask & HEAP_XMAX_IS_MULTI);
  
  	/*
  	 * Since we know the LOCK_ONLY bit is not set, this cannot be a multi from
  	 * pre-pg_upgrade.
  	 */
  	nmembers = GetMultiXactIdMembers(xmax, &members, false, false);
  
  	if (nmembers > 0)
  	{
  		int			i;
  
  		for (i = 0; i < nmembers; i++)
  		{
  			/* Ignore lockers */
  			if (!ISUPDATE_from_mxstatus(members[i].status))
  				continue;
  
  			/* there can be at most one updater */
  			Assert(update_xact == InvalidTransactionId);
  			update_xact = members[i].xid;
  #ifndef USE_ASSERT_CHECKING
  
  			/*
  			 * in an assert-enabled build, walk the whole array to ensure
  			 * there's no other updater.
  			 */
  			break;
  #endif
  		}
  
  		pfree(members);
  	}
  
  	return update_xact;
  }
  
  /*
   * HeapTupleGetUpdateXid
   *		As above, but use a HeapTupleHeader
   *
   * See also HeapTupleHeaderGetUpdateXid, which can be used without previously
   * checking the hint bits.
   */
  TransactionId
  HeapTupleGetUpdateXid(HeapTupleHeader tuple)
  {
  	return MultiXactIdGetUpdateXid(HeapTupleHeaderGetRawXmax(tuple),
  								   tuple->t_infomask);
  }
  
  /*
   * Does the given multixact conflict with the current transaction grabbing a
   * tuple lock of the given strength?
   *
   * The passed infomask pairs up with the given multixact in the tuple header.
   *
   * If current_is_member is not NULL, it is set to 'true' if the current
   * transaction is a member of the given multixact.
   */
  static bool
  DoesMultiXactIdConflict(MultiXactId multi, uint16 infomask,
  						LockTupleMode lockmode, bool *current_is_member)
  {
  	int			nmembers;
  	MultiXactMember *members;
  	bool	result = false;
  	LOCKMODE wanted = tupleLockExtraInfo[lockmode].hwlock;
  
  	if (HEAP_LOCKED_UPGRADED(infomask))
  		return false;
  
  	nmembers = GetMultiXactIdMembers(multi, &members, false,
  									 HEAP_XMAX_IS_LOCKED_ONLY(infomask));
  	if (nmembers >= 0)
  	{
  		int			i;
  
  		for (i = 0; i < nmembers; i++)
  		{
  			TransactionId memxid;
  			LOCKMODE	memlockmode;
  
  			if (result && (current_is_member == NULL || *current_is_member))
  				break;
  
  			memlockmode = LOCKMODE_from_mxstatus(members[i].status);
  
  			/* ignore members from current xact (but track their presence) */
  			memxid = members[i].xid;
  			if (TransactionIdIsCurrentTransactionId(memxid))
  			{
  				if (current_is_member != NULL)
  					*current_is_member = true;
  				continue;
  			}
  			else if (result)
  				continue;
  
  			/* ignore members that don't conflict with the lock we want */
  			if (!DoLockModesConflict(memlockmode, wanted))
  				continue;
  
  			if (ISUPDATE_from_mxstatus(members[i].status))
  			{
  				/* ignore aborted updaters */
  				if (TransactionIdDidAbort(memxid))
  					continue;
  			}
  			else
  			{
  				/* ignore lockers-only that are no longer in progress */
  				if (!TransactionIdIsInProgress(memxid))
  					continue;
  			}
  
  			/*
  			 * Whatever remains are either live lockers that conflict with our
  			 * wanted lock, and updaters that are not aborted.  Those conflict
  			 * with what we want.  Set up to return true, but keep going to
  			 * look for the current transaction among the multixact members,
  			 * if needed.
  			 */
  			result = true;
  		}
  		pfree(members);
  	}
  
  	return result;
  }
  
  /*
   * Do_MultiXactIdWait
   *		Actual implementation for the two functions below.
   *
   * 'multi', 'status' and 'infomask' indicate what to sleep on (the status is
   * needed to ensure we only sleep on conflicting members, and the infomask is
   * used to optimize multixact access in case it's a lock-only multi); 'nowait'
   * indicates whether to use conditional lock acquisition, to allow callers to
   * fail if lock is unavailable.  'rel', 'ctid' and 'oper' are used to set up
   * context information for error messages.  'remaining', if not NULL, receives
   * the number of members that are still running, including any (non-aborted)
   * subtransactions of our own transaction.
   *
   * We do this by sleeping on each member using XactLockTableWait.  Any
   * members that belong to the current backend are *not* waited for, however;
   * this would not merely be useless but would lead to Assert failure inside
   * XactLockTableWait.  By the time this returns, it is certain that all
   * transactions *of other backends* that were members of the MultiXactId
   * that conflict with the requested status are dead (and no new ones can have
   * been added, since it is not legal to add members to an existing
   * MultiXactId).
   *
   * But by the time we finish sleeping, someone else may have changed the Xmax
   * of the containing tuple, so the caller needs to iterate on us somehow.
   *
   * Note that in case we return false, the number of remaining members is
   * not to be trusted.
   */
  static bool
  Do_MultiXactIdWait(MultiXactId multi, MultiXactStatus status,
  				   uint16 infomask, bool nowait,
  				   Relation rel, ItemPointer ctid, XLTW_Oper oper,
  				   int *remaining)
  {
  	bool		result = true;
  	MultiXactMember *members;
  	int			nmembers;
  	int			remain = 0;
  
  	/* for pre-pg_upgrade tuples, no need to sleep at all */
  	nmembers = HEAP_LOCKED_UPGRADED(infomask) ? -1 :
  		GetMultiXactIdMembers(multi, &members, false,
  							  HEAP_XMAX_IS_LOCKED_ONLY(infomask));
  
  	if (nmembers >= 0)
  	{
  		int			i;
  
  		for (i = 0; i < nmembers; i++)
  		{
  			TransactionId memxid = members[i].xid;
  			MultiXactStatus memstatus = members[i].status;
  
  			if (TransactionIdIsCurrentTransactionId(memxid))
  			{
  				remain++;
  				continue;
  			}
  
  			if (!DoLockModesConflict(LOCKMODE_from_mxstatus(memstatus),
  									 LOCKMODE_from_mxstatus(status)))
  			{
  				if (remaining && TransactionIdIsInProgress(memxid))
  					remain++;
  				continue;
  			}
  
  			/*
  			 * This member conflicts with our multi, so we have to sleep (or
  			 * return failure, if asked to avoid waiting.)
  			 *
  			 * Note that we don't set up an error context callback ourselves,
  			 * but instead we pass the info down to XactLockTableWait.  This
  			 * might seem a bit wasteful because the context is set up and
  			 * tore down for each member of the multixact, but in reality it
  			 * should be barely noticeable, and it avoids duplicate code.
  			 */
  			if (nowait)
  			{
  				result = ConditionalXactLockTableWait(memxid);
  				if (!result)
  					break;
  			}
  			else
  				XactLockTableWait(memxid, rel, ctid, oper);
  		}
  
  		pfree(members);
  	}
  
  	if (remaining)
  		*remaining = remain;
  
  	return result;
  }
  
  /*
   * MultiXactIdWait
   *		Sleep on a MultiXactId.
   *
   * By the time we finish sleeping, someone else may have changed the Xmax
   * of the containing tuple, so the caller needs to iterate on us somehow.
   *
   * We return (in *remaining, if not NULL) the number of members that are still
   * running, including any (non-aborted) subtransactions of our own transaction.
   */
  static void
  MultiXactIdWait(MultiXactId multi, MultiXactStatus status, uint16 infomask,
  				Relation rel, ItemPointer ctid, XLTW_Oper oper,
  				int *remaining)
  {
  	(void) Do_MultiXactIdWait(multi, status, infomask, false,
  							  rel, ctid, oper, remaining);
  }
  
  /*
   * ConditionalMultiXactIdWait
   *		As above, but only lock if we can get the lock without blocking.
   *
   * By the time we finish sleeping, someone else may have changed the Xmax
   * of the containing tuple, so the caller needs to iterate on us somehow.
   *
   * If the multixact is now all gone, return true.  Returns false if some
   * transactions might still be running.
   *
   * We return (in *remaining, if not NULL) the number of members that are still
   * running, including any (non-aborted) subtransactions of our own transaction.
   */
  static bool
  ConditionalMultiXactIdWait(MultiXactId multi, MultiXactStatus status,
  						   uint16 infomask, Relation rel, int *remaining)
  {
  	return Do_MultiXactIdWait(multi, status, infomask, true,
  							  rel, NULL, XLTW_None, remaining);
  }
  
  /*
   * heap_tuple_needs_eventual_freeze
   *
   * Check to see whether any of the XID fields of a tuple (xmin, xmax, xvac)
   * will eventually require freezing.  Similar to heap_tuple_needs_freeze,
   * but there's no cutoff, since we're trying to figure out whether freezing
   * will ever be needed, not whether it's needed now.
   */
  bool
  heap_tuple_needs_eventual_freeze(HeapTupleHeader tuple)
  {
  	TransactionId xid;
  
  	/*
  	 * If xmin is a normal transaction ID, this tuple is definitely not
  	 * frozen.
  	 */
  	xid = HeapTupleHeaderGetXmin(tuple);
  	if (TransactionIdIsNormal(xid))
  		return true;
  
  	/*
  	 * If xmax is a valid xact or multixact, this tuple is also not frozen.
  	 */
  	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
  	{
  		MultiXactId multi;
  
  		multi = HeapTupleHeaderGetRawXmax(tuple);
  		if (MultiXactIdIsValid(multi))
  			return true;
  	}
  	else
  	{
  		xid = HeapTupleHeaderGetRawXmax(tuple);
  		if (TransactionIdIsNormal(xid))
  			return true;
  	}
  
  	if (tuple->t_infomask & HEAP_MOVED)
  	{
  		xid = HeapTupleHeaderGetXvac(tuple);
  		if (TransactionIdIsNormal(xid))
  			return true;
  	}
  
  	return false;
  }
  
  /*
   * heap_tuple_needs_freeze
   *
   * Check to see whether any of the XID fields of a tuple (xmin, xmax, xvac)
   * are older than the specified cutoff XID or MultiXactId.  If so, return true.
   *
   * It doesn't matter whether the tuple is alive or dead, we are checking
   * to see if a tuple needs to be removed or frozen to avoid wraparound.
   *
   * NB: Cannot rely on hint bits here, they might not be set after a crash or
   * on a standby.
   */
  bool
  heap_tuple_needs_freeze(HeapTupleHeader tuple, TransactionId cutoff_xid,
  						MultiXactId cutoff_multi, Buffer buf)
  {
  	TransactionId xid;
  
  	xid = HeapTupleHeaderGetXmin(tuple);
  	if (TransactionIdIsNormal(xid) &&
  		TransactionIdPrecedes(xid, cutoff_xid))
  		return true;
  
  	/*
  	 * The considerations for multixacts are complicated; look at
  	 * heap_prepare_freeze_tuple for justifications.  This routine had better
  	 * be in sync with that one!
  	 */
  	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
  	{
  		MultiXactId multi;
  
  		multi = HeapTupleHeaderGetRawXmax(tuple);
  		if (!MultiXactIdIsValid(multi))
  		{
  			/* no xmax set, ignore */
  			;
  		}
  		else if (HEAP_LOCKED_UPGRADED(tuple->t_infomask))
  			return true;
  		else if (MultiXactIdPrecedes(multi, cutoff_multi))
  			return true;
  		else
  		{
  			MultiXactMember *members;
  			int			nmembers;
  			int			i;
  
  			/* need to check whether any member of the mxact is too old */
  
  			nmembers = GetMultiXactIdMembers(multi, &members, false,
  											 HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask));
  
  			for (i = 0; i < nmembers; i++)
  			{
  				if (TransactionIdPrecedes(members[i].xid, cutoff_xid))
  				{
  					pfree(members);
  					return true;
  				}
  			}
  			if (nmembers > 0)
  				pfree(members);
  		}
  	}
  	else
  	{
  		xid = HeapTupleHeaderGetRawXmax(tuple);
  		if (TransactionIdIsNormal(xid) &&
  			TransactionIdPrecedes(xid, cutoff_xid))
  			return true;
  	}
  
  	if (tuple->t_infomask & HEAP_MOVED)
  	{
  		xid = HeapTupleHeaderGetXvac(tuple);
  		if (TransactionIdIsNormal(xid) &&
  			TransactionIdPrecedes(xid, cutoff_xid))
  			return true;
  	}
  
  	return false;
  }
  
  /*
   * If 'tuple' contains any visible XID greater than latestRemovedXid,
   * ratchet forwards latestRemovedXid to the greatest one found.
   * This is used as the basis for generating Hot Standby conflicts, so
   * if a tuple was never visible then removing it should not conflict
   * with queries.
   */
  void
  HeapTupleHeaderAdvanceLatestRemovedXid(HeapTupleHeader tuple,
  									   TransactionId *latestRemovedXid)
  {
  	TransactionId xmin = HeapTupleHeaderGetXmin(tuple);
  	TransactionId xmax = HeapTupleHeaderGetUpdateXid(tuple);
  	TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
  
  	if (tuple->t_infomask & HEAP_MOVED)
  	{
  		if (TransactionIdPrecedes(*latestRemovedXid, xvac))
  			*latestRemovedXid = xvac;
  	}
  
  	/*
  	 * Ignore tuples inserted by an aborted transaction or if the tuple was
  	 * updated/deleted by the inserting transaction.
  	 *
  	 * Look for a committed hint bit, or if no xmin bit is set, check clog.
  	 * This needs to work on both master and standby, where it is used to
  	 * assess btree delete records.
  	 */
  	if (HeapTupleHeaderXminCommitted(tuple) ||
  		(!HeapTupleHeaderXminInvalid(tuple) && TransactionIdDidCommit(xmin)))
  	{
  		if (xmax != xmin &&
  			TransactionIdFollows(xmax, *latestRemovedXid))
  			*latestRemovedXid = xmax;
  	}
  
  	/* *latestRemovedXid may still be invalid at end */
  }
  
  #ifdef USE_PREFETCH
  /*
   * Helper function for heap_compute_xid_horizon_for_tuples.  Issue prefetch
   * requests for the number of buffers indicated by prefetch_count.  The
   * prefetch_state keeps track of all the buffers that we can prefetch and
   * which ones have already been prefetched; each call to this function picks
   * up where the previous call left off.
   */
  static void
  xid_horizon_prefetch_buffer(Relation rel,
  							XidHorizonPrefetchState *prefetch_state,
  							int prefetch_count)
  {
  	BlockNumber cur_hblkno = prefetch_state->cur_hblkno;
  	int			count = 0;
  	int			i;
  	int			nitems = prefetch_state->nitems;
  	ItemPointerData *tids = prefetch_state->tids;
  
  	for (i = prefetch_state->next_item;
  		 i < nitems && count < prefetch_count;
  		 i++)
  	{
  		ItemPointer htid = &tids[i];
  
  		if (cur_hblkno == InvalidBlockNumber ||
  			ItemPointerGetBlockNumber(htid) != cur_hblkno)
  		{
  			cur_hblkno = ItemPointerGetBlockNumber(htid);
  			PrefetchBuffer(rel, MAIN_FORKNUM, cur_hblkno);
  			count++;
  		}
  	}
  
  	/*
  	 * Save the prefetch position so that next time we can continue from that
  	 * position.
  	 */
  	prefetch_state->next_item = i;
  	prefetch_state->cur_hblkno = cur_hblkno;
  }
  #endif
  
  /*
   * Get the latestRemovedXid from the heap pages pointed at by the index
   * tuples being deleted.
   *
   * We used to do this during recovery rather than on the primary, but that
   * approach now appears inferior.  It meant that the master could generate
   * a lot of work for the standby without any back-pressure to slow down the
   * master, and it required the standby to have reached consistency, whereas
   * we want to have correct information available even before that point.
   *
   * It's possible for this to generate a fair amount of I/O, since we may be
   * deleting hundreds of tuples from a single index block.  To amortize that
   * cost to some degree, this uses prefetching and combines repeat accesses to
   * the same block.
   */
  TransactionId
  heap_compute_xid_horizon_for_tuples(Relation rel,
  									ItemPointerData *tids,
  									int nitems)
  {
  	TransactionId latestRemovedXid = InvalidTransactionId;
  	BlockNumber hblkno;
  	Buffer		buf = InvalidBuffer;
  	Page		hpage;
  #ifdef USE_PREFETCH
  	XidHorizonPrefetchState prefetch_state;
  	int			io_concurrency;
  	int			prefetch_distance;
  #endif
  
  	/*
  	 * Sort to avoid repeated lookups for the same page, and to make it more
  	 * likely to access items in an efficient order. In particular, this
  	 * ensures that if there are multiple pointers to the same page, they all
  	 * get processed looking up and locking the page just once.
  	 */
  	qsort((void *) tids, nitems, sizeof(ItemPointerData),
  		  (int (*) (const void *, const void *)) ItemPointerCompare);
  
  #ifdef USE_PREFETCH
  	/* Initialize prefetch state. */
  	prefetch_state.cur_hblkno = InvalidBlockNumber;
  	prefetch_state.next_item = 0;
  	prefetch_state.nitems = nitems;
  	prefetch_state.tids = tids;
  
  	/*
  	 * Compute the prefetch distance that we will attempt to maintain.
  	 *
  	 * We don't use the regular formula to determine how much to prefetch
  	 * here, but instead just add a constant to effective_io_concurrency.
  	 * That's because it seems best to do some prefetching here even when
  	 * effective_io_concurrency is set to 0, but if the DBA thinks it's OK to
  	 * do more prefetching for other operations, then it's probably OK to do
  	 * more prefetching in this case, too. It may be that this formula is too
  	 * simplistic, but at the moment there is no evidence of that or any idea
  	 * about what would work better.
  	 *
  	 * Since the caller holds a buffer lock somewhere in rel, we'd better make
  	 * sure that isn't a catalog relation before we call code that does
  	 * syscache lookups, to avoid risk of deadlock.
  	 */
  	if (IsCatalogRelation(rel))
  		io_concurrency = effective_io_concurrency;
  	else
  		io_concurrency = get_tablespace_io_concurrency(rel->rd_rel->reltablespace);
  	prefetch_distance = Min((io_concurrency) + 10, MAX_IO_CONCURRENCY);
  
  	/* Start prefetching. */
  	xid_horizon_prefetch_buffer(rel, &prefetch_state, prefetch_distance);
  #endif
  
  	/* Iterate over all tids, and check their horizon */
  	hblkno = InvalidBlockNumber;
  	hpage = NULL;
  	for (int i = 0; i < nitems; i++)
  	{
  		ItemPointer htid = &tids[i];
  		ItemId		hitemid;
  		OffsetNumber hoffnum;
  
  		/*
  		 * Read heap buffer, but avoid refetching if it's the same block as
  		 * required for the last tid.
  		 */
  		if (hblkno == InvalidBlockNumber ||
  			ItemPointerGetBlockNumber(htid) != hblkno)
  		{
  			/* release old buffer */
  			if (BufferIsValid(buf))
  			{
  				LockBuffer(buf, BUFFER_LOCK_UNLOCK);
  				ReleaseBuffer(buf);
  			}
  
  			hblkno = ItemPointerGetBlockNumber(htid);
  
  			buf = ReadBuffer(rel, hblkno);
  
  #ifdef USE_PREFETCH
  
  			/*
  			 * To maintain the prefetch distance, prefetch one more page for
  			 * each page we read.
  			 */
  			xid_horizon_prefetch_buffer(rel, &prefetch_state, 1);
  #endif
  
  			hpage = BufferGetPage(buf);
  
  			LockBuffer(buf, BUFFER_LOCK_SHARE);
  		}
  
  		hoffnum = ItemPointerGetOffsetNumber(htid);
  		hitemid = PageGetItemId(hpage, hoffnum);
  
  		/*
  		 * Follow any redirections until we find something useful.
  		 */
  		while (ItemIdIsRedirected(hitemid))
  		{
  			hoffnum = ItemIdGetRedirect(hitemid);
  			hitemid = PageGetItemId(hpage, hoffnum);
  			CHECK_FOR_INTERRUPTS();
  		}
  
  		/*
  		 * If the heap item has storage, then read the header and use that to
  		 * set latestRemovedXid.
  		 *
  		 * Some LP_DEAD items may not be accessible, so we ignore them.
  		 */
  		if (ItemIdHasStorage(hitemid))
  		{
  			HeapTupleHeader htuphdr;
  
  			htuphdr = (HeapTupleHeader) PageGetItem(hpage, hitemid);
  
  			HeapTupleHeaderAdvanceLatestRemovedXid(htuphdr, &latestRemovedXid);
  		}
  		else if (ItemIdIsDead(hitemid))
  		{
  			/*
  			 * Conjecture: if hitemid is dead then it had xids before the xids
  			 * marked on LP_NORMAL items. So we just ignore this item and move
  			 * onto the next, for the purposes of calculating
  			 * latestRemovedXid.
  			 */
  		}
  		else
  			Assert(!ItemIdIsUsed(hitemid));
  
  	}
  
  	if (BufferIsValid(buf))
  	{
  		LockBuffer(buf, BUFFER_LOCK_UNLOCK);
  		ReleaseBuffer(buf);
  	}
  
  	/*
  	 * If all heap tuples were LP_DEAD then we will be returning
  	 * InvalidTransactionId here, which avoids conflicts. This matches
  	 * existing logic which assumes that LP_DEAD tuples must already be older
  	 * than the latestRemovedXid on the cleanup record that set them as
  	 * LP_DEAD, hence must already have generated a conflict.
  	 */
  
  	return latestRemovedXid;
  }
  
  /*
   * 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;
  
  	xlrec.node = rnode;
  	xlrec.latestRemovedXid = latestRemovedXid;
  
  	XLogBeginInsert();
  	XLogRegisterData((char *) &xlrec, SizeOfHeapCleanupInfo);
  
  	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_CLEANUP_INFO);
  
  	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;
  	XLogRecPtr	recptr;
  
  	/* Caller should not call me on a non-WAL-logged relation */
  	Assert(RelationNeedsWAL(reln));
  
  	xlrec.latestRemovedXid = latestRemovedXid;
  	xlrec.nredirected = nredirected;
  	xlrec.ndead = ndead;
  
  	XLogBeginInsert();
  	XLogRegisterData((char *) &xlrec, SizeOfHeapClean);
  
  	XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
  
  	/*
  	 * The OffsetNumber arrays are not actually in the buffer, but we pretend
  	 * that they are.  When XLogInsert stores the whole buffer, the offset
  	 * arrays need not be stored too.  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 line pointers changed state.
  	 */
  	if (nredirected > 0)
  		XLogRegisterBufData(0, (char *) redirected,
  							nredirected * sizeof(OffsetNumber) * 2);
  
  	if (ndead > 0)
  		XLogRegisterBufData(0, (char *) nowdead,
  							ndead * sizeof(OffsetNumber));
  
  	if (nunused > 0)
  		XLogRegisterBufData(0, (char *) nowunused,
  							nunused * sizeof(OffsetNumber));
  
  	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_CLEAN);
  
  	return recptr;
  }
  
  /*
   * Perform XLogInsert for a heap-freeze operation.  Caller must have already
   * modified the buffer and marked it dirty.
   */
  XLogRecPtr
  log_heap_freeze(Relation reln, Buffer buffer, TransactionId cutoff_xid,
  				xl_heap_freeze_tuple *tuples, int ntuples)
  {
  	xl_heap_freeze_page xlrec;
  	XLogRecPtr	recptr;
  
  	/* Caller should not call me on a non-WAL-logged relation */
  	Assert(RelationNeedsWAL(reln));
  	/* nor when there are no tuples to freeze */
  	Assert(ntuples > 0);
  
  	xlrec.cutoff_xid = cutoff_xid;
  	xlrec.ntuples = ntuples;
  
  	XLogBeginInsert();
  	XLogRegisterData((char *) &xlrec, SizeOfHeapFreezePage);
  
  	/*
  	 * The freeze plan array is not actually in the buffer, but pretend that
  	 * it is.  When XLogInsert stores the whole buffer, the freeze plan need
  	 * not be stored too.
  	 */
  	XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
  	XLogRegisterBufData(0, (char *) tuples,
  						ntuples * sizeof(xl_heap_freeze_tuple));
  
  	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_FREEZE_PAGE);
  
  	return recptr;
  }
  
  /*
   * Perform XLogInsert for a heap-visible operation.  'block' is the block
   * being marked all-visible, and vm_buffer is the buffer containing the
   * corresponding visibility map block.  Both should have already been modified
   * and dirtied.
   *
   * If checksums are enabled, we also generate a full-page image of
   * heap_buffer, if necessary.
   */
  XLogRecPtr
  log_heap_visible(RelFileNode rnode, Buffer heap_buffer, Buffer vm_buffer,
  				 TransactionId cutoff_xid, uint8 vmflags)
  {
  	xl_heap_visible xlrec;
  	XLogRecPtr	recptr;
  	uint8		flags;
  
  	Assert(BufferIsValid(heap_buffer));
  	Assert(BufferIsValid(vm_buffer));
  
  	xlrec.cutoff_xid = cutoff_xid;
  	xlrec.flags = vmflags;
  	XLogBeginInsert();
  	XLogRegisterData((char *) &xlrec, SizeOfHeapVisible);
  
  	XLogRegisterBuffer(0, vm_buffer, 0);
  
  	flags = REGBUF_STANDARD;
  	if (!XLogHintBitIsNeeded())
  		flags |= REGBUF_NO_IMAGE;
  	XLogRegisterBuffer(1, heap_buffer, flags);
  
  	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_VISIBLE);
  
  	return recptr;
  }
  
  /*
   * Perform XLogInsert for a heap-update operation.  Caller must already
   * have modified the buffer(s) and marked them dirty.
   */
  static XLogRecPtr
  log_heap_update(Relation reln, Buffer oldbuf,
  				Buffer newbuf, HeapTuple oldtup, HeapTuple newtup,
  				HeapTuple old_key_tuple,
  				bool all_visible_cleared, bool new_all_visible_cleared)
  {
  	xl_heap_update xlrec;
  	xl_heap_header xlhdr;
  	xl_heap_header xlhdr_idx;
  	uint8		info;
  	uint16		prefix_suffix[2];
  	uint16		prefixlen = 0,
  				suffixlen = 0;
  	XLogRecPtr	recptr;
  	Page		page = BufferGetPage(newbuf);
  	bool		need_tuple_data = RelationIsLogicallyLogged(reln);
  	bool		init;
  	int			bufflags;
  
  	/* Caller should not call me on a non-WAL-logged relation */
  	Assert(RelationNeedsWAL(reln));
  
  	XLogBeginInsert();
  
  	if (HeapTupleIsHeapOnly(newtup))
  		info = XLOG_HEAP_HOT_UPDATE;
  	else
  		info = XLOG_HEAP_UPDATE;
  
  	/*
  	 * If the old and new tuple are on the same page, we only need to log the
  	 * parts of the new tuple that were changed.  That saves on the amount of
  	 * WAL we need to write.  Currently, we just count any unchanged bytes in
  	 * the beginning and end of the tuple.  That's quick to check, and
  	 * perfectly covers the common case that only one field is updated.
  	 *
  	 * We could do this even if the old and new tuple are on different pages,
  	 * but only if we don't make a full-page image of the old page, which is
  	 * difficult to know in advance.  Also, if the old tuple is corrupt for
  	 * some reason, it would allow the corruption to propagate the new page,
  	 * so it seems best to avoid.  Under the general assumption that most
  	 * updates tend to create the new tuple version on the same page, there
  	 * isn't much to be gained by doing this across pages anyway.
  	 *
  	 * Skip this if we're taking a full-page image of the new page, as we
  	 * don't include the new tuple in the WAL record in that case.  Also
  	 * disable if wal_level='logical', as logical decoding needs to be able to
  	 * read the new tuple in whole from the WAL record alone.
  	 */
  	if (oldbuf == newbuf && !need_tuple_data &&
  		!XLogCheckBufferNeedsBackup(newbuf))
  	{
  		char	   *oldp = (char *) oldtup->t_data + oldtup->t_data->t_hoff;
  		char	   *newp = (char *) newtup->t_data + newtup->t_data->t_hoff;
  		int			oldlen = oldtup->t_len - oldtup->t_data->t_hoff;
  		int			newlen = newtup->t_len - newtup->t_data->t_hoff;
  
  		/* Check for common prefix between old and new tuple */
  		for (prefixlen = 0; prefixlen < Min(oldlen, newlen); prefixlen++)
  		{
  			if (newp[prefixlen] != oldp[prefixlen])
  				break;
  		}
  
  		/*
  		 * Storing the length of the prefix takes 2 bytes, so we need to save
  		 * at least 3 bytes or there's no point.
  		 */
  		if (prefixlen < 3)
  			prefixlen = 0;
  
  		/* Same for suffix */
  		for (suffixlen = 0; suffixlen < Min(oldlen, newlen) - prefixlen; suffixlen++)
  		{
  			if (newp[newlen - suffixlen - 1] != oldp[oldlen - suffixlen - 1])
  				break;
  		}
  		if (suffixlen < 3)
  			suffixlen = 0;
  	}
  
  	/* Prepare main WAL data chain */
  	xlrec.flags = 0;
  	if (all_visible_cleared)
  		xlrec.flags |= XLH_UPDATE_OLD_ALL_VISIBLE_CLEARED;
  	if (new_all_visible_cleared)
  		xlrec.flags |= XLH_UPDATE_NEW_ALL_VISIBLE_CLEARED;
  	if (prefixlen > 0)
  		xlrec.flags |= XLH_UPDATE_PREFIX_FROM_OLD;
  	if (suffixlen > 0)
  		xlrec.flags |= XLH_UPDATE_SUFFIX_FROM_OLD;
  	if (need_tuple_data)
  	{
  		xlrec.flags |= XLH_UPDATE_CONTAINS_NEW_TUPLE;
  		if (old_key_tuple)
  		{
  			if (reln->rd_rel->relreplident == REPLICA_IDENTITY_FULL)
  				xlrec.flags |= XLH_UPDATE_CONTAINS_OLD_TUPLE;
  			else
  				xlrec.flags |= XLH_UPDATE_CONTAINS_OLD_KEY;
  		}
  	}
  
  	/* If new tuple is the single and first tuple on page... */
  	if (ItemPointerGetOffsetNumber(&(newtup->t_self)) == FirstOffsetNumber &&
  		PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
  	{
  		info |= XLOG_HEAP_INIT_PAGE;
  		init = true;
  	}
  	else
  		init = false;
  
  	/* Prepare WAL data for the old page */
  	xlrec.old_offnum = ItemPointerGetOffsetNumber(&oldtup->t_self);
  	xlrec.old_xmax = HeapTupleHeaderGetRawXmax(oldtup->t_data);
  	xlrec.old_infobits_set = compute_infobits(oldtup->t_data->t_infomask,
  											  oldtup->t_data->t_infomask2);
  
  	/* Prepare WAL data for the new page */
  	xlrec.new_offnum = ItemPointerGetOffsetNumber(&newtup->t_self);
  	xlrec.new_xmax = HeapTupleHeaderGetRawXmax(newtup->t_data);
  
  	bufflags = REGBUF_STANDARD;
  	if (init)
  		bufflags |= REGBUF_WILL_INIT;
  	if (need_tuple_data)
  		bufflags |= REGBUF_KEEP_DATA;
  
  	XLogRegisterBuffer(0, newbuf, bufflags);
  	if (oldbuf != newbuf)
  		XLogRegisterBuffer(1, oldbuf, REGBUF_STANDARD);
  
  	XLogRegisterData((char *) &xlrec, SizeOfHeapUpdate);
  
  	/*
  	 * Prepare WAL data for the new tuple.
  	 */
  	if (prefixlen > 0 || suffixlen > 0)
  	{
  		if (prefixlen > 0 && suffixlen > 0)
  		{
  			prefix_suffix[0] = prefixlen;
  			prefix_suffix[1] = suffixlen;
  			XLogRegisterBufData(0, (char *) &prefix_suffix, sizeof(uint16) * 2);
  		}
  		else if (prefixlen > 0)
  		{
  			XLogRegisterBufData(0, (char *) &prefixlen, sizeof(uint16));
  		}
  		else
  		{
  			XLogRegisterBufData(0, (char *) &suffixlen, sizeof(uint16));
  		}
  	}
  
  	xlhdr.t_infomask2 = newtup->t_data->t_infomask2;
  	xlhdr.t_infomask = newtup->t_data->t_infomask;
  	xlhdr.t_hoff = newtup->t_data->t_hoff;
  	Assert(SizeofHeapTupleHeader + prefixlen + suffixlen <= newtup->t_len);
  
  	/*
  	 * PG73FORMAT: write bitmap [+ padding] [+ oid] + data
  	 *
  	 * The 'data' doesn't include the common prefix or suffix.
  	 */
  	XLogRegisterBufData(0, (char *) &xlhdr, SizeOfHeapHeader);
  	if (prefixlen == 0)
  	{
  		XLogRegisterBufData(0,
  							((char *) newtup->t_data) + SizeofHeapTupleHeader,
  							newtup->t_len - SizeofHeapTupleHeader - suffixlen);
  	}
  	else
  	{
  		/*
  		 * Have to write the null bitmap and data after the common prefix as
  		 * two separate rdata entries.
  		 */
  		/* bitmap [+ padding] [+ oid] */
  		if (newtup->t_data->t_hoff - SizeofHeapTupleHeader > 0)
  		{
  			XLogRegisterBufData(0,
  								((char *) newtup->t_data) + SizeofHeapTupleHeader,
  								newtup->t_data->t_hoff - SizeofHeapTupleHeader);
  		}
  
  		/* data after common prefix */
  		XLogRegisterBufData(0,
  							((char *) newtup->t_data) + newtup->t_data->t_hoff + prefixlen,
  							newtup->t_len - newtup->t_data->t_hoff - prefixlen - suffixlen);
  	}
  
  	/* We need to log a tuple identity */
  	if (need_tuple_data && old_key_tuple)
  	{
  		/* don't really need this, but its more comfy to decode */
  		xlhdr_idx.t_infomask2 = old_key_tuple->t_data->t_infomask2;
  		xlhdr_idx.t_infomask = old_key_tuple->t_data->t_infomask;
  		xlhdr_idx.t_hoff = old_key_tuple->t_data->t_hoff;
  
  		XLogRegisterData((char *) &xlhdr_idx, SizeOfHeapHeader);
  
  		/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
  		XLogRegisterData((char *) old_key_tuple->t_data + SizeofHeapTupleHeader,
  						 old_key_tuple->t_len - SizeofHeapTupleHeader);
  	}
  
  	/* filtering by origin on a row level is much more efficient */
  	XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
  
  	recptr = XLogInsert(RM_HEAP_ID, info);
  
  	return recptr;
  }
  
  /*
   * Perform XLogInsert of an XLOG_HEAP2_NEW_CID record
   *
   * This is only used in wal_level >= WAL_LEVEL_LOGICAL, and only for catalog
   * tuples.
   */
  static XLogRecPtr
  log_heap_new_cid(Relation relation, HeapTuple tup)
  {
  	xl_heap_new_cid xlrec;
  
  	XLogRecPtr	recptr;
  	HeapTupleHeader hdr = tup->t_data;
  
  	Assert(ItemPointerIsValid(&tup->t_self));
  	Assert(tup->t_tableOid != InvalidOid);
  
  	xlrec.top_xid = GetTopTransactionId();
  	xlrec.target_node = relation->rd_node;
  	xlrec.target_tid = tup->t_self;
  
  	/*
  	 * If the tuple got inserted & deleted in the same TX we definitely have a
  	 * combocid, set cmin and cmax.
  	 */
  	if (hdr->t_infomask & HEAP_COMBOCID)
  	{
  		Assert(!(hdr->t_infomask & HEAP_XMAX_INVALID));
  		Assert(!HeapTupleHeaderXminInvalid(hdr));
  		xlrec.cmin = HeapTupleHeaderGetCmin(hdr);
  		xlrec.cmax = HeapTupleHeaderGetCmax(hdr);
  		xlrec.combocid = HeapTupleHeaderGetRawCommandId(hdr);
  	}
  	/* No combocid, so only cmin or cmax can be set by this TX */
  	else
  	{
  		/*
  		 * Tuple inserted.
  		 *
  		 * We need to check for LOCK ONLY because multixacts might be
  		 * transferred to the new tuple in case of FOR KEY SHARE updates in
  		 * which case there will be an xmax, although the tuple just got
  		 * inserted.
  		 */
  		if (hdr->t_infomask & HEAP_XMAX_INVALID ||
  			HEAP_XMAX_IS_LOCKED_ONLY(hdr->t_infomask))
  		{
  			xlrec.cmin = HeapTupleHeaderGetRawCommandId(hdr);
  			xlrec.cmax = InvalidCommandId;
  		}
  		/* Tuple from a different tx updated or deleted. */
  		else
  		{
  			xlrec.cmin = InvalidCommandId;
  			xlrec.cmax = HeapTupleHeaderGetRawCommandId(hdr);
  
  		}
  		xlrec.combocid = InvalidCommandId;
  	}
  
  	/*
  	 * Note that we don't need to register the buffer here, because this
  	 * operation does not modify the page. The insert/update/delete that
  	 * called us certainly did, but that's WAL-logged separately.
  	 */
  	XLogBeginInsert();
  	XLogRegisterData((char *) &xlrec, SizeOfHeapNewCid);
  
  	/* will be looked at irrespective of origin */
  
  	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_NEW_CID);
  
  	return recptr;
  }
  
  /*
   * Build a heap tuple representing the configured REPLICA IDENTITY to represent
   * the old tuple in a UPDATE or DELETE.
   *
   * Returns NULL if there's no need to log an identity or if there's no suitable
   * key in the Relation relation.
   */
  static HeapTuple
  ExtractReplicaIdentity(Relation relation, HeapTuple tp, bool key_changed, bool *copy)
  {
  	TupleDesc	desc = RelationGetDescr(relation);
  	Oid			replidindex;
  	Relation	idx_rel;
  	char		replident = relation->rd_rel->relreplident;
  	HeapTuple	key_tuple = NULL;
  	bool		nulls[MaxHeapAttributeNumber];
  	Datum		values[MaxHeapAttributeNumber];
  	int			natt;
  
  	*copy = false;
  
  	if (!RelationIsLogicallyLogged(relation))
  		return NULL;
  
  	if (replident == REPLICA_IDENTITY_NOTHING)
  		return NULL;
  
  	if (replident == REPLICA_IDENTITY_FULL)
  	{
  		/*
  		 * When logging the entire old tuple, it very well could contain
  		 * toasted columns. If so, force them to be inlined.
  		 */
  		if (HeapTupleHasExternal(tp))
  		{
  			*copy = true;
  			tp = toast_flatten_tuple(tp, RelationGetDescr(relation));
  		}
  		return tp;
  	}
  
  	/* if the key hasn't changed and we're only logging the key, we're done */
  	if (!key_changed)
  		return NULL;
  
  	/* find the replica identity index */
  	replidindex = RelationGetReplicaIndex(relation);
  	if (!OidIsValid(replidindex))
  	{
  		elog(DEBUG4, "could not find configured replica identity for table \"%s\"",
  			 RelationGetRelationName(relation));
  		return NULL;
  	}
  
  	idx_rel = RelationIdGetRelation(replidindex);
  
  	Assert(CheckRelationLockedByMe(idx_rel, AccessShareLock, true));
  
  	/* deform tuple, so we have fast access to columns */
  	heap_deform_tuple(tp, desc, values, nulls);
  
  	/* set all columns to NULL, regardless of whether they actually are */
  	memset(nulls, 1, sizeof(nulls));
  
  	/*
  	 * Now set all columns contained in the index to NOT NULL, they cannot
  	 * currently be NULL.
  	 */
  	for (natt = 0; natt < IndexRelationGetNumberOfKeyAttributes(idx_rel); natt++)
  	{
  		int			attno = idx_rel->rd_index->indkey.values[natt];
  
  		if (attno < 0)
  			elog(ERROR, "system column in index");
  		nulls[attno - 1] = false;
  	}
  
  	key_tuple = heap_form_tuple(desc, values, nulls);
  	*copy = true;
  	RelationClose(idx_rel);
  
  	/*
  	 * If the tuple, which by here only contains indexed columns, still has
  	 * toasted columns, force them to be inlined. This is somewhat unlikely
  	 * since there's limits on the size of indexed columns, so we don't
  	 * duplicate toast_flatten_tuple()s functionality in the above loop over
  	 * the indexed columns, even if it would be more efficient.
  	 */
  	if (HeapTupleHasExternal(key_tuple))
  	{
  		HeapTuple	oldtup = key_tuple;
  
  		key_tuple = toast_flatten_tuple(oldtup, RelationGetDescr(relation));
  		heap_freetuple(oldtup);
  	}
  
  	return key_tuple;
  }
  
  /*
   * Handles CLEANUP_INFO
   */
  static void
  heap_xlog_cleanup_info(XLogReaderState *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(!XLogRecHasAnyBlockRefs(record));
  }
  
  /*
   * Handles XLOG_HEAP2_CLEAN record type
   */
  static void
  heap_xlog_clean(XLogReaderState *record)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_clean *xlrec = (xl_heap_clean *) XLogRecGetData(record);
  	Buffer		buffer;
  	RelFileNode rnode;
  	BlockNumber blkno;
  	XLogRedoAction action;
  
  	XLogRecGetBlockTag(record, 0, &rnode, NULL, &blkno);
  
  	/*
  	 * We're about to remove tuples. In Hot Standby mode, ensure that there's
  	 * no queries running for which the removed tuples are still visible.
  	 *
  	 * 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, rnode);
  
  	/*
  	 * If we have a full-page image, restore it (using a cleanup lock) and
  	 * we're done.
  	 */
  	action = XLogReadBufferForRedoExtended(record, 0, RBM_NORMAL, true,
  										   &buffer);
  	if (action == BLK_NEEDS_REDO)
  	{
  		Page		page = (Page) BufferGetPage(buffer);
  		OffsetNumber *end;
  		OffsetNumber *redirected;
  		OffsetNumber *nowdead;
  		OffsetNumber *nowunused;
  		int			nredirected;
  		int			ndead;
  		int			nunused;
  		Size		datalen;
  
  		redirected = (OffsetNumber *) XLogRecGetBlockData(record, 0, &datalen);
  
  		nredirected = xlrec->nredirected;
  		ndead = xlrec->ndead;
  		end = (OffsetNumber *) ((char *) redirected + datalen);
  		nowdead = redirected + (nredirected * 2);
  		nowunused = nowdead + ndead;
  		nunused = (end - nowunused);
  		Assert(nunused >= 0);
  
  		/* Update all line pointers per the record, and repair fragmentation */
  		heap_page_prune_execute(buffer,
  								redirected, nredirected,
  								nowdead, ndead,
  								nowunused, nunused);
  
  		/*
  		 * Note: we don't worry about updating the page's prunability hints.
  		 * At worst this will cause an extra prune cycle to occur soon.
  		 */
  
  		PageSetLSN(page, lsn);
  		MarkBufferDirty(buffer);
  	}
  
  	if (BufferIsValid(buffer))
  	{
  		Size		freespace = PageGetHeapFreeSpace(BufferGetPage(buffer));
  
  		UnlockReleaseBuffer(buffer);
  
  		/*
  		 * After cleaning records from a page, it's useful to update the FSM
  		 * about it, as it may cause the page become target for insertions
  		 * later even if vacuum decides not to visit it (which is possible if
  		 * gets marked all-visible.)
  		 *
  		 * Do this regardless of a full-page image being applied, since the
  		 * FSM data is not in the page anyway.
  		 */
  		XLogRecordPageWithFreeSpace(rnode, blkno, freespace);
  	}
  }
  
  /*
   * Replay XLOG_HEAP2_VISIBLE record.
   *
   * The critical integrity requirement here is that we must never end up with
   * a situation where the visibility map bit is set, and the page-level
   * PD_ALL_VISIBLE bit is clear.  If that were to occur, then a subsequent
   * page modification would fail to clear the visibility map bit.
   */
  static void
  heap_xlog_visible(XLogReaderState *record)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_visible *xlrec = (xl_heap_visible *) XLogRecGetData(record);
  	Buffer		vmbuffer = InvalidBuffer;
  	Buffer		buffer;
  	Page		page;
  	RelFileNode rnode;
  	BlockNumber blkno;
  	XLogRedoAction action;
  
  	XLogRecGetBlockTag(record, 1, &rnode, NULL, &blkno);
  
  	/*
  	 * If there are any Hot Standby transactions running that have an xmin
  	 * horizon old enough that this page isn't all-visible for them, they
  	 * might incorrectly decide that an index-only scan can skip a heap fetch.
  	 *
  	 * NB: It might be better to throw some kind of "soft" conflict here that
  	 * forces any index-only scan that is in flight to perform heap fetches,
  	 * rather than killing the transaction outright.
  	 */
  	if (InHotStandby)
  		ResolveRecoveryConflictWithSnapshot(xlrec->cutoff_xid, rnode);
  
  	/*
  	 * Read the heap page, if it still exists. If the heap file has dropped or
  	 * truncated later in recovery, we don't need to update the page, but we'd
  	 * better still update the visibility map.
  	 */
  	action = XLogReadBufferForRedo(record, 1, &buffer);
  	if (action == BLK_NEEDS_REDO)
  	{
  		/*
  		 * We don't bump the LSN of the heap page when setting the visibility
  		 * map bit (unless checksums or wal_hint_bits is enabled, in which
  		 * case we must), because that would generate an unworkable volume of
  		 * full-page writes.  This exposes us to torn page hazards, but since
  		 * we're not inspecting the existing page contents in any way, we
  		 * don't care.
  		 *
  		 * However, all operations that clear the visibility map bit *do* bump
  		 * the LSN, and those operations will only be replayed if the XLOG LSN
  		 * follows the page LSN.  Thus, if the page LSN has advanced past our
  		 * XLOG record's LSN, we mustn't mark the page all-visible, because
  		 * the subsequent update won't be replayed to clear the flag.
  		 */
  		page = BufferGetPage(buffer);
  
  		PageSetAllVisible(page);
  
  		MarkBufferDirty(buffer);
  	}
  	else if (action == BLK_RESTORED)
  	{
  		/*
  		 * If heap block was backed up, we already restored it and there's
  		 * nothing more to do. (This can only happen with checksums or
  		 * wal_log_hints enabled.)
  		 */
  	}
  
  	if (BufferIsValid(buffer))
  	{
  		Size		space = PageGetFreeSpace(BufferGetPage(buffer));
  
  		UnlockReleaseBuffer(buffer);
  
  		/*
  		 * Since FSM is not WAL-logged and only updated heuristically, it
  		 * easily becomes stale in standbys.  If the standby is later promoted
  		 * and runs VACUUM, it will skip updating individual free space
  		 * figures for pages that became all-visible (or all-frozen, depending
  		 * on the vacuum mode,) which is troublesome when FreeSpaceMapVacuum
  		 * propagates too optimistic free space values to upper FSM layers;
  		 * later inserters try to use such pages only to find out that they
  		 * are unusable.  This can cause long stalls when there are many such
  		 * pages.
  		 *
  		 * Forestall those problems by updating FSM's idea about a page that
  		 * is becoming all-visible or all-frozen.
  		 *
  		 * Do this regardless of a full-page image being applied, since the
  		 * FSM data is not in the page anyway.
  		 */
  		if (xlrec->flags & VISIBILITYMAP_VALID_BITS)
  			XLogRecordPageWithFreeSpace(rnode, blkno, space);
  	}
  
  	/*
  	 * Even if we skipped the heap page update due to the LSN interlock, it's
  	 * still safe to update the visibility map.  Any WAL record that clears
  	 * the visibility map bit does so before checking the page LSN, so any
  	 * bits that need to be cleared will still be cleared.
  	 */
  	if (XLogReadBufferForRedoExtended(record, 0, RBM_ZERO_ON_ERROR, false,
  									  &vmbuffer) == BLK_NEEDS_REDO)
  	{
  		Page		vmpage = BufferGetPage(vmbuffer);
  		Relation	reln;
  
  		/* initialize the page if it was read as zeros */
  		if (PageIsNew(vmpage))
  			PageInit(vmpage, BLCKSZ, 0);
  
  		/*
  		 * XLogReadBufferForRedoExtended locked the buffer. But
  		 * visibilitymap_set will handle locking itself.
  		 */
  		LockBuffer(vmbuffer, BUFFER_LOCK_UNLOCK);
  
  		reln = CreateFakeRelcacheEntry(rnode);
  		visibilitymap_pin(reln, blkno, &vmbuffer);
  
  		/*
  		 * Don't set the bit if replay has already passed this point.
  		 *
  		 * It might be safe to do this unconditionally; if replay has passed
  		 * this point, we'll replay at least as far this time as we did
  		 * before, and if this bit needs to be cleared, the record responsible
  		 * for doing so should be again replayed, and clear it.  For right
  		 * now, out of an abundance of conservatism, we use the same test here
  		 * we did for the heap page.  If this results in a dropped bit, no
  		 * real harm is done; and the next VACUUM will fix it.
  		 */
  
  		/*
  		 * CDB: don't use PageGetLSN here, GPDB PageGetLSN checks the buffer
  		 * is locked. But here vmbuffer is in function visibilitymap_set().
  		 *
  		 * if (lsn > PageGetLSN(vmpage))
  		 * 		visibilitymap_set(reln, blkno, InvalidBuffer, lsn, vmbuffer,
  		 * 				xlrec->cutoff_xid);
  		 */
  		if (lsn > PageXLogRecPtrGet(((PageHeader) vmpage)->pd_lsn))
  			visibilitymap_set(reln, blkno, InvalidBuffer, lsn, vmbuffer,
  							  xlrec->cutoff_xid, xlrec->flags);
  
  		ReleaseBuffer(vmbuffer);
  		FreeFakeRelcacheEntry(reln);
  	}
  	else if (BufferIsValid(vmbuffer))
  		UnlockReleaseBuffer(vmbuffer);
  }
  
  /*
   * Replay XLOG_HEAP2_FREEZE_PAGE records
   */
  static void
  heap_xlog_freeze_page(XLogReaderState *record)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_freeze_page *xlrec = (xl_heap_freeze_page *) XLogRecGetData(record);
  	TransactionId cutoff_xid = xlrec->cutoff_xid;
  	Buffer		buffer;
  	int			ntup;
  
  	/*
  	 * In Hot Standby mode, ensure that there's no queries running which still
  	 * consider the frozen xids as running.
  	 */
  	if (InHotStandby)
  	{
  		RelFileNode rnode;
  		TransactionId latestRemovedXid = cutoff_xid;
  
  		TransactionIdRetreat(latestRemovedXid);
  
  		XLogRecGetBlockTag(record, 0, &rnode, NULL, NULL);
  		ResolveRecoveryConflictWithSnapshot(latestRemovedXid, rnode);
  	}
  
  	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
  	{
  		Page		page = BufferGetPage(buffer);
  		xl_heap_freeze_tuple *tuples;
  
  		tuples = (xl_heap_freeze_tuple *) XLogRecGetBlockData(record, 0, NULL);
  
  		/* now execute freeze plan for each frozen tuple */
  		for (ntup = 0; ntup < xlrec->ntuples; ntup++)
  		{
  			xl_heap_freeze_tuple *xlrec_tp;
  			ItemId		lp;
  			HeapTupleHeader tuple;
  
  			xlrec_tp = &tuples[ntup];
  			lp = PageGetItemId(page, xlrec_tp->offset); /* offsets are one-based */
  			tuple = (HeapTupleHeader) PageGetItem(page, lp);
  
  			heap_execute_freeze_tuple(tuple, xlrec_tp);
  		}
  
  		PageSetLSN(page, lsn);
  		MarkBufferDirty(buffer);
  	}
  	if (BufferIsValid(buffer))
  		UnlockReleaseBuffer(buffer);
  }
  
  /*
   * Given an "infobits" field from an XLog record, set the correct bits in the
   * given infomask and infomask2 for the tuple touched by the record.
   *
   * (This is the reverse of compute_infobits).
   */
  static void
  fix_infomask_from_infobits(uint8 infobits, uint16 *infomask, uint16 *infomask2)
  {
  	*infomask &= ~(HEAP_XMAX_IS_MULTI | HEAP_XMAX_LOCK_ONLY |
  				   HEAP_XMAX_KEYSHR_LOCK | HEAP_XMAX_EXCL_LOCK);
  	*infomask2 &= ~HEAP_KEYS_UPDATED;
  
  	if (infobits & XLHL_XMAX_IS_MULTI)
  		*infomask |= HEAP_XMAX_IS_MULTI;
  	if (infobits & XLHL_XMAX_LOCK_ONLY)
  		*infomask |= HEAP_XMAX_LOCK_ONLY;
  	if (infobits & XLHL_XMAX_EXCL_LOCK)
  		*infomask |= HEAP_XMAX_EXCL_LOCK;
  	/* note HEAP_XMAX_SHR_LOCK isn't considered here */
  	if (infobits & XLHL_XMAX_KEYSHR_LOCK)
  		*infomask |= HEAP_XMAX_KEYSHR_LOCK;
  
  	if (infobits & XLHL_KEYS_UPDATED)
  		*infomask2 |= HEAP_KEYS_UPDATED;
  }
  
  static void
  heap_xlog_delete(XLogReaderState *record)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_delete *xlrec = (xl_heap_delete *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  	BlockNumber blkno;
  	RelFileNode target_node;
  	ItemPointerData target_tid;
  
  	XLogRecGetBlockTag(record, 0, &target_node, NULL, &blkno);
  	ItemPointerSetBlockNumber(&target_tid, blkno);
  	ItemPointerSetOffsetNumber(&target_tid, xlrec->offnum);
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->flags & XLH_DELETE_ALL_VISIBLE_CLEARED)
  	{
  		Relation	reln = CreateFakeRelcacheEntry(target_node);
  		Buffer		vmbuffer = InvalidBuffer;
  
  		visibilitymap_pin(reln, blkno, &vmbuffer);
  		visibilitymap_clear(reln, blkno, vmbuffer, VISIBILITYMAP_VALID_BITS);
  		ReleaseBuffer(vmbuffer);
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
  	{
  		page = BufferGetPage(buffer);
  
  		if (PageGetMaxOffsetNumber(page) >= xlrec->offnum)
  			lp = PageGetItemId(page, xlrec->offnum);
  
  		if (PageGetMaxOffsetNumber(page) < xlrec->offnum || !ItemIdIsNormal(lp))
  			elog(PANIC, "invalid lp");
  
  		htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  		htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
  		htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  		HeapTupleHeaderClearHotUpdated(htup);
  		fix_infomask_from_infobits(xlrec->infobits_set,
  								   &htup->t_infomask, &htup->t_infomask2);
  		if (!(xlrec->flags & XLH_DELETE_IS_SUPER))
  			HeapTupleHeaderSetXmax(htup, xlrec->xmax);
  		else
  			HeapTupleHeaderSetXmin(htup, InvalidTransactionId);
  		HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
  
  		/* Mark the page as a candidate for pruning */
  		PageSetPrunable(page, XLogRecGetXid(record));
  
  		if (xlrec->flags & XLH_DELETE_ALL_VISIBLE_CLEARED)
  			PageClearAllVisible(page);
  
  		/* Make sure t_ctid is set correctly */
  		if (xlrec->flags & XLH_DELETE_IS_PARTITION_MOVE)
  			HeapTupleHeaderSetMovedPartitions(htup);
  		else
  			htup->t_ctid = target_tid;
  		PageSetLSN(page, lsn);
  		MarkBufferDirty(buffer);
  	}
  	if (BufferIsValid(buffer))
  		UnlockReleaseBuffer(buffer);
  }
  
  static void
  heap_xlog_insert(XLogReaderState *record)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_insert *xlrec = (xl_heap_insert *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  	union
  	{
  		HeapTupleHeaderData hdr;
  		char		data[MaxHeapTupleSize];
  	}			tbuf;
  	HeapTupleHeader htup;
  	xl_heap_header xlhdr;
  	uint32		newlen;
  	Size		freespace = 0;
  	RelFileNode target_node;
  	BlockNumber blkno;
  	ItemPointerData target_tid;
  	XLogRedoAction action;
  
  	XLogRecGetBlockTag(record, 0, &target_node, NULL, &blkno);
  	ItemPointerSetBlockNumber(&target_tid, blkno);
  	ItemPointerSetOffsetNumber(&target_tid, xlrec->offnum);
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->flags & XLH_INSERT_ALL_VISIBLE_CLEARED)
  	{
  		Relation	reln = CreateFakeRelcacheEntry(target_node);
  		Buffer		vmbuffer = InvalidBuffer;
  
  		visibilitymap_pin(reln, blkno, &vmbuffer);
  		visibilitymap_clear(reln, blkno, vmbuffer, VISIBILITYMAP_VALID_BITS);
  		ReleaseBuffer(vmbuffer);
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	/*
  	 * If we inserted the first and only tuple on the page, re-initialize the
  	 * page from scratch.
  	 */
  	if (XLogRecGetInfo(record) & XLOG_HEAP_INIT_PAGE)
  	{
  		buffer = XLogInitBufferForRedo(record, 0);
  		page = BufferGetPage(buffer);
  		PageInit(page, BufferGetPageSize(buffer), 0);
  		action = BLK_NEEDS_REDO;
  	}
  	else
  		action = XLogReadBufferForRedo(record, 0, &buffer);
  	if (action == BLK_NEEDS_REDO)
  	{
  		Size		datalen;
  		char	   *data;
  
  		page = BufferGetPage(buffer);
  
  		if (PageGetMaxOffsetNumber(page) + 1 < xlrec->offnum)
  			elog(PANIC, "invalid max offset number");
  
  		data = XLogRecGetBlockData(record, 0, &datalen);
  
  		newlen = datalen - SizeOfHeapHeader;
  		Assert(datalen > SizeOfHeapHeader && newlen <= MaxHeapTupleSize);
  		memcpy((char *) &xlhdr, data, SizeOfHeapHeader);
  		data += SizeOfHeapHeader;
  
  		htup = &tbuf.hdr;
  		MemSet((char *) htup, 0, SizeofHeapTupleHeader);
  		/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
  		memcpy((char *) htup + SizeofHeapTupleHeader,
  			   data,
  			   newlen);
  		newlen += SizeofHeapTupleHeader;
  		htup->t_infomask2 = xlhdr.t_infomask2;
  		htup->t_infomask = xlhdr.t_infomask;
  		htup->t_hoff = xlhdr.t_hoff;
  		HeapTupleHeaderSetXmin(htup, XLogRecGetXid(record));
  		HeapTupleHeaderSetCmin(htup, FirstCommandId);
  		htup->t_ctid = target_tid;
  
  		if (PageAddItem(page, (Item) htup, newlen, xlrec->offnum,
  						true, true) == InvalidOffsetNumber)
  			elog(PANIC, "failed to add tuple");
  
  		freespace = PageGetHeapFreeSpace(page); /* needed to update FSM below */
  
  		PageSetLSN(page, lsn);
  
  		if (xlrec->flags & XLH_INSERT_ALL_VISIBLE_CLEARED)
  			PageClearAllVisible(page);
  
  		MarkBufferDirty(buffer);
  	}
  	if (BufferIsValid(buffer))
  		UnlockReleaseBuffer(buffer);
  
  	/*
  	 * If the page is running low on free space, update the FSM as well.
  	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
  	 * better than that without knowing the fill-factor for the table.
  	 *
  	 * XXX: Don't do this if the page was restored from full page image. We
  	 * don't bother to update the FSM in that case, it doesn't need to be
  	 * totally accurate anyway.
  	 */
  	if (action == BLK_NEEDS_REDO && freespace < BLCKSZ / 5)
  		XLogRecordPageWithFreeSpace(target_node, blkno, freespace);
  }
  
  /*
   * Handles MULTI_INSERT record type.
   */
  static void
  heap_xlog_multi_insert(XLogReaderState *record)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_multi_insert *xlrec;
  	RelFileNode rnode;
  	BlockNumber blkno;
  	Buffer		buffer;
  	Page		page;
  	union
  	{
  		HeapTupleHeaderData hdr;
  		char		data[MaxHeapTupleSize];
  	}			tbuf;
  	HeapTupleHeader htup;
  	uint32		newlen;
  	Size		freespace = 0;
  	int			i;
  	bool		isinit = (XLogRecGetInfo(record) & XLOG_HEAP_INIT_PAGE) != 0;
  	XLogRedoAction action;
  
  	/*
  	 * Insertion doesn't overwrite MVCC data, so no conflict processing is
  	 * required.
  	 */
  	xlrec = (xl_heap_multi_insert *) XLogRecGetData(record);
  
  	XLogRecGetBlockTag(record, 0, &rnode, NULL, &blkno);
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->flags & XLH_INSERT_ALL_VISIBLE_CLEARED)
  	{
  		Relation	reln = CreateFakeRelcacheEntry(rnode);
  		Buffer		vmbuffer = InvalidBuffer;
  
  		visibilitymap_pin(reln, blkno, &vmbuffer);
  		visibilitymap_clear(reln, blkno, vmbuffer, VISIBILITYMAP_VALID_BITS);
  		ReleaseBuffer(vmbuffer);
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	if (isinit)
  	{
  		buffer = XLogInitBufferForRedo(record, 0);
  		page = BufferGetPage(buffer);
  		PageInit(page, BufferGetPageSize(buffer), 0);
  		action = BLK_NEEDS_REDO;
  	}
  	else
  		action = XLogReadBufferForRedo(record, 0, &buffer);
  	if (action == BLK_NEEDS_REDO)
  	{
  		char	   *tupdata;
  		char	   *endptr;
  		Size		len;
  
  		/* Tuples are stored as block data */
  		tupdata = XLogRecGetBlockData(record, 0, &len);
  		endptr = tupdata + len;
  
  		page = (Page) BufferGetPage(buffer);
  
  		for (i = 0; i < xlrec->ntuples; i++)
  		{
  			OffsetNumber offnum;
  			xl_multi_insert_tuple *xlhdr;
  
  			/*
  			 * If we're reinitializing the page, the tuples are stored in
  			 * order from FirstOffsetNumber. Otherwise there's an array of
  			 * offsets in the WAL record, and the tuples come after that.
  			 */
  			if (isinit)
  				offnum = FirstOffsetNumber + i;
  			else
  				offnum = xlrec->offsets[i];
  			if (PageGetMaxOffsetNumber(page) + 1 < offnum)
  				elog(PANIC, "invalid max offset number");
  
  			xlhdr = (xl_multi_insert_tuple *) SHORTALIGN(tupdata);
  			tupdata = ((char *) xlhdr) + SizeOfMultiInsertTuple;
  
  			newlen = xlhdr->datalen;
  			Assert(newlen <= MaxHeapTupleSize);
  			htup = &tbuf.hdr;
  			MemSet((char *) htup, 0, SizeofHeapTupleHeader);
  			/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
  			memcpy((char *) htup + SizeofHeapTupleHeader,
  				   (char *) tupdata,
  				   newlen);
  			tupdata += newlen;
  
  			newlen += SizeofHeapTupleHeader;
  			htup->t_infomask2 = xlhdr->t_infomask2;
  			htup->t_infomask = xlhdr->t_infomask;
  			htup->t_hoff = xlhdr->t_hoff;
  			HeapTupleHeaderSetXmin(htup, XLogRecGetXid(record));
  			HeapTupleHeaderSetCmin(htup, FirstCommandId);
  			ItemPointerSetBlockNumber(&htup->t_ctid, blkno);
  			ItemPointerSetOffsetNumber(&htup->t_ctid, offnum);
  
  			offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
  			if (offnum == InvalidOffsetNumber)
  				elog(PANIC, "failed to add tuple");
  		}
  		if (tupdata != endptr)
  			elog(PANIC, "total tuple length mismatch");
  
  		freespace = PageGetHeapFreeSpace(page); /* needed to update FSM below */
  
  		PageSetLSN(page, lsn);
  
  		if (xlrec->flags & XLH_INSERT_ALL_VISIBLE_CLEARED)
  			PageClearAllVisible(page);
  
  		MarkBufferDirty(buffer);
  	}
  	if (BufferIsValid(buffer))
  		UnlockReleaseBuffer(buffer);
  
  	/*
  	 * If the page is running low on free space, update the FSM as well.
  	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
  	 * better than that without knowing the fill-factor for the table.
  	 *
  	 * XXX: Don't do this if the page was restored from full page image. We
  	 * don't bother to update the FSM in that case, it doesn't need to be
  	 * totally accurate anyway.
  	 */
  	if (action == BLK_NEEDS_REDO && freespace < BLCKSZ / 5)
  		XLogRecordPageWithFreeSpace(rnode, blkno, freespace);
  }
  
  /*
   * Handles UPDATE and HOT_UPDATE
   */
  static void
  heap_xlog_update(XLogReaderState *record, bool hot_update)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_update *xlrec = (xl_heap_update *) XLogRecGetData(record);
  	RelFileNode rnode;
  	BlockNumber oldblk;
  	BlockNumber newblk;
  	ItemPointerData newtid;
  	Buffer		obuffer,
  				nbuffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleData oldtup;
  	HeapTupleHeader htup;
  	uint16		prefixlen = 0,
  				suffixlen = 0;
  	char	   *newp;
  	union
  	{
  		HeapTupleHeaderData hdr;
  		char		data[MaxHeapTupleSize];
  	}			tbuf;
  	xl_heap_header xlhdr;
  	uint32		newlen;
  	Size		freespace = 0;
  	XLogRedoAction oldaction;
  	XLogRedoAction newaction;
  
  	/* initialize to keep the compiler quiet */
  	oldtup.t_data = NULL;
  	oldtup.t_len = 0;
  
  	XLogRecGetBlockTag(record, 0, &rnode, NULL, &newblk);
  	if (XLogRecGetBlockTag(record, 1, NULL, NULL, &oldblk))
  	{
  		/* HOT updates are never done across pages */
  		Assert(!hot_update);
  	}
  	else
  		oldblk = newblk;
  
  	ItemPointerSet(&newtid, newblk, xlrec->new_offnum);
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->flags & XLH_UPDATE_OLD_ALL_VISIBLE_CLEARED)
  	{
  		Relation	reln = CreateFakeRelcacheEntry(rnode);
  		Buffer		vmbuffer = InvalidBuffer;
  
  		visibilitymap_pin(reln, oldblk, &vmbuffer);
  		visibilitymap_clear(reln, oldblk, vmbuffer, VISIBILITYMAP_VALID_BITS);
  		ReleaseBuffer(vmbuffer);
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	/*
  	 * In normal operation, it is important to lock the two pages in
  	 * page-number order, to avoid possible deadlocks against other update
  	 * operations going the other way.  However, during WAL replay there can
  	 * be no other update happening, so we don't need to worry about that. But
  	 * we *do* need to worry that we don't expose an inconsistent state to Hot
  	 * Standby queries --- so the original page can't be unlocked before we've
  	 * added the new tuple to the new page.
  	 */
  
  	/* Deal with old tuple version */
  	oldaction = XLogReadBufferForRedo(record, (oldblk == newblk) ? 0 : 1,
  									  &obuffer);
  	if (oldaction == BLK_NEEDS_REDO)
  	{
  		page = BufferGetPage(obuffer);
  		offnum = xlrec->old_offnum;
  		if (PageGetMaxOffsetNumber(page) >= offnum)
  			lp = PageGetItemId(page, offnum);
  
  		if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  			elog(PANIC, "invalid lp");
  
  		htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  		oldtup.t_data = htup;
  		oldtup.t_len = ItemIdGetLength(lp);
  
  		htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
  		htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  		if (hot_update)
  			HeapTupleHeaderSetHotUpdated(htup);
  		else
  			HeapTupleHeaderClearHotUpdated(htup);
  		fix_infomask_from_infobits(xlrec->old_infobits_set, &htup->t_infomask,
  								   &htup->t_infomask2);
  		HeapTupleHeaderSetXmax(htup, xlrec->old_xmax);
  		HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
  		/* Set forward chain link in t_ctid */
  		htup->t_ctid = newtid;
  
  		/* Mark the page as a candidate for pruning */
  		PageSetPrunable(page, XLogRecGetXid(record));
  
  		if (xlrec->flags & XLH_UPDATE_OLD_ALL_VISIBLE_CLEARED)
  			PageClearAllVisible(page);
  
  		PageSetLSN(page, lsn);
  		MarkBufferDirty(obuffer);
  	}
  
  	/*
  	 * Read the page the new tuple goes into, if different from old.
  	 */
  	if (oldblk == newblk)
  	{
  		nbuffer = obuffer;
  		newaction = oldaction;
  	}
  	else if (XLogRecGetInfo(record) & XLOG_HEAP_INIT_PAGE)
  	{
  		nbuffer = XLogInitBufferForRedo(record, 0);
  		page = (Page) BufferGetPage(nbuffer);
  		PageInit(page, BufferGetPageSize(nbuffer), 0);
  		newaction = BLK_NEEDS_REDO;
  	}
  	else
  		newaction = XLogReadBufferForRedo(record, 0, &nbuffer);
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->flags & XLH_UPDATE_NEW_ALL_VISIBLE_CLEARED)
  	{
  		Relation	reln = CreateFakeRelcacheEntry(rnode);
  		Buffer		vmbuffer = InvalidBuffer;
  
  		visibilitymap_pin(reln, newblk, &vmbuffer);
  		visibilitymap_clear(reln, newblk, vmbuffer, VISIBILITYMAP_VALID_BITS);
  		ReleaseBuffer(vmbuffer);
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	/* Deal with new tuple */
  	if (newaction == BLK_NEEDS_REDO)
  	{
  		char	   *recdata;
  		char	   *recdata_end;
  		Size		datalen;
  		Size		tuplen;
  
  		recdata = XLogRecGetBlockData(record, 0, &datalen);
  		recdata_end = recdata + datalen;
  
  		page = BufferGetPage(nbuffer);
  
  		offnum = xlrec->new_offnum;
  		if (PageGetMaxOffsetNumber(page) + 1 < offnum)
  			elog(PANIC, "invalid max offset number");
  
  		if (xlrec->flags & XLH_UPDATE_PREFIX_FROM_OLD)
  		{
  			Assert(newblk == oldblk);
  			memcpy(&prefixlen, recdata, sizeof(uint16));
  			recdata += sizeof(uint16);
  		}
  		if (xlrec->flags & XLH_UPDATE_SUFFIX_FROM_OLD)
  		{
  			Assert(newblk == oldblk);
  			memcpy(&suffixlen, recdata, sizeof(uint16));
  			recdata += sizeof(uint16);
  		}
  
  		memcpy((char *) &xlhdr, recdata, SizeOfHeapHeader);
  		recdata += SizeOfHeapHeader;
  
  		tuplen = recdata_end - recdata;
  		Assert(tuplen <= MaxHeapTupleSize);
  
  		htup = &tbuf.hdr;
  		MemSet((char *) htup, 0, SizeofHeapTupleHeader);
  
  		/*
  		 * Reconstruct the new tuple using the prefix and/or suffix from the
  		 * old tuple, and the data stored in the WAL record.
  		 */
  		newp = (char *) htup + SizeofHeapTupleHeader;
  		if (prefixlen > 0)
  		{
  			int			len;
  
  			/* copy bitmap [+ padding] [+ oid] from WAL record */
  			len = xlhdr.t_hoff - SizeofHeapTupleHeader;
  			memcpy(newp, recdata, len);
  			recdata += len;
  			newp += len;
  
  			/* copy prefix from old tuple */
  			memcpy(newp, (char *) oldtup.t_data + oldtup.t_data->t_hoff, prefixlen);
  			newp += prefixlen;
  
  			/* copy new tuple data from WAL record */
  			len = tuplen - (xlhdr.t_hoff - SizeofHeapTupleHeader);
  			memcpy(newp, recdata, len);
  			recdata += len;
  			newp += len;
  		}
  		else
  		{
  			/*
  			 * copy bitmap [+ padding] [+ oid] + data from record, all in one
  			 * go
  			 */
  			memcpy(newp, recdata, tuplen);
  			recdata += tuplen;
  			newp += tuplen;
  		}
  		Assert(recdata == recdata_end);
  
  		/* copy suffix from old tuple */
  		if (suffixlen > 0)
  			memcpy(newp, (char *) oldtup.t_data + oldtup.t_len - suffixlen, suffixlen);
  
  		newlen = SizeofHeapTupleHeader + tuplen + prefixlen + suffixlen;
  		htup->t_infomask2 = xlhdr.t_infomask2;
  		htup->t_infomask = xlhdr.t_infomask;
  		htup->t_hoff = xlhdr.t_hoff;
  
  		HeapTupleHeaderSetXmin(htup, XLogRecGetXid(record));
  		HeapTupleHeaderSetCmin(htup, FirstCommandId);
  		HeapTupleHeaderSetXmax(htup, xlrec->new_xmax);
  		/* Make sure there is no forward chain link in t_ctid */
  		htup->t_ctid = newtid;
  
  		offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
  		if (offnum == InvalidOffsetNumber)
  			elog(PANIC, "failed to add tuple");
  
  		if (xlrec->flags & XLH_UPDATE_NEW_ALL_VISIBLE_CLEARED)
  			PageClearAllVisible(page);
  
  		freespace = PageGetHeapFreeSpace(page); /* needed to update FSM below */
  
  		PageSetLSN(page, lsn);
  		MarkBufferDirty(nbuffer);
  	}
  
  	if (BufferIsValid(nbuffer) && nbuffer != obuffer)
  		UnlockReleaseBuffer(nbuffer);
  	if (BufferIsValid(obuffer))
  		UnlockReleaseBuffer(obuffer);
  
  	/*
  	 * If the new page is running low on free space, update the FSM as well.
  	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
  	 * better than that without knowing the fill-factor for the table.
  	 *
  	 * However, don't update the FSM on HOT updates, because after crash
  	 * recovery, either the old or the new tuple will certainly be dead and
  	 * prunable. After pruning, the page will have roughly as much free space
  	 * as it did before the update, assuming the new tuple is about the same
  	 * size as the old one.
  	 *
  	 * XXX: Don't do this if the page was restored from full page image. We
  	 * don't bother to update the FSM in that case, it doesn't need to be
  	 * totally accurate anyway.
  	 */
  	if (newaction == BLK_NEEDS_REDO && !hot_update && freespace < BLCKSZ / 5)
  		XLogRecordPageWithFreeSpace(rnode, newblk, freespace);
  }
  
  static void
  heap_xlog_confirm(XLogReaderState *record)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_confirm *xlrec = (xl_heap_confirm *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  
  	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
  	{
  		page = BufferGetPage(buffer);
  
  		offnum = xlrec->offnum;
  		if (PageGetMaxOffsetNumber(page) >= offnum)
  			lp = PageGetItemId(page, offnum);
  
  		if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  			elog(PANIC, "invalid lp");
  
  		htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  		/*
  		 * Confirm tuple as actually inserted
  		 */
  		ItemPointerSet(&htup->t_ctid, BufferGetBlockNumber(buffer), offnum);
  
  		PageSetLSN(page, lsn);
  		MarkBufferDirty(buffer);
  	}
  	if (BufferIsValid(buffer))
  		UnlockReleaseBuffer(buffer);
  }
  
  static void
  heap_xlog_lock(XLogReaderState *record)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_lock *xlrec = (xl_heap_lock *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->flags & XLH_LOCK_ALL_FROZEN_CLEARED)
  	{
  		RelFileNode rnode;
  		Buffer		vmbuffer = InvalidBuffer;
  		BlockNumber block;
  		Relation	reln;
  
  		XLogRecGetBlockTag(record, 0, &rnode, NULL, &block);
  		reln = CreateFakeRelcacheEntry(rnode);
  
  		visibilitymap_pin(reln, block, &vmbuffer);
  		visibilitymap_clear(reln, block, vmbuffer, VISIBILITYMAP_ALL_FROZEN);
  
  		ReleaseBuffer(vmbuffer);
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
  	{
  		page = (Page) BufferGetPage(buffer);
  
  		offnum = xlrec->offnum;
  		if (PageGetMaxOffsetNumber(page) >= offnum)
  			lp = PageGetItemId(page, offnum);
  
  		if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  			elog(PANIC, "invalid lp");
  
  		htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  		htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
  		htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  		fix_infomask_from_infobits(xlrec->infobits_set, &htup->t_infomask,
  								   &htup->t_infomask2);
  
  		/*
  		 * Clear relevant update flags, but only if the modified infomask says
  		 * there's no update.
  		 */
  		if (HEAP_XMAX_IS_LOCKED_ONLY(htup->t_infomask))
  		{
  			HeapTupleHeaderClearHotUpdated(htup);
  			/* Make sure there is no forward chain link in t_ctid */
  			ItemPointerSet(&htup->t_ctid,
  						   BufferGetBlockNumber(buffer),
  						   offnum);
  		}
  		HeapTupleHeaderSetXmax(htup, xlrec->locking_xid);
  		HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
  		PageSetLSN(page, lsn);
  		MarkBufferDirty(buffer);
  	}
  	if (BufferIsValid(buffer))
  		UnlockReleaseBuffer(buffer);
  }
  
  static void
  heap_xlog_lock_updated(XLogReaderState *record)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_lock_updated *xlrec;
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  
  	xlrec = (xl_heap_lock_updated *) XLogRecGetData(record);
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->flags & XLH_LOCK_ALL_FROZEN_CLEARED)
  	{
  		RelFileNode rnode;
  		Buffer		vmbuffer = InvalidBuffer;
  		BlockNumber block;
  		Relation	reln;
  
  		XLogRecGetBlockTag(record, 0, &rnode, NULL, &block);
  		reln = CreateFakeRelcacheEntry(rnode);
  
  		visibilitymap_pin(reln, block, &vmbuffer);
  		visibilitymap_clear(reln, block, vmbuffer, VISIBILITYMAP_ALL_FROZEN);
  
  		ReleaseBuffer(vmbuffer);
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
  	{
  		page = BufferGetPage(buffer);
  
  		offnum = xlrec->offnum;
  		if (PageGetMaxOffsetNumber(page) >= offnum)
  			lp = PageGetItemId(page, offnum);
  
  		if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  			elog(PANIC, "invalid lp");
  
  		htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  		htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
  		htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
  		fix_infomask_from_infobits(xlrec->infobits_set, &htup->t_infomask,
  								   &htup->t_infomask2);
  		HeapTupleHeaderSetXmax(htup, xlrec->xmax);
  
  		PageSetLSN(page, lsn);
  		MarkBufferDirty(buffer);
  	}
  	if (BufferIsValid(buffer))
  		UnlockReleaseBuffer(buffer);
  }
  
  static void
  heap_xlog_inplace(XLogReaderState *record)
  {
  	XLogRecPtr	lsn = record->EndRecPtr;
  	xl_heap_inplace *xlrec = (xl_heap_inplace *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  	uint32		oldlen;
  	Size		newlen;
  
  	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
  	{
  		char	   *newtup = XLogRecGetBlockData(record, 0, &newlen);
  
  		page = BufferGetPage(buffer);
  
  		offnum = xlrec->offnum;
  		if (PageGetMaxOffsetNumber(page) >= offnum)
  			lp = PageGetItemId(page, offnum);
  
  		if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  			elog(PANIC, "invalid lp");
  
  		htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  		oldlen = ItemIdGetLength(lp) - htup->t_hoff;
  		if (oldlen != newlen)
  			elog(PANIC, "wrong tuple length");
  
  		memcpy((char *) htup + htup->t_hoff, newtup, newlen);
  
  		PageSetLSN(page, lsn);
  		MarkBufferDirty(buffer);
  	}
  	if (BufferIsValid(buffer))
  		UnlockReleaseBuffer(buffer);
  }
  
  void
  heap_redo(XLogReaderState *record)
  {
  	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
  
  	/*
  	 * These operations don't overwrite MVCC data so no conflict processing is
  	 * required. The ones in heap2 rmgr do.
  	 */
  
  	switch (info & XLOG_HEAP_OPMASK)
  	{
  		case XLOG_HEAP_INSERT:
  			heap_xlog_insert(record);
  			break;
  		case XLOG_HEAP_DELETE:
  			heap_xlog_delete(record);
  			break;
  		case XLOG_HEAP_UPDATE:
  			heap_xlog_update(record, false);
  			break;
  		case XLOG_HEAP_TRUNCATE:
  
  			/*
  			 * TRUNCATE is a no-op because the actions are already logged as
  			 * SMGR WAL records.  TRUNCATE WAL record only exists for logical
  			 * decoding.
  			 */
  			break;
  		case XLOG_HEAP_HOT_UPDATE:
  			heap_xlog_update(record, true);
  			break;
  		case XLOG_HEAP_CONFIRM:
  			heap_xlog_confirm(record);
  			break;
  		case XLOG_HEAP_LOCK:
  			heap_xlog_lock(record);
  			break;
  		case XLOG_HEAP_INPLACE:
  			heap_xlog_inplace(record);
  			break;
  		default:
  			elog(PANIC, "heap_redo: unknown op code %u", info);
  	}
  }
  
  void
  heap2_redo(XLogReaderState *record)
  {
  	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
  
  	switch (info & XLOG_HEAP_OPMASK)
  	{
  		case XLOG_HEAP2_CLEAN:
  			heap_xlog_clean(record);
  			break;
  		case XLOG_HEAP2_FREEZE_PAGE:
  			heap_xlog_freeze_page(record);
  			break;
  		case XLOG_HEAP2_CLEANUP_INFO:
  			heap_xlog_cleanup_info(record);
  			break;
  		case XLOG_HEAP2_VISIBLE:
  			heap_xlog_visible(record);
  			break;
  		case XLOG_HEAP2_MULTI_INSERT:
  			heap_xlog_multi_insert(record);
  			break;
  		case XLOG_HEAP2_LOCK_UPDATED:
  			heap_xlog_lock_updated(record);
  			break;
  		case XLOG_HEAP2_NEW_CID:
  
  			/*
  			 * Nothing to do on a real replay, only used during logical
  			 * decoding.
  			 */
  			break;
  		case XLOG_HEAP2_REWRITE:
  			heap_xlog_logical_rewrite(record);
  			break;
  		default:
  			elog(PANIC, "heap2_redo: unknown op code %u", info);
  	}
  }
  
  /*
   *	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 = table_open(rel->rd_rel->reltoastrelid, AccessShareLock);
  		FlushRelationBuffers(toastrel);
  		smgrimmedsync(toastrel->rd_smgr, MAIN_FORKNUM);
  		table_close(toastrel, AccessShareLock);
  	}
  }
  
  /*
   * Mask a heap page before performing consistency checks on it.
   */
  void
  heap_mask(char *pagedata, BlockNumber blkno)
  {
  	Page		page = (Page) pagedata;
  	OffsetNumber off;
  
  	mask_page_lsn_and_checksum(page);
  
  	mask_page_hint_bits(page);
  	mask_unused_space(page);
  
  	for (off = 1; off <= PageGetMaxOffsetNumber(page); off++)
  	{
  		ItemId		iid = PageGetItemId(page, off);
  		char	   *page_item;
  
  		page_item = (char *) (page + ItemIdGetOffset(iid));
  
  		if (ItemIdIsNormal(iid))
  		{
  			HeapTupleHeader page_htup = (HeapTupleHeader) page_item;
  
  			/*
  			 * If xmin of a tuple is not yet frozen, we should ignore
  			 * differences in hint bits, since they can be set without
  			 * emitting WAL.
  			 */
  			if (!HeapTupleHeaderXminFrozen(page_htup))
  				page_htup->t_infomask &= ~HEAP_XACT_MASK;
  			else
  			{
  				/* Still we need to mask xmax hint bits. */
  				page_htup->t_infomask &= ~HEAP_XMAX_INVALID;
  				page_htup->t_infomask &= ~HEAP_XMAX_COMMITTED;
  			}
  
  			/* mask out GPDB specific hint-bits */
  			page_htup->t_infomask2 &= ~HEAP_XMIN_DISTRIBUTED_SNAPSHOT_IGNORE;
  			page_htup->t_infomask2 &= ~HEAP_XMAX_DISTRIBUTED_SNAPSHOT_IGNORE;
  
  			/*
  			 * During replay, we set Command Id to FirstCommandId. Hence, mask
  			 * it. See heap_xlog_insert() for details.
  			 */
  			page_htup->t_choice.t_heap.t_field3.t_cid = MASK_MARKER;
  
  			/*
  			 * For a speculative tuple, heap_insert() does not set ctid in the
  			 * caller-passed heap tuple itself, leaving the ctid field to
  			 * contain a speculative token value - a per-backend monotonically
  			 * increasing identifier. Besides, it does not WAL-log ctid under
  			 * any circumstances.
  			 *
  			 * During redo, heap_xlog_insert() sets t_ctid to current block
  			 * number and self offset number. It doesn't care about any
  			 * speculative insertions in master. Hence, we set t_ctid to
  			 * current block number and self offset number to ignore any
  			 * inconsistency.
  			 */
  			if (HeapTupleHeaderIsSpeculative(page_htup))
  				ItemPointerSet(&page_htup->t_ctid, blkno, off);
  
  			/*
  			 * NB: Not ignoring ctid changes due to the tuple having moved
  			 * (i.e. HeapTupleHeaderIndicatesMovedPartitions), because that's
  			 * important information that needs to be in-sync between primary
  			 * and standby, and thus is WAL logged.
  			 */
  		}
  
  		/*
  		 * Ignore any padding bytes after the tuple, when the length of the
  		 * item is not MAXALIGNed.
  		 */
  		if (ItemIdHasStorage(iid))
  		{
  			int			len = ItemIdGetLength(iid);
  			int			padlen = MAXALIGN(len) - len;
  
  			if (padlen > 0)
  				memset(page_item + len, MASK_MARKER, padlen);
  		}
  	}
  }
  