text: /*-------------------------------------------------------------------------
   *
   * heapam.c
   *	  heap access method code
   *
   * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   *
   * IDENTIFICATION
   *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.277.2.1 2009/08/24 02:18:40 tgl Exp $
   *
   *
   * INTERFACE ROUTINES
   *		relation_open	- open any relation by relation OID
   *		relation_openrv - open any relation specified by a RangeVar
   *		relation_close	- close any relation
   *		heap_open		- open a heap relation by relation OID
   *		heap_openrv		- open a heap relation specified by a RangeVar
   *		heap_close		- (now just a macro for relation_close)
   *		heap_beginscan	- begin relation scan
   *		heap_rescan		- restart a relation scan
   *		heap_endscan	- end relation scan
   *		heap_getnext	- retrieve next tuple in scan
   *		heap_fetch		- retrieve tuple with given tid
   *		heap_insert		- insert tuple into a relation
   *		heap_delete		- delete a tuple from a relation
   *		heap_update		- replace a tuple in a relation with another tuple
   *		heap_markpos	- mark scan position
   *		heap_restrpos	- restore position to marked location
   *		heap_sync		- sync heap, for when no WAL has been written
   *
   * NOTES
   *	  This file contains the heap_ routines which implement
   *	  the POSTGRES heap access method used for all POSTGRES
   *	  relations.
   *
   *-------------------------------------------------------------------------
   */
  #include "postgres.h"
  
  #include "access/heapam.h"
  #include "access/hio.h"
  #include "access/multixact.h"
  #include "access/relscan.h"
  #include "access/sysattr.h"
  #include "access/transam.h"
  #include "access/tuptoaster.h"
  #include "access/valid.h"
  #include "access/visibilitymap.h"
  #include "access/xact.h"
  #include "access/xlogutils.h"
  #include "catalog/catalog.h"
  #include "catalog/namespace.h"
  #include "miscadmin.h"
  #include "pgstat.h"
  #include "storage/bufmgr.h"
  #include "storage/freespace.h"
  #include "storage/lmgr.h"
  #include "storage/procarray.h"
  #include "storage/smgr.h"
  #include "utils/datum.h"
  #include "utils/inval.h"
  #include "utils/lsyscache.h"
  #include "utils/relcache.h"
  #include "utils/snapmgr.h"
  #include "utils/syscache.h"
  #include "utils/tqual.h"
  
  
  /* GUC variable */
  bool		synchronize_seqscans = true;
  
  
  static HeapScanDesc heap_beginscan_internal(Relation relation,
  						Snapshot snapshot,
  						int nkeys, ScanKey key,
  						bool allow_strat, bool allow_sync,
  						bool is_bitmapscan);
  static XLogRecPtr log_heap_update(Relation reln, Buffer oldbuf,
  		   ItemPointerData from, Buffer newbuf, HeapTuple newtup, bool move,
  		   bool all_visible_cleared, bool new_all_visible_cleared);
  static bool HeapSatisfiesHOTUpdate(Relation relation, Bitmapset *hot_attrs,
  					   HeapTuple oldtup, HeapTuple newtup);
  
  
  /* ----------------------------------------------------------------
   *						 heap support routines
   * ----------------------------------------------------------------
   */
  
  /* ----------------
   *		initscan - scan code common to heap_beginscan and heap_rescan
   * ----------------
   */
  static void
  initscan(HeapScanDesc scan, ScanKey key, bool is_rescan)
  {
  	bool		allow_strat;
  	bool		allow_sync;
  
  	/*
  	 * Determine the number of blocks we have to scan.
  	 *
  	 * It is sufficient to do this once at scan start, since any tuples added
  	 * while the scan is in progress will be invisible to my snapshot anyway.
  	 * (That is not true when using a non-MVCC snapshot.  However, we couldn't
  	 * guarantee to return tuples added after scan start anyway, since they
  	 * might go into pages we already scanned.	To guarantee consistent
  	 * results for a non-MVCC snapshot, the caller must hold some higher-level
  	 * lock that ensures the interesting tuple(s) won't change.)
  	 */
  	scan->rs_nblocks = RelationGetNumberOfBlocks(scan->rs_rd);
  
  	/*
  	 * If the table is large relative to NBuffers, use a bulk-read access
  	 * strategy and enable synchronized scanning (see syncscan.c).	Although
  	 * the thresholds for these features could be different, we make them the
  	 * same so that there are only two behaviors to tune rather than four.
  	 * (However, some callers need to be able to disable one or both of these
  	 * behaviors, independently of the size of the table; also there is a GUC
  	 * variable that can disable synchronized scanning.)
  	 *
  	 * During a rescan, don't make a new strategy object if we don't have to.
  	 */
  	if (!scan->rs_rd->rd_istemp &&
  		scan->rs_nblocks > NBuffers / 4)
  	{
  		allow_strat = scan->rs_allow_strat;
  		allow_sync = scan->rs_allow_sync;
  	}
  	else
  		allow_strat = allow_sync = false;
  
  	if (allow_strat)
  	{
  		if (scan->rs_strategy == NULL)
  			scan->rs_strategy = GetAccessStrategy(BAS_BULKREAD);
  	}
  	else
  	{
  		if (scan->rs_strategy != NULL)
  			FreeAccessStrategy(scan->rs_strategy);
  		scan->rs_strategy = NULL;
  	}
  
  	if (is_rescan)
  	{
  		/*
  		 * If rescan, keep the previous startblock setting so that rewinding a
  		 * cursor doesn't generate surprising results.  Reset the syncscan
  		 * setting, though.
  		 */
  		scan->rs_syncscan = (allow_sync && synchronize_seqscans);
  	}
  	else if (allow_sync && synchronize_seqscans)
  	{
  		scan->rs_syncscan = true;
  		scan->rs_startblock = ss_get_location(scan->rs_rd, scan->rs_nblocks);
  	}
  	else
  	{
  		scan->rs_syncscan = false;
  		scan->rs_startblock = 0;
  	}
  
  	scan->rs_inited = false;
  	scan->rs_ctup.t_data = NULL;
  	ItemPointerSetInvalid(&scan->rs_ctup.t_self);
  	scan->rs_cbuf = InvalidBuffer;
  	scan->rs_cblock = InvalidBlockNumber;
  
  	/* we don't have a marked position... */
  	ItemPointerSetInvalid(&(scan->rs_mctid));
  
  	/* page-at-a-time fields are always invalid when not rs_inited */
  
  	/*
  	 * copy the scan key, if appropriate
  	 */
  	if (key != NULL)
  		memcpy(scan->rs_key, key, scan->rs_nkeys * sizeof(ScanKeyData));
  
  	/*
  	 * Currently, we don't have a stats counter for bitmap heap scans (but the
  	 * underlying bitmap index scans will be counted).
  	 */
  	if (!scan->rs_bitmapscan)
  		pgstat_count_heap_scan(scan->rs_rd);
  }
  
  /*
   * heapgetpage - subroutine for heapgettup()
   *
   * This routine reads and pins the specified page of the relation.
   * In page-at-a-time mode it performs additional work, namely determining
   * which tuples on the page are visible.
   */
  static void
  heapgetpage(HeapScanDesc scan, BlockNumber page)
  {
  	Buffer		buffer;
  	Snapshot	snapshot;
  	Page		dp;
  	int			lines;
  	int			ntup;
  	OffsetNumber lineoff;
  	ItemId		lpp;
  	bool		all_visible;
  
  	Assert(page < scan->rs_nblocks);
  
  	/* release previous scan buffer, if any */
  	if (BufferIsValid(scan->rs_cbuf))
  	{
  		ReleaseBuffer(scan->rs_cbuf);
  		scan->rs_cbuf = InvalidBuffer;
  	}
  
  	/* read page using selected strategy */
  	scan->rs_cbuf = ReadBufferExtended(scan->rs_rd, MAIN_FORKNUM, page,
  									   RBM_NORMAL, scan->rs_strategy);
  	scan->rs_cblock = page;
  
  	if (!scan->rs_pageatatime)
  		return;
  
  	buffer = scan->rs_cbuf;
  	snapshot = scan->rs_snapshot;
  
  	/*
  	 * Prune and repair fragmentation for the whole page, if possible.
  	 */
  	Assert(TransactionIdIsValid(RecentGlobalXmin));
  	heap_page_prune_opt(scan->rs_rd, buffer, RecentGlobalXmin);
  
  	/*
  	 * We must hold share lock on the buffer content while examining tuple
  	 * visibility.	Afterwards, however, the tuples we have found to be
  	 * visible are guaranteed good as long as we hold the buffer pin.
  	 */
  	LockBuffer(buffer, BUFFER_LOCK_SHARE);
  
  	dp = (Page) BufferGetPage(buffer);
  	lines = PageGetMaxOffsetNumber(dp);
  	ntup = 0;
  
  	/*
  	 * If the all-visible flag indicates that all tuples on the page are
  	 * visible to everyone, we can skip the per-tuple visibility tests.
  	 */
  	all_visible = PageIsAllVisible(dp);
  
  	for (lineoff = FirstOffsetNumber, lpp = PageGetItemId(dp, lineoff);
  		 lineoff <= lines;
  		 lineoff++, lpp++)
  	{
  		if (ItemIdIsNormal(lpp))
  		{
  			bool		valid;
  
  			if (all_visible)
  				valid = true;
  			else
  			{
  				HeapTupleData loctup;
  
  				loctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
  				loctup.t_len = ItemIdGetLength(lpp);
  				ItemPointerSet(&(loctup.t_self), page, lineoff);
  
  				valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer);
  			}
  			if (valid)
  				scan->rs_vistuples[ntup++] = lineoff;
  		}
  	}
  
  	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  	Assert(ntup <= MaxHeapTuplesPerPage);
  	scan->rs_ntuples = ntup;
  }
  
  /* ----------------
   *		heapgettup - fetch next heap tuple
   *
   *		Initialize the scan if not already done; then advance to the next
   *		tuple as indicated by "dir"; return the next tuple in scan->rs_ctup,
   *		or set scan->rs_ctup.t_data = NULL if no more tuples.
   *
   * dir == NoMovementScanDirection means "re-fetch the tuple indicated
   * by scan->rs_ctup".
   *
   * Note: the reason nkeys/key are passed separately, even though they are
   * kept in the scan descriptor, is that the caller may not want us to check
   * the scankeys.
   *
   * Note: when we fall off the end of the scan in either direction, we
   * reset rs_inited.  This means that a further request with the same
   * scan direction will restart the scan, which is a bit odd, but a
   * request with the opposite scan direction will start a fresh scan
   * in the proper direction.  The latter is required behavior for cursors,
   * while the former case is generally undefined behavior in Postgres
   * so we don't care too much.
   * ----------------
   */
  static void
  heapgettup(HeapScanDesc scan,
  		   ScanDirection dir,
  		   int nkeys,
  		   ScanKey key)
  {
  	HeapTuple	tuple = &(scan->rs_ctup);
  	Snapshot	snapshot = scan->rs_snapshot;
  	bool		backward = ScanDirectionIsBackward(dir);
  	BlockNumber page;
  	bool		finished;
  	Page		dp;
  	int			lines;
  	OffsetNumber lineoff;
  	int			linesleft;
  	ItemId		lpp;
  
  	/*
  	 * calculate next starting lineoff, given scan direction
  	 */
  	if (ScanDirectionIsForward(dir))
  	{
  		if (!scan->rs_inited)
  		{
  			/*
  			 * return null immediately if relation is empty
  			 */
  			if (scan->rs_nblocks == 0)
  			{
  				Assert(!BufferIsValid(scan->rs_cbuf));
  				tuple->t_data = NULL;
  				return;
  			}
  			page = scan->rs_startblock; /* first page */
  			heapgetpage(scan, page);
  			lineoff = FirstOffsetNumber;		/* first offnum */
  			scan->rs_inited = true;
  		}
  		else
  		{
  			/* continue from previously returned page/tuple */
  			page = scan->rs_cblock;		/* current page */
  			lineoff =			/* next offnum */
  				OffsetNumberNext(ItemPointerGetOffsetNumber(&(tuple->t_self)));
  		}
  
  		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
  
  		dp = (Page) BufferGetPage(scan->rs_cbuf);
  		lines = PageGetMaxOffsetNumber(dp);
  		/* page and lineoff now reference the physically next tid */
  
  		linesleft = lines - lineoff + 1;
  	}
  	else if (backward)
  	{
  		if (!scan->rs_inited)
  		{
  			/*
  			 * return null immediately if relation is empty
  			 */
  			if (scan->rs_nblocks == 0)
  			{
  				Assert(!BufferIsValid(scan->rs_cbuf));
  				tuple->t_data = NULL;
  				return;
  			}
  
  			/*
  			 * Disable reporting to syncscan logic in a backwards scan; it's
  			 * not very likely anyone else is doing the same thing at the same
  			 * time, and much more likely that we'll just bollix things for
  			 * forward scanners.
  			 */
  			scan->rs_syncscan = false;
  			/* start from last page of the scan */
  			if (scan->rs_startblock > 0)
  				page = scan->rs_startblock - 1;
  			else
  				page = scan->rs_nblocks - 1;
  			heapgetpage(scan, page);
  		}
  		else
  		{
  			/* continue from previously returned page/tuple */
  			page = scan->rs_cblock;		/* current page */
  		}
  
  		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
  
  		dp = (Page) BufferGetPage(scan->rs_cbuf);
  		lines = PageGetMaxOffsetNumber(dp);
  
  		if (!scan->rs_inited)
  		{
  			lineoff = lines;	/* final offnum */
  			scan->rs_inited = true;
  		}
  		else
  		{
  			lineoff =			/* previous offnum */
  				OffsetNumberPrev(ItemPointerGetOffsetNumber(&(tuple->t_self)));
  		}
  		/* page and lineoff now reference the physically previous tid */
  
  		linesleft = lineoff;
  	}
  	else
  	{
  		/*
  		 * ``no movement'' scan direction: refetch prior tuple
  		 */
  		if (!scan->rs_inited)
  		{
  			Assert(!BufferIsValid(scan->rs_cbuf));
  			tuple->t_data = NULL;
  			return;
  		}
  
  		page = ItemPointerGetBlockNumber(&(tuple->t_self));
  		if (page != scan->rs_cblock)
  			heapgetpage(scan, page);
  
  		/* Since the tuple was previously fetched, needn't lock page here */
  		dp = (Page) BufferGetPage(scan->rs_cbuf);
  		lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
  		lpp = PageGetItemId(dp, lineoff);
  		Assert(ItemIdIsNormal(lpp));
  
  		tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
  		tuple->t_len = ItemIdGetLength(lpp);
  
  		return;
  	}
  
  	/*
  	 * advance the scan until we find a qualifying tuple or run out of stuff
  	 * to scan
  	 */
  	lpp = PageGetItemId(dp, lineoff);
  	for (;;)
  	{
  		while (linesleft > 0)
  		{
  			if (ItemIdIsNormal(lpp))
  			{
  				bool		valid;
  
  				tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
  				tuple->t_len = ItemIdGetLength(lpp);
  				ItemPointerSet(&(tuple->t_self), page, lineoff);
  
  				/*
  				 * if current tuple qualifies, return it.
  				 */
  				valid = HeapTupleSatisfiesVisibility(tuple,
  													 snapshot,
  													 scan->rs_cbuf);
  
  				if (valid && key != NULL)
  					HeapKeyTest(tuple, RelationGetDescr(scan->rs_rd),
  								nkeys, key, valid);
  
  				if (valid)
  				{
  					LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
  					return;
  				}
  			}
  
  			/*
  			 * otherwise move to the next item on the page
  			 */
  			--linesleft;
  			if (backward)
  			{
  				--lpp;			/* move back in this page's ItemId array */
  				--lineoff;
  			}
  			else
  			{
  				++lpp;			/* move forward in this page's ItemId array */
  				++lineoff;
  			}
  		}
  
  		/*
  		 * if we get here, it means we've exhausted the items on this page and
  		 * it's time to move to the next.
  		 */
  		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
  
  		/*
  		 * advance to next/prior page and detect end of scan
  		 */
  		if (backward)
  		{
  			finished = (page == scan->rs_startblock);
  			if (page == 0)
  				page = scan->rs_nblocks;
  			page--;
  		}
  		else
  		{
  			page++;
  			if (page >= scan->rs_nblocks)
  				page = 0;
  			finished = (page == scan->rs_startblock);
  
  			/*
  			 * Report our new scan position for synchronization purposes. We
  			 * don't do that when moving backwards, however. That would just
  			 * mess up any other forward-moving scanners.
  			 *
  			 * Note: we do this before checking for end of scan so that the
  			 * final state of the position hint is back at the start of the
  			 * rel.  That's not strictly necessary, but otherwise when you run
  			 * the same query multiple times the starting position would shift
  			 * a little bit backwards on every invocation, which is confusing.
  			 * We don't guarantee any specific ordering in general, though.
  			 */
  			if (scan->rs_syncscan)
  				ss_report_location(scan->rs_rd, page);
  		}
  
  		/*
  		 * return NULL if we've exhausted all the pages
  		 */
  		if (finished)
  		{
  			if (BufferIsValid(scan->rs_cbuf))
  				ReleaseBuffer(scan->rs_cbuf);
  			scan->rs_cbuf = InvalidBuffer;
  			scan->rs_cblock = InvalidBlockNumber;
  			tuple->t_data = NULL;
  			scan->rs_inited = false;
  			return;
  		}
  
  		heapgetpage(scan, page);
  
  		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
  
  		dp = (Page) BufferGetPage(scan->rs_cbuf);
  		lines = PageGetMaxOffsetNumber((Page) dp);
  		linesleft = lines;
  		if (backward)
  		{
  			lineoff = lines;
  			lpp = PageGetItemId(dp, lines);
  		}
  		else
  		{
  			lineoff = FirstOffsetNumber;
  			lpp = PageGetItemId(dp, FirstOffsetNumber);
  		}
  	}
  }
  
  /* ----------------
   *		heapgettup_pagemode - fetch next heap tuple in page-at-a-time mode
   *
   *		Same API as heapgettup, but used in page-at-a-time mode
   *
   * The internal logic is much the same as heapgettup's too, but there are some
   * differences: we do not take the buffer content lock (that only needs to
   * happen inside heapgetpage), and we iterate through just the tuples listed
   * in rs_vistuples[] rather than all tuples on the page.  Notice that
   * lineindex is 0-based, where the corresponding loop variable lineoff in
   * heapgettup is 1-based.
   * ----------------
   */
  static void
  heapgettup_pagemode(HeapScanDesc scan,
  					ScanDirection dir,
  					int nkeys,
  					ScanKey key)
  {
  	HeapTuple	tuple = &(scan->rs_ctup);
  	bool		backward = ScanDirectionIsBackward(dir);
  	BlockNumber page;
  	bool		finished;
  	Page		dp;
  	int			lines;
  	int			lineindex;
  	OffsetNumber lineoff;
  	int			linesleft;
  	ItemId		lpp;
  
  	/*
  	 * calculate next starting lineindex, given scan direction
  	 */
  	if (ScanDirectionIsForward(dir))
  	{
  		if (!scan->rs_inited)
  		{
  			/*
  			 * return null immediately if relation is empty
  			 */
  			if (scan->rs_nblocks == 0)
  			{
  				Assert(!BufferIsValid(scan->rs_cbuf));
  				tuple->t_data = NULL;
  				return;
  			}
  			page = scan->rs_startblock; /* first page */
  			heapgetpage(scan, page);
  			lineindex = 0;
  			scan->rs_inited = true;
  		}
  		else
  		{
  			/* continue from previously returned page/tuple */
  			page = scan->rs_cblock;		/* current page */
  			lineindex = scan->rs_cindex + 1;
  		}
  
  		dp = (Page) BufferGetPage(scan->rs_cbuf);
  		lines = scan->rs_ntuples;
  		/* page and lineindex now reference the next visible tid */
  
  		linesleft = lines - lineindex;
  	}
  	else if (backward)
  	{
  		if (!scan->rs_inited)
  		{
  			/*
  			 * return null immediately if relation is empty
  			 */
  			if (scan->rs_nblocks == 0)
  			{
  				Assert(!BufferIsValid(scan->rs_cbuf));
  				tuple->t_data = NULL;
  				return;
  			}
  
  			/*
  			 * Disable reporting to syncscan logic in a backwards scan; it's
  			 * not very likely anyone else is doing the same thing at the same
  			 * time, and much more likely that we'll just bollix things for
  			 * forward scanners.
  			 */
  			scan->rs_syncscan = false;
  			/* start from last page of the scan */
  			if (scan->rs_startblock > 0)
  				page = scan->rs_startblock - 1;
  			else
  				page = scan->rs_nblocks - 1;
  			heapgetpage(scan, page);
  		}
  		else
  		{
  			/* continue from previously returned page/tuple */
  			page = scan->rs_cblock;		/* current page */
  		}
  
  		dp = (Page) BufferGetPage(scan->rs_cbuf);
  		lines = scan->rs_ntuples;
  
  		if (!scan->rs_inited)
  		{
  			lineindex = lines - 1;
  			scan->rs_inited = true;
  		}
  		else
  		{
  			lineindex = scan->rs_cindex - 1;
  		}
  		/* page and lineindex now reference the previous visible tid */
  
  		linesleft = lineindex + 1;
  	}
  	else
  	{
  		/*
  		 * ``no movement'' scan direction: refetch prior tuple
  		 */
  		if (!scan->rs_inited)
  		{
  			Assert(!BufferIsValid(scan->rs_cbuf));
  			tuple->t_data = NULL;
  			return;
  		}
  
  		page = ItemPointerGetBlockNumber(&(tuple->t_self));
  		if (page != scan->rs_cblock)
  			heapgetpage(scan, page);
  
  		/* Since the tuple was previously fetched, needn't lock page here */
  		dp = (Page) BufferGetPage(scan->rs_cbuf);
  		lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
  		lpp = PageGetItemId(dp, lineoff);
  		Assert(ItemIdIsNormal(lpp));
  
  		tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
  		tuple->t_len = ItemIdGetLength(lpp);
  
  		/* check that rs_cindex is in sync */
  		Assert(scan->rs_cindex < scan->rs_ntuples);
  		Assert(lineoff == scan->rs_vistuples[scan->rs_cindex]);
  
  		return;
  	}
  
  	/*
  	 * advance the scan until we find a qualifying tuple or run out of stuff
  	 * to scan
  	 */
  	for (;;)
  	{
  		while (linesleft > 0)
  		{
  			lineoff = scan->rs_vistuples[lineindex];
  			lpp = PageGetItemId(dp, lineoff);
  			Assert(ItemIdIsNormal(lpp));
  
  			tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
  			tuple->t_len = ItemIdGetLength(lpp);
  			ItemPointerSet(&(tuple->t_self), page, lineoff);
  
  			/*
  			 * if current tuple qualifies, return it.
  			 */
  			if (key != NULL)
  			{
  				bool		valid;
  
  				HeapKeyTest(tuple, RelationGetDescr(scan->rs_rd),
  							nkeys, key, valid);
  				if (valid)
  				{
  					scan->rs_cindex = lineindex;
  					return;
  				}
  			}
  			else
  			{
  				scan->rs_cindex = lineindex;
  				return;
  			}
  
  			/*
  			 * otherwise move to the next item on the page
  			 */
  			--linesleft;
  			if (backward)
  				--lineindex;
  			else
  				++lineindex;
  		}
  
  		/*
  		 * if we get here, it means we've exhausted the items on this page and
  		 * it's time to move to the next.
  		 */
  		if (backward)
  		{
  			finished = (page == scan->rs_startblock);
  			if (page == 0)
  				page = scan->rs_nblocks;
  			page--;
  		}
  		else
  		{
  			page++;
  			if (page >= scan->rs_nblocks)
  				page = 0;
  			finished = (page == scan->rs_startblock);
  
  			/*
  			 * Report our new scan position for synchronization purposes. We
  			 * don't do that when moving backwards, however. That would just
  			 * mess up any other forward-moving scanners.
  			 *
  			 * Note: we do this before checking for end of scan so that the
  			 * final state of the position hint is back at the start of the
  			 * rel.  That's not strictly necessary, but otherwise when you run
  			 * the same query multiple times the starting position would shift
  			 * a little bit backwards on every invocation, which is confusing.
  			 * We don't guarantee any specific ordering in general, though.
  			 */
  			if (scan->rs_syncscan)
  				ss_report_location(scan->rs_rd, page);
  		}
  
  		/*
  		 * return NULL if we've exhausted all the pages
  		 */
  		if (finished)
  		{
  			if (BufferIsValid(scan->rs_cbuf))
  				ReleaseBuffer(scan->rs_cbuf);
  			scan->rs_cbuf = InvalidBuffer;
  			scan->rs_cblock = InvalidBlockNumber;
  			tuple->t_data = NULL;
  			scan->rs_inited = false;
  			return;
  		}
  
  		heapgetpage(scan, page);
  
  		dp = (Page) BufferGetPage(scan->rs_cbuf);
  		lines = scan->rs_ntuples;
  		linesleft = lines;
  		if (backward)
  			lineindex = lines - 1;
  		else
  			lineindex = 0;
  	}
  }
  
  
  #if defined(DISABLE_COMPLEX_MACRO)
  /*
   * This is formatted so oddly so that the correspondence to the macro
   * definition in access/heapam.h is maintained.
   */
  Datum
  fastgetattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
  			bool *isnull)
  {
  	return (
  			(attnum) > 0 ?
  			(
  			 ((isnull) ? (*(isnull) = false) : (dummyret) NULL),
  			 HeapTupleNoNulls(tup) ?
  			 (
  			  (tupleDesc)->attrs[(attnum) - 1]->attcacheoff >= 0 ?
  			  (
  			   fetchatt((tupleDesc)->attrs[(attnum) - 1],
  						(char *) (tup)->t_data + (tup)->t_data->t_hoff +
  						(tupleDesc)->attrs[(attnum) - 1]->attcacheoff)
  			   )
  			  :
  			  nocachegetattr((tup), (attnum), (tupleDesc), (isnull))
  			  )
  			 :
  			 (
  			  att_isnull((attnum) - 1, (tup)->t_data->t_bits) ?
  			  (
  			   ((isnull) ? (*(isnull) = true) : (dummyret) NULL),
  			   (Datum) NULL
  			   )
  			  :
  			  (
  			   nocachegetattr((tup), (attnum), (tupleDesc), (isnull))
  			   )
  			  )
  			 )
  			:
  			(
  			 (Datum) NULL
  			 )
  		);
  }
  #endif   /* defined(DISABLE_COMPLEX_MACRO) */
  
  
  /* ----------------------------------------------------------------
   *					 heap access method interface
   * ----------------------------------------------------------------
   */
  
  /* ----------------
   *		relation_open - open any relation by relation OID
   *
   *		If lockmode is not "NoLock", the specified kind of lock is
   *		obtained on the relation.  (Generally, NoLock should only be
   *		used if the caller knows it has some appropriate lock on the
   *		relation already.)
   *
   *		An error is raised if the relation does not exist.
   *
   *		NB: a "relation" is anything with a pg_class entry.  The caller is
   *		expected to check whether the relkind is something it can handle.
   * ----------------
   */
  Relation
  relation_open(Oid relationId, LOCKMODE lockmode)
  {
  	Relation	r;
  
  	Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);
  
  	/* Get the lock before trying to open the relcache entry */
  	if (lockmode != NoLock)
  		LockRelationOid(relationId, lockmode);
  
  	/* The relcache does all the real work... */
  	r = RelationIdGetRelation(relationId);
  
  	if (!RelationIsValid(r))
  		elog(ERROR, "could not open relation with OID %u", relationId);
  
  	/* Make note that we've accessed a temporary relation */
  	if (r->rd_istemp)
  		MyXactAccessedTempRel = true;
  
  	pgstat_initstats(r);
  
  	return r;
  }
  
  /* ----------------
   *		try_relation_open - open any relation by relation OID
   *
   *		Same as relation_open, except return NULL instead of failing
   *		if the relation does not exist.
   * ----------------
   */
  Relation
  try_relation_open(Oid relationId, LOCKMODE lockmode)
  {
  	Relation	r;
  
  	Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);
  
  	/* Get the lock first */
  	if (lockmode != NoLock)
  		LockRelationOid(relationId, lockmode);
  
  	/*
  	 * Now that we have the lock, probe to see if the relation really exists
  	 * or not.
  	 */
  	if (!SearchSysCacheExists(RELOID,
  							  ObjectIdGetDatum(relationId),
  							  0, 0, 0))
  	{
  		/* Release useless lock */
  		if (lockmode != NoLock)
  			UnlockRelationOid(relationId, lockmode);
  
  		return NULL;
  	}
  
  	/* Should be safe to do a relcache load */
  	r = RelationIdGetRelation(relationId);
  
  	if (!RelationIsValid(r))
  		elog(ERROR, "could not open relation with OID %u", relationId);
  
  	/* Make note that we've accessed a temporary relation */
  	if (r->rd_istemp)
  		MyXactAccessedTempRel = true;
  
  	pgstat_initstats(r);
  
  	return r;
  }
  
  /* ----------------
   *		relation_openrv - open any relation specified by a RangeVar
   *
   *		Same as relation_open, but the relation is specified by a RangeVar.
   * ----------------
   */
  Relation
  relation_openrv(const RangeVar *relation, LOCKMODE lockmode)
  {
  	Oid			relOid;
  
  	/*
  	 * Check for shared-cache-inval messages before trying to open the
  	 * relation.  This is needed to cover the case where the name identifies a
  	 * rel that has been dropped and recreated since the start of our
  	 * transaction: if we don't flush the old syscache entry then we'll latch
  	 * onto that entry and suffer an error when we do RelationIdGetRelation.
  	 * Note that relation_open does not need to do this, since a relation's
  	 * OID never changes.
  	 *
  	 * We skip this if asked for NoLock, on the assumption that the caller has
  	 * already ensured some appropriate lock is held.
  	 */
  	if (lockmode != NoLock)
  		AcceptInvalidationMessages();
  
  	/* Look up the appropriate relation using namespace search */
  	relOid = RangeVarGetRelid(relation, false);
  
  	/* Let relation_open do the rest */
  	return relation_open(relOid, lockmode);
  }
  
  /* ----------------
   *		try_relation_openrv - open any relation specified by a RangeVar
   *
   *		Same as relation_openrv, but return NULL instead of failing for
   *		relation-not-found.  (Note that some other causes, such as
   *		permissions problems, will still result in an ereport.)
   * ----------------
   */
  Relation
  try_relation_openrv(const RangeVar *relation, LOCKMODE lockmode)
  {
  	Oid			relOid;
  
  	/*
  	 * Check for shared-cache-inval messages before trying to open the
  	 * relation.  This is needed to cover the case where the name identifies a
  	 * rel that has been dropped and recreated since the start of our
  	 * transaction: if we don't flush the old syscache entry then we'll latch
  	 * onto that entry and suffer an error when we do RelationIdGetRelation.
  	 * Note that relation_open does not need to do this, since a relation's
  	 * OID never changes.
  	 *
  	 * We skip this if asked for NoLock, on the assumption that the caller has
  	 * already ensured some appropriate lock is held.
  	 */
  	if (lockmode != NoLock)
  		AcceptInvalidationMessages();
  
  	/* Look up the appropriate relation using namespace search */
  	relOid = RangeVarGetRelid(relation, true);
  
  	/* Return NULL on not-found */
  	if (!OidIsValid(relOid))
  		return NULL;
  
  	/* Let relation_open do the rest */
  	return relation_open(relOid, lockmode);
  }
  
  /* ----------------
   *		relation_close - close any relation
   *
   *		If lockmode is not "NoLock", we then release the specified lock.
   *
   *		Note that it is often sensible to hold a lock beyond relation_close;
   *		in that case, the lock is released automatically at xact end.
   * ----------------
   */
  void
  relation_close(Relation relation, LOCKMODE lockmode)
  {
  	LockRelId	relid = relation->rd_lockInfo.lockRelId;
  
  	Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);
  
  	/* The relcache does the real work... */
  	RelationClose(relation);
  
  	if (lockmode != NoLock)
  		UnlockRelationId(&relid, lockmode);
  }
  
  
  /* ----------------
   *		heap_open - open a heap relation by relation OID
   *
   *		This is essentially relation_open plus check that the relation
   *		is not an index nor a composite type.  (The caller should also
   *		check that it's not a view before assuming it has storage.)
   * ----------------
   */
  Relation
  heap_open(Oid relationId, LOCKMODE lockmode)
  {
  	Relation	r;
  
  	r = relation_open(relationId, lockmode);
  
  	if (r->rd_rel->relkind == RELKIND_INDEX)
  		ereport(ERROR,
  				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
  				 errmsg("\"%s\" is an index",
  						RelationGetRelationName(r))));
  	else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
  		ereport(ERROR,
  				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
  				 errmsg("\"%s\" is a composite type",
  						RelationGetRelationName(r))));
  
  	return r;
  }
  
  /* ----------------
   *		heap_openrv - open a heap relation specified
   *		by a RangeVar node
   *
   *		As above, but relation is specified by a RangeVar.
   * ----------------
   */
  Relation
  heap_openrv(const RangeVar *relation, LOCKMODE lockmode)
  {
  	Relation	r;
  
  	r = relation_openrv(relation, lockmode);
  
  	if (r->rd_rel->relkind == RELKIND_INDEX)
  		ereport(ERROR,
  				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
  				 errmsg("\"%s\" is an index",
  						RelationGetRelationName(r))));
  	else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
  		ereport(ERROR,
  				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
  				 errmsg("\"%s\" is a composite type",
  						RelationGetRelationName(r))));
  
  	return r;
  }
  
  /* ----------------
   *		try_heap_openrv - open a heap relation specified
   *		by a RangeVar node
   *
   *		As above, but return NULL instead of failing for relation-not-found.
   * ----------------
   */
  Relation
  try_heap_openrv(const RangeVar *relation, LOCKMODE lockmode)
  {
  	Relation	r;
  
  	r = try_relation_openrv(relation, lockmode);
  
  	if (r)
  	{
  		if (r->rd_rel->relkind == RELKIND_INDEX)
  			ereport(ERROR,
  					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
  					 errmsg("\"%s\" is an index",
  							RelationGetRelationName(r))));
  		else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
  			ereport(ERROR,
  					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
  					 errmsg("\"%s\" is a composite type",
  							RelationGetRelationName(r))));
  	}
  
  	return r;
  }
  
  
  /* ----------------
   *		heap_beginscan	- begin relation scan
   *
   * heap_beginscan_strat offers an extended API that lets the caller control
   * whether a nondefault buffer access strategy can be used, and whether
   * syncscan can be chosen (possibly resulting in the scan not starting from
   * block zero).  Both of these default to TRUE with plain heap_beginscan.
   *
   * heap_beginscan_bm is an alternative entry point for setting up a
   * HeapScanDesc for a bitmap heap scan.  Although that scan technology is
   * really quite unlike a standard seqscan, there is just enough commonality
   * to make it worth using the same data structure.
   * ----------------
   */
  HeapScanDesc
  heap_beginscan(Relation relation, Snapshot snapshot,
  			   int nkeys, ScanKey key)
  {
  	return heap_beginscan_internal(relation, snapshot, nkeys, key,
  								   true, true, false);
  }
  
  HeapScanDesc
  heap_beginscan_strat(Relation relation, Snapshot snapshot,
  					 int nkeys, ScanKey key,
  					 bool allow_strat, bool allow_sync)
  {
  	return heap_beginscan_internal(relation, snapshot, nkeys, key,
  								   allow_strat, allow_sync, false);
  }
  
  HeapScanDesc
  heap_beginscan_bm(Relation relation, Snapshot snapshot,
  				  int nkeys, ScanKey key)
  {
  	return heap_beginscan_internal(relation, snapshot, nkeys, key,
  								   false, false, true);
  }
  
  static HeapScanDesc
  heap_beginscan_internal(Relation relation, Snapshot snapshot,
  						int nkeys, ScanKey key,
  						bool allow_strat, bool allow_sync,
  						bool is_bitmapscan)
  {
  	HeapScanDesc scan;
  
  	/*
  	 * increment relation ref count while scanning relation
  	 *
  	 * This is just to make really sure the relcache entry won't go away while
  	 * the scan has a pointer to it.  Caller should be holding the rel open
  	 * anyway, so this is redundant in all normal scenarios...
  	 */
  	RelationIncrementReferenceCount(relation);
  
  	/*
  	 * allocate and initialize scan descriptor
  	 */
  	scan = (HeapScanDesc) palloc(sizeof(HeapScanDescData));
  
  	scan->rs_rd = relation;
  	scan->rs_snapshot = snapshot;
  	scan->rs_nkeys = nkeys;
  	scan->rs_bitmapscan = is_bitmapscan;
  	scan->rs_strategy = NULL;	/* set in initscan */
  	scan->rs_allow_strat = allow_strat;
  	scan->rs_allow_sync = allow_sync;
  
  	/*
  	 * we can use page-at-a-time mode if it's an MVCC-safe snapshot
  	 */
  	scan->rs_pageatatime = IsMVCCSnapshot(snapshot);
  
  	/* we only need to set this up once */
  	scan->rs_ctup.t_tableOid = RelationGetRelid(relation);
  
  	/*
  	 * we do this here instead of in initscan() because heap_rescan also calls
  	 * initscan() and we don't want to allocate memory again
  	 */
  	if (nkeys > 0)
  		scan->rs_key = (ScanKey) palloc(sizeof(ScanKeyData) * nkeys);
  	else
  		scan->rs_key = NULL;
  
  	initscan(scan, key, false);
  
  	return scan;
  }
  
  /* ----------------
   *		heap_rescan		- restart a relation scan
   * ----------------
   */
  void
  heap_rescan(HeapScanDesc scan,
  			ScanKey key)
  {
  	/*
  	 * unpin scan buffers
  	 */
  	if (BufferIsValid(scan->rs_cbuf))
  		ReleaseBuffer(scan->rs_cbuf);
  
  	/*
  	 * reinitialize scan descriptor
  	 */
  	initscan(scan, key, true);
  }
  
  /* ----------------
   *		heap_endscan	- end relation scan
   *
   *		See how to integrate with index scans.
   *		Check handling if reldesc caching.
   * ----------------
   */
  void
  heap_endscan(HeapScanDesc scan)
  {
  	/* Note: no locking manipulations needed */
  
  	/*
  	 * unpin scan buffers
  	 */
  	if (BufferIsValid(scan->rs_cbuf))
  		ReleaseBuffer(scan->rs_cbuf);
  
  	/*
  	 * decrement relation reference count and free scan descriptor storage
  	 */
  	RelationDecrementReferenceCount(scan->rs_rd);
  
  	if (scan->rs_key)
  		pfree(scan->rs_key);
  
  	if (scan->rs_strategy != NULL)
  		FreeAccessStrategy(scan->rs_strategy);
  
  	pfree(scan);
  }
  
  /* ----------------
   *		heap_getnext	- retrieve next tuple in scan
   *
   *		Fix to work with index relations.
   *		We don't return the buffer anymore, but you can get it from the
   *		returned HeapTuple.
   * ----------------
   */
  
  #ifdef HEAPDEBUGALL
  #define HEAPDEBUG_1 \
  	elog(DEBUG2, "heap_getnext([%s,nkeys=%d],dir=%d) called", \
  		 RelationGetRelationName(scan->rs_rd), scan->rs_nkeys, (int) direction)
  #define HEAPDEBUG_2 \
  	elog(DEBUG2, "heap_getnext returning EOS")
  #define HEAPDEBUG_3 \
  	elog(DEBUG2, "heap_getnext returning tuple")
  #else
  #define HEAPDEBUG_1
  #define HEAPDEBUG_2
  #define HEAPDEBUG_3
  #endif   /* !defined(HEAPDEBUGALL) */
  
  
  HeapTuple
  heap_getnext(HeapScanDesc scan, ScanDirection direction)
  {
  	/* Note: no locking manipulations needed */
  
  	HEAPDEBUG_1;				/* heap_getnext( info ) */
  
  	if (scan->rs_pageatatime)
  		heapgettup_pagemode(scan, direction,
  							scan->rs_nkeys, scan->rs_key);
  	else
  		heapgettup(scan, direction, scan->rs_nkeys, scan->rs_key);
  
  	if (scan->rs_ctup.t_data == NULL)
  	{
  		HEAPDEBUG_2;			/* heap_getnext returning EOS */
  		return NULL;
  	}
  
  	/*
  	 * if we get here it means we have a new current scan tuple, so point to
  	 * the proper return buffer and return the tuple.
  	 */
  	HEAPDEBUG_3;				/* heap_getnext returning tuple */
  
  	pgstat_count_heap_getnext(scan->rs_rd);
  
  	return &(scan->rs_ctup);
  }
  
  /*
   *	heap_fetch		- retrieve tuple with given tid
   *
   * On entry, tuple->t_self is the TID to fetch.  We pin the buffer holding
   * the tuple, fill in the remaining fields of *tuple, and check the tuple
   * against the specified snapshot.
   *
   * If successful (tuple found and passes snapshot time qual), then *userbuf
   * is set to the buffer holding the tuple and TRUE is returned.  The caller
   * must unpin the buffer when done with the tuple.
   *
   * If the tuple is not found (ie, item number references a deleted slot),
   * then tuple->t_data is set to NULL and FALSE is returned.
   *
   * If the tuple is found but fails the time qual check, then FALSE is returned
   * but tuple->t_data is left pointing to the tuple.
   *
   * keep_buf determines what is done with the buffer in the FALSE-result cases.
   * When the caller specifies keep_buf = true, we retain the pin on the buffer
   * and return it in *userbuf (so the caller must eventually unpin it); when
   * keep_buf = false, the pin is released and *userbuf is set to InvalidBuffer.
   *
   * stats_relation is the relation to charge the heap_fetch operation against
   * for statistical purposes.  (This could be the heap rel itself, an
   * associated index, or NULL to not count the fetch at all.)
   *
   * heap_fetch does not follow HOT chains: only the exact TID requested will
   * be fetched.
   *
   * It is somewhat inconsistent that we ereport() on invalid block number but
   * return false on invalid item number.  There are a couple of reasons though.
   * One is that the caller can relatively easily check the block number for
   * validity, but cannot check the item number without reading the page
   * himself.  Another is that when we are following a t_ctid link, we can be
   * reasonably confident that the page number is valid (since VACUUM shouldn't
   * truncate off the destination page without having killed the referencing
   * tuple first), but the item number might well not be good.
   */
  bool
  heap_fetch(Relation relation,
  		   Snapshot snapshot,
  		   HeapTuple tuple,
  		   Buffer *userbuf,
  		   bool keep_buf,
  		   Relation stats_relation)
  {
  	ItemPointer tid = &(tuple->t_self);
  	ItemId		lp;
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	bool		valid;
  
  	/*
  	 * Fetch and pin the appropriate page of the relation.
  	 */
  	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
  
  	/*
  	 * Need share lock on buffer to examine tuple commit status.
  	 */
  	LockBuffer(buffer, BUFFER_LOCK_SHARE);
  	page = BufferGetPage(buffer);
  
  	/*
  	 * We'd better check for out-of-range offnum in case of VACUUM since the
  	 * TID was obtained.
  	 */
  	offnum = ItemPointerGetOffsetNumber(tid);
  	if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(page))
  	{
  		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  		if (keep_buf)
  			*userbuf = buffer;
  		else
  		{
  			ReleaseBuffer(buffer);
  			*userbuf = InvalidBuffer;
  		}
  		tuple->t_data = NULL;
  		return false;
  	}
  
  	/*
  	 * get the item line pointer corresponding to the requested tid
  	 */
  	lp = PageGetItemId(page, offnum);
  
  	/*
  	 * Must check for deleted tuple.
  	 */
  	if (!ItemIdIsNormal(lp))
  	{
  		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  		if (keep_buf)
  			*userbuf = buffer;
  		else
  		{
  			ReleaseBuffer(buffer);
  			*userbuf = InvalidBuffer;
  		}
  		tuple->t_data = NULL;
  		return false;
  	}
  
  	/*
  	 * fill in *tuple fields
  	 */
  	tuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
  	tuple->t_len = ItemIdGetLength(lp);
  	tuple->t_tableOid = RelationGetRelid(relation);
  
  	/*
  	 * check time qualification of tuple, then release lock
  	 */
  	valid = HeapTupleSatisfiesVisibility(tuple, snapshot, buffer);
  
  	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  	if (valid)
  	{
  		/*
  		 * All checks passed, so return the tuple as valid. Caller is now
  		 * responsible for releasing the buffer.
  		 */
  		*userbuf = buffer;
  
  		/* Count the successful fetch against appropriate rel, if any */
  		if (stats_relation != NULL)
  			pgstat_count_heap_fetch(stats_relation);
  
  		return true;
  	}
  
  	/* Tuple failed time qual, but maybe caller wants to see it anyway. */
  	if (keep_buf)
  		*userbuf = buffer;
  	else
  	{
  		ReleaseBuffer(buffer);
  		*userbuf = InvalidBuffer;
  	}
  
  	return false;
  }
  
  /*
   *	heap_hot_search_buffer	- search HOT chain for tuple satisfying snapshot
   *
   * On entry, *tid is the TID of a tuple (either a simple tuple, or the root
   * of a HOT chain), and buffer is the buffer holding this tuple.  We search
   * for the first chain member satisfying the given snapshot.  If one is
   * found, we update *tid to reference that tuple's offset number, and
   * return TRUE.  If no match, return FALSE without modifying *tid.
   *
   * 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, Buffer buffer, Snapshot snapshot,
  					   bool *all_dead)
  {
  	Page		dp = (Page) BufferGetPage(buffer);
  	TransactionId prev_xmax = InvalidTransactionId;
  	OffsetNumber offnum;
  	bool		at_chain_start;
  
  	if (all_dead)
  		*all_dead = true;
  
  	Assert(TransactionIdIsValid(RecentGlobalXmin));
  
  	Assert(ItemPointerGetBlockNumber(tid) == BufferGetBlockNumber(buffer));
  	offnum = ItemPointerGetOffsetNumber(tid);
  	at_chain_start = true;
  
  	/* Scan through possible multiple members of HOT-chain */
  	for (;;)
  	{
  		ItemId		lp;
  		HeapTupleData heapTuple;
  
  		/* 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);
  
  		/*
  		 * 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;
  
  		/* If it's visible per the snapshot, we must return it */
  		if (HeapTupleSatisfiesVisibility(&heapTuple, snapshot, buffer))
  		{
  			ItemPointerSetOffsetNumber(tid, offnum);
  			if (all_dead)
  				*all_dead = false;
  			return true;
  		}
  
  		/*
  		 * If we can't see it, maybe no one else can either.  At caller
  		 * request, check whether all chain members are dead to all
  		 * transactions.
  		 */
  		if (all_dead && *all_dead &&
  			HeapTupleSatisfiesVacuum(heapTuple.t_data, RecentGlobalXmin,
  									 buffer) != HEAPTUPLE_DEAD)
  			*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 = HeapTupleHeaderGetXmax(heapTuple.t_data);
  		}
  		else
  			break;				/* end of chain */
  	}
  
  	return false;
  }
  
  /*
   *	heap_hot_search		- search HOT chain for tuple satisfying snapshot
   *
   * This has the same API as heap_hot_search_buffer, except that the caller
   * does not provide the buffer containing the page, rather we access it
   * locally.
   */
  bool
  heap_hot_search(ItemPointer tid, Relation relation, Snapshot snapshot,
  				bool *all_dead)
  {
  	bool		result;
  	Buffer		buffer;
  
  	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
  	LockBuffer(buffer, BUFFER_LOCK_SHARE);
  	result = heap_hot_search_buffer(tid, buffer, snapshot, all_dead);
  	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  	ReleaseBuffer(buffer);
  	return result;
  }
  
  /*
   *	heap_get_latest_tid -  get the latest tid of a specified tuple
   *
   * Actually, this gets the latest version that is visible according to
   * the passed snapshot.  You can pass SnapshotDirty to get the very latest,
   * possibly uncommitted version.
   *
   * *tid is both an input and an output parameter: it is updated to
   * show the latest version of the row.	Note that it will not be changed
   * if no version of the row passes the snapshot test.
   */
  void
  heap_get_latest_tid(Relation relation,
  					Snapshot snapshot,
  					ItemPointer tid)
  {
  	BlockNumber blk;
  	ItemPointerData ctid;
  	TransactionId priorXmax;
  
  	/* this is to avoid Assert failures on bad input */
  	if (!ItemPointerIsValid(tid))
  		return;
  
  	/*
  	 * Since this can be called with user-supplied TID, don't trust the input
  	 * too much.  (RelationGetNumberOfBlocks is an expensive check, so we
  	 * don't check t_ctid links again this way.  Note that it would not do to
  	 * call it just once and save the result, either.)
  	 */
  	blk = ItemPointerGetBlockNumber(tid);
  	if (blk >= RelationGetNumberOfBlocks(relation))
  		elog(ERROR, "block number %u is out of range for relation \"%s\"",
  			 blk, RelationGetRelationName(relation));
  
  	/*
  	 * Loop to chase down t_ctid links.  At top of loop, ctid is the tuple we
  	 * need to examine, and *tid is the TID we will return if ctid turns out
  	 * to be bogus.
  	 *
  	 * Note that we will loop until we reach the end of the t_ctid chain.
  	 * Depending on the snapshot passed, there might be at most one visible
  	 * version of the row, but we don't try to optimize for that.
  	 */
  	ctid = *tid;
  	priorXmax = InvalidTransactionId;	/* cannot check first XMIN */
  	for (;;)
  	{
  		Buffer		buffer;
  		Page		page;
  		OffsetNumber offnum;
  		ItemId		lp;
  		HeapTupleData tp;
  		bool		valid;
  
  		/*
  		 * Read, pin, and lock the page.
  		 */
  		buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&ctid));
  		LockBuffer(buffer, BUFFER_LOCK_SHARE);
  		page = BufferGetPage(buffer);
  
  		/*
  		 * Check for bogus item number.  This is not treated as an error
  		 * condition because it can happen while following a t_ctid link. We
  		 * just assume that the prior tid is OK and return it unchanged.
  		 */
  		offnum = ItemPointerGetOffsetNumber(&ctid);
  		if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(page))
  		{
  			UnlockReleaseBuffer(buffer);
  			break;
  		}
  		lp = PageGetItemId(page, offnum);
  		if (!ItemIdIsNormal(lp))
  		{
  			UnlockReleaseBuffer(buffer);
  			break;
  		}
  
  		/* OK to access the tuple */
  		tp.t_self = ctid;
  		tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
  		tp.t_len = ItemIdGetLength(lp);
  
  		/*
  		 * After following a t_ctid link, we might arrive at an unrelated
  		 * tuple.  Check for XMIN match.
  		 */
  		if (TransactionIdIsValid(priorXmax) &&
  		  !TransactionIdEquals(priorXmax, HeapTupleHeaderGetXmin(tp.t_data)))
  		{
  			UnlockReleaseBuffer(buffer);
  			break;
  		}
  
  		/*
  		 * Check time qualification of tuple; if visible, set it as the new
  		 * result candidate.
  		 */
  		valid = HeapTupleSatisfiesVisibility(&tp, snapshot, buffer);
  		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 | HEAP_IS_LOCKED)) ||
  			ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid))
  		{
  			UnlockReleaseBuffer(buffer);
  			break;
  		}
  
  		ctid = tp.t_data->t_ctid;
  		priorXmax = HeapTupleHeaderGetXmax(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.  Hence callers should look
   * only at XMAX_INVALID.
   */
  static void
  UpdateXmaxHintBits(HeapTupleHeader tuple, Buffer buffer, TransactionId xid)
  {
  	Assert(TransactionIdEquals(HeapTupleHeaderGetXmax(tuple), xid));
  
  	if (!(tuple->t_infomask & (HEAP_XMAX_COMMITTED | HEAP_XMAX_INVALID)))
  	{
  		if (TransactionIdDidCommit(xid))
  			HeapTupleSetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
  								 xid);
  		else
  			HeapTupleSetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
  								 InvalidTransactionId);
  	}
  }
  
  
  /*
   * GetBulkInsertState - prepare status object for a bulk insert
   */
  BulkInsertState
  GetBulkInsertState(void)
  {
  	BulkInsertState bistate;
  
  	bistate = (BulkInsertState) palloc(sizeof(BulkInsertStateData));
  	bistate->strategy = GetAccessStrategy(BAS_BULKWRITE);
  	bistate->current_buf = InvalidBuffer;
  	return bistate;
  }
  
  /*
   * FreeBulkInsertState - clean up after finishing a bulk insert
   */
  void
  FreeBulkInsertState(BulkInsertState bistate)
  {
  	if (bistate->current_buf != InvalidBuffer)
  		ReleaseBuffer(bistate->current_buf);
  	FreeAccessStrategy(bistate->strategy);
  	pfree(bistate);
  }
  
  
  /*
   *	heap_insert		- insert tuple into a heap
   *
   * The new tuple is stamped with current transaction ID and the specified
   * command ID.
   *
   * If the HEAP_INSERT_SKIP_WAL option is specified, the new tuple is not
   * logged in WAL, even for a non-temp relation.  Safe usage of this behavior
   * requires that we arrange that all new tuples go into new pages not
   * containing any tuples from other transactions, and that the relation gets
   * fsync'd before commit.  (See also heap_sync() comments)
   *
   * The HEAP_INSERT_SKIP_FSM option is passed directly to
   * RelationGetBufferForTuple, which see for more info.
   *
   * Note that these options will be applied when inserting into the heap's
   * TOAST table, too, if the tuple requires any out-of-line data.
   *
   * The BulkInsertState object (if any; bistate can be NULL for default
   * behavior) is also just passed through to RelationGetBufferForTuple.
   *
   * The return value is the OID assigned to the tuple (either here or by the
   * caller), or InvalidOid if no OID.  The header fields of *tup are updated
   * to match the stored tuple; in particular tup->t_self receives the actual
   * TID where the tuple was stored.	But note that any toasting of fields
   * within the tuple data is NOT reflected into *tup.
   */
  Oid
  heap_insert(Relation relation, HeapTuple tup, CommandId cid,
  			int options, BulkInsertState bistate)
  {
  	TransactionId xid = GetCurrentTransactionId();
  	HeapTuple	heaptup;
  	Buffer		buffer;
  	bool		all_visible_cleared = false;
  
  	if (relation->rd_rel->relhasoids)
  	{
  #ifdef NOT_USED
  		/* this is redundant with an Assert in HeapTupleSetOid */
  		Assert(tup->t_data->t_infomask & HEAP_HASOID);
  #endif
  
  		/*
  		 * If the object id of this tuple has already been assigned, trust the
  		 * caller.	There are a couple of ways this can happen.  At initial db
  		 * creation, the backend program sets oids for tuples. When we define
  		 * an index, we set the oid.  Finally, in the future, we may allow
  		 * users to set their own object ids in order to support a persistent
  		 * object store (objects need to contain pointers to one another).
  		 */
  		if (!OidIsValid(HeapTupleGetOid(tup)))
  			HeapTupleSetOid(tup, GetNewOid(relation));
  	}
  	else
  	{
  		/* check there is not space for an OID */
  		Assert(!(tup->t_data->t_infomask & HEAP_HASOID));
  	}
  
  	tup->t_data->t_infomask &= ~(HEAP_XACT_MASK);
  	tup->t_data->t_infomask2 &= ~(HEAP2_XACT_MASK);
  	tup->t_data->t_infomask |= HEAP_XMAX_INVALID;
  	HeapTupleHeaderSetXmin(tup->t_data, xid);
  	HeapTupleHeaderSetCmin(tup->t_data, cid);
  	HeapTupleHeaderSetXmax(tup->t_data, 0);		/* for cleanliness */
  	tup->t_tableOid = RelationGetRelid(relation);
  
  	/*
  	 * If the new tuple is too big for storage or contains already toasted
  	 * out-of-line attributes from some other relation, invoke the toaster.
  	 *
  	 * Note: below this point, heaptup is the data we actually intend to store
  	 * into the relation; tup is the caller's original untoasted data.
  	 */
  	if (relation->rd_rel->relkind != RELKIND_RELATION)
  	{
  		/* toast table entries should never be recursively toasted */
  		Assert(!HeapTupleHasExternal(tup));
  		heaptup = tup;
  	}
  	else if (HeapTupleHasExternal(tup) || tup->t_len > TOAST_TUPLE_THRESHOLD)
  		heaptup = toast_insert_or_update(relation, tup, NULL, options);
  	else
  		heaptup = tup;
  
  	/* Find buffer to insert this tuple into */
  	buffer = RelationGetBufferForTuple(relation, heaptup->t_len,
  									   InvalidBuffer, options, bistate);
  
  	/* NO EREPORT(ERROR) from here till changes are logged */
  	START_CRIT_SECTION();
  
  	RelationPutHeapTuple(relation, buffer, heaptup);
  
  	if (PageIsAllVisible(BufferGetPage(buffer)))
  	{
  		all_visible_cleared = true;
  		PageClearAllVisible(BufferGetPage(buffer));
  	}
  
  	/*
  	 * XXX Should we set PageSetPrunable on this page ?
  	 *
  	 * The inserting transaction may eventually abort thus making this tuple
  	 * DEAD and hence available for pruning. Though we don't want to optimize
  	 * for aborts, if no other tuple in this page is UPDATEd/DELETEd, the
  	 * aborted tuple will never be pruned until next vacuum is triggered.
  	 *
  	 * If you do add PageSetPrunable here, add it in heap_xlog_insert too.
  	 */
  
  	MarkBufferDirty(buffer);
  
  	/* XLOG stuff */
  	if (!(options & HEAP_INSERT_SKIP_WAL) && !relation->rd_istemp)
  	{
  		xl_heap_insert xlrec;
  		xl_heap_header xlhdr;
  		XLogRecPtr	recptr;
  		XLogRecData rdata[3];
  		Page		page = BufferGetPage(buffer);
  		uint8		info = XLOG_HEAP_INSERT;
  
  		xlrec.all_visible_cleared = all_visible_cleared;
  		xlrec.target.node = relation->rd_node;
  		xlrec.target.tid = heaptup->t_self;
  		rdata[0].data = (char *) &xlrec;
  		rdata[0].len = SizeOfHeapInsert;
  		rdata[0].buffer = InvalidBuffer;
  		rdata[0].next = &(rdata[1]);
  
  		xlhdr.t_infomask2 = heaptup->t_data->t_infomask2;
  		xlhdr.t_infomask = heaptup->t_data->t_infomask;
  		xlhdr.t_hoff = heaptup->t_data->t_hoff;
  
  		/*
  		 * note we mark rdata[1] as belonging to buffer; if XLogInsert decides
  		 * to write the whole page to the xlog, we don't need to store
  		 * xl_heap_header in the xlog.
  		 */
  		rdata[1].data = (char *) &xlhdr;
  		rdata[1].len = SizeOfHeapHeader;
  		rdata[1].buffer = buffer;
  		rdata[1].buffer_std = true;
  		rdata[1].next = &(rdata[2]);
  
  		/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
  		rdata[2].data = (char *) heaptup->t_data + offsetof(HeapTupleHeaderData, t_bits);
  		rdata[2].len = heaptup->t_len - offsetof(HeapTupleHeaderData, t_bits);
  		rdata[2].buffer = buffer;
  		rdata[2].buffer_std = true;
  		rdata[2].next = NULL;
  
  		/*
  		 * If this is the single and first tuple on page, we can reinit the
  		 * page instead of restoring the whole thing.  Set flag, and hide
  		 * buffer references from XLogInsert.
  		 */
  		if (ItemPointerGetOffsetNumber(&(heaptup->t_self)) == FirstOffsetNumber &&
  			PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
  		{
  			info |= XLOG_HEAP_INIT_PAGE;
  			rdata[1].buffer = rdata[2].buffer = InvalidBuffer;
  		}
  
  		recptr = XLogInsert(RM_HEAP_ID, info, rdata);
  
  		PageSetLSN(page, recptr);
  		PageSetTLI(page, ThisTimeLineID);
  	}
  
  	END_CRIT_SECTION();
  
  	UnlockReleaseBuffer(buffer);
  
  	/* Clear the bit in the visibility map if necessary */
  	if (all_visible_cleared)
  		visibilitymap_clear(relation,
  							ItemPointerGetBlockNumber(&(heaptup->t_self)));
  
  	/*
  	 * If tuple is cachable, mark it for invalidation from the caches in case
  	 * we abort.  Note it is OK to do this after releasing the buffer, because
  	 * the heaptup data structure is all in local memory, not in the shared
  	 * buffer.
  	 */
  	CacheInvalidateHeapTuple(relation, heaptup);
  
  	pgstat_count_heap_insert(relation);
  
  	/*
  	 * If heaptup is a private copy, release it.  Don't forget to copy t_self
  	 * back to the caller's image, too.
  	 */
  	if (heaptup != tup)
  	{
  		tup->t_self = heaptup->t_self;
  		heap_freetuple(heaptup);
  	}
  
  	return HeapTupleGetOid(tup);
  }
  
  /*
   *	simple_heap_insert - insert a tuple
   *
   * Currently, this routine differs from heap_insert only in supplying
   * a default command ID and not allowing access to the speedup options.
   *
   * This should be used rather than using heap_insert directly in most places
   * where we are modifying system catalogs.
   */
  Oid
  simple_heap_insert(Relation relation, HeapTuple tup)
  {
  	return heap_insert(relation, tup, GetCurrentCommandId(true), 0, NULL);
  }
  
  /*
   *	heap_delete - delete a tuple
   *
   * NB: do not call this directly unless you are prepared to deal with
   * concurrent-update conditions.  Use simple_heap_delete instead.
   *
   *	relation - table to be modified (caller must hold suitable lock)
   *	tid - TID of tuple to be deleted
   *	ctid - output parameter, used only for failure case (see below)
   *	update_xmax - output parameter, used only for failure case (see below)
   *	cid - delete command ID (used for visibility test, and stored into
   *		cmax if successful)
   *	crosscheck - if not InvalidSnapshot, also check tuple against this
   *	wait - true if should wait for any conflicting update to commit/abort
   *
   * Normal, successful return value is HeapTupleMayBeUpdated, which
   * actually means we did delete it.  Failure return codes are
   * HeapTupleSelfUpdated, HeapTupleUpdated, or HeapTupleBeingUpdated
   * (the last only possible if wait == false).
   *
   * In the failure cases, the routine returns the tuple's t_ctid and t_xmax.
   * If t_ctid is the same as tid, the tuple was deleted; if different, the
   * tuple was updated, and t_ctid is the location of the replacement tuple.
   * (t_xmax is needed to verify that the replacement tuple matches.)
   */
  HTSU_Result
  heap_delete(Relation relation, ItemPointer tid,
  			ItemPointer ctid, TransactionId *update_xmax,
  			CommandId cid, Snapshot crosscheck, bool wait)
  {
  	HTSU_Result result;
  	TransactionId xid = GetCurrentTransactionId();
  	ItemId		lp;
  	HeapTupleData tp;
  	Page		page;
  	Buffer		buffer;
  	bool		have_tuple_lock = false;
  	bool		iscombo;
  	bool		all_visible_cleared = false;
  
  	Assert(ItemPointerIsValid(tid));
  
  	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
  	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  	page = BufferGetPage(buffer);
  	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
  	Assert(ItemIdIsNormal(lp));
  
  	tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
  	tp.t_len = ItemIdGetLength(lp);
  	tp.t_self = *tid;
  
  l1:
  	result = HeapTupleSatisfiesUpdate(tp.t_data, cid, buffer);
  
  	if (result == HeapTupleInvisible)
  	{
  		UnlockReleaseBuffer(buffer);
  		elog(ERROR, "attempted to delete invisible tuple");
  	}
  	else if (result == HeapTupleBeingUpdated && wait)
  	{
  		TransactionId xwait;
  		uint16		infomask;
  
  		/* must copy state data before unlocking buffer */
  		xwait = HeapTupleHeaderGetXmax(tp.t_data);
  		infomask = tp.t_data->t_infomask;
  
  		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  		/*
  		 * Acquire tuple lock to establish our priority for the tuple (see
  		 * heap_lock_tuple).  LockTuple will release us when we are
  		 * next-in-line for the tuple.
  		 *
  		 * If we are forced to "start over" below, we keep the tuple lock;
  		 * this arranges that we stay at the head of the line while rechecking
  		 * tuple state.
  		 */
  		if (!have_tuple_lock)
  		{
  			LockTuple(relation, &(tp.t_self), ExclusiveLock);
  			have_tuple_lock = true;
  		}
  
  		/*
  		 * Sleep until concurrent transaction ends.  Note that we don't care
  		 * if the locker has an exclusive or shared lock, because we need
  		 * exclusive.
  		 */
  
  		if (infomask & HEAP_XMAX_IS_MULTI)
  		{
  			/* wait for multixact */
  			MultiXactIdWait((MultiXactId) xwait);
  			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  			/*
  			 * If xwait had just locked the tuple then some other xact could
  			 * update this tuple before we get to this point.  Check for xmax
  			 * change, and start over if so.
  			 */
  			if (!(tp.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
  				!TransactionIdEquals(HeapTupleHeaderGetXmax(tp.t_data),
  									 xwait))
  				goto l1;
  
  			/*
  			 * You might think the multixact is necessarily done here, but not
  			 * so: it could have surviving members, namely our own xact or
  			 * other subxacts of this backend.	It is legal for us to delete
  			 * the tuple in either case, however (the latter case is
  			 * essentially a situation of upgrading our former shared lock to
  			 * exclusive).	We don't bother changing the on-disk hint bits
  			 * since we are about to overwrite the xmax altogether.
  			 */
  		}
  		else
  		{
  			/* wait for regular transaction to end */
  			XactLockTableWait(xwait);
  			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  			/*
  			 * xwait is done, but if xwait had just locked the tuple then some
  			 * other xact could update this tuple before we get to this point.
  			 * Check for xmax change, and start over if so.
  			 */
  			if ((tp.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
  				!TransactionIdEquals(HeapTupleHeaderGetXmax(tp.t_data),
  									 xwait))
  				goto l1;
  
  			/* Otherwise check if it committed or aborted */
  			UpdateXmaxHintBits(tp.t_data, buffer, xwait);
  		}
  
  		/*
  		 * We may overwrite if previous xmax aborted, or if it committed but
  		 * only locked the tuple without updating it.
  		 */
  		if (tp.t_data->t_infomask & (HEAP_XMAX_INVALID |
  									 HEAP_IS_LOCKED))
  			result = HeapTupleMayBeUpdated;
  		else
  			result = HeapTupleUpdated;
  	}
  
  	if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
  	{
  		/* Perform additional check for serializable RI updates */
  		if (!HeapTupleSatisfiesVisibility(&tp, crosscheck, buffer))
  			result = HeapTupleUpdated;
  	}
  
  	if (result != HeapTupleMayBeUpdated)
  	{
  		Assert(result == HeapTupleSelfUpdated ||
  			   result == HeapTupleUpdated ||
  			   result == HeapTupleBeingUpdated);
  		Assert(!(tp.t_data->t_infomask & HEAP_XMAX_INVALID));
  		*ctid = tp.t_data->t_ctid;
  		*update_xmax = HeapTupleHeaderGetXmax(tp.t_data);
  		UnlockReleaseBuffer(buffer);
  		if (have_tuple_lock)
  			UnlockTuple(relation, &(tp.t_self), ExclusiveLock);
  		return result;
  	}
  
  	/* replace cid with a combo cid if necessary */
  	HeapTupleHeaderAdjustCmax(tp.t_data, &cid, &iscombo);
  
  	START_CRIT_SECTION();
  
  	/*
  	 * If this transaction commits, the tuple will become DEAD sooner or
  	 * later.  Set flag that this page is a candidate for pruning once our xid
  	 * falls below the OldestXmin horizon.	If the transaction finally aborts,
  	 * the subsequent page pruning will be a no-op and the hint will be
  	 * cleared.
  	 */
  	PageSetPrunable(page, xid);
  
  	if (PageIsAllVisible(page))
  	{
  		all_visible_cleared = true;
  		PageClearAllVisible(page);
  	}
  
  	/* store transaction information of xact deleting the tuple */
  	tp.t_data->t_infomask &= ~(HEAP_XMAX_COMMITTED |
  							   HEAP_XMAX_INVALID |
  							   HEAP_XMAX_IS_MULTI |
  							   HEAP_IS_LOCKED |
  							   HEAP_MOVED);
  	HeapTupleHeaderClearHotUpdated(tp.t_data);
  	HeapTupleHeaderSetXmax(tp.t_data, xid);
  	HeapTupleHeaderSetCmax(tp.t_data, cid, iscombo);
  	/* Make sure there is no forward chain link in t_ctid */
  	tp.t_data->t_ctid = tp.t_self;
  
  	MarkBufferDirty(buffer);
  
  	/* XLOG stuff */
  	if (!relation->rd_istemp)
  	{
  		xl_heap_delete xlrec;
  		XLogRecPtr	recptr;
  		XLogRecData rdata[2];
  
  		xlrec.all_visible_cleared = all_visible_cleared;
  		xlrec.target.node = relation->rd_node;
  		xlrec.target.tid = tp.t_self;
  		rdata[0].data = (char *) &xlrec;
  		rdata[0].len = SizeOfHeapDelete;
  		rdata[0].buffer = InvalidBuffer;
  		rdata[0].next = &(rdata[1]);
  
  		rdata[1].data = NULL;
  		rdata[1].len = 0;
  		rdata[1].buffer = buffer;
  		rdata[1].buffer_std = true;
  		rdata[1].next = NULL;
  
  		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_DELETE, rdata);
  
  		PageSetLSN(page, recptr);
  		PageSetTLI(page, ThisTimeLineID);
  	}
  
  	END_CRIT_SECTION();
  
  	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  	/*
  	 * 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)
  	{
  		/* toast table entries should never be recursively toasted */
  		Assert(!HeapTupleHasExternal(&tp));
  	}
  	else if (HeapTupleHasExternal(&tp))
  		toast_delete(relation, &tp);
  
  	/*
  	 * Mark tuple for invalidation from system caches at next command
  	 * boundary. We have to do this before releasing the buffer because we
  	 * need to look at the contents of the tuple.
  	 */
  	CacheInvalidateHeapTuple(relation, &tp);
  
  	/* Clear the bit in the visibility map if necessary */
  	if (all_visible_cleared)
  		visibilitymap_clear(relation, BufferGetBlockNumber(buffer));
  
  	/* Now we can release the buffer */
  	ReleaseBuffer(buffer);
  
  	/*
  	 * Release the lmgr tuple lock, if we had it.
  	 */
  	if (have_tuple_lock)
  		UnlockTuple(relation, &(tp.t_self), ExclusiveLock);
  
  	pgstat_count_heap_delete(relation);
  
  	return HeapTupleMayBeUpdated;
  }
  
  /*
   *	simple_heap_delete - delete a tuple
   *
   * This routine may be used to delete a tuple when concurrent updates of
   * the target tuple are not expected (for example, because we have a lock
   * on the relation associated with the tuple).	Any failure is reported
   * via ereport().
   */
  void
  simple_heap_delete(Relation relation, ItemPointer tid)
  {
  	HTSU_Result result;
  	ItemPointerData update_ctid;
  	TransactionId update_xmax;
  
  	result = heap_delete(relation, tid,
  						 &update_ctid, &update_xmax,
  						 GetCurrentCommandId(true), InvalidSnapshot,
  						 true /* wait for commit */ );
  	switch (result)
  	{
  		case HeapTupleSelfUpdated:
  			/* Tuple was already updated in current command? */
  			elog(ERROR, "tuple already updated by self");
  			break;
  
  		case HeapTupleMayBeUpdated:
  			/* done successfully */
  			break;
  
  		case HeapTupleUpdated:
  			elog(ERROR, "tuple concurrently updated");
  			break;
  
  		default:
  			elog(ERROR, "unrecognized heap_delete status: %u", result);
  			break;
  	}
  }
  
  /*
   *	heap_update - replace a tuple
   *
   * NB: do not call this directly unless you are prepared to deal with
   * concurrent-update conditions.  Use simple_heap_update instead.
   *
   *	relation - table to be modified (caller must hold suitable lock)
   *	otid - TID of old tuple to be replaced
   *	newtup - newly constructed tuple data to store
   *	ctid - output parameter, used only for failure case (see below)
   *	update_xmax - output parameter, used only for failure case (see below)
   *	cid - update command ID (used for visibility test, and stored into
   *		cmax/cmin if successful)
   *	crosscheck - if not InvalidSnapshot, also check old tuple against this
   *	wait - true if should wait for any conflicting update to commit/abort
   *
   * Normal, successful return value is HeapTupleMayBeUpdated, which
   * actually means we *did* update it.  Failure return codes are
   * HeapTupleSelfUpdated, HeapTupleUpdated, or HeapTupleBeingUpdated
   * (the last only possible if wait == false).
   *
   * On success, the header fields of *newtup are updated to match the new
   * stored tuple; in particular, newtup->t_self is set to the TID where the
   * new tuple was inserted, and its HEAP_ONLY_TUPLE flag is set iff a HOT
   * update was done.  However, any TOAST changes in the new tuple's
   * data are not reflected into *newtup.
   *
   * In the failure cases, the routine returns the tuple's t_ctid and t_xmax.
   * If t_ctid is the same as otid, the tuple was deleted; if different, the
   * tuple was updated, and t_ctid is the location of the replacement tuple.
   * (t_xmax is needed to verify that the replacement tuple matches.)
   */
  HTSU_Result
  heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
  			ItemPointer ctid, TransactionId *update_xmax,
  			CommandId cid, Snapshot crosscheck, bool wait)
  {
  	HTSU_Result result;
  	TransactionId xid = GetCurrentTransactionId();
  	Bitmapset  *hot_attrs;
  	ItemId		lp;
  	HeapTupleData oldtup;
  	HeapTuple	heaptup;
  	Page		page;
  	Buffer		buffer,
  				newbuf;
  	bool		need_toast,
  				already_marked;
  	Size		newtupsize,
  				pagefree;
  	bool		have_tuple_lock = false;
  	bool		iscombo;
  	bool		use_hot_update = false;
  	bool		all_visible_cleared = false;
  	bool		all_visible_cleared_new = false;
  
  	Assert(ItemPointerIsValid(otid));
  
  	/*
  	 * Fetch the list of attributes to be checked for HOT update.  This is
  	 * wasted effort if we fail to update or have to put the new tuple on a
  	 * different page.	But we must compute the list before obtaining buffer
  	 * lock --- in the worst case, if we are doing an update on one of the
  	 * relevant system catalogs, we could deadlock if we try to fetch the list
  	 * later.  In any case, the relcache caches the data so this is usually
  	 * pretty cheap.
  	 *
  	 * Note that we get a copy here, so we need not worry about relcache flush
  	 * happening midway through.
  	 */
  	hot_attrs = RelationGetIndexAttrBitmap(relation);
  
  	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(otid));
  	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  	page = BufferGetPage(buffer);
  	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(otid));
  	Assert(ItemIdIsNormal(lp));
  
  	oldtup.t_data = (HeapTupleHeader) PageGetItem(page, lp);
  	oldtup.t_len = ItemIdGetLength(lp);
  	oldtup.t_self = *otid;
  
  	/*
  	 * 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:
  	result = HeapTupleSatisfiesUpdate(oldtup.t_data, cid, buffer);
  
  	if (result == HeapTupleInvisible)
  	{
  		UnlockReleaseBuffer(buffer);
  		elog(ERROR, "attempted to update invisible tuple");
  	}
  	else if (result == HeapTupleBeingUpdated && wait)
  	{
  		TransactionId xwait;
  		uint16		infomask;
  
  		/* must copy state data before unlocking buffer */
  		xwait = HeapTupleHeaderGetXmax(oldtup.t_data);
  		infomask = oldtup.t_data->t_infomask;
  
  		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  		/*
  		 * Acquire tuple lock to establish our priority for the tuple (see
  		 * heap_lock_tuple).  LockTuple will release us when we are
  		 * next-in-line for the tuple.
  		 *
  		 * If we are forced to "start over" below, we keep the tuple lock;
  		 * this arranges that we stay at the head of the line while rechecking
  		 * tuple state.
  		 */
  		if (!have_tuple_lock)
  		{
  			LockTuple(relation, &(oldtup.t_self), ExclusiveLock);
  			have_tuple_lock = true;
  		}
  
  		/*
  		 * Sleep until concurrent transaction ends.  Note that we don't care
  		 * if the locker has an exclusive or shared lock, because we need
  		 * exclusive.
  		 */
  
  		if (infomask & HEAP_XMAX_IS_MULTI)
  		{
  			/* wait for multixact */
  			MultiXactIdWait((MultiXactId) xwait);
  			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  			/*
  			 * If xwait had just locked the tuple then some other xact could
  			 * update this tuple before we get to this point.  Check for xmax
  			 * change, and start over if so.
  			 */
  			if (!(oldtup.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
  				!TransactionIdEquals(HeapTupleHeaderGetXmax(oldtup.t_data),
  									 xwait))
  				goto l2;
  
  			/*
  			 * 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 update
  			 * the tuple in either case, however (the latter case is
  			 * essentially a situation of upgrading our former shared lock to
  			 * exclusive).	We don't bother changing the on-disk hint bits
  			 * since we are about to overwrite the xmax altogether.
  			 */
  		}
  		else
  		{
  			/* wait for regular transaction to end */
  			XactLockTableWait(xwait);
  			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  
  			/*
  			 * xwait is done, but if xwait had just locked the tuple then some
  			 * other xact could update this tuple before we get to this point.
  			 * Check for xmax change, and start over if so.
  			 */
  			if ((oldtup.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
  				!TransactionIdEquals(HeapTupleHeaderGetXmax(oldtup.t_data),
  									 xwait))
  				goto l2;
  
  			/* Otherwise check if it committed or aborted */
  			UpdateXmaxHintBits(oldtup.t_data, buffer, xwait);
  		}
  
  		/*
  		 * We may overwrite if previous xmax aborted, or if it committed but
  		 * only locked the tuple without updating it.
  		 */
  		if (oldtup.t_data->t_infomask & (HEAP_XMAX_INVALID |
  										 HEAP_IS_LOCKED))
  			result = HeapTupleMayBeUpdated;
  		else
  			result = HeapTupleUpdated;
  	}
  
  	if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
  	{
  		/* Perform additional check for serializable RI updates */
  		if (!HeapTupleSatisfiesVisibility(&oldtup, crosscheck, buffer))
  			result = HeapTupleUpdated;
  	}
  
  	if (result != HeapTupleMayBeUpdated)
  	{
  		Assert(result == HeapTupleSelfUpdated ||
  			   result == HeapTupleUpdated ||
  			   result == HeapTupleBeingUpdated);
  		Assert(!(oldtup.t_data->t_infomask & HEAP_XMAX_INVALID));
  		*ctid = oldtup.t_data->t_ctid;
  		*update_xmax = HeapTupleHeaderGetXmax(oldtup.t_data);
  		UnlockReleaseBuffer(buffer);
  		if (have_tuple_lock)
  			UnlockTuple(relation, &(oldtup.t_self), ExclusiveLock);
  		bms_free(hot_attrs);
  		return result;
  	}
  
  	/* Fill in OID and transaction status data for newtup */
  	if (relation->rd_rel->relhasoids)
  	{
  #ifdef NOT_USED
  		/* this is redundant with an Assert in HeapTupleSetOid */
  		Assert(newtup->t_data->t_infomask & HEAP_HASOID);
  #endif
  		HeapTupleSetOid(newtup, HeapTupleGetOid(&oldtup));
  	}
  	else
  	{
  		/* check there is not space for an OID */
  		Assert(!(newtup->t_data->t_infomask & HEAP_HASOID));
  	}
  
  	newtup->t_data->t_infomask &= ~(HEAP_XACT_MASK);
  	newtup->t_data->t_infomask2 &= ~(HEAP2_XACT_MASK);
  	newtup->t_data->t_infomask |= (HEAP_XMAX_INVALID | HEAP_UPDATED);
  	HeapTupleHeaderSetXmin(newtup->t_data, xid);
  	HeapTupleHeaderSetCmin(newtup->t_data, cid);
  	HeapTupleHeaderSetXmax(newtup->t_data, 0);	/* for cleanliness */
  	newtup->t_tableOid = RelationGetRelid(relation);
  
  	/*
  	 * Replace cid with a combo cid if necessary.  Note that we already put
  	 * the plain cid into the new tuple.
  	 */
  	HeapTupleHeaderAdjustCmax(oldtup.t_data, &cid, &iscombo);
  
  	/*
  	 * If the toaster needs to be activated, OR if the new tuple will not fit
  	 * on the same page as the old, then we need to release the content lock
  	 * (but not the pin!) on the old tuple's buffer while we are off doing
  	 * TOAST and/or table-file-extension work.	We must mark the old tuple to
  	 * show that it's already being updated, else other processes may try to
  	 * update it themselves.
  	 *
  	 * We need to invoke the toaster if there are already any out-of-line
  	 * toasted values present, or if the new tuple is over-threshold.
  	 */
  	if (relation->rd_rel->relkind != RELKIND_RELATION)
  	{
  		/* toast table entries should never be recursively toasted */
  		Assert(!HeapTupleHasExternal(&oldtup));
  		Assert(!HeapTupleHasExternal(newtup));
  		need_toast = false;
  	}
  	else
  		need_toast = (HeapTupleHasExternal(&oldtup) ||
  					  HeapTupleHasExternal(newtup) ||
  					  newtup->t_len > TOAST_TUPLE_THRESHOLD);
  
  	pagefree = PageGetHeapFreeSpace(page);
  
  	newtupsize = MAXALIGN(newtup->t_len);
  
  	if (need_toast || newtupsize > pagefree)
  	{
  		/* Clear obsolete visibility flags ... */
  		oldtup.t_data->t_infomask &= ~(HEAP_XMAX_COMMITTED |
  									   HEAP_XMAX_INVALID |
  									   HEAP_XMAX_IS_MULTI |
  									   HEAP_IS_LOCKED |
  									   HEAP_MOVED);
  		HeapTupleClearHotUpdated(&oldtup);
  		/* ... and store info about transaction updating this tuple */
  		HeapTupleHeaderSetXmax(oldtup.t_data, xid);
  		HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
  		/* temporarily make it look not-updated */
  		oldtup.t_data->t_ctid = oldtup.t_self;
  		already_marked = true;
  		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
  
  		/*
  		 * Let the toaster do its thing, if needed.
  		 *
  		 * Note: below this point, heaptup is the data we actually intend to
  		 * store into the relation; newtup is the caller's original untoasted
  		 * data.
  		 */
  		if (need_toast)
  		{
  			/* Note we always use WAL and FSM during updates */
  			heaptup = toast_insert_or_update(relation, newtup, &oldtup, 0);
  			newtupsize = MAXALIGN(heaptup->t_len);
  		}
  		else
  			heaptup = newtup;
  
  		/*
  		 * Now, do we need a new page for the tuple, or not?  This is a bit
  		 * tricky since someone else could have added tuples to the page while
  		 * we weren't looking.  We have to recheck the available space after
  		 * reacquiring the buffer lock.  But don't bother to do that if the
  		 * former amount of free space is still not enough; it's unlikely
  		 * there's more free now than before.
  		 *
  		 * What's more, if we need to get a new page, we will need to acquire
  		 * buffer locks on both old and new pages.	To avoid deadlock against
  		 * some other backend trying to get the same two locks in the other
  		 * order, we must be consistent about the order we get the locks in.
  		 * We use the rule "lock the lower-numbered page of the relation
  		 * first".  To implement this, we must do RelationGetBufferForTuple
  		 * while not holding the lock on the old page, and we must rely on it
  		 * to get the locks on both pages in the correct order.
  		 */
  		if (newtupsize > pagefree)
  		{
  			/* Assume there's no chance to put heaptup on same page. */
  			newbuf = RelationGetBufferForTuple(relation, heaptup->t_len,
  											   buffer, 0, NULL);
  		}
  		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);
  			}
  			else
  			{
  				/* OK, it fits here, so we're done. */
  				newbuf = buffer;
  			}
  		}
  	}
  	else
  	{
  		/* No TOAST work needed, and it'll fit on same page */
  		already_marked = false;
  		newbuf = buffer;
  		heaptup = newtup;
  	}
  
  	/*
  	 * At this point newbuf and buffer are both pinned and locked, and newbuf
  	 * has enough space for the new tuple.	If they are the same buffer, only
  	 * one pin is held.
  	 */
  
  	if (newbuf == buffer)
  	{
  		/*
  		 * Since the new tuple is going into the same page, we might be able
  		 * to do a HOT update.	Check if any of the index columns have been
  		 * changed.  If not, then HOT update is possible.
  		 */
  		if (HeapSatisfiesHOTUpdate(relation, hot_attrs, &oldtup, heaptup))
  			use_hot_update = true;
  	}
  	else
  	{
  		/* Set a hint that the old page could use prune/defrag */
  		PageSetFull(page);
  	}
  
  	/* NO EREPORT(ERROR) from here till changes are logged */
  	START_CRIT_SECTION();
  
  	/*
  	 * If this transaction commits, the old tuple will become DEAD sooner or
  	 * later.  Set flag that this page is a candidate for pruning once our xid
  	 * falls below the OldestXmin horizon.	If the transaction finally aborts,
  	 * the subsequent page pruning will be a no-op and the hint will be
  	 * cleared.
  	 *
  	 * XXX Should we set hint on newbuf as well?  If the transaction aborts,
  	 * there would be a prunable tuple in the newbuf; but for now we choose
  	 * not to optimize for aborts.	Note that heap_xlog_update must be kept in
  	 * sync if this decision changes.
  	 */
  	PageSetPrunable(page, xid);
  
  	if (use_hot_update)
  	{
  		/* Mark the old tuple as HOT-updated */
  		HeapTupleSetHotUpdated(&oldtup);
  		/* And mark the new tuple as heap-only */
  		HeapTupleSetHeapOnly(heaptup);
  		/* Mark the caller's copy too, in case different from heaptup */
  		HeapTupleSetHeapOnly(newtup);
  	}
  	else
  	{
  		/* Make sure tuples are correctly marked as not-HOT */
  		HeapTupleClearHotUpdated(&oldtup);
  		HeapTupleClearHeapOnly(heaptup);
  		HeapTupleClearHeapOnly(newtup);
  	}
  
  	RelationPutHeapTuple(relation, newbuf, heaptup);	/* insert new tuple */
  
  	if (!already_marked)
  	{
  		/* Clear obsolete visibility flags ... */
  		oldtup.t_data->t_infomask &= ~(HEAP_XMAX_COMMITTED |
  									   HEAP_XMAX_INVALID |
  									   HEAP_XMAX_IS_MULTI |
  									   HEAP_IS_LOCKED |
  									   HEAP_MOVED);
  		/* ... and store info about transaction updating this tuple */
  		HeapTupleHeaderSetXmax(oldtup.t_data, xid);
  		HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
  	}
  
  	/* record address of new tuple in t_ctid of old one */
  	oldtup.t_data->t_ctid = heaptup->t_self;
  
  	/* clear PD_ALL_VISIBLE flags */
  	if (PageIsAllVisible(BufferGetPage(buffer)))
  	{
  		all_visible_cleared = true;
  		PageClearAllVisible(BufferGetPage(buffer));
  	}
  	if (newbuf != buffer && PageIsAllVisible(BufferGetPage(newbuf)))
  	{
  		all_visible_cleared_new = true;
  		PageClearAllVisible(BufferGetPage(newbuf));
  	}
  
  	if (newbuf != buffer)
  		MarkBufferDirty(newbuf);
  	MarkBufferDirty(buffer);
  
  	/* XLOG stuff */
  	if (!relation->rd_istemp)
  	{
  		XLogRecPtr	recptr = log_heap_update(relation, buffer, oldtup.t_self,
  											 newbuf, heaptup, false,
  											 all_visible_cleared,
  											 all_visible_cleared_new);
  
  		if (newbuf != buffer)
  		{
  			PageSetLSN(BufferGetPage(newbuf), recptr);
  			PageSetTLI(BufferGetPage(newbuf), ThisTimeLineID);
  		}
  		PageSetLSN(BufferGetPage(buffer), recptr);
  		PageSetTLI(BufferGetPage(buffer), ThisTimeLineID);
  	}
  
  	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. We have to do this before releasing the buffer because we
  	 * need to look at the contents of the tuple.
  	 */
  	CacheInvalidateHeapTuple(relation, &oldtup);
  
  	/* Clear bits in visibility map */
  	if (all_visible_cleared)
  		visibilitymap_clear(relation, BufferGetBlockNumber(buffer));
  	if (all_visible_cleared_new)
  		visibilitymap_clear(relation, BufferGetBlockNumber(newbuf));
  
  	/* Now we can release the buffer(s) */
  	if (newbuf != buffer)
  		ReleaseBuffer(newbuf);
  	ReleaseBuffer(buffer);
  
  	/*
  	 * If new tuple is cachable, mark it for invalidation from the caches in
  	 * case we abort.  Note it is OK to do this after releasing the buffer,
  	 * because the heaptup data structure is all in local memory, not in the
  	 * shared buffer.
  	 */
  	CacheInvalidateHeapTuple(relation, heaptup);
  
  	/*
  	 * Release the lmgr tuple lock, if we had it.
  	 */
  	if (have_tuple_lock)
  		UnlockTuple(relation, &(oldtup.t_self), ExclusiveLock);
  
  	pgstat_count_heap_update(relation, use_hot_update);
  
  	/*
  	 * If heaptup is a private copy, release it.  Don't forget to copy t_self
  	 * back to the caller's image, too.
  	 */
  	if (heaptup != newtup)
  	{
  		newtup->t_self = heaptup->t_self;
  		heap_freetuple(heaptup);
  	}
  
  	bms_free(hot_attrs);
  
  	return HeapTupleMayBeUpdated;
  }
  
  /*
   * Check if the specified attribute's value is same in both given tuples.
   * Subroutine for HeapSatisfiesHOTUpdate.
   */
  static bool
  heap_tuple_attr_equals(TupleDesc tupdesc, int attrnum,
  					   HeapTuple tup1, HeapTuple tup2)
  {
  	Datum		value1,
  				value2;
  	bool		isnull1,
  				isnull2;
  	Form_pg_attribute att;
  
  	/*
  	 * If it's a whole-tuple reference, say "not equal".  It's not really
  	 * worth supporting this case, since it could only succeed after a no-op
  	 * update, which is hardly a case worth optimizing for.
  	 */
  	if (attrnum == 0)
  		return false;
  
  	/*
  	 * Likewise, automatically say "not equal" for any system attribute other
  	 * than OID and tableOID; we cannot expect these to be consistent in a HOT
  	 * chain, or even to be set correctly yet in the new tuple.
  	 */
  	if (attrnum < 0)
  	{
  		if (attrnum != ObjectIdAttributeNumber &&
  			attrnum != TableOidAttributeNumber)
  			return false;
  	}
  
  	/*
  	 * Extract the corresponding values.  XXX this is pretty inefficient if
  	 * there are many indexed columns.	Should HeapSatisfiesHOTUpdate do a
  	 * single heap_deform_tuple call on each tuple, instead?  But that doesn't
  	 * work for system columns ...
  	 */
  	value1 = heap_getattr(tup1, attrnum, tupdesc, &isnull1);
  	value2 = heap_getattr(tup2, attrnum, tupdesc, &isnull2);
  
  	/*
  	 * If one value is NULL and other is not, then they are certainly not
  	 * equal
  	 */
  	if (isnull1 != isnull2)
  		return false;
  
  	/*
  	 * If both are NULL, they can be considered equal.
  	 */
  	if (isnull1)
  		return true;
  
  	/*
  	 * We do simple binary comparison of the two datums.  This may be overly
  	 * strict because there can be multiple binary representations for the
  	 * same logical value.	But we should be OK as long as there are no false
  	 * positives.  Using a type-specific equality operator is messy because
  	 * there could be multiple notions of equality in different operator
  	 * classes; furthermore, we cannot safely invoke user-defined functions
  	 * while holding exclusive buffer lock.
  	 */
  	if (attrnum <= 0)
  	{
  		/* The only allowed system columns are OIDs, so do this */
  		return (DatumGetObjectId(value1) == DatumGetObjectId(value2));
  	}
  	else
  	{
  		Assert(attrnum <= tupdesc->natts);
  		att = tupdesc->attrs[attrnum - 1];
  		return datumIsEqual(value1, value2, att->attbyval, att->attlen);
  	}
  }
  
  /*
   * Check if the old and new tuples represent a HOT-safe update. To be able
   * to do a HOT update, we must not have changed any columns used in index
   * definitions.
   *
   * The set of attributes to be checked is passed in (we dare not try to
   * compute it while holding exclusive buffer lock...)  NOTE that hot_attrs
   * is destructively modified!  That is OK since this is invoked at most once
   * by heap_update().
   *
   * Returns true if safe to do HOT update.
   */
  static bool
  HeapSatisfiesHOTUpdate(Relation relation, Bitmapset *hot_attrs,
  					   HeapTuple oldtup, HeapTuple newtup)
  {
  	int			attrnum;
  
  	while ((attrnum = bms_first_member(hot_attrs)) >= 0)
  	{
  		/* Adjust for system attributes */
  		attrnum += FirstLowInvalidHeapAttributeNumber;
  
  		/* If the attribute value has changed, we can't do HOT update */
  		if (!heap_tuple_attr_equals(RelationGetDescr(relation), attrnum,
  									oldtup, newtup))
  			return false;
  	}
  
  	return true;
  }
  
  /*
   *	simple_heap_update - replace a tuple
   *
   * This routine may be used to update a tuple when concurrent updates of
   * the target tuple are not expected (for example, because we have a lock
   * on the relation associated with the tuple).	Any failure is reported
   * via ereport().
   */
  void
  simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
  {
  	HTSU_Result result;
  	ItemPointerData update_ctid;
  	TransactionId update_xmax;
  
  	result = heap_update(relation, otid, tup,
  						 &update_ctid, &update_xmax,
  						 GetCurrentCommandId(true), InvalidSnapshot,
  						 true /* wait for commit */ );
  	switch (result)
  	{
  		case HeapTupleSelfUpdated:
  			/* Tuple was already updated in current command? */
  			elog(ERROR, "tuple already updated by self");
  			break;
  
  		case HeapTupleMayBeUpdated:
  			/* done successfully */
  			break;
  
  		case HeapTupleUpdated:
  			elog(ERROR, "tuple concurrently updated");
  			break;
  
  		default:
  			elog(ERROR, "unrecognized heap_update status: %u", result);
  			break;
  	}
  }
  
  /*
   *	heap_lock_tuple - lock a tuple in shared or exclusive mode
   *
   * Note that this acquires a buffer pin, which the caller must release.
   *
   * Input parameters:
   *	relation: relation containing tuple (caller must hold suitable lock)
   *	tuple->t_self: TID of tuple to lock (rest of struct need not be valid)
   *	cid: current command ID (used for visibility test, and stored into
   *		tuple's cmax if lock is successful)
   *	mode: indicates if shared or exclusive tuple lock is desired
   *	nowait: if true, ereport rather than blocking if lock not available
   *
   * Output parameters:
   *	*tuple: all fields filled in
   *	*buffer: set to buffer holding tuple (pinned but not locked at exit)
   *	*ctid: set to tuple's t_ctid, but only in failure cases
   *	*update_xmax: set to tuple's xmax, but only in failure cases
   *
   * Function result may be:
   *	HeapTupleMayBeUpdated: lock was successfully acquired
   *	HeapTupleSelfUpdated: lock failed because tuple updated by self
   *	HeapTupleUpdated: lock failed because tuple updated by other xact
   *
   * In the failure cases, the routine returns the tuple's t_ctid and t_xmax.
   * If t_ctid is the same as t_self, the tuple was deleted; if different, the
   * tuple was updated, and t_ctid is the location of the replacement tuple.
   * (t_xmax is needed to verify that the replacement tuple matches.)
   *
   *
   * NOTES: because the shared-memory lock table is of finite size, but users
   * could reasonably want to lock large numbers of tuples, we do not rely on
   * the standard lock manager to store tuple-level locks over the long term.
   * Instead, a tuple is marked as locked by setting the current transaction's
   * XID as its XMAX, and setting additional infomask bits to distinguish this
   * usage from the more normal case of having deleted the tuple.  When
   * multiple transactions concurrently share-lock a tuple, the first locker's
   * XID is replaced in XMAX with a MultiTransactionId representing the set of
   * XIDs currently holding share-locks.
   *
   * When it is necessary to wait for a tuple-level lock to be released, the
   * basic delay is provided by XactLockTableWait or MultiXactIdWait on the
   * contents of the tuple's XMAX.  However, that mechanism will release all
   * waiters concurrently, so there would be a race condition as to which
   * waiter gets the tuple, potentially leading to indefinite starvation of
   * some waiters.  The possibility of share-locking makes the problem much
   * worse --- a steady stream of share-lockers can easily block an exclusive
   * locker forever.	To provide more reliable semantics about who gets a
   * tuple-level lock first, we use the standard lock manager.  The protocol
   * for waiting for a tuple-level lock is really
   *		LockTuple()
   *		XactLockTableWait()
   *		mark tuple as locked by me
   *		UnlockTuple()
   * When there are multiple waiters, arbitration of who is to get the lock next
   * is provided by LockTuple().	However, at most one tuple-level lock will
   * be held or awaited per backend at any time, so we don't risk overflow
   * of the lock table.  Note that incoming share-lockers are required to
   * do LockTuple as well, if there is any conflict, to ensure that they don't
   * starve out waiting exclusive-lockers.  However, if there is not any active
   * conflict for a tuple, we don't incur any extra overhead.
   */
  HTSU_Result
  heap_lock_tuple(Relation relation, HeapTuple tuple, Buffer *buffer,
  				ItemPointer ctid, TransactionId *update_xmax,
  				CommandId cid, LockTupleMode mode, bool nowait)
  {
  	HTSU_Result result;
  	ItemPointer tid = &(tuple->t_self);
  	ItemId		lp;
  	Page		page;
  	TransactionId xid;
  	TransactionId xmax;
  	uint16		old_infomask;
  	uint16		new_infomask;
  	LOCKMODE	tuple_lock_type;
  	bool		have_tuple_lock = false;
  
  	tuple_lock_type = (mode == LockTupleShared) ? ShareLock : ExclusiveLock;
  
  	*buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
  	LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  
  	page = BufferGetPage(*buffer);
  	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
  	Assert(ItemIdIsNormal(lp));
  
  	tuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
  	tuple->t_len = ItemIdGetLength(lp);
  	tuple->t_tableOid = RelationGetRelid(relation);
  
  l3:
  	result = HeapTupleSatisfiesUpdate(tuple->t_data, cid, *buffer);
  
  	if (result == HeapTupleInvisible)
  	{
  		UnlockReleaseBuffer(*buffer);
  		elog(ERROR, "attempted to lock invisible tuple");
  	}
  	else if (result == HeapTupleBeingUpdated)
  	{
  		TransactionId xwait;
  		uint16		infomask;
  
  		/* must copy state data before unlocking buffer */
  		xwait = HeapTupleHeaderGetXmax(tuple->t_data);
  		infomask = tuple->t_data->t_infomask;
  
  		LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
  
  		/*
  		 * If we wish to acquire share lock, and the tuple is already
  		 * share-locked by a multixact that includes any subtransaction of the
  		 * current top transaction, then we effectively hold the desired lock
  		 * already.  We *must* succeed without trying to take the tuple lock,
  		 * else we will deadlock against anyone waiting to acquire exclusive
  		 * lock.  We don't need to make any state changes in this case.
  		 */
  		if (mode == LockTupleShared &&
  			(infomask & HEAP_XMAX_IS_MULTI) &&
  			MultiXactIdIsCurrent((MultiXactId) xwait))
  		{
  			Assert(infomask & HEAP_XMAX_SHARED_LOCK);
  			/* Probably can't hold tuple lock here, but may as well check */
  			if (have_tuple_lock)
  				UnlockTuple(relation, tid, tuple_lock_type);
  			return HeapTupleMayBeUpdated;
  		}
  
  		/*
  		 * Acquire tuple lock to establish our priority for the tuple.
  		 * LockTuple will release us when we are next-in-line for the tuple.
  		 * We must do this even if we are share-locking.
  		 *
  		 * If we are forced to "start over" below, we keep the tuple lock;
  		 * this arranges that we stay at the head of the line while rechecking
  		 * tuple state.
  		 */
  		if (!have_tuple_lock)
  		{
  			if (nowait)
  			{
  				if (!ConditionalLockTuple(relation, tid, tuple_lock_type))
  					ereport(ERROR,
  							(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
  					errmsg("could not obtain lock on row in relation \"%s\"",
  						   RelationGetRelationName(relation))));
  			}
  			else
  				LockTuple(relation, tid, tuple_lock_type);
  			have_tuple_lock = true;
  		}
  
  		if (mode == LockTupleShared && (infomask & HEAP_XMAX_SHARED_LOCK))
  		{
  			/*
  			 * Acquiring sharelock when there's at least one sharelocker
  			 * already.  We need not wait for him/them to complete.
  			 */
  			LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  
  			/*
  			 * Make sure it's still a shared lock, else start over.  (It's OK
  			 * if the ownership of the shared lock has changed, though.)
  			 */
  			if (!(tuple->t_data->t_infomask & HEAP_XMAX_SHARED_LOCK))
  				goto l3;
  		}
  		else if (infomask & HEAP_XMAX_IS_MULTI)
  		{
  			/* wait for multixact to end */
  			if (nowait)
  			{
  				if (!ConditionalMultiXactIdWait((MultiXactId) xwait))
  					ereport(ERROR,
  							(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
  					errmsg("could not obtain lock on row in relation \"%s\"",
  						   RelationGetRelationName(relation))));
  			}
  			else
  				MultiXactIdWait((MultiXactId) xwait);
  
  			LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  
  			/*
  			 * If xwait had just locked the tuple then some other xact could
  			 * update this tuple before we get to this point. Check for xmax
  			 * change, and start over if so.
  			 */
  			if (!(tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
  				!TransactionIdEquals(HeapTupleHeaderGetXmax(tuple->t_data),
  									 xwait))
  				goto l3;
  
  			/*
  			 * 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 lock the
  			 * tuple in either case, however.  We don't bother changing the
  			 * on-disk hint bits since we are about to overwrite the xmax
  			 * altogether.
  			 */
  		}
  		else
  		{
  			/* wait for regular transaction to end */
  			if (nowait)
  			{
  				if (!ConditionalXactLockTableWait(xwait))
  					ereport(ERROR,
  							(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
  					errmsg("could not obtain lock on row in relation \"%s\"",
  						   RelationGetRelationName(relation))));
  			}
  			else
  				XactLockTableWait(xwait);
  
  			LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
  
  			/*
  			 * xwait is done, but if xwait had just locked the tuple then some
  			 * other xact could update this tuple before we get to this point.
  			 * Check for xmax change, and start over if so.
  			 */
  			if ((tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
  				!TransactionIdEquals(HeapTupleHeaderGetXmax(tuple->t_data),
  									 xwait))
  				goto l3;
  
  			/* Otherwise check if it committed or aborted */
  			UpdateXmaxHintBits(tuple->t_data, *buffer, xwait);
  		}
  
  		/*
  		 * We may lock if previous xmax aborted, or if it committed but only
  		 * locked the tuple without updating it.  The case where we didn't
  		 * wait because we are joining an existing shared lock is correctly
  		 * handled, too.
  		 */
  		if (tuple->t_data->t_infomask & (HEAP_XMAX_INVALID |
  										 HEAP_IS_LOCKED))
  			result = HeapTupleMayBeUpdated;
  		else
  			result = HeapTupleUpdated;
  	}
  
  	if (result != HeapTupleMayBeUpdated)
  	{
  		Assert(result == HeapTupleSelfUpdated || result == HeapTupleUpdated);
  		Assert(!(tuple->t_data->t_infomask & HEAP_XMAX_INVALID));
  		*ctid = tuple->t_data->t_ctid;
  		*update_xmax = HeapTupleHeaderGetXmax(tuple->t_data);
  		LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
  		if (have_tuple_lock)
  			UnlockTuple(relation, tid, tuple_lock_type);
  		return result;
  	}
  
  	/*
  	 * We might already hold the desired lock (or stronger), possibly under a
  	 * different subtransaction of the current top transaction.  If so, there
  	 * is no need to change state or issue a WAL record.  We already handled
  	 * the case where this is true for xmax being a MultiXactId, so now check
  	 * for cases where it is a plain TransactionId.
  	 *
  	 * Note in particular that this covers the case where we already hold
  	 * exclusive lock on the tuple and the caller only wants shared lock. It
  	 * would certainly not do to give up the exclusive lock.
  	 */
  	xmax = HeapTupleHeaderGetXmax(tuple->t_data);
  	old_infomask = tuple->t_data->t_infomask;
  
  	if (!(old_infomask & (HEAP_XMAX_INVALID |
  						  HEAP_XMAX_COMMITTED |
  						  HEAP_XMAX_IS_MULTI)) &&
  		(mode == LockTupleShared ?
  		 (old_infomask & HEAP_IS_LOCKED) :
  		 (old_infomask & HEAP_XMAX_EXCL_LOCK)) &&
  		TransactionIdIsCurrentTransactionId(xmax))
  	{
  		LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
  		/* Probably can't hold tuple lock here, but may as well check */
  		if (have_tuple_lock)
  			UnlockTuple(relation, tid, tuple_lock_type);
  		return HeapTupleMayBeUpdated;
  	}
  
  	/*
  	 * 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.
  	 */
  	xid = GetCurrentTransactionId();
  
  	new_infomask = old_infomask & ~(HEAP_XMAX_COMMITTED |
  									HEAP_XMAX_INVALID |
  									HEAP_XMAX_IS_MULTI |
  									HEAP_IS_LOCKED |
  									HEAP_MOVED);
  
  	if (mode == LockTupleShared)
  	{
  		/*
  		 * If this is the first acquisition of a shared lock 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();
  
  		new_infomask |= HEAP_XMAX_SHARED_LOCK;
  
  		/*
  		 * Check to see if we need a MultiXactId because there are multiple
  		 * lockers.
  		 *
  		 * HeapTupleSatisfiesUpdate 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 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.
  		 */
  		if (!(old_infomask & (HEAP_XMAX_INVALID | HEAP_XMAX_COMMITTED)))
  		{
  			if (old_infomask & HEAP_XMAX_IS_MULTI)
  			{
  				/*
  				 * If the XMAX is already a MultiXactId, then we need to
  				 * expand it to include our own TransactionId.
  				 */
  				xid = MultiXactIdExpand((MultiXactId) xmax, xid);
  				new_infomask |= HEAP_XMAX_IS_MULTI;
  			}
  			else if (TransactionIdIsInProgress(xmax))
  			{
  				/*
  				 * If the XMAX is a valid TransactionId, then we need to
  				 * create a new MultiXactId that includes both the old locker
  				 * and our own TransactionId.
  				 */
  				xid = MultiXactIdCreate(xmax, xid);
  				new_infomask |= HEAP_XMAX_IS_MULTI;
  			}
  			else
  			{
  				/*
  				 * Can get here iff HeapTupleSatisfiesUpdate saw the old xmax
  				 * as running, but it finished before
  				 * TransactionIdIsInProgress() got to run.	Treat it like
  				 * there's no locker in the tuple.
  				 */
  			}
  		}
  		else
  		{
  			/*
  			 * There was no previous locker, so just insert our own
  			 * TransactionId.
  			 */
  		}
  	}
  	else
  	{
  		/* We want an exclusive lock on the tuple */
  		new_infomask |= HEAP_XMAX_EXCL_LOCK;
  	}
  
  	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.
  	 */
  	tuple->t_data->t_infomask = new_infomask;
  	HeapTupleHeaderClearHotUpdated(tuple->t_data);
  	HeapTupleHeaderSetXmax(tuple->t_data, xid);
  	/* Make sure there is no forward chain link in t_ctid */
  	tuple->t_data->t_ctid = *tid;
  
  	MarkBufferDirty(*buffer);
  
  	/*
  	 * XLOG stuff.	You might think that we don't need an XLOG record because
  	 * there is no state change worth restoring after a crash.	You would be
  	 * wrong however: we have just written either a TransactionId or a
  	 * MultiXactId that may never have been seen on disk before, and we need
  	 * to make sure that there are XLOG entries covering those ID numbers.
  	 * Else the same IDs might be re-used after a crash, which would be
  	 * disastrous if this page made it to disk before the crash.  Essentially
  	 * we have to enforce the WAL log-before-data rule even in this case.
  	 * (Also, in a PITR log-shipping or 2PC environment, we have to have XLOG
  	 * entries for everything anyway.)
  	 */
  	if (!relation->rd_istemp)
  	{
  		xl_heap_lock xlrec;
  		XLogRecPtr	recptr;
  		XLogRecData rdata[2];
  
  		xlrec.target.node = relation->rd_node;
  		xlrec.target.tid = tuple->t_self;
  		xlrec.locking_xid = xid;
  		xlrec.xid_is_mxact = ((new_infomask & HEAP_XMAX_IS_MULTI) != 0);
  		xlrec.shared_lock = (mode == LockTupleShared);
  		rdata[0].data = (char *) &xlrec;
  		rdata[0].len = SizeOfHeapLock;
  		rdata[0].buffer = InvalidBuffer;
  		rdata[0].next = &(rdata[1]);
  
  		rdata[1].data = NULL;
  		rdata[1].len = 0;
  		rdata[1].buffer = *buffer;
  		rdata[1].buffer_std = true;
  		rdata[1].next = NULL;
  
  		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_LOCK, rdata);
  
  		PageSetLSN(page, recptr);
  		PageSetTLI(page, ThisTimeLineID);
  	}
  
  	END_CRIT_SECTION();
  
  	LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
  
  	/*
  	 * Don't update the visibility map here. Locking a tuple doesn't change
  	 * visibility info.
  	 */
  
  	/*
  	 * Now that we have successfully marked the tuple as locked, we can
  	 * release the lmgr tuple lock, if we had it.
  	 */
  	if (have_tuple_lock)
  		UnlockTuple(relation, tid, tuple_lock_type);
  
  	return HeapTupleMayBeUpdated;
  }
  
  
  /*
   * heap_inplace_update - update a tuple "in place" (ie, overwrite it)
   *
   * Overwriting violates both MVCC and transactional safety, so the uses
   * of this function in Postgres are extremely limited.	Nonetheless we
   * find some places to use it.
   *
   * The tuple cannot change size, and therefore it's reasonable to assume
   * that its null bitmap (if any) doesn't change either.  So we just
   * overwrite the data portion of the tuple without touching the null
   * bitmap or any of the header fields.
   *
   * tuple is an in-memory tuple structure containing the data to be written
   * over the target tuple.  Also, tuple->t_self identifies the target tuple.
   */
  void
  heap_inplace_update(Relation relation, HeapTuple tuple)
  {
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  	uint32		oldlen;
  	uint32		newlen;
  
  	buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&(tuple->t_self)));
  	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
  	page = (Page) BufferGetPage(buffer);
  
  	offnum = ItemPointerGetOffsetNumber(&(tuple->t_self));
  	if (PageGetMaxOffsetNumber(page) >= offnum)
  		lp = PageGetItemId(page, offnum);
  
  	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  		elog(ERROR, "heap_inplace_update: invalid lp");
  
  	htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  	oldlen = ItemIdGetLength(lp) - htup->t_hoff;
  	newlen = tuple->t_len - tuple->t_data->t_hoff;
  	if (oldlen != newlen || htup->t_hoff != tuple->t_data->t_hoff)
  		elog(ERROR, "heap_inplace_update: wrong tuple length");
  
  	/* NO EREPORT(ERROR) from here till changes are logged */
  	START_CRIT_SECTION();
  
  	memcpy((char *) htup + htup->t_hoff,
  		   (char *) tuple->t_data + tuple->t_data->t_hoff,
  		   newlen);
  
  	MarkBufferDirty(buffer);
  
  	/* XLOG stuff */
  	if (!relation->rd_istemp)
  	{
  		xl_heap_inplace xlrec;
  		XLogRecPtr	recptr;
  		XLogRecData rdata[2];
  
  		xlrec.target.node = relation->rd_node;
  		xlrec.target.tid = tuple->t_self;
  
  		rdata[0].data = (char *) &xlrec;
  		rdata[0].len = SizeOfHeapInplace;
  		rdata[0].buffer = InvalidBuffer;
  		rdata[0].next = &(rdata[1]);
  
  		rdata[1].data = (char *) htup + htup->t_hoff;
  		rdata[1].len = newlen;
  		rdata[1].buffer = buffer;
  		rdata[1].buffer_std = true;
  		rdata[1].next = NULL;
  
  		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_INPLACE, rdata);
  
  		PageSetLSN(page, recptr);
  		PageSetTLI(page, ThisTimeLineID);
  	}
  
  	END_CRIT_SECTION();
  
  	UnlockReleaseBuffer(buffer);
  
  	/* Send out shared cache inval if necessary */
  	if (!IsBootstrapProcessingMode())
  		CacheInvalidateHeapTuple(relation, tuple);
  }
  
  
  /*
   * heap_freeze_tuple
   *
   * Check to see whether any of the XID fields of a tuple (xmin, xmax, xvac)
   * are older than the specified cutoff XID.  If so, replace them with
   * FrozenTransactionId or InvalidTransactionId as appropriate, and return
   * TRUE.  Return FALSE if nothing was changed.
   *
   * It is assumed that the caller has checked the tuple with
   * HeapTupleSatisfiesVacuum() and determined that it is not HEAPTUPLE_DEAD
   * (else we should be removing the tuple, not freezing it).
   *
   * NB: cutoff_xid *must* be <= the current global xmin, to ensure that any
   * XID older than it could neither be running nor seen as running by any
   * open transaction.  This ensures that the replacement will not change
   * anyone's idea of the tuple state.  Also, since we assume the tuple is
   * not HEAPTUPLE_DEAD, the fact that an XID is not still running allows us
   * to assume that it is either committed good or aborted, as appropriate;
   * so we need no external state checks to decide what to do.  (This is good
   * because this function is applied during WAL recovery, when we don't have
   * access to any such state, and can't depend on the hint bits to be set.)
   *
   * In lazy VACUUM, we call this while initially holding only a shared lock
   * on the tuple's buffer.  If any change is needed, we trade that in for an
   * exclusive lock before making the change.  Caller should pass the buffer ID
   * if shared lock is held, InvalidBuffer if exclusive lock is already held.
   *
   * Note: it might seem we could make the changes without exclusive lock, since
   * TransactionId read/write is assumed atomic anyway.  However there is a race
   * condition: someone who just fetched an old XID that we overwrite here could
   * conceivably not finish checking the XID against pg_clog before we finish
   * the VACUUM and perhaps truncate off the part of pg_clog he needs.  Getting
   * exclusive lock ensures no other backend is in process of checking the
   * tuple status.  Also, getting exclusive lock makes it safe to adjust the
   * infomask bits.
   */
  bool
  heap_freeze_tuple(HeapTupleHeader tuple, TransactionId cutoff_xid,
  				  Buffer buf)
  {
  	bool		changed = false;
  	TransactionId xid;
  
  	xid = HeapTupleHeaderGetXmin(tuple);
  	if (TransactionIdIsNormal(xid) &&
  		TransactionIdPrecedes(xid, cutoff_xid))
  	{
  		if (buf != InvalidBuffer)
  		{
  			/* trade in share lock for exclusive lock */
  			LockBuffer(buf, BUFFER_LOCK_UNLOCK);
  			LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
  			buf = InvalidBuffer;
  		}
  		HeapTupleHeaderSetXmin(tuple, FrozenTransactionId);
  
  		/*
  		 * Might as well fix the hint bits too; usually XMIN_COMMITTED will
  		 * already be set here, but there's a small chance not.
  		 */
  		Assert(!(tuple->t_infomask & HEAP_XMIN_INVALID));
  		tuple->t_infomask |= HEAP_XMIN_COMMITTED;
  		changed = true;
  	}
  
  	/*
  	 * When we release shared lock, it's possible for someone else to change
  	 * xmax before we get the lock back, so repeat the check after acquiring
  	 * exclusive lock.	(We don't need this pushup for xmin, because only
  	 * VACUUM could be interested in changing an existing tuple's xmin, and
  	 * there's only one VACUUM allowed on a table at a time.)
  	 */
  recheck_xmax:
  	if (!(tuple->t_infomask & HEAP_XMAX_IS_MULTI))
  	{
  		xid = HeapTupleHeaderGetXmax(tuple);
  		if (TransactionIdIsNormal(xid) &&
  			TransactionIdPrecedes(xid, cutoff_xid))
  		{
  			if (buf != InvalidBuffer)
  			{
  				/* trade in share lock for exclusive lock */
  				LockBuffer(buf, BUFFER_LOCK_UNLOCK);
  				LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
  				buf = InvalidBuffer;
  				goto recheck_xmax;		/* see comment above */
  			}
  			HeapTupleHeaderSetXmax(tuple, InvalidTransactionId);
  
  			/*
  			 * The tuple might be marked either XMAX_INVALID or XMAX_COMMITTED
  			 * + LOCKED.  Normalize to INVALID just to be sure no one gets
  			 * confused.
  			 */
  			tuple->t_infomask &= ~HEAP_XMAX_COMMITTED;
  			tuple->t_infomask |= HEAP_XMAX_INVALID;
  			HeapTupleHeaderClearHotUpdated(tuple);
  			changed = true;
  		}
  	}
  	else
  	{
  		/*----------
  		 * XXX perhaps someday we should zero out very old MultiXactIds here?
  		 *
  		 * The only way a stale MultiXactId could pose a problem is if a
  		 * tuple, having once been multiply-share-locked, is not touched by
  		 * any vacuum or attempted lock or deletion for just over 4G MultiXact
  		 * creations, and then in the probably-narrow window where its xmax
  		 * is again a live MultiXactId, someone tries to lock or delete it.
  		 * Even then, another share-lock attempt would work fine.  An
  		 * exclusive-lock or delete attempt would face unexpected delay, or
  		 * in the very worst case get a deadlock error.  This seems an
  		 * extremely low-probability scenario with minimal downside even if
  		 * it does happen, so for now we don't do the extra bookkeeping that
  		 * would be needed to clean out MultiXactIds.
  		 *----------
  		 */
  	}
  
  	/*
  	 * Although xvac per se could only be set by VACUUM, it shares physical
  	 * storage space with cmax, and so could be wiped out by someone setting
  	 * xmax.  Hence recheck after changing lock, same as for xmax itself.
  	 */
  recheck_xvac:
  	if (tuple->t_infomask & HEAP_MOVED)
  	{
  		xid = HeapTupleHeaderGetXvac(tuple);
  		if (TransactionIdIsNormal(xid) &&
  			TransactionIdPrecedes(xid, cutoff_xid))
  		{
  			if (buf != InvalidBuffer)
  			{
  				/* trade in share lock for exclusive lock */
  				LockBuffer(buf, BUFFER_LOCK_UNLOCK);
  				LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
  				buf = InvalidBuffer;
  				goto recheck_xvac;		/* see comment above */
  			}
  
  			/*
  			 * If a MOVED_OFF tuple is not dead, the xvac transaction must
  			 * have failed; whereas a non-dead MOVED_IN tuple must mean the
  			 * xvac transaction succeeded.
  			 */
  			if (tuple->t_infomask & HEAP_MOVED_OFF)
  				HeapTupleHeaderSetXvac(tuple, InvalidTransactionId);
  			else
  				HeapTupleHeaderSetXvac(tuple, FrozenTransactionId);
  
  			/*
  			 * Might as well fix the hint bits too; usually XMIN_COMMITTED
  			 * will already be set here, but there's a small chance not.
  			 */
  			Assert(!(tuple->t_infomask & HEAP_XMIN_INVALID));
  			tuple->t_infomask |= HEAP_XMIN_COMMITTED;
  			changed = true;
  		}
  	}
  
  	return changed;
  }
  
  
  /* ----------------
   *		heap_markpos	- mark scan position
   * ----------------
   */
  void
  heap_markpos(HeapScanDesc scan)
  {
  	/* Note: no locking manipulations needed */
  
  	if (scan->rs_ctup.t_data != NULL)
  	{
  		scan->rs_mctid = scan->rs_ctup.t_self;
  		if (scan->rs_pageatatime)
  			scan->rs_mindex = scan->rs_cindex;
  	}
  	else
  		ItemPointerSetInvalid(&scan->rs_mctid);
  }
  
  /* ----------------
   *		heap_restrpos	- restore position to marked location
   * ----------------
   */
  void
  heap_restrpos(HeapScanDesc scan)
  {
  	/* XXX no amrestrpos checking that ammarkpos called */
  
  	if (!ItemPointerIsValid(&scan->rs_mctid))
  	{
  		scan->rs_ctup.t_data = NULL;
  
  		/*
  		 * unpin scan buffers
  		 */
  		if (BufferIsValid(scan->rs_cbuf))
  			ReleaseBuffer(scan->rs_cbuf);
  		scan->rs_cbuf = InvalidBuffer;
  		scan->rs_cblock = InvalidBlockNumber;
  		scan->rs_inited = false;
  	}
  	else
  	{
  		/*
  		 * If we reached end of scan, rs_inited will now be false.	We must
  		 * reset it to true to keep heapgettup from doing the wrong thing.
  		 */
  		scan->rs_inited = true;
  		scan->rs_ctup.t_self = scan->rs_mctid;
  		if (scan->rs_pageatatime)
  		{
  			scan->rs_cindex = scan->rs_mindex;
  			heapgettup_pagemode(scan,
  								NoMovementScanDirection,
  								0,		/* needn't recheck scan keys */
  								NULL);
  		}
  		else
  			heapgettup(scan,
  					   NoMovementScanDirection,
  					   0,		/* needn't recheck scan keys */
  					   NULL);
  	}
  }
  
  /*
   * 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.
   */
  XLogRecPtr
  log_heap_clean(Relation reln, Buffer buffer,
  			   OffsetNumber *redirected, int nredirected,
  			   OffsetNumber *nowdead, int ndead,
  			   OffsetNumber *nowunused, int nunused,
  			   bool redirect_move)
  {
  	xl_heap_clean xlrec;
  	uint8		info;
  	XLogRecPtr	recptr;
  	XLogRecData rdata[4];
  
  	/* Caller should not call me on a temp relation */
  	Assert(!reln->rd_istemp);
  
  	xlrec.node = reln->rd_node;
  	xlrec.block = BufferGetBlockNumber(buffer);
  	xlrec.nredirected = nredirected;
  	xlrec.ndead = ndead;
  
  	rdata[0].data = (char *) &xlrec;
  	rdata[0].len = SizeOfHeapClean;
  	rdata[0].buffer = InvalidBuffer;
  	rdata[0].next = &(rdata[1]);
  
  	/*
  	 * The OffsetNumber arrays are not actually in the buffer, but we pretend
  	 * that they are.  When XLogInsert stores the whole buffer, the offset
  	 * arrays need not be stored too.  Note that even if all three arrays are
  	 * empty, we want to expose the buffer as a candidate for whole-page
  	 * storage, since this record type implies a defragmentation operation
  	 * even if no item pointers changed state.
  	 */
  	if (nredirected > 0)
  	{
  		rdata[1].data = (char *) redirected;
  		rdata[1].len = nredirected * sizeof(OffsetNumber) * 2;
  	}
  	else
  	{
  		rdata[1].data = NULL;
  		rdata[1].len = 0;
  	}
  	rdata[1].buffer = buffer;
  	rdata[1].buffer_std = true;
  	rdata[1].next = &(rdata[2]);
  
  	if (ndead > 0)
  	{
  		rdata[2].data = (char *) nowdead;
  		rdata[2].len = ndead * sizeof(OffsetNumber);
  	}
  	else
  	{
  		rdata[2].data = NULL;
  		rdata[2].len = 0;
  	}
  	rdata[2].buffer = buffer;
  	rdata[2].buffer_std = true;
  	rdata[2].next = &(rdata[3]);
  
  	if (nunused > 0)
  	{
  		rdata[3].data = (char *) nowunused;
  		rdata[3].len = nunused * sizeof(OffsetNumber);
  	}
  	else
  	{
  		rdata[3].data = NULL;
  		rdata[3].len = 0;
  	}
  	rdata[3].buffer = buffer;
  	rdata[3].buffer_std = true;
  	rdata[3].next = NULL;
  
  	info = redirect_move ? XLOG_HEAP2_CLEAN_MOVE : XLOG_HEAP2_CLEAN;
  	recptr = XLogInsert(RM_HEAP2_ID, info, rdata);
  
  	return recptr;
  }
  
  /*
   * Perform XLogInsert for a heap-freeze operation.	Caller must already
   * have modified the buffer and marked it dirty.
   */
  XLogRecPtr
  log_heap_freeze(Relation reln, Buffer buffer,
  				TransactionId cutoff_xid,
  				OffsetNumber *offsets, int offcnt)
  {
  	xl_heap_freeze xlrec;
  	XLogRecPtr	recptr;
  	XLogRecData rdata[2];
  
  	/* Caller should not call me on a temp relation */
  	Assert(!reln->rd_istemp);
  	/* nor when there are no tuples to freeze */
  	Assert(offcnt > 0);
  
  	xlrec.node = reln->rd_node;
  	xlrec.block = BufferGetBlockNumber(buffer);
  	xlrec.cutoff_xid = cutoff_xid;
  
  	rdata[0].data = (char *) &xlrec;
  	rdata[0].len = SizeOfHeapFreeze;
  	rdata[0].buffer = InvalidBuffer;
  	rdata[0].next = &(rdata[1]);
  
  	/*
  	 * The tuple-offsets array is not actually in the buffer, but pretend that
  	 * it is.  When XLogInsert stores the whole buffer, the offsets array need
  	 * not be stored too.
  	 */
  	rdata[1].data = (char *) offsets;
  	rdata[1].len = offcnt * sizeof(OffsetNumber);
  	rdata[1].buffer = buffer;
  	rdata[1].buffer_std = true;
  	rdata[1].next = NULL;
  
  	recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_FREEZE, rdata);
  
  	return recptr;
  }
  
  /*
   * Perform XLogInsert for a heap-update operation.	Caller must already
   * have modified the buffer(s) and marked them dirty.
   */
  static XLogRecPtr
  log_heap_update(Relation reln, Buffer oldbuf, ItemPointerData from,
  				Buffer newbuf, HeapTuple newtup, bool move,
  				bool all_visible_cleared, bool new_all_visible_cleared)
  {
  	/*
  	 * Note: xlhdr is declared to have adequate size and correct alignment for
  	 * an xl_heap_header.  However the two tids, if present at all, will be
  	 * packed in with no wasted space after the xl_heap_header; they aren't
  	 * necessarily aligned as implied by this struct declaration.
  	 */
  	struct
  	{
  		xl_heap_header hdr;
  		TransactionId tid1;
  		TransactionId tid2;
  	}			xlhdr;
  	int			hsize = SizeOfHeapHeader;
  	xl_heap_update xlrec;
  	uint8		info;
  	XLogRecPtr	recptr;
  	XLogRecData rdata[4];
  	Page		page = BufferGetPage(newbuf);
  
  	/* Caller should not call me on a temp relation */
  	Assert(!reln->rd_istemp);
  
  	if (move)
  	{
  		Assert(!HeapTupleIsHeapOnly(newtup));
  		info = XLOG_HEAP_MOVE;
  	}
  	else if (HeapTupleIsHeapOnly(newtup))
  		info = XLOG_HEAP_HOT_UPDATE;
  	else
  		info = XLOG_HEAP_UPDATE;
  
  	xlrec.target.node = reln->rd_node;
  	xlrec.target.tid = from;
  	xlrec.all_visible_cleared = all_visible_cleared;
  	xlrec.newtid = newtup->t_self;
  	xlrec.new_all_visible_cleared = new_all_visible_cleared;
  
  	rdata[0].data = (char *) &xlrec;
  	rdata[0].len = SizeOfHeapUpdate;
  	rdata[0].buffer = InvalidBuffer;
  	rdata[0].next = &(rdata[1]);
  
  	rdata[1].data = NULL;
  	rdata[1].len = 0;
  	rdata[1].buffer = oldbuf;
  	rdata[1].buffer_std = true;
  	rdata[1].next = &(rdata[2]);
  
  	xlhdr.hdr.t_infomask2 = newtup->t_data->t_infomask2;
  	xlhdr.hdr.t_infomask = newtup->t_data->t_infomask;
  	xlhdr.hdr.t_hoff = newtup->t_data->t_hoff;
  	if (move)					/* remember xmax & xmin */
  	{
  		TransactionId xid[2];	/* xmax, xmin */
  
  		if (newtup->t_data->t_infomask & (HEAP_XMAX_INVALID | HEAP_IS_LOCKED))
  			xid[0] = InvalidTransactionId;
  		else
  			xid[0] = HeapTupleHeaderGetXmax(newtup->t_data);
  		xid[1] = HeapTupleHeaderGetXmin(newtup->t_data);
  		memcpy((char *) &xlhdr + hsize,
  			   (char *) xid,
  			   2 * sizeof(TransactionId));
  		hsize += 2 * sizeof(TransactionId);
  	}
  
  	/*
  	 * As with insert records, we need not store the rdata[2] segment if we
  	 * decide to store the whole buffer instead.
  	 */
  	rdata[2].data = (char *) &xlhdr;
  	rdata[2].len = hsize;
  	rdata[2].buffer = newbuf;
  	rdata[2].buffer_std = true;
  	rdata[2].next = &(rdata[3]);
  
  	/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
  	rdata[3].data = (char *) newtup->t_data + offsetof(HeapTupleHeaderData, t_bits);
  	rdata[3].len = newtup->t_len - offsetof(HeapTupleHeaderData, t_bits);
  	rdata[3].buffer = newbuf;
  	rdata[3].buffer_std = true;
  	rdata[3].next = NULL;
  
  	/* If new tuple is the single and first tuple on page... */
  	if (ItemPointerGetOffsetNumber(&(newtup->t_self)) == FirstOffsetNumber &&
  		PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
  	{
  		info |= XLOG_HEAP_INIT_PAGE;
  		rdata[2].buffer = rdata[3].buffer = InvalidBuffer;
  	}
  
  	recptr = XLogInsert(RM_HEAP_ID, info, rdata);
  
  	return recptr;
  }
  
  /*
   * Perform XLogInsert for a heap-move operation.  Caller must already
   * have modified the buffers and marked them dirty.
   */
  XLogRecPtr
  log_heap_move(Relation reln, Buffer oldbuf, ItemPointerData from,
  			  Buffer newbuf, HeapTuple newtup,
  			  bool all_visible_cleared, bool new_all_visible_cleared)
  {
  	return log_heap_update(reln, oldbuf, from, newbuf, newtup, true,
  						   all_visible_cleared, new_all_visible_cleared);
  }
  
  /*
   * Perform XLogInsert of a HEAP_NEWPAGE record to WAL. Caller is responsible
   * for writing the page to disk after calling this routine.
   *
   * Note: all current callers build pages in private memory and write them
   * directly to smgr, rather than using bufmgr.	Therefore there is no need
   * to pass a buffer ID to XLogInsert, nor to perform MarkBufferDirty within
   * the critical section.
   *
   * Note: the NEWPAGE log record is used for both heaps and indexes, so do
   * not do anything that assumes we are touching a heap.
   */
  XLogRecPtr
  log_newpage(RelFileNode *rnode, ForkNumber forkNum, BlockNumber blkno,
  			Page page)
  {
  	xl_heap_newpage xlrec;
  	XLogRecPtr	recptr;
  	XLogRecData rdata[2];
  
  	/* NO ELOG(ERROR) from here till newpage op is logged */
  	START_CRIT_SECTION();
  
  	xlrec.node = *rnode;
  	xlrec.forknum = forkNum;
  	xlrec.blkno = blkno;
  
  	rdata[0].data = (char *) &xlrec;
  	rdata[0].len = SizeOfHeapNewpage;
  	rdata[0].buffer = InvalidBuffer;
  	rdata[0].next = &(rdata[1]);
  
  	rdata[1].data = (char *) page;
  	rdata[1].len = BLCKSZ;
  	rdata[1].buffer = InvalidBuffer;
  	rdata[1].next = NULL;
  
  	recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_NEWPAGE, rdata);
  
  	PageSetLSN(page, recptr);
  	PageSetTLI(page, ThisTimeLineID);
  
  	END_CRIT_SECTION();
  
  	return recptr;
  }
  
  /*
   * Handles CLEAN and CLEAN_MOVE record types
   */
  static void
  heap_xlog_clean(XLogRecPtr lsn, XLogRecord *record, bool clean_move)
  {
  	xl_heap_clean *xlrec = (xl_heap_clean *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber *end;
  	OffsetNumber *redirected;
  	OffsetNumber *nowdead;
  	OffsetNumber *nowunused;
  	int			nredirected;
  	int			ndead;
  	int			nunused;
  	Size		freespace;
  
  	if (record->xl_info & XLR_BKP_BLOCK_1)
  		return;
  
  	buffer = XLogReadBuffer(xlrec->node, xlrec->block, false);
  	if (!BufferIsValid(buffer))
  		return;
  	page = (Page) BufferGetPage(buffer);
  
  	if (XLByteLE(lsn, PageGetLSN(page)))
  	{
  		UnlockReleaseBuffer(buffer);
  		return;
  	}
  
  	nredirected = xlrec->nredirected;
  	ndead = xlrec->ndead;
  	end = (OffsetNumber *) ((char *) xlrec + record->xl_len);
  	redirected = (OffsetNumber *) ((char *) xlrec + SizeOfHeapClean);
  	nowdead = redirected + (nredirected * 2);
  	nowunused = nowdead + ndead;
  	nunused = (end - nowunused);
  	Assert(nunused >= 0);
  
  	/* Update all item pointers per the record, and repair fragmentation */
  	heap_page_prune_execute(buffer,
  							redirected, nredirected,
  							nowdead, ndead,
  							nowunused, nunused,
  							clean_move);
  
  	freespace = PageGetHeapFreeSpace(page);		/* needed to update FSM below */
  
  	/*
  	 * Note: we don't worry about updating the page's prunability hints. At
  	 * worst this will cause an extra prune cycle to occur soon.
  	 */
  
  	PageSetLSN(page, lsn);
  	PageSetTLI(page, ThisTimeLineID);
  	MarkBufferDirty(buffer);
  	UnlockReleaseBuffer(buffer);
  
  	/*
  	 * Update the FSM as well.
  	 *
  	 * XXX: We don't get here if the page was restored from full page image.
  	 * We don't bother to update the FSM in that case, it doesn't need to be
  	 * totally accurate anyway.
  	 */
  	XLogRecordPageWithFreeSpace(xlrec->node, xlrec->block, freespace);
  }
  
  static void
  heap_xlog_freeze(XLogRecPtr lsn, XLogRecord *record)
  {
  	xl_heap_freeze *xlrec = (xl_heap_freeze *) XLogRecGetData(record);
  	TransactionId cutoff_xid = xlrec->cutoff_xid;
  	Buffer		buffer;
  	Page		page;
  
  	if (record->xl_info & XLR_BKP_BLOCK_1)
  		return;
  
  	buffer = XLogReadBuffer(xlrec->node, xlrec->block, false);
  	if (!BufferIsValid(buffer))
  		return;
  	page = (Page) BufferGetPage(buffer);
  
  	if (XLByteLE(lsn, PageGetLSN(page)))
  	{
  		UnlockReleaseBuffer(buffer);
  		return;
  	}
  
  	if (record->xl_len > SizeOfHeapFreeze)
  	{
  		OffsetNumber *offsets;
  		OffsetNumber *offsets_end;
  
  		offsets = (OffsetNumber *) ((char *) xlrec + SizeOfHeapFreeze);
  		offsets_end = (OffsetNumber *) ((char *) xlrec + record->xl_len);
  
  		while (offsets < offsets_end)
  		{
  			/* offsets[] entries are one-based */
  			ItemId		lp = PageGetItemId(page, *offsets);
  			HeapTupleHeader tuple = (HeapTupleHeader) PageGetItem(page, lp);
  
  			(void) heap_freeze_tuple(tuple, cutoff_xid, InvalidBuffer);
  			offsets++;
  		}
  	}
  
  	PageSetLSN(page, lsn);
  	PageSetTLI(page, ThisTimeLineID);
  	MarkBufferDirty(buffer);
  	UnlockReleaseBuffer(buffer);
  }
  
  static void
  heap_xlog_newpage(XLogRecPtr lsn, XLogRecord *record)
  {
  	xl_heap_newpage *xlrec = (xl_heap_newpage *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  
  	/*
  	 * Note: the NEWPAGE log record is used for both heaps and indexes, so do
  	 * not do anything that assumes we are touching a heap.
  	 */
  	buffer = XLogReadBuffer(xlrec->node, xlrec->blkno, true);
  	Assert(BufferIsValid(buffer));
  	page = (Page) BufferGetPage(buffer);
  
  	Assert(record->xl_len == SizeOfHeapNewpage + BLCKSZ);
  	memcpy(page, (char *) xlrec + SizeOfHeapNewpage, BLCKSZ);
  
  	PageSetLSN(page, lsn);
  	PageSetTLI(page, ThisTimeLineID);
  	MarkBufferDirty(buffer);
  	UnlockReleaseBuffer(buffer);
  }
  
  static void
  heap_xlog_delete(XLogRecPtr lsn, XLogRecord *record)
  {
  	xl_heap_delete *xlrec = (xl_heap_delete *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  	BlockNumber blkno;
  
  	blkno = ItemPointerGetBlockNumber(&(xlrec->target.tid));
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->all_visible_cleared)
  	{
  		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
  
  		visibilitymap_clear(reln, blkno);
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	if (record->xl_info & XLR_BKP_BLOCK_1)
  		return;
  
  	buffer = XLogReadBuffer(xlrec->target.node, blkno, false);
  	if (!BufferIsValid(buffer))
  		return;
  	page = (Page) BufferGetPage(buffer);
  
  	if (XLByteLE(lsn, PageGetLSN(page)))		/* changes are applied */
  	{
  		UnlockReleaseBuffer(buffer);
  		return;
  	}
  
  	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
  	if (PageGetMaxOffsetNumber(page) >= offnum)
  		lp = PageGetItemId(page, offnum);
  
  	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  		elog(PANIC, "heap_delete_redo: invalid lp");
  
  	htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  	htup->t_infomask &= ~(HEAP_XMAX_COMMITTED |
  						  HEAP_XMAX_INVALID |
  						  HEAP_XMAX_IS_MULTI |
  						  HEAP_IS_LOCKED |
  						  HEAP_MOVED);
  	HeapTupleHeaderClearHotUpdated(htup);
  	HeapTupleHeaderSetXmax(htup, record->xl_xid);
  	HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
  
  	/* Mark the page as a candidate for pruning */
  	PageSetPrunable(page, record->xl_xid);
  
  	if (xlrec->all_visible_cleared)
  		PageClearAllVisible(page);
  
  	/* Make sure there is no forward chain link in t_ctid */
  	htup->t_ctid = xlrec->target.tid;
  	PageSetLSN(page, lsn);
  	PageSetTLI(page, ThisTimeLineID);
  	MarkBufferDirty(buffer);
  	UnlockReleaseBuffer(buffer);
  }
  
  static void
  heap_xlog_insert(XLogRecPtr lsn, XLogRecord *record)
  {
  	xl_heap_insert *xlrec = (xl_heap_insert *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	struct
  	{
  		HeapTupleHeaderData hdr;
  		char		data[MaxHeapTupleSize];
  	}			tbuf;
  	HeapTupleHeader htup;
  	xl_heap_header xlhdr;
  	uint32		newlen;
  	Size		freespace;
  	BlockNumber blkno;
  
  	blkno = ItemPointerGetBlockNumber(&(xlrec->target.tid));
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->all_visible_cleared)
  	{
  		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
  
  		visibilitymap_clear(reln, blkno);
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	if (record->xl_info & XLR_BKP_BLOCK_1)
  		return;
  
  	if (record->xl_info & XLOG_HEAP_INIT_PAGE)
  	{
  		buffer = XLogReadBuffer(xlrec->target.node, blkno, true);
  		Assert(BufferIsValid(buffer));
  		page = (Page) BufferGetPage(buffer);
  
  		PageInit(page, BufferGetPageSize(buffer), 0);
  	}
  	else
  	{
  		buffer = XLogReadBuffer(xlrec->target.node, blkno, false);
  		if (!BufferIsValid(buffer))
  			return;
  		page = (Page) BufferGetPage(buffer);
  
  		if (XLByteLE(lsn, PageGetLSN(page)))	/* changes are applied */
  		{
  			UnlockReleaseBuffer(buffer);
  			return;
  		}
  	}
  
  	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
  	if (PageGetMaxOffsetNumber(page) + 1 < offnum)
  		elog(PANIC, "heap_insert_redo: invalid max offset number");
  
  	newlen = record->xl_len - SizeOfHeapInsert - SizeOfHeapHeader;
  	Assert(newlen <= MaxHeapTupleSize);
  	memcpy((char *) &xlhdr,
  		   (char *) xlrec + SizeOfHeapInsert,
  		   SizeOfHeapHeader);
  	htup = &tbuf.hdr;
  	MemSet((char *) htup, 0, sizeof(HeapTupleHeaderData));
  	/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
  	memcpy((char *) htup + offsetof(HeapTupleHeaderData, t_bits),
  		   (char *) xlrec + SizeOfHeapInsert + SizeOfHeapHeader,
  		   newlen);
  	newlen += offsetof(HeapTupleHeaderData, t_bits);
  	htup->t_infomask2 = xlhdr.t_infomask2;
  	htup->t_infomask = xlhdr.t_infomask;
  	htup->t_hoff = xlhdr.t_hoff;
  	HeapTupleHeaderSetXmin(htup, record->xl_xid);
  	HeapTupleHeaderSetCmin(htup, FirstCommandId);
  	htup->t_ctid = xlrec->target.tid;
  
  	offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
  	if (offnum == InvalidOffsetNumber)
  		elog(PANIC, "heap_insert_redo: failed to add tuple");
  
  	freespace = PageGetHeapFreeSpace(page);		/* needed to update FSM below */
  
  	PageSetLSN(page, lsn);
  	PageSetTLI(page, ThisTimeLineID);
  
  	if (xlrec->all_visible_cleared)
  		PageClearAllVisible(page);
  
  	MarkBufferDirty(buffer);
  	UnlockReleaseBuffer(buffer);
  
  	/*
  	 * If the page is running low on free space, update the FSM as well.
  	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
  	 * better than that without knowing the fill-factor for the table.
  	 *
  	 * XXX: We don't get here if the page was restored from full page image.
  	 * We don't bother to update the FSM in that case, it doesn't need to be
  	 * totally accurate anyway.
  	 */
  	if (freespace < BLCKSZ / 5)
  		XLogRecordPageWithFreeSpace(xlrec->target.node, blkno, freespace);
  }
  
  /*
   * Handles UPDATE, HOT_UPDATE & MOVE
   */
  static void
  heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool move, bool hot_update)
  {
  	xl_heap_update *xlrec = (xl_heap_update *) XLogRecGetData(record);
  	Buffer		buffer;
  	bool		samepage = (ItemPointerGetBlockNumber(&(xlrec->newtid)) ==
  							ItemPointerGetBlockNumber(&(xlrec->target.tid)));
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  	struct
  	{
  		HeapTupleHeaderData hdr;
  		char		data[MaxHeapTupleSize];
  	}			tbuf;
  	xl_heap_header xlhdr;
  	int			hsize;
  	uint32		newlen;
  	Size		freespace;
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->all_visible_cleared)
  	{
  		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
  
  		visibilitymap_clear(reln,
  							ItemPointerGetBlockNumber(&xlrec->target.tid));
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	if (record->xl_info & XLR_BKP_BLOCK_1)
  	{
  		if (samepage)
  			return;				/* backup block covered both changes */
  		goto newt;
  	}
  
  	/* Deal with old tuple version */
  
  	buffer = XLogReadBuffer(xlrec->target.node,
  							ItemPointerGetBlockNumber(&(xlrec->target.tid)),
  							false);
  	if (!BufferIsValid(buffer))
  		goto newt;
  	page = (Page) BufferGetPage(buffer);
  
  	if (XLByteLE(lsn, PageGetLSN(page)))		/* changes are applied */
  	{
  		UnlockReleaseBuffer(buffer);
  		if (samepage)
  			return;
  		goto newt;
  	}
  
  	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
  	if (PageGetMaxOffsetNumber(page) >= offnum)
  		lp = PageGetItemId(page, offnum);
  
  	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  		elog(PANIC, "heap_update_redo: invalid lp");
  
  	htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  	if (move)
  	{
  		htup->t_infomask &= ~(HEAP_XMIN_COMMITTED |
  							  HEAP_XMIN_INVALID |
  							  HEAP_MOVED_IN);
  		htup->t_infomask |= HEAP_MOVED_OFF;
  		HeapTupleHeaderClearHotUpdated(htup);
  		HeapTupleHeaderSetXvac(htup, record->xl_xid);
  		/* Make sure there is no forward chain link in t_ctid */
  		htup->t_ctid = xlrec->target.tid;
  	}
  	else
  	{
  		htup->t_infomask &= ~(HEAP_XMAX_COMMITTED |
  							  HEAP_XMAX_INVALID |
  							  HEAP_XMAX_IS_MULTI |
  							  HEAP_IS_LOCKED |
  							  HEAP_MOVED);
  		if (hot_update)
  			HeapTupleHeaderSetHotUpdated(htup);
  		else
  			HeapTupleHeaderClearHotUpdated(htup);
  		HeapTupleHeaderSetXmax(htup, record->xl_xid);
  		HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
  		/* Set forward chain link in t_ctid */
  		htup->t_ctid = xlrec->newtid;
  	}
  
  	/* Mark the page as a candidate for pruning */
  	PageSetPrunable(page, record->xl_xid);
  
  	if (xlrec->all_visible_cleared)
  		PageClearAllVisible(page);
  
  	/*
  	 * this test is ugly, but necessary to avoid thinking that insert change
  	 * is already applied
  	 */
  	if (samepage)
  		goto newsame;
  	PageSetLSN(page, lsn);
  	PageSetTLI(page, ThisTimeLineID);
  	MarkBufferDirty(buffer);
  	UnlockReleaseBuffer(buffer);
  
  	/* Deal with new tuple */
  
  newt:;
  
  	/*
  	 * The visibility map may need to be fixed even if the heap page is
  	 * already up-to-date.
  	 */
  	if (xlrec->new_all_visible_cleared)
  	{
  		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
  
  		visibilitymap_clear(reln, ItemPointerGetBlockNumber(&xlrec->newtid));
  		FreeFakeRelcacheEntry(reln);
  	}
  
  	if (record->xl_info & XLR_BKP_BLOCK_2)
  		return;
  
  	if (record->xl_info & XLOG_HEAP_INIT_PAGE)
  	{
  		buffer = XLogReadBuffer(xlrec->target.node,
  								ItemPointerGetBlockNumber(&(xlrec->newtid)),
  								true);
  		Assert(BufferIsValid(buffer));
  		page = (Page) BufferGetPage(buffer);
  
  		PageInit(page, BufferGetPageSize(buffer), 0);
  	}
  	else
  	{
  		buffer = XLogReadBuffer(xlrec->target.node,
  								ItemPointerGetBlockNumber(&(xlrec->newtid)),
  								false);
  		if (!BufferIsValid(buffer))
  			return;
  		page = (Page) BufferGetPage(buffer);
  
  		if (XLByteLE(lsn, PageGetLSN(page)))	/* changes are applied */
  		{
  			UnlockReleaseBuffer(buffer);
  			return;
  		}
  	}
  
  newsame:;
  
  	offnum = ItemPointerGetOffsetNumber(&(xlrec->newtid));
  	if (PageGetMaxOffsetNumber(page) + 1 < offnum)
  		elog(PANIC, "heap_update_redo: invalid max offset number");
  
  	hsize = SizeOfHeapUpdate + SizeOfHeapHeader;
  	if (move)
  		hsize += (2 * sizeof(TransactionId));
  
  	newlen = record->xl_len - hsize;
  	Assert(newlen <= MaxHeapTupleSize);
  	memcpy((char *) &xlhdr,
  		   (char *) xlrec + SizeOfHeapUpdate,
  		   SizeOfHeapHeader);
  	htup = &tbuf.hdr;
  	MemSet((char *) htup, 0, sizeof(HeapTupleHeaderData));
  	/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
  	memcpy((char *) htup + offsetof(HeapTupleHeaderData, t_bits),
  		   (char *) xlrec + hsize,
  		   newlen);
  	newlen += offsetof(HeapTupleHeaderData, t_bits);
  	htup->t_infomask2 = xlhdr.t_infomask2;
  	htup->t_infomask = xlhdr.t_infomask;
  	htup->t_hoff = xlhdr.t_hoff;
  
  	if (move)
  	{
  		TransactionId xid[2];	/* xmax, xmin */
  
  		memcpy((char *) xid,
  			   (char *) xlrec + SizeOfHeapUpdate + SizeOfHeapHeader,
  			   2 * sizeof(TransactionId));
  		HeapTupleHeaderSetXmin(htup, xid[1]);
  		HeapTupleHeaderSetXmax(htup, xid[0]);
  		HeapTupleHeaderSetXvac(htup, record->xl_xid);
  	}
  	else
  	{
  		HeapTupleHeaderSetXmin(htup, record->xl_xid);
  		HeapTupleHeaderSetCmin(htup, FirstCommandId);
  	}
  	/* Make sure there is no forward chain link in t_ctid */
  	htup->t_ctid = xlrec->newtid;
  
  	offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
  	if (offnum == InvalidOffsetNumber)
  		elog(PANIC, "heap_update_redo: failed to add tuple");
  
  	if (xlrec->new_all_visible_cleared)
  		PageClearAllVisible(page);
  
  	freespace = PageGetHeapFreeSpace(page);		/* needed to update FSM below */
  
  	PageSetLSN(page, lsn);
  	PageSetTLI(page, ThisTimeLineID);
  	MarkBufferDirty(buffer);
  	UnlockReleaseBuffer(buffer);
  
  	/*
  	 * If the page is running low on free space, update the FSM as well.
  	 * Arbitrarily, our definition of "low" is less than 20%. We can't do much
  	 * better than that without knowing the fill-factor for the table.
  	 *
  	 * However, don't update the FSM on HOT updates, because after crash
  	 * recovery, either the old or the new tuple will certainly be dead and
  	 * prunable. After pruning, the page will have roughly as much free space
  	 * as it did before the update, assuming the new tuple is about the same
  	 * size as the old one.
  	 *
  	 * XXX: We don't get here if the page was restored from full page image.
  	 * We don't bother to update the FSM in that case, it doesn't need to be
  	 * totally accurate anyway.
  	 */
  	if (!hot_update && freespace < BLCKSZ / 5)
  		XLogRecordPageWithFreeSpace(xlrec->target.node,
  					 ItemPointerGetBlockNumber(&(xlrec->newtid)), freespace);
  }
  
  static void
  heap_xlog_lock(XLogRecPtr lsn, XLogRecord *record)
  {
  	xl_heap_lock *xlrec = (xl_heap_lock *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  
  	if (record->xl_info & XLR_BKP_BLOCK_1)
  		return;
  
  	buffer = XLogReadBuffer(xlrec->target.node,
  							ItemPointerGetBlockNumber(&(xlrec->target.tid)),
  							false);
  	if (!BufferIsValid(buffer))
  		return;
  	page = (Page) BufferGetPage(buffer);
  
  	if (XLByteLE(lsn, PageGetLSN(page)))		/* changes are applied */
  	{
  		UnlockReleaseBuffer(buffer);
  		return;
  	}
  
  	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
  	if (PageGetMaxOffsetNumber(page) >= offnum)
  		lp = PageGetItemId(page, offnum);
  
  	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  		elog(PANIC, "heap_lock_redo: invalid lp");
  
  	htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  	htup->t_infomask &= ~(HEAP_XMAX_COMMITTED |
  						  HEAP_XMAX_INVALID |
  						  HEAP_XMAX_IS_MULTI |
  						  HEAP_IS_LOCKED |
  						  HEAP_MOVED);
  	if (xlrec->xid_is_mxact)
  		htup->t_infomask |= HEAP_XMAX_IS_MULTI;
  	if (xlrec->shared_lock)
  		htup->t_infomask |= HEAP_XMAX_SHARED_LOCK;
  	else
  		htup->t_infomask |= HEAP_XMAX_EXCL_LOCK;
  	HeapTupleHeaderClearHotUpdated(htup);
  	HeapTupleHeaderSetXmax(htup, xlrec->locking_xid);
  	HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
  	/* Make sure there is no forward chain link in t_ctid */
  	htup->t_ctid = xlrec->target.tid;
  	PageSetLSN(page, lsn);
  	PageSetTLI(page, ThisTimeLineID);
  	MarkBufferDirty(buffer);
  	UnlockReleaseBuffer(buffer);
  }
  
  static void
  heap_xlog_inplace(XLogRecPtr lsn, XLogRecord *record)
  {
  	xl_heap_inplace *xlrec = (xl_heap_inplace *) XLogRecGetData(record);
  	Buffer		buffer;
  	Page		page;
  	OffsetNumber offnum;
  	ItemId		lp = NULL;
  	HeapTupleHeader htup;
  	uint32		oldlen;
  	uint32		newlen;
  
  	if (record->xl_info & XLR_BKP_BLOCK_1)
  		return;
  
  	buffer = XLogReadBuffer(xlrec->target.node,
  							ItemPointerGetBlockNumber(&(xlrec->target.tid)),
  							false);
  	if (!BufferIsValid(buffer))
  		return;
  	page = (Page) BufferGetPage(buffer);
  
  	if (XLByteLE(lsn, PageGetLSN(page)))		/* changes are applied */
  	{
  		UnlockReleaseBuffer(buffer);
  		return;
  	}
  
  	offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
  	if (PageGetMaxOffsetNumber(page) >= offnum)
  		lp = PageGetItemId(page, offnum);
  
  	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
  		elog(PANIC, "heap_inplace_redo: invalid lp");
  
  	htup = (HeapTupleHeader) PageGetItem(page, lp);
  
  	oldlen = ItemIdGetLength(lp) - htup->t_hoff;
  	newlen = record->xl_len - SizeOfHeapInplace;
  	if (oldlen != newlen)
  		elog(PANIC, "heap_inplace_redo: wrong tuple length");
  
  	memcpy((char *) htup + htup->t_hoff,
  		   (char *) xlrec + SizeOfHeapInplace,
  		   newlen);
  
  	PageSetLSN(page, lsn);
  	PageSetTLI(page, ThisTimeLineID);
  	MarkBufferDirty(buffer);
  	UnlockReleaseBuffer(buffer);
  }
  
  void
  heap_redo(XLogRecPtr lsn, XLogRecord *record)
  {
  	uint8		info = record->xl_info & ~XLR_INFO_MASK;
  
  	RestoreBkpBlocks(lsn, record, false);
  
  	switch (info & XLOG_HEAP_OPMASK)
  	{
  		case XLOG_HEAP_INSERT:
  			heap_xlog_insert(lsn, record);
  			break;
  		case XLOG_HEAP_DELETE:
  			heap_xlog_delete(lsn, record);
  			break;
  		case XLOG_HEAP_UPDATE:
  			heap_xlog_update(lsn, record, false, false);
  			break;
  		case XLOG_HEAP_MOVE:
  			heap_xlog_update(lsn, record, true, false);
  			break;
  		case XLOG_HEAP_HOT_UPDATE:
  			heap_xlog_update(lsn, record, false, true);
  			break;
  		case XLOG_HEAP_NEWPAGE:
  			heap_xlog_newpage(lsn, record);
  			break;
  		case XLOG_HEAP_LOCK:
  			heap_xlog_lock(lsn, record);
  			break;
  		case XLOG_HEAP_INPLACE:
  			heap_xlog_inplace(lsn, record);
  			break;
  		default:
  			elog(PANIC, "heap_redo: unknown op code %u", info);
  	}
  }
  
  void
  heap2_redo(XLogRecPtr lsn, XLogRecord *record)
  {
  	uint8		info = record->xl_info & ~XLR_INFO_MASK;
  
  	switch (info & XLOG_HEAP_OPMASK)
  	{
  		case XLOG_HEAP2_FREEZE:
  			RestoreBkpBlocks(lsn, record, false);
  			heap_xlog_freeze(lsn, record);
  			break;
  		case XLOG_HEAP2_CLEAN:
  			RestoreBkpBlocks(lsn, record, true);
  			heap_xlog_clean(lsn, record, false);
  			break;
  		case XLOG_HEAP2_CLEAN_MOVE:
  			RestoreBkpBlocks(lsn, record, true);
  			heap_xlog_clean(lsn, record, true);
  			break;
  		default:
  			elog(PANIC, "heap2_redo: unknown op code %u", info);
  	}
  }
  
  static void
  out_target(StringInfo buf, xl_heaptid *target)
  {
  	appendStringInfo(buf, "rel %u/%u/%u; tid %u/%u",
  			 target->node.spcNode, target->node.dbNode, target->node.relNode,
  					 ItemPointerGetBlockNumber(&(target->tid)),
  					 ItemPointerGetOffsetNumber(&(target->tid)));
  }
  
  void
  heap_desc(StringInfo buf, uint8 xl_info, char *rec)
  {
  	uint8		info = xl_info & ~XLR_INFO_MASK;
  
  	info &= XLOG_HEAP_OPMASK;
  	if (info == XLOG_HEAP_INSERT)
  	{
  		xl_heap_insert *xlrec = (xl_heap_insert *) rec;
  
  		if (xl_info & XLOG_HEAP_INIT_PAGE)
  			appendStringInfo(buf, "insert(init): ");
  		else
  			appendStringInfo(buf, "insert: ");
  		out_target(buf, &(xlrec->target));
  	}
  	else if (info == XLOG_HEAP_DELETE)
  	{
  		xl_heap_delete *xlrec = (xl_heap_delete *) rec;
  
  		appendStringInfo(buf, "delete: ");
  		out_target(buf, &(xlrec->target));
  	}
  	else if (info == XLOG_HEAP_UPDATE)
  	{
  		xl_heap_update *xlrec = (xl_heap_update *) rec;
  
  		if (xl_info & XLOG_HEAP_INIT_PAGE)
  			appendStringInfo(buf, "update(init): ");
  		else
  			appendStringInfo(buf, "update: ");
  		out_target(buf, &(xlrec->target));
  		appendStringInfo(buf, "; new %u/%u",
  						 ItemPointerGetBlockNumber(&(xlrec->newtid)),
  						 ItemPointerGetOffsetNumber(&(xlrec->newtid)));
  	}
  	else if (info == XLOG_HEAP_MOVE)
  	{
  		xl_heap_update *xlrec = (xl_heap_update *) rec;
  
  		if (xl_info & XLOG_HEAP_INIT_PAGE)
  			appendStringInfo(buf, "move(init): ");
  		else
  			appendStringInfo(buf, "move: ");
  		out_target(buf, &(xlrec->target));
  		appendStringInfo(buf, "; new %u/%u",
  						 ItemPointerGetBlockNumber(&(xlrec->newtid)),
  						 ItemPointerGetOffsetNumber(&(xlrec->newtid)));
  	}
  	else if (info == XLOG_HEAP_HOT_UPDATE)
  	{
  		xl_heap_update *xlrec = (xl_heap_update *) rec;
  
  		if (xl_info & XLOG_HEAP_INIT_PAGE)		/* can this case happen? */
  			appendStringInfo(buf, "hot_update(init): ");
  		else
  			appendStringInfo(buf, "hot_update: ");
  		out_target(buf, &(xlrec->target));
  		appendStringInfo(buf, "; new %u/%u",
  						 ItemPointerGetBlockNumber(&(xlrec->newtid)),
  						 ItemPointerGetOffsetNumber(&(xlrec->newtid)));
  	}
  	else if (info == XLOG_HEAP_NEWPAGE)
  	{
  		xl_heap_newpage *xlrec = (xl_heap_newpage *) rec;
  
  		appendStringInfo(buf, "newpage: rel %u/%u/%u; blk %u",
  						 xlrec->node.spcNode, xlrec->node.dbNode,
  						 xlrec->node.relNode, xlrec->blkno);
  	}
  	else if (info == XLOG_HEAP_LOCK)
  	{
  		xl_heap_lock *xlrec = (xl_heap_lock *) rec;
  
  		if (xlrec->shared_lock)
  			appendStringInfo(buf, "shared_lock: ");
  		else
  			appendStringInfo(buf, "exclusive_lock: ");
  		if (xlrec->xid_is_mxact)
  			appendStringInfo(buf, "mxid ");
  		else
  			appendStringInfo(buf, "xid ");
  		appendStringInfo(buf, "%u ", xlrec->locking_xid);
  		out_target(buf, &(xlrec->target));
  	}
  	else if (info == XLOG_HEAP_INPLACE)
  	{
  		xl_heap_inplace *xlrec = (xl_heap_inplace *) rec;
  
  		appendStringInfo(buf, "inplace: ");
  		out_target(buf, &(xlrec->target));
  	}
  	else
  		appendStringInfo(buf, "UNKNOWN");
  }
  
  void
  heap2_desc(StringInfo buf, uint8 xl_info, char *rec)
  {
  	uint8		info = xl_info & ~XLR_INFO_MASK;
  
  	info &= XLOG_HEAP_OPMASK;
  	if (info == XLOG_HEAP2_FREEZE)
  	{
  		xl_heap_freeze *xlrec = (xl_heap_freeze *) rec;
  
  		appendStringInfo(buf, "freeze: rel %u/%u/%u; blk %u; cutoff %u",
  						 xlrec->node.spcNode, xlrec->node.dbNode,
  						 xlrec->node.relNode, xlrec->block,
  						 xlrec->cutoff_xid);
  	}
  	else if (info == XLOG_HEAP2_CLEAN)
  	{
  		xl_heap_clean *xlrec = (xl_heap_clean *) rec;
  
  		appendStringInfo(buf, "clean: rel %u/%u/%u; blk %u",
  						 xlrec->node.spcNode, xlrec->node.dbNode,
  						 xlrec->node.relNode, xlrec->block);
  	}
  	else if (info == XLOG_HEAP2_CLEAN_MOVE)
  	{
  		xl_heap_clean *xlrec = (xl_heap_clean *) rec;
  
  		appendStringInfo(buf, "clean_move: rel %u/%u/%u; blk %u",
  						 xlrec->node.spcNode, xlrec->node.dbNode,
  						 xlrec->node.relNode, xlrec->block);
  	}
  	else
  		appendStringInfo(buf, "UNKNOWN");
  }
  
  /*
   *	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 it's not a temp relation, 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)
  {
  	/* temp tables never need fsync */
  	if (rel->rd_istemp)
  		return;
  
  	/* main heap */
  	FlushRelationBuffers(rel);
  	/* FlushRelationBuffers will have opened rd_smgr */
  	smgrimmedsync(rel->rd_smgr, MAIN_FORKNUM);
  
  	/* FSM is not critical, don't bother syncing it */
  
  	/* toast heap, if any */
  	if (OidIsValid(rel->rd_rel->reltoastrelid))
  	{
  		Relation	toastrel;
  
  		toastrel = heap_open(rel->rd_rel->reltoastrelid, AccessShareLock);
  		FlushRelationBuffers(toastrel);
  		smgrimmedsync(toastrel->rd_smgr, MAIN_FORKNUM);
  		heap_close(toastrel, AccessShareLock);
  	}
  }
  