Fix LOCK TABLE to eliminate the race condition that could make it give weird

[postgresql] / src / backend / access / heap / heapam.c

/*-------------------------------------------------------------------------
 *
 * 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 1.275 2009/05/12 16:43:32 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);
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            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 (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);

        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);
}

/* ----------------
 *              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;

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

        /*
         * Note: we mustn't clear PD_ALL_VISIBLE flags before writing the WAL
         * record, because log_heap_update looks at those flags to set the
         * corresponding flags in the WAL record.
         */

        /* XLOG stuff */
        if (!relation->rd_istemp)
        {
                XLogRecPtr      recptr = log_heap_update(relation, buffer, oldtup.t_self,
                                                                                         newbuf, heaptup, false);

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

        /* 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));
        }

        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)
{
        /*
         * 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 = PageIsAllVisible(BufferGetPage(oldbuf));
        xlrec.newtid = newtup->t_self;
        xlrec.new_all_visible_cleared = PageIsAllVisible(BufferGetPage(newbuf));

        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)
{
        return log_heap_update(reln, oldbuf, from, newbuf, newtup, true);
}

/*
 * 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 always needs to be updated, 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 always needs to be updated, 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 always needs to be updated, 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 always needs to be updated, 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);
        }
}