Fix initialization of fake LSN for unlogged relations

[postgresql] / src / backend / access / nbtree / nbtree.c

/*-------------------------------------------------------------------------
 *
 * nbtree.c
 *        Implementation of Lehman and Yao's btree management algorithm for
 *        Postgres.
 *
 * NOTES
 *        This file contains only the public interface routines.
 *
 *
 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *        src/backend/access/nbtree/nbtree.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/nbtree.h"
#include "access/nbtxlog.h"
#include "access/relscan.h"
#include "access/xlog.h"
#include "commands/progress.h"
#include "commands/vacuum.h"
#include "miscadmin.h"
#include "nodes/execnodes.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
#include "storage/condition_variable.h"
#include "storage/indexfsm.h"
#include "storage/ipc.h"
#include "storage/lmgr.h"
#include "storage/smgr.h"
#include "utils/builtins.h"
#include "utils/index_selfuncs.h"
#include "utils/memutils.h"


/* Working state needed by btvacuumpage */
typedef struct
{
        IndexVacuumInfo *info;
        IndexBulkDeleteResult *stats;
        IndexBulkDeleteCallback callback;
        void       *callback_state;
        BTCycleId       cycleid;
        BlockNumber lastBlockVacuumed;  /* highest blkno actually vacuumed */
        BlockNumber lastBlockLocked;    /* highest blkno we've cleanup-locked */
        BlockNumber totFreePages;       /* true total # of free pages */
        TransactionId oldestBtpoXact;
        MemoryContext pagedelcontext;
} BTVacState;

/*
 * BTPARALLEL_NOT_INITIALIZED indicates that the scan has not started.
 *
 * BTPARALLEL_ADVANCING indicates that some process is advancing the scan to
 * a new page; others must wait.
 *
 * BTPARALLEL_IDLE indicates that no backend is currently advancing the scan
 * to a new page; some process can start doing that.
 *
 * BTPARALLEL_DONE indicates that the scan is complete (including error exit).
 * We reach this state once for every distinct combination of array keys.
 */
typedef enum
{
        BTPARALLEL_NOT_INITIALIZED,
        BTPARALLEL_ADVANCING,
        BTPARALLEL_IDLE,
        BTPARALLEL_DONE
} BTPS_State;

/*
 * BTParallelScanDescData contains btree specific shared information required
 * for parallel scan.
 */
typedef struct BTParallelScanDescData
{
        BlockNumber btps_scanPage;      /* latest or next page to be scanned */
        BTPS_State      btps_pageStatus;        /* indicates whether next page is
                                                                         * available for scan. see above for
                                                                         * possible states of parallel scan. */
        int                     btps_arrayKeyCount; /* count indicating number of array scan
                                                                         * keys processed by parallel scan */
        slock_t         btps_mutex;             /* protects above variables */
        ConditionVariable btps_cv;      /* used to synchronize parallel scan */
}                       BTParallelScanDescData;

typedef struct BTParallelScanDescData *BTParallelScanDesc;


static void btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
                                                 IndexBulkDeleteCallback callback, void *callback_state,
                                                 BTCycleId cycleid, TransactionId *oldestBtpoXact);
static void btvacuumpage(BTVacState *vstate, BlockNumber blkno,
                                                 BlockNumber orig_blkno);


/*
 * Btree handler function: return IndexAmRoutine with access method parameters
 * and callbacks.
 */
Datum
bthandler(PG_FUNCTION_ARGS)
{
        IndexAmRoutine *amroutine = makeNode(IndexAmRoutine);

        amroutine->amstrategies = BTMaxStrategyNumber;
        amroutine->amsupport = BTNProcs;
        amroutine->amcanorder = true;
        amroutine->amcanorderbyop = false;
        amroutine->amcanbackward = true;
        amroutine->amcanunique = true;
        amroutine->amcanmulticol = true;
        amroutine->amoptionalkey = true;
        amroutine->amsearcharray = true;
        amroutine->amsearchnulls = true;
        amroutine->amstorage = false;
        amroutine->amclusterable = true;
        amroutine->ampredlocks = true;
        amroutine->amcanparallel = true;
        amroutine->amcaninclude = true;
        amroutine->amkeytype = InvalidOid;

        amroutine->ambuild = btbuild;
        amroutine->ambuildempty = btbuildempty;
        amroutine->aminsert = btinsert;
        amroutine->ambulkdelete = btbulkdelete;
        amroutine->amvacuumcleanup = btvacuumcleanup;
        amroutine->amcanreturn = btcanreturn;
        amroutine->amcostestimate = btcostestimate;
        amroutine->amoptions = btoptions;
        amroutine->amproperty = btproperty;
        amroutine->ambuildphasename = btbuildphasename;
        amroutine->amvalidate = btvalidate;
        amroutine->ambeginscan = btbeginscan;
        amroutine->amrescan = btrescan;
        amroutine->amgettuple = btgettuple;
        amroutine->amgetbitmap = btgetbitmap;
        amroutine->amendscan = btendscan;
        amroutine->ammarkpos = btmarkpos;
        amroutine->amrestrpos = btrestrpos;
        amroutine->amestimateparallelscan = btestimateparallelscan;
        amroutine->aminitparallelscan = btinitparallelscan;
        amroutine->amparallelrescan = btparallelrescan;

        PG_RETURN_POINTER(amroutine);
}

/*
 *      btbuildempty() -- build an empty btree index in the initialization fork
 */
void
btbuildempty(Relation index)
{
        Page            metapage;

        /* Construct metapage. */
        metapage = (Page) palloc(BLCKSZ);
        _bt_initmetapage(metapage, P_NONE, 0);

        /*
         * Write the page and log it.  It might seem that an immediate sync would
         * be sufficient to guarantee that the file exists on disk, but recovery
         * itself might remove it while replaying, for example, an
         * XLOG_DBASE_CREATE or XLOG_TBLSPC_CREATE record.  Therefore, we need
         * this even when wal_level=minimal.
         */
        PageSetChecksumInplace(metapage, BTREE_METAPAGE);
        smgrwrite(index->rd_smgr, INIT_FORKNUM, BTREE_METAPAGE,
                          (char *) metapage, true);
        log_newpage(&index->rd_smgr->smgr_rnode.node, INIT_FORKNUM,
                                BTREE_METAPAGE, metapage, true);

        /*
         * An immediate sync is required even if we xlog'd the page, because the
         * write did not go through shared_buffers and therefore a concurrent
         * checkpoint may have moved the redo pointer past our xlog record.
         */
        smgrimmedsync(index->rd_smgr, INIT_FORKNUM);
}

/*
 *      btinsert() -- insert an index tuple into a btree.
 *
 *              Descend the tree recursively, find the appropriate location for our
 *              new tuple, and put it there.
 */
bool
btinsert(Relation rel, Datum *values, bool *isnull,
                 ItemPointer ht_ctid, Relation heapRel,
                 IndexUniqueCheck checkUnique,
                 IndexInfo *indexInfo)
{
        bool            result;
        IndexTuple      itup;

        /* generate an index tuple */
        itup = index_form_tuple(RelationGetDescr(rel), values, isnull);
        itup->t_tid = *ht_ctid;

        result = _bt_doinsert(rel, itup, checkUnique, heapRel);

        pfree(itup);

        return result;
}

/*
 *      btgettuple() -- Get the next tuple in the scan.
 */
bool
btgettuple(IndexScanDesc scan, ScanDirection dir)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;
        bool            res;

        /* btree indexes are never lossy */
        scan->xs_recheck = false;

        /*
         * If we have any array keys, initialize them during first call for a
         * scan.  We can't do this in btrescan because we don't know the scan
         * direction at that time.
         */
        if (so->numArrayKeys && !BTScanPosIsValid(so->currPos))
        {
                /* punt if we have any unsatisfiable array keys */
                if (so->numArrayKeys < 0)
                        return false;

                _bt_start_array_keys(scan, dir);
        }

        /* This loop handles advancing to the next array elements, if any */
        do
        {
                /*
                 * If we've already initialized this scan, we can just advance it in
                 * the appropriate direction.  If we haven't done so yet, we call
                 * _bt_first() to get the first item in the scan.
                 */
                if (!BTScanPosIsValid(so->currPos))
                        res = _bt_first(scan, dir);
                else
                {
                        /*
                         * Check to see if we should kill the previously-fetched tuple.
                         */
                        if (scan->kill_prior_tuple)
                        {
                                /*
                                 * Yes, remember it for later. (We'll deal with all such
                                 * tuples at once right before leaving the index page.)  The
                                 * test for numKilled overrun is not just paranoia: if the
                                 * caller reverses direction in the indexscan then the same
                                 * item might get entered multiple times. It's not worth
                                 * trying to optimize that, so we don't detect it, but instead
                                 * just forget any excess entries.
                                 */
                                if (so->killedItems == NULL)
                                        so->killedItems = (int *)
                                                palloc(MaxIndexTuplesPerPage * sizeof(int));
                                if (so->numKilled < MaxIndexTuplesPerPage)
                                        so->killedItems[so->numKilled++] = so->currPos.itemIndex;
                        }

                        /*
                         * Now continue the scan.
                         */
                        res = _bt_next(scan, dir);
                }

                /* If we have a tuple, return it ... */
                if (res)
                        break;
                /* ... otherwise see if we have more array keys to deal with */
        } while (so->numArrayKeys && _bt_advance_array_keys(scan, dir));

        return res;
}

/*
 * btgetbitmap() -- gets all matching tuples, and adds them to a bitmap
 */
int64
btgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;
        int64           ntids = 0;
        ItemPointer heapTid;

        /*
         * If we have any array keys, initialize them.
         */
        if (so->numArrayKeys)
        {
                /* punt if we have any unsatisfiable array keys */
                if (so->numArrayKeys < 0)
                        return ntids;

                _bt_start_array_keys(scan, ForwardScanDirection);
        }

        /* This loop handles advancing to the next array elements, if any */
        do
        {
                /* Fetch the first page & tuple */
                if (_bt_first(scan, ForwardScanDirection))
                {
                        /* Save tuple ID, and continue scanning */
                        heapTid = &scan->xs_heaptid;
                        tbm_add_tuples(tbm, heapTid, 1, false);
                        ntids++;

                        for (;;)
                        {
                                /*
                                 * Advance to next tuple within page.  This is the same as the
                                 * easy case in _bt_next().
                                 */
                                if (++so->currPos.itemIndex > so->currPos.lastItem)
                                {
                                        /* let _bt_next do the heavy lifting */
                                        if (!_bt_next(scan, ForwardScanDirection))
                                                break;
                                }

                                /* Save tuple ID, and continue scanning */
                                heapTid = &so->currPos.items[so->currPos.itemIndex].heapTid;
                                tbm_add_tuples(tbm, heapTid, 1, false);
                                ntids++;
                        }
                }
                /* Now see if we have more array keys to deal with */
        } while (so->numArrayKeys && _bt_advance_array_keys(scan, ForwardScanDirection));

        return ntids;
}

/*
 *      btbeginscan() -- start a scan on a btree index
 */
IndexScanDesc
btbeginscan(Relation rel, int nkeys, int norderbys)
{
        IndexScanDesc scan;
        BTScanOpaque so;

        /* no order by operators allowed */
        Assert(norderbys == 0);

        /* get the scan */
        scan = RelationGetIndexScan(rel, nkeys, norderbys);

        /* allocate private workspace */
        so = (BTScanOpaque) palloc(sizeof(BTScanOpaqueData));
        BTScanPosInvalidate(so->currPos);
        BTScanPosInvalidate(so->markPos);
        if (scan->numberOfKeys > 0)
                so->keyData = (ScanKey) palloc(scan->numberOfKeys * sizeof(ScanKeyData));
        else
                so->keyData = NULL;

        so->arrayKeyData = NULL;        /* assume no array keys for now */
        so->numArrayKeys = 0;
        so->arrayKeys = NULL;
        so->arrayContext = NULL;

        so->killedItems = NULL;         /* until needed */
        so->numKilled = 0;

        /*
         * We don't know yet whether the scan will be index-only, so we do not
         * allocate the tuple workspace arrays until btrescan.  However, we set up
         * scan->xs_itupdesc whether we'll need it or not, since that's so cheap.
         */
        so->currTuples = so->markTuples = NULL;

        scan->xs_itupdesc = RelationGetDescr(rel);

        scan->opaque = so;

        return scan;
}

/*
 *      btrescan() -- rescan an index relation
 */
void
btrescan(IndexScanDesc scan, ScanKey scankey, int nscankeys,
                 ScanKey orderbys, int norderbys)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;

        /* we aren't holding any read locks, but gotta drop the pins */
        if (BTScanPosIsValid(so->currPos))
        {
                /* Before leaving current page, deal with any killed items */
                if (so->numKilled > 0)
                        _bt_killitems(scan);
                BTScanPosUnpinIfPinned(so->currPos);
                BTScanPosInvalidate(so->currPos);
        }

        so->markItemIndex = -1;
        so->arrayKeyCount = 0;
        BTScanPosUnpinIfPinned(so->markPos);
        BTScanPosInvalidate(so->markPos);

        /*
         * Allocate tuple workspace arrays, if needed for an index-only scan and
         * not already done in a previous rescan call.  To save on palloc
         * overhead, both workspaces are allocated as one palloc block; only this
         * function and btendscan know that.
         *
         * NOTE: this data structure also makes it safe to return data from a
         * "name" column, even though btree name_ops uses an underlying storage
         * datatype of cstring.  The risk there is that "name" is supposed to be
         * padded to NAMEDATALEN, but the actual index tuple is probably shorter.
         * However, since we only return data out of tuples sitting in the
         * currTuples array, a fetch of NAMEDATALEN bytes can at worst pull some
         * data out of the markTuples array --- running off the end of memory for
         * a SIGSEGV is not possible.  Yeah, this is ugly as sin, but it beats
         * adding special-case treatment for name_ops elsewhere.
         */
        if (scan->xs_want_itup && so->currTuples == NULL)
        {
                so->currTuples = (char *) palloc(BLCKSZ * 2);
                so->markTuples = so->currTuples + BLCKSZ;
        }

        /*
         * Reset the scan keys. Note that keys ordering stuff moved to _bt_first.
         * - vadim 05/05/97
         */
        if (scankey && scan->numberOfKeys > 0)
                memmove(scan->keyData,
                                scankey,
                                scan->numberOfKeys * sizeof(ScanKeyData));
        so->numberOfKeys = 0;           /* until _bt_preprocess_keys sets it */

        /* If any keys are SK_SEARCHARRAY type, set up array-key info */
        _bt_preprocess_array_keys(scan);
}

/*
 *      btendscan() -- close down a scan
 */
void
btendscan(IndexScanDesc scan)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;

        /* we aren't holding any read locks, but gotta drop the pins */
        if (BTScanPosIsValid(so->currPos))
        {
                /* Before leaving current page, deal with any killed items */
                if (so->numKilled > 0)
                        _bt_killitems(scan);
                BTScanPosUnpinIfPinned(so->currPos);
        }

        so->markItemIndex = -1;
        BTScanPosUnpinIfPinned(so->markPos);

        /* No need to invalidate positions, the RAM is about to be freed. */

        /* Release storage */
        if (so->keyData != NULL)
                pfree(so->keyData);
        /* so->arrayKeyData and so->arrayKeys are in arrayContext */
        if (so->arrayContext != NULL)
                MemoryContextDelete(so->arrayContext);
        if (so->killedItems != NULL)
                pfree(so->killedItems);
        if (so->currTuples != NULL)
                pfree(so->currTuples);
        /* so->markTuples should not be pfree'd, see btrescan */
        pfree(so);
}

/*
 *      btmarkpos() -- save current scan position
 */
void
btmarkpos(IndexScanDesc scan)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;

        /* There may be an old mark with a pin (but no lock). */
        BTScanPosUnpinIfPinned(so->markPos);

        /*
         * Just record the current itemIndex.  If we later step to next page
         * before releasing the marked position, _bt_steppage makes a full copy of
         * the currPos struct in markPos.  If (as often happens) the mark is moved
         * before we leave the page, we don't have to do that work.
         */
        if (BTScanPosIsValid(so->currPos))
                so->markItemIndex = so->currPos.itemIndex;
        else
        {
                BTScanPosInvalidate(so->markPos);
                so->markItemIndex = -1;
        }

        /* Also record the current positions of any array keys */
        if (so->numArrayKeys)
                _bt_mark_array_keys(scan);
}

/*
 *      btrestrpos() -- restore scan to last saved position
 */
void
btrestrpos(IndexScanDesc scan)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;

        /* Restore the marked positions of any array keys */
        if (so->numArrayKeys)
                _bt_restore_array_keys(scan);

        if (so->markItemIndex >= 0)
        {
                /*
                 * The scan has never moved to a new page since the last mark.  Just
                 * restore the itemIndex.
                 *
                 * NB: In this case we can't count on anything in so->markPos to be
                 * accurate.
                 */
                so->currPos.itemIndex = so->markItemIndex;
        }
        else
        {
                /*
                 * The scan moved to a new page after last mark or restore, and we are
                 * now restoring to the marked page.  We aren't holding any read
                 * locks, but if we're still holding the pin for the current position,
                 * we must drop it.
                 */
                if (BTScanPosIsValid(so->currPos))
                {
                        /* Before leaving current page, deal with any killed items */
                        if (so->numKilled > 0)
                                _bt_killitems(scan);
                        BTScanPosUnpinIfPinned(so->currPos);
                }

                if (BTScanPosIsValid(so->markPos))
                {
                        /* bump pin on mark buffer for assignment to current buffer */
                        if (BTScanPosIsPinned(so->markPos))
                                IncrBufferRefCount(so->markPos.buf);
                        memcpy(&so->currPos, &so->markPos,
                                   offsetof(BTScanPosData, items[1]) +
                                   so->markPos.lastItem * sizeof(BTScanPosItem));
                        if (so->currTuples)
                                memcpy(so->currTuples, so->markTuples,
                                           so->markPos.nextTupleOffset);
                }
                else
                        BTScanPosInvalidate(so->currPos);
        }
}

/*
 * btestimateparallelscan -- estimate storage for BTParallelScanDescData
 */
Size
btestimateparallelscan(void)
{
        return sizeof(BTParallelScanDescData);
}

/*
 * btinitparallelscan -- initialize BTParallelScanDesc for parallel btree scan
 */
void
btinitparallelscan(void *target)
{
        BTParallelScanDesc bt_target = (BTParallelScanDesc) target;

        SpinLockInit(&bt_target->btps_mutex);
        bt_target->btps_scanPage = InvalidBlockNumber;
        bt_target->btps_pageStatus = BTPARALLEL_NOT_INITIALIZED;
        bt_target->btps_arrayKeyCount = 0;
        ConditionVariableInit(&bt_target->btps_cv);
}

/*
 *      btparallelrescan() -- reset parallel scan
 */
void
btparallelrescan(IndexScanDesc scan)
{
        BTParallelScanDesc btscan;
        ParallelIndexScanDesc parallel_scan = scan->parallel_scan;

        Assert(parallel_scan);

        btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
                                                                                                  parallel_scan->ps_offset);

        /*
         * In theory, we don't need to acquire the spinlock here, because there
         * shouldn't be any other workers running at this point, but we do so for
         * consistency.
         */
        SpinLockAcquire(&btscan->btps_mutex);
        btscan->btps_scanPage = InvalidBlockNumber;
        btscan->btps_pageStatus = BTPARALLEL_NOT_INITIALIZED;
        btscan->btps_arrayKeyCount = 0;
        SpinLockRelease(&btscan->btps_mutex);
}

/*
 * _bt_parallel_seize() -- Begin the process of advancing the scan to a new
 *              page.  Other scans must wait until we call _bt_parallel_release()
 *              or _bt_parallel_done().
 *
 * The return value is true if we successfully seized the scan and false
 * if we did not.  The latter case occurs if no pages remain for the current
 * set of scankeys.
 *
 * If the return value is true, *pageno returns the next or current page
 * of the scan (depending on the scan direction).  An invalid block number
 * means the scan hasn't yet started, and P_NONE means we've reached the end.
 * The first time a participating process reaches the last page, it will return
 * true and set *pageno to P_NONE; after that, further attempts to seize the
 * scan will return false.
 *
 * Callers should ignore the value of pageno if the return value is false.
 */
bool
_bt_parallel_seize(IndexScanDesc scan, BlockNumber *pageno)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;
        BTPS_State      pageStatus;
        bool            exit_loop = false;
        bool            status = true;
        ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
        BTParallelScanDesc btscan;

        *pageno = P_NONE;

        btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
                                                                                                  parallel_scan->ps_offset);

        while (1)
        {
                SpinLockAcquire(&btscan->btps_mutex);
                pageStatus = btscan->btps_pageStatus;

                if (so->arrayKeyCount < btscan->btps_arrayKeyCount)
                {
                        /* Parallel scan has already advanced to a new set of scankeys. */
                        status = false;
                }
                else if (pageStatus == BTPARALLEL_DONE)
                {
                        /*
                         * We're done with this set of scankeys.  This may be the end, or
                         * there could be more sets to try.
                         */
                        status = false;
                }
                else if (pageStatus != BTPARALLEL_ADVANCING)
                {
                        /*
                         * We have successfully seized control of the scan for the purpose
                         * of advancing it to a new page!
                         */
                        btscan->btps_pageStatus = BTPARALLEL_ADVANCING;
                        *pageno = btscan->btps_scanPage;
                        exit_loop = true;
                }
                SpinLockRelease(&btscan->btps_mutex);
                if (exit_loop || !status)
                        break;
                ConditionVariableSleep(&btscan->btps_cv, WAIT_EVENT_BTREE_PAGE);
        }
        ConditionVariableCancelSleep();

        return status;
}

/*
 * _bt_parallel_release() -- Complete the process of advancing the scan to a
 *              new page.  We now have the new value btps_scanPage; some other backend
 *              can now begin advancing the scan.
 */
void
_bt_parallel_release(IndexScanDesc scan, BlockNumber scan_page)
{
        ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
        BTParallelScanDesc btscan;

        btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
                                                                                                  parallel_scan->ps_offset);

        SpinLockAcquire(&btscan->btps_mutex);
        btscan->btps_scanPage = scan_page;
        btscan->btps_pageStatus = BTPARALLEL_IDLE;
        SpinLockRelease(&btscan->btps_mutex);
        ConditionVariableSignal(&btscan->btps_cv);
}

/*
 * _bt_parallel_done() -- Mark the parallel scan as complete.
 *
 * When there are no pages left to scan, this function should be called to
 * notify other workers.  Otherwise, they might wait forever for the scan to
 * advance to the next page.
 */
void
_bt_parallel_done(IndexScanDesc scan)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;
        ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
        BTParallelScanDesc btscan;
        bool            status_changed = false;

        /* Do nothing, for non-parallel scans */
        if (parallel_scan == NULL)
                return;

        btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
                                                                                                  parallel_scan->ps_offset);

        /*
         * Mark the parallel scan as done for this combination of scan keys,
         * unless some other process already did so.  See also
         * _bt_advance_array_keys.
         */
        SpinLockAcquire(&btscan->btps_mutex);
        if (so->arrayKeyCount >= btscan->btps_arrayKeyCount &&
                btscan->btps_pageStatus != BTPARALLEL_DONE)
        {
                btscan->btps_pageStatus = BTPARALLEL_DONE;
                status_changed = true;
        }
        SpinLockRelease(&btscan->btps_mutex);

        /* wake up all the workers associated with this parallel scan */
        if (status_changed)
                ConditionVariableBroadcast(&btscan->btps_cv);
}

/*
 * _bt_parallel_advance_array_keys() -- Advances the parallel scan for array
 *                      keys.
 *
 * Updates the count of array keys processed for both local and parallel
 * scans.
 */
void
_bt_parallel_advance_array_keys(IndexScanDesc scan)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;
        ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
        BTParallelScanDesc btscan;

        btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
                                                                                                  parallel_scan->ps_offset);

        so->arrayKeyCount++;
        SpinLockAcquire(&btscan->btps_mutex);
        if (btscan->btps_pageStatus == BTPARALLEL_DONE)
        {
                btscan->btps_scanPage = InvalidBlockNumber;
                btscan->btps_pageStatus = BTPARALLEL_NOT_INITIALIZED;
                btscan->btps_arrayKeyCount++;
        }
        SpinLockRelease(&btscan->btps_mutex);
}

/*
 * _bt_vacuum_needs_cleanup() -- Checks if index needs cleanup assuming that
 *                      btbulkdelete() wasn't called.
 */
static bool
_bt_vacuum_needs_cleanup(IndexVacuumInfo *info)
{
        Buffer          metabuf;
        Page            metapg;
        BTMetaPageData *metad;
        bool            result = false;

        metabuf = _bt_getbuf(info->index, BTREE_METAPAGE, BT_READ);
        metapg = BufferGetPage(metabuf);
        metad = BTPageGetMeta(metapg);

        if (metad->btm_version < BTREE_NOVAC_VERSION)
        {
                /*
                 * Do cleanup if metapage needs upgrade, because we don't have
                 * cleanup-related meta-information yet.
                 */
                result = true;
        }
        else if (TransactionIdIsValid(metad->btm_oldest_btpo_xact) &&
                         TransactionIdPrecedes(metad->btm_oldest_btpo_xact,
                                                                   RecentGlobalXmin))
        {
                /*
                 * If oldest btpo.xact in the deleted pages is older than
                 * RecentGlobalXmin, then at least one deleted page can be recycled.
                 */
                result = true;
        }
        else
        {
                StdRdOptions *relopts;
                float8          cleanup_scale_factor;
                float8          prev_num_heap_tuples;

                /*
                 * If table receives enough insertions and no cleanup was performed,
                 * then index would appear have stale statistics.  If scale factor is
                 * set, we avoid that by performing cleanup if the number of inserted
                 * tuples exceeds vacuum_cleanup_index_scale_factor fraction of
                 * original tuples count.
                 */
                relopts = (StdRdOptions *) info->index->rd_options;
                cleanup_scale_factor = (relopts &&
                                                                relopts->vacuum_cleanup_index_scale_factor >= 0)
                        ? relopts->vacuum_cleanup_index_scale_factor
                        : vacuum_cleanup_index_scale_factor;
                prev_num_heap_tuples = metad->btm_last_cleanup_num_heap_tuples;

                if (cleanup_scale_factor <= 0 ||
                        prev_num_heap_tuples <= 0 ||
                        (info->num_heap_tuples - prev_num_heap_tuples) /
                        prev_num_heap_tuples >= cleanup_scale_factor)
                        result = true;
        }

        _bt_relbuf(info->index, metabuf);
        return result;
}

/*
 * Bulk deletion of all index entries pointing to a set of heap tuples.
 * The set of target tuples is specified via a callback routine that tells
 * whether any given heap tuple (identified by ItemPointer) is being deleted.
 *
 * Result: a palloc'd struct containing statistical info for VACUUM displays.
 */
IndexBulkDeleteResult *
btbulkdelete(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
                         IndexBulkDeleteCallback callback, void *callback_state)
{
        Relation        rel = info->index;
        BTCycleId       cycleid;

        /* allocate stats if first time through, else re-use existing struct */
        if (stats == NULL)
                stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));

        /* Establish the vacuum cycle ID to use for this scan */
        /* The ENSURE stuff ensures we clean up shared memory on failure */
        PG_ENSURE_ERROR_CLEANUP(_bt_end_vacuum_callback, PointerGetDatum(rel));
        {
                TransactionId oldestBtpoXact;

                cycleid = _bt_start_vacuum(rel);

                btvacuumscan(info, stats, callback, callback_state, cycleid,
                                         &oldestBtpoXact);

                /*
                 * Update cleanup-related information in metapage. This information is
                 * used only for cleanup but keeping them up to date can avoid
                 * unnecessary cleanup even after bulkdelete.
                 */
                _bt_update_meta_cleanup_info(info->index, oldestBtpoXact,
                                                                         info->num_heap_tuples);
        }
        PG_END_ENSURE_ERROR_CLEANUP(_bt_end_vacuum_callback, PointerGetDatum(rel));
        _bt_end_vacuum(rel);

        return stats;
}

/*
 * Post-VACUUM cleanup.
 *
 * Result: a palloc'd struct containing statistical info for VACUUM displays.
 */
IndexBulkDeleteResult *
btvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats)
{
        /* No-op in ANALYZE ONLY mode */
        if (info->analyze_only)
                return stats;

        /*
         * If btbulkdelete was called, we need not do anything, just return the
         * stats from the latest btbulkdelete call.  If it wasn't called, we might
         * still need to do a pass over the index, to recycle any newly-recyclable
         * pages or to obtain index statistics.  _bt_vacuum_needs_cleanup
         * determines if either are needed.
         *
         * Since we aren't going to actually delete any leaf items, there's no
         * need to go through all the vacuum-cycle-ID pushups.
         */
        if (stats == NULL)
        {
                TransactionId oldestBtpoXact;

                /* Check if we need a cleanup */
                if (!_bt_vacuum_needs_cleanup(info))
                        return NULL;

                stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));
                btvacuumscan(info, stats, NULL, NULL, 0, &oldestBtpoXact);

                /* Update cleanup-related information in the metapage */
                _bt_update_meta_cleanup_info(info->index, oldestBtpoXact,
                                                                         info->num_heap_tuples);
        }

        /*
         * It's quite possible for us to be fooled by concurrent page splits into
         * double-counting some index tuples, so disbelieve any total that exceeds
         * the underlying heap's count ... if we know that accurately.  Otherwise
         * this might just make matters worse.
         */
        if (!info->estimated_count)
        {
                if (stats->num_index_tuples > info->num_heap_tuples)
                        stats->num_index_tuples = info->num_heap_tuples;
        }

        return stats;
}

/*
 * btvacuumscan --- scan the index for VACUUMing purposes
 *
 * This combines the functions of looking for leaf tuples that are deletable
 * according to the vacuum callback, looking for empty pages that can be
 * deleted, and looking for old deleted pages that can be recycled.  Both
 * btbulkdelete and btvacuumcleanup invoke this (the latter only if no
 * btbulkdelete call occurred).
 *
 * The caller is responsible for initially allocating/zeroing a stats struct
 * and for obtaining a vacuum cycle ID if necessary.
 */
static void
btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
                         IndexBulkDeleteCallback callback, void *callback_state,
                         BTCycleId cycleid, TransactionId *oldestBtpoXact)
{
        Relation        rel = info->index;
        BTVacState      vstate;
        BlockNumber num_pages;
        BlockNumber blkno;
        bool            needLock;

        /*
         * Reset counts that will be incremented during the scan; needed in case
         * of multiple scans during a single VACUUM command
         */
        stats->estimated_count = false;
        stats->num_index_tuples = 0;
        stats->pages_deleted = 0;

        /* Set up info to pass down to btvacuumpage */
        vstate.info = info;
        vstate.stats = stats;
        vstate.callback = callback;
        vstate.callback_state = callback_state;
        vstate.cycleid = cycleid;
        vstate.lastBlockVacuumed = BTREE_METAPAGE;      /* Initialise at first block */
        vstate.lastBlockLocked = BTREE_METAPAGE;
        vstate.totFreePages = 0;
        vstate.oldestBtpoXact = InvalidTransactionId;

        /* Create a temporary memory context to run _bt_pagedel in */
        vstate.pagedelcontext = AllocSetContextCreate(CurrentMemoryContext,
                                                                                                  "_bt_pagedel",
                                                                                                  ALLOCSET_DEFAULT_SIZES);

        /*
         * The outer loop iterates over all index pages except the metapage, in
         * physical order (we hope the kernel will cooperate in providing
         * read-ahead for speed).  It is critical that we visit all leaf pages,
         * including ones added after we start the scan, else we might fail to
         * delete some deletable tuples.  Hence, we must repeatedly check the
         * relation length.  We must acquire the relation-extension lock while
         * doing so to avoid a race condition: if someone else is extending the
         * relation, there is a window where bufmgr/smgr have created a new
         * all-zero page but it hasn't yet been write-locked by _bt_getbuf(). If
         * we manage to scan such a page here, we'll improperly assume it can be
         * recycled.  Taking the lock synchronizes things enough to prevent a
         * problem: either num_pages won't include the new page, or _bt_getbuf
         * already has write lock on the buffer and it will be fully initialized
         * before we can examine it.  (See also vacuumlazy.c, which has the same
         * issue.)      Also, we need not worry if a page is added immediately after
         * we look; the page splitting code already has write-lock on the left
         * page before it adds a right page, so we must already have processed any
         * tuples due to be moved into such a page.
         *
         * We can skip locking for new or temp relations, however, since no one
         * else could be accessing them.
         */
        needLock = !RELATION_IS_LOCAL(rel);

        blkno = BTREE_METAPAGE + 1;
        for (;;)
        {
                /* Get the current relation length */
                if (needLock)
                        LockRelationForExtension(rel, ExclusiveLock);
                num_pages = RelationGetNumberOfBlocks(rel);
                if (needLock)
                        UnlockRelationForExtension(rel, ExclusiveLock);

                if (info->report_progress)
                        pgstat_progress_update_param(PROGRESS_SCAN_BLOCKS_TOTAL,
                                                                                 num_pages);

                /* Quit if we've scanned the whole relation */
                if (blkno >= num_pages)
                        break;
                /* Iterate over pages, then loop back to recheck length */
                for (; blkno < num_pages; blkno++)
                {
                        btvacuumpage(&vstate, blkno, blkno);
                        if (info->report_progress)
                                pgstat_progress_update_param(PROGRESS_SCAN_BLOCKS_DONE,
                                                                                         blkno);
                }
        }

        /*
         * Check to see if we need to issue one final WAL record for this index,
         * which may be needed for correctness on a hot standby node when non-MVCC
         * index scans could take place.
         *
         * If the WAL is replayed in hot standby, the replay process needs to get
         * cleanup locks on all index leaf pages, just as we've been doing here.
         * However, we won't issue any WAL records about pages that have no items
         * to be deleted.  For pages between pages we've vacuumed, the replay code
         * will take locks under the direction of the lastBlockVacuumed fields in
         * the XLOG_BTREE_VACUUM WAL records.  To cover pages after the last one
         * we vacuum, we need to issue a dummy XLOG_BTREE_VACUUM WAL record
         * against the last leaf page in the index, if that one wasn't vacuumed.
         */
        if (XLogStandbyInfoActive() &&
                vstate.lastBlockVacuumed < vstate.lastBlockLocked)
        {
                Buffer          buf;

                /*
                 * The page should be valid, but we can't use _bt_getbuf() because we
                 * want to use a nondefault buffer access strategy.  Since we aren't
                 * going to delete any items, getting cleanup lock again is probably
                 * overkill, but for consistency do that anyway.
                 */
                buf = ReadBufferExtended(rel, MAIN_FORKNUM, vstate.lastBlockLocked,
                                                                 RBM_NORMAL, info->strategy);
                LockBufferForCleanup(buf);
                _bt_checkpage(rel, buf);
                _bt_delitems_vacuum(rel, buf, NULL, 0, vstate.lastBlockVacuumed);
                _bt_relbuf(rel, buf);
        }

        MemoryContextDelete(vstate.pagedelcontext);

        /*
         * If we found any recyclable pages (and recorded them in the FSM), then
         * forcibly update the upper-level FSM pages to ensure that searchers can
         * find them.  It's possible that the pages were also found during
         * previous scans and so this is a waste of time, but it's cheap enough
         * relative to scanning the index that it shouldn't matter much, and
         * making sure that free pages are available sooner not later seems
         * worthwhile.
         *
         * Note that if no recyclable pages exist, we don't bother vacuuming the
         * FSM at all.
         */
        if (vstate.totFreePages > 0)
                IndexFreeSpaceMapVacuum(rel);

        /* update statistics */
        stats->num_pages = num_pages;
        stats->pages_free = vstate.totFreePages;

        if (oldestBtpoXact)
                *oldestBtpoXact = vstate.oldestBtpoXact;
}

/*
 * btvacuumpage --- VACUUM one page
 *
 * This processes a single page for btvacuumscan().  In some cases we
 * must go back and re-examine previously-scanned pages; this routine
 * recurses when necessary to handle that case.
 *
 * blkno is the page to process.  orig_blkno is the highest block number
 * reached by the outer btvacuumscan loop (the same as blkno, unless we
 * are recursing to re-examine a previous page).
 */
static void
btvacuumpage(BTVacState *vstate, BlockNumber blkno, BlockNumber orig_blkno)
{
        IndexVacuumInfo *info = vstate->info;
        IndexBulkDeleteResult *stats = vstate->stats;
        IndexBulkDeleteCallback callback = vstate->callback;
        void       *callback_state = vstate->callback_state;
        Relation        rel = info->index;
        bool            delete_now;
        BlockNumber recurse_to;
        Buffer          buf;
        Page            page;
        BTPageOpaque opaque = NULL;

restart:
        delete_now = false;
        recurse_to = P_NONE;

        /* call vacuum_delay_point while not holding any buffer lock */
        vacuum_delay_point();

        /*
         * We can't use _bt_getbuf() here because it always applies
         * _bt_checkpage(), which will barf on an all-zero page. We want to
         * recycle all-zero pages, not fail.  Also, we want to use a nondefault
         * buffer access strategy.
         */
        buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
                                                         info->strategy);
        LockBuffer(buf, BT_READ);
        page = BufferGetPage(buf);
        if (!PageIsNew(page))
        {
                _bt_checkpage(rel, buf);
                opaque = (BTPageOpaque) PageGetSpecialPointer(page);
        }

        /*
         * If we are recursing, the only case we want to do anything with is a
         * live leaf page having the current vacuum cycle ID.  Any other state
         * implies we already saw the page (eg, deleted it as being empty).
         */
        if (blkno != orig_blkno)
        {
                if (_bt_page_recyclable(page) ||
                        P_IGNORE(opaque) ||
                        !P_ISLEAF(opaque) ||
                        opaque->btpo_cycleid != vstate->cycleid)
                {
                        _bt_relbuf(rel, buf);
                        return;
                }
        }

        /* Page is valid, see what to do with it */
        if (_bt_page_recyclable(page))
        {
                /* Okay to recycle this page */
                RecordFreeIndexPage(rel, blkno);
                vstate->totFreePages++;
                stats->pages_deleted++;
        }
        else if (P_ISDELETED(opaque))
        {
                /* Already deleted, but can't recycle yet */
                stats->pages_deleted++;

                /* Update the oldest btpo.xact */
                if (!TransactionIdIsValid(vstate->oldestBtpoXact) ||
                        TransactionIdPrecedes(opaque->btpo.xact, vstate->oldestBtpoXact))
                        vstate->oldestBtpoXact = opaque->btpo.xact;
        }
        else if (P_ISHALFDEAD(opaque))
        {
                /* Half-dead, try to delete */
                delete_now = true;
        }
        else if (P_ISLEAF(opaque))
        {
                OffsetNumber deletable[MaxOffsetNumber];
                int                     ndeletable;
                OffsetNumber offnum,
                                        minoff,
                                        maxoff;

                /*
                 * Trade in the initial read lock for a super-exclusive write lock on
                 * this page.  We must get such a lock on every leaf page over the
                 * course of the vacuum scan, whether or not it actually contains any
                 * deletable tuples --- see nbtree/README.
                 */
                LockBuffer(buf, BUFFER_LOCK_UNLOCK);
                LockBufferForCleanup(buf);

                /*
                 * Remember highest leaf page number we've taken cleanup lock on; see
                 * notes in btvacuumscan
                 */
                if (blkno > vstate->lastBlockLocked)
                        vstate->lastBlockLocked = blkno;

                /*
                 * Check whether we need to recurse back to earlier pages.  What we
                 * are concerned about is a page split that happened since we started
                 * the vacuum scan.  If the split moved some tuples to a lower page
                 * then we might have missed 'em.  If so, set up for tail recursion.
                 * (Must do this before possibly clearing btpo_cycleid below!)
                 */
                if (vstate->cycleid != 0 &&
                        opaque->btpo_cycleid == vstate->cycleid &&
                        !(opaque->btpo_flags & BTP_SPLIT_END) &&
                        !P_RIGHTMOST(opaque) &&
                        opaque->btpo_next < orig_blkno)
                        recurse_to = opaque->btpo_next;

                /*
                 * Scan over all items to see which ones need deleted according to the
                 * callback function.
                 */
                ndeletable = 0;
                minoff = P_FIRSTDATAKEY(opaque);
                maxoff = PageGetMaxOffsetNumber(page);
                if (callback)
                {
                        for (offnum = minoff;
                                 offnum <= maxoff;
                                 offnum = OffsetNumberNext(offnum))
                        {
                                IndexTuple      itup;
                                ItemPointer htup;

                                itup = (IndexTuple) PageGetItem(page,
                                                                                                PageGetItemId(page, offnum));
                                htup = &(itup->t_tid);

                                /*
                                 * During Hot Standby we currently assume that
                                 * XLOG_BTREE_VACUUM records do not produce conflicts. That is
                                 * only true as long as the callback function depends only
                                 * upon whether the index tuple refers to heap tuples removed
                                 * in the initial heap scan. When vacuum starts it derives a
                                 * value of OldestXmin. Backends taking later snapshots could
                                 * have a RecentGlobalXmin with a later xid than the vacuum's
                                 * OldestXmin, so it is possible that row versions deleted
                                 * after OldestXmin could be marked as killed by other
                                 * backends. The callback function *could* look at the index
                                 * tuple state in isolation and decide to delete the index
                                 * tuple, though currently it does not. If it ever did, we
                                 * would need to reconsider whether XLOG_BTREE_VACUUM records
                                 * should cause conflicts. If they did cause conflicts they
                                 * would be fairly harsh conflicts, since we haven't yet
                                 * worked out a way to pass a useful value for
                                 * latestRemovedXid on the XLOG_BTREE_VACUUM records. This
                                 * applies to *any* type of index that marks index tuples as
                                 * killed.
                                 */
                                if (callback(htup, callback_state))
                                        deletable[ndeletable++] = offnum;
                        }
                }

                /*
                 * Apply any needed deletes.  We issue just one _bt_delitems_vacuum()
                 * call per page, so as to minimize WAL traffic.
                 */
                if (ndeletable > 0)
                {
                        /*
                         * Notice that the issued XLOG_BTREE_VACUUM WAL record includes
                         * all information to the replay code to allow it to get a cleanup
                         * lock on all pages between the previous lastBlockVacuumed and
                         * this page. This ensures that WAL replay locks all leaf pages at
                         * some point, which is important should non-MVCC scans be
                         * requested. This is currently unused on standby, but we record
                         * it anyway, so that the WAL contains the required information.
                         *
                         * Since we can visit leaf pages out-of-order when recursing,
                         * replay might end up locking such pages an extra time, but it
                         * doesn't seem worth the amount of bookkeeping it'd take to avoid
                         * that.
                         */
                        _bt_delitems_vacuum(rel, buf, deletable, ndeletable,
                                                                vstate->lastBlockVacuumed);

                        /*
                         * Remember highest leaf page number we've issued a
                         * XLOG_BTREE_VACUUM WAL record for.
                         */
                        if (blkno > vstate->lastBlockVacuumed)
                                vstate->lastBlockVacuumed = blkno;

                        stats->tuples_removed += ndeletable;
                        /* must recompute maxoff */
                        maxoff = PageGetMaxOffsetNumber(page);
                }
                else
                {
                        /*
                         * If the page has been split during this vacuum cycle, it seems
                         * worth expending a write to clear btpo_cycleid even if we don't
                         * have any deletions to do.  (If we do, _bt_delitems_vacuum takes
                         * care of this.)  This ensures we won't process the page again.
                         *
                         * We treat this like a hint-bit update because there's no need to
                         * WAL-log it.
                         */
                        if (vstate->cycleid != 0 &&
                                opaque->btpo_cycleid == vstate->cycleid)
                        {
                                opaque->btpo_cycleid = 0;
                                MarkBufferDirtyHint(buf, true);
                        }
                }

                /*
                 * If it's now empty, try to delete; else count the live tuples. We
                 * don't delete when recursing, though, to avoid putting entries into
                 * freePages out-of-order (doesn't seem worth any extra code to handle
                 * the case).
                 */
                if (minoff > maxoff)
                        delete_now = (blkno == orig_blkno);
                else
                        stats->num_index_tuples += maxoff - minoff + 1;
        }

        if (delete_now)
        {
                MemoryContext oldcontext;
                int                     ndel;

                /* Run pagedel in a temp context to avoid memory leakage */
                MemoryContextReset(vstate->pagedelcontext);
                oldcontext = MemoryContextSwitchTo(vstate->pagedelcontext);

                ndel = _bt_pagedel(rel, buf);

                /* count only this page, else may double-count parent */
                if (ndel)
                {
                        stats->pages_deleted++;
                        if (!TransactionIdIsValid(vstate->oldestBtpoXact) ||
                                TransactionIdPrecedes(opaque->btpo.xact, vstate->oldestBtpoXact))
                                vstate->oldestBtpoXact = opaque->btpo.xact;
                }

                MemoryContextSwitchTo(oldcontext);
                /* pagedel released buffer, so we shouldn't */
        }
        else
                _bt_relbuf(rel, buf);

        /*
         * This is really tail recursion, but if the compiler is too stupid to
         * optimize it as such, we'd eat an uncomfortably large amount of stack
         * space per recursion level (due to the deletable[] array). A failure is
         * improbable since the number of levels isn't likely to be large ... but
         * just in case, let's hand-optimize into a loop.
         */
        if (recurse_to != P_NONE)
        {
                blkno = recurse_to;
                goto restart;
        }
}

/*
 *      btcanreturn() -- Check whether btree indexes support index-only scans.
 *
 * btrees always do, so this is trivial.
 */
bool
btcanreturn(Relation index, int attno)
{
        return true;
}