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-rw-r--r--src/backend/access/gist/gistget.c803
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diff --git a/src/backend/access/gist/gistget.c b/src/backend/access/gist/gistget.c
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+++ b/src/backend/access/gist/gistget.c
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+/*-------------------------------------------------------------------------
+ *
+ * gistget.c
+ * fetch tuples from a GiST scan.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ * src/backend/access/gist/gistget.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/genam.h"
+#include "access/gist_private.h"
+#include "access/relscan.h"
+#include "lib/pairingheap.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "storage/lmgr.h"
+#include "storage/predicate.h"
+#include "utils/float.h"
+#include "utils/memutils.h"
+#include "utils/rel.h"
+
+/*
+ * gistkillitems() -- set LP_DEAD state for items an indexscan caller has
+ * told us were killed.
+ *
+ * We re-read page here, so it's important to check page LSN. If the page
+ * has been modified since the last read (as determined by LSN), we cannot
+ * flag any entries because it is possible that the old entry was vacuumed
+ * away and the TID was re-used by a completely different heap tuple.
+ */
+static void
+gistkillitems(IndexScanDesc scan)
+{
+ GISTScanOpaque so = (GISTScanOpaque) scan->opaque;
+ Buffer buffer;
+ Page page;
+ OffsetNumber offnum;
+ ItemId iid;
+ int i;
+ bool killedsomething = false;
+
+ Assert(so->curBlkno != InvalidBlockNumber);
+ Assert(!XLogRecPtrIsInvalid(so->curPageLSN));
+ Assert(so->killedItems != NULL);
+
+ buffer = ReadBuffer(scan->indexRelation, so->curBlkno);
+ if (!BufferIsValid(buffer))
+ return;
+
+ LockBuffer(buffer, GIST_SHARE);
+ gistcheckpage(scan->indexRelation, buffer);
+ page = BufferGetPage(buffer);
+
+ /*
+ * If page LSN differs it means that the page was modified since the last
+ * read. killedItems could be not valid so LP_DEAD hints applying is not
+ * safe.
+ */
+ if (BufferGetLSNAtomic(buffer) != so->curPageLSN)
+ {
+ UnlockReleaseBuffer(buffer);
+ so->numKilled = 0; /* reset counter */
+ return;
+ }
+
+ Assert(GistPageIsLeaf(page));
+
+ /*
+ * Mark all killedItems as dead. We need no additional recheck, because,
+ * if page was modified, curPageLSN must have changed.
+ */
+ for (i = 0; i < so->numKilled; i++)
+ {
+ offnum = so->killedItems[i];
+ iid = PageGetItemId(page, offnum);
+ ItemIdMarkDead(iid);
+ killedsomething = true;
+ }
+
+ if (killedsomething)
+ {
+ GistMarkPageHasGarbage(page);
+ MarkBufferDirtyHint(buffer, true);
+ }
+
+ UnlockReleaseBuffer(buffer);
+
+ /*
+ * Always reset the scan state, so we don't look for same items on other
+ * pages.
+ */
+ so->numKilled = 0;
+}
+
+/*
+ * gistindex_keytest() -- does this index tuple satisfy the scan key(s)?
+ *
+ * The index tuple might represent either a heap tuple or a lower index page,
+ * depending on whether the containing page is a leaf page or not.
+ *
+ * On success return for a heap tuple, *recheck_p is set to indicate whether
+ * the quals need to be rechecked. We recheck if any of the consistent()
+ * functions request it. recheck is not interesting when examining a non-leaf
+ * entry, since we must visit the lower index page if there's any doubt.
+ * Similarly, *recheck_distances_p is set to indicate whether the distances
+ * need to be rechecked, and it is also ignored for non-leaf entries.
+ *
+ * If we are doing an ordered scan, so->distances[] is filled with distance
+ * data from the distance() functions before returning success.
+ *
+ * We must decompress the key in the IndexTuple before passing it to the
+ * sk_funcs (which actually are the opclass Consistent or Distance methods).
+ *
+ * Note that this function is always invoked in a short-lived memory context,
+ * so we don't need to worry about cleaning up allocated memory, either here
+ * or in the implementation of any Consistent or Distance methods.
+ */
+static bool
+gistindex_keytest(IndexScanDesc scan,
+ IndexTuple tuple,
+ Page page,
+ OffsetNumber offset,
+ bool *recheck_p,
+ bool *recheck_distances_p)
+{
+ GISTScanOpaque so = (GISTScanOpaque) scan->opaque;
+ GISTSTATE *giststate = so->giststate;
+ ScanKey key = scan->keyData;
+ int keySize = scan->numberOfKeys;
+ IndexOrderByDistance *distance_p;
+ Relation r = scan->indexRelation;
+
+ *recheck_p = false;
+ *recheck_distances_p = false;
+
+ /*
+ * If it's a leftover invalid tuple from pre-9.1, treat it as a match with
+ * minimum possible distances. This means we'll always follow it to the
+ * referenced page.
+ */
+ if (GistTupleIsInvalid(tuple))
+ {
+ int i;
+
+ if (GistPageIsLeaf(page)) /* shouldn't happen */
+ elog(ERROR, "invalid GiST tuple found on leaf page");
+ for (i = 0; i < scan->numberOfOrderBys; i++)
+ {
+ so->distances[i].value = -get_float8_infinity();
+ so->distances[i].isnull = false;
+ }
+ return true;
+ }
+
+ /* Check whether it matches according to the Consistent functions */
+ while (keySize > 0)
+ {
+ Datum datum;
+ bool isNull;
+
+ datum = index_getattr(tuple,
+ key->sk_attno,
+ giststate->leafTupdesc,
+ &isNull);
+
+ if (key->sk_flags & SK_ISNULL)
+ {
+ /*
+ * On non-leaf page we can't conclude that child hasn't NULL
+ * values because of assumption in GiST: union (VAL, NULL) is VAL.
+ * But if on non-leaf page key IS NULL, then all children are
+ * NULL.
+ */
+ if (key->sk_flags & SK_SEARCHNULL)
+ {
+ if (GistPageIsLeaf(page) && !isNull)
+ return false;
+ }
+ else
+ {
+ Assert(key->sk_flags & SK_SEARCHNOTNULL);
+ if (isNull)
+ return false;
+ }
+ }
+ else if (isNull)
+ {
+ return false;
+ }
+ else
+ {
+ Datum test;
+ bool recheck;
+ GISTENTRY de;
+
+ gistdentryinit(giststate, key->sk_attno - 1, &de,
+ datum, r, page, offset,
+ false, isNull);
+
+ /*
+ * Call the Consistent function to evaluate the test. The
+ * arguments are the index datum (as a GISTENTRY*), the comparison
+ * datum, the comparison operator's strategy number and subtype
+ * from pg_amop, and the recheck flag.
+ *
+ * (Presently there's no need to pass the subtype since it'll
+ * always be zero, but might as well pass it for possible future
+ * use.)
+ *
+ * We initialize the recheck flag to true (the safest assumption)
+ * in case the Consistent function forgets to set it.
+ */
+ recheck = true;
+
+ test = FunctionCall5Coll(&key->sk_func,
+ key->sk_collation,
+ PointerGetDatum(&de),
+ key->sk_argument,
+ Int16GetDatum(key->sk_strategy),
+ ObjectIdGetDatum(key->sk_subtype),
+ PointerGetDatum(&recheck));
+
+ if (!DatumGetBool(test))
+ return false;
+ *recheck_p |= recheck;
+ }
+
+ key++;
+ keySize--;
+ }
+
+ /* OK, it passes --- now let's compute the distances */
+ key = scan->orderByData;
+ distance_p = so->distances;
+ keySize = scan->numberOfOrderBys;
+ while (keySize > 0)
+ {
+ Datum datum;
+ bool isNull;
+
+ datum = index_getattr(tuple,
+ key->sk_attno,
+ giststate->leafTupdesc,
+ &isNull);
+
+ if ((key->sk_flags & SK_ISNULL) || isNull)
+ {
+ /* Assume distance computes as null */
+ distance_p->value = 0.0;
+ distance_p->isnull = true;
+ }
+ else
+ {
+ Datum dist;
+ bool recheck;
+ GISTENTRY de;
+
+ gistdentryinit(giststate, key->sk_attno - 1, &de,
+ datum, r, page, offset,
+ false, isNull);
+
+ /*
+ * Call the Distance function to evaluate the distance. The
+ * arguments are the index datum (as a GISTENTRY*), the comparison
+ * datum, the ordering operator's strategy number and subtype from
+ * pg_amop, and the recheck flag.
+ *
+ * (Presently there's no need to pass the subtype since it'll
+ * always be zero, but might as well pass it for possible future
+ * use.)
+ *
+ * If the function sets the recheck flag, the returned distance is
+ * a lower bound on the true distance and needs to be rechecked.
+ * We initialize the flag to 'false'. This flag was added in
+ * version 9.5; distance functions written before that won't know
+ * about the flag, but are expected to never be lossy.
+ */
+ recheck = false;
+ dist = FunctionCall5Coll(&key->sk_func,
+ key->sk_collation,
+ PointerGetDatum(&de),
+ key->sk_argument,
+ Int16GetDatum(key->sk_strategy),
+ ObjectIdGetDatum(key->sk_subtype),
+ PointerGetDatum(&recheck));
+ *recheck_distances_p |= recheck;
+ distance_p->value = DatumGetFloat8(dist);
+ distance_p->isnull = false;
+ }
+
+ key++;
+ distance_p++;
+ keySize--;
+ }
+
+ return true;
+}
+
+/*
+ * Scan all items on the GiST index page identified by *pageItem, and insert
+ * them into the queue (or directly to output areas)
+ *
+ * scan: index scan we are executing
+ * pageItem: search queue item identifying an index page to scan
+ * myDistances: distances array associated with pageItem, or NULL at the root
+ * tbm: if not NULL, gistgetbitmap's output bitmap
+ * ntids: if not NULL, gistgetbitmap's output tuple counter
+ *
+ * If tbm/ntids aren't NULL, we are doing an amgetbitmap scan, and heap
+ * tuples should be reported directly into the bitmap. If they are NULL,
+ * we're doing a plain or ordered indexscan. For a plain indexscan, heap
+ * tuple TIDs are returned into so->pageData[]. For an ordered indexscan,
+ * heap tuple TIDs are pushed into individual search queue items. In an
+ * index-only scan, reconstructed index tuples are returned along with the
+ * TIDs.
+ *
+ * If we detect that the index page has split since we saw its downlink
+ * in the parent, we push its new right sibling onto the queue so the
+ * sibling will be processed next.
+ */
+static void
+gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem,
+ IndexOrderByDistance *myDistances, TIDBitmap *tbm, int64 *ntids)
+{
+ GISTScanOpaque so = (GISTScanOpaque) scan->opaque;
+ GISTSTATE *giststate = so->giststate;
+ Relation r = scan->indexRelation;
+ Buffer buffer;
+ Page page;
+ GISTPageOpaque opaque;
+ OffsetNumber maxoff;
+ OffsetNumber i;
+ MemoryContext oldcxt;
+
+ Assert(!GISTSearchItemIsHeap(*pageItem));
+
+ buffer = ReadBuffer(scan->indexRelation, pageItem->blkno);
+ LockBuffer(buffer, GIST_SHARE);
+ PredicateLockPage(r, BufferGetBlockNumber(buffer), scan->xs_snapshot);
+ gistcheckpage(scan->indexRelation, buffer);
+ page = BufferGetPage(buffer);
+ TestForOldSnapshot(scan->xs_snapshot, r, page);
+ opaque = GistPageGetOpaque(page);
+
+ /*
+ * Check if we need to follow the rightlink. We need to follow it if the
+ * page was concurrently split since we visited the parent (in which case
+ * parentlsn < nsn), or if the system crashed after a page split but
+ * before the downlink was inserted into the parent.
+ */
+ if (!XLogRecPtrIsInvalid(pageItem->data.parentlsn) &&
+ (GistFollowRight(page) ||
+ pageItem->data.parentlsn < GistPageGetNSN(page)) &&
+ opaque->rightlink != InvalidBlockNumber /* sanity check */ )
+ {
+ /* There was a page split, follow right link to add pages */
+ GISTSearchItem *item;
+
+ /* This can't happen when starting at the root */
+ Assert(myDistances != NULL);
+
+ oldcxt = MemoryContextSwitchTo(so->queueCxt);
+
+ /* Create new GISTSearchItem for the right sibling index page */
+ item = palloc(SizeOfGISTSearchItem(scan->numberOfOrderBys));
+ item->blkno = opaque->rightlink;
+ item->data.parentlsn = pageItem->data.parentlsn;
+
+ /* Insert it into the queue using same distances as for this page */
+ memcpy(item->distances, myDistances,
+ sizeof(item->distances[0]) * scan->numberOfOrderBys);
+
+ pairingheap_add(so->queue, &item->phNode);
+
+ MemoryContextSwitchTo(oldcxt);
+ }
+
+ /*
+ * Check if the page was deleted after we saw the downlink. There's
+ * nothing of interest on a deleted page. Note that we must do this after
+ * checking the NSN for concurrent splits! It's possible that the page
+ * originally contained some tuples that are visible to us, but was split
+ * so that all the visible tuples were moved to another page, and then
+ * this page was deleted.
+ */
+ if (GistPageIsDeleted(page))
+ {
+ UnlockReleaseBuffer(buffer);
+ return;
+ }
+
+ so->nPageData = so->curPageData = 0;
+ scan->xs_hitup = NULL; /* might point into pageDataCxt */
+ if (so->pageDataCxt)
+ MemoryContextReset(so->pageDataCxt);
+
+ /*
+ * We save the LSN of the page as we read it, so that we know whether it
+ * safe to apply LP_DEAD hints to the page later. This allows us to drop
+ * the pin for MVCC scans, which allows vacuum to avoid blocking.
+ */
+ so->curPageLSN = BufferGetLSNAtomic(buffer);
+
+ /*
+ * check all tuples on page
+ */
+ maxoff = PageGetMaxOffsetNumber(page);
+ for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
+ {
+ ItemId iid = PageGetItemId(page, i);
+ IndexTuple it;
+ bool match;
+ bool recheck;
+ bool recheck_distances;
+
+ /*
+ * If the scan specifies not to return killed tuples, then we treat a
+ * killed tuple as not passing the qual.
+ */
+ if (scan->ignore_killed_tuples && ItemIdIsDead(iid))
+ continue;
+
+ it = (IndexTuple) PageGetItem(page, iid);
+
+ /*
+ * Must call gistindex_keytest in tempCxt, and clean up any leftover
+ * junk afterward.
+ */
+ oldcxt = MemoryContextSwitchTo(so->giststate->tempCxt);
+
+ match = gistindex_keytest(scan, it, page, i,
+ &recheck, &recheck_distances);
+
+ MemoryContextSwitchTo(oldcxt);
+ MemoryContextReset(so->giststate->tempCxt);
+
+ /* Ignore tuple if it doesn't match */
+ if (!match)
+ continue;
+
+ if (tbm && GistPageIsLeaf(page))
+ {
+ /*
+ * getbitmap scan, so just push heap tuple TIDs into the bitmap
+ * without worrying about ordering
+ */
+ tbm_add_tuples(tbm, &it->t_tid, 1, recheck);
+ (*ntids)++;
+ }
+ else if (scan->numberOfOrderBys == 0 && GistPageIsLeaf(page))
+ {
+ /*
+ * Non-ordered scan, so report tuples in so->pageData[]
+ */
+ so->pageData[so->nPageData].heapPtr = it->t_tid;
+ so->pageData[so->nPageData].recheck = recheck;
+ so->pageData[so->nPageData].offnum = i;
+
+ /*
+ * In an index-only scan, also fetch the data from the tuple. The
+ * reconstructed tuples are stored in pageDataCxt.
+ */
+ if (scan->xs_want_itup)
+ {
+ oldcxt = MemoryContextSwitchTo(so->pageDataCxt);
+ so->pageData[so->nPageData].recontup =
+ gistFetchTuple(giststate, r, it);
+ MemoryContextSwitchTo(oldcxt);
+ }
+ so->nPageData++;
+ }
+ else
+ {
+ /*
+ * Must push item into search queue. We get here for any lower
+ * index page, and also for heap tuples if doing an ordered
+ * search.
+ */
+ GISTSearchItem *item;
+ int nOrderBys = scan->numberOfOrderBys;
+
+ oldcxt = MemoryContextSwitchTo(so->queueCxt);
+
+ /* Create new GISTSearchItem for this item */
+ item = palloc(SizeOfGISTSearchItem(scan->numberOfOrderBys));
+
+ if (GistPageIsLeaf(page))
+ {
+ /* Creating heap-tuple GISTSearchItem */
+ item->blkno = InvalidBlockNumber;
+ item->data.heap.heapPtr = it->t_tid;
+ item->data.heap.recheck = recheck;
+ item->data.heap.recheckDistances = recheck_distances;
+
+ /*
+ * In an index-only scan, also fetch the data from the tuple.
+ */
+ if (scan->xs_want_itup)
+ item->data.heap.recontup = gistFetchTuple(giststate, r, it);
+ }
+ else
+ {
+ /* Creating index-page GISTSearchItem */
+ item->blkno = ItemPointerGetBlockNumber(&it->t_tid);
+
+ /*
+ * LSN of current page is lsn of parent page for child. We
+ * only have a shared lock, so we need to get the LSN
+ * atomically.
+ */
+ item->data.parentlsn = BufferGetLSNAtomic(buffer);
+ }
+
+ /* Insert it into the queue using new distance data */
+ memcpy(item->distances, so->distances,
+ sizeof(item->distances[0]) * nOrderBys);
+
+ pairingheap_add(so->queue, &item->phNode);
+
+ MemoryContextSwitchTo(oldcxt);
+ }
+ }
+
+ UnlockReleaseBuffer(buffer);
+}
+
+/*
+ * Extract next item (in order) from search queue
+ *
+ * Returns a GISTSearchItem or NULL. Caller must pfree item when done with it.
+ */
+static GISTSearchItem *
+getNextGISTSearchItem(GISTScanOpaque so)
+{
+ GISTSearchItem *item;
+
+ if (!pairingheap_is_empty(so->queue))
+ {
+ item = (GISTSearchItem *) pairingheap_remove_first(so->queue);
+ }
+ else
+ {
+ /* Done when both heaps are empty */
+ item = NULL;
+ }
+
+ /* Return item; caller is responsible to pfree it */
+ return item;
+}
+
+/*
+ * Fetch next heap tuple in an ordered search
+ */
+static bool
+getNextNearest(IndexScanDesc scan)
+{
+ GISTScanOpaque so = (GISTScanOpaque) scan->opaque;
+ bool res = false;
+
+ if (scan->xs_hitup)
+ {
+ /* free previously returned tuple */
+ pfree(scan->xs_hitup);
+ scan->xs_hitup = NULL;
+ }
+
+ do
+ {
+ GISTSearchItem *item = getNextGISTSearchItem(so);
+
+ if (!item)
+ break;
+
+ if (GISTSearchItemIsHeap(*item))
+ {
+ /* found a heap item at currently minimal distance */
+ scan->xs_heaptid = item->data.heap.heapPtr;
+ scan->xs_recheck = item->data.heap.recheck;
+
+ index_store_float8_orderby_distances(scan, so->orderByTypes,
+ item->distances,
+ item->data.heap.recheckDistances);
+
+ /* in an index-only scan, also return the reconstructed tuple. */
+ if (scan->xs_want_itup)
+ scan->xs_hitup = item->data.heap.recontup;
+ res = true;
+ }
+ else
+ {
+ /* visit an index page, extract its items into queue */
+ CHECK_FOR_INTERRUPTS();
+
+ gistScanPage(scan, item, item->distances, NULL, NULL);
+ }
+
+ pfree(item);
+ } while (!res);
+
+ return res;
+}
+
+/*
+ * gistgettuple() -- Get the next tuple in the scan
+ */
+bool
+gistgettuple(IndexScanDesc scan, ScanDirection dir)
+{
+ GISTScanOpaque so = (GISTScanOpaque) scan->opaque;
+
+ if (dir != ForwardScanDirection)
+ elog(ERROR, "GiST only supports forward scan direction");
+
+ if (!so->qual_ok)
+ return false;
+
+ if (so->firstCall)
+ {
+ /* Begin the scan by processing the root page */
+ GISTSearchItem fakeItem;
+
+ pgstat_count_index_scan(scan->indexRelation);
+
+ so->firstCall = false;
+ so->curPageData = so->nPageData = 0;
+ scan->xs_hitup = NULL;
+ if (so->pageDataCxt)
+ MemoryContextReset(so->pageDataCxt);
+
+ fakeItem.blkno = GIST_ROOT_BLKNO;
+ memset(&fakeItem.data.parentlsn, 0, sizeof(GistNSN));
+ gistScanPage(scan, &fakeItem, NULL, NULL, NULL);
+ }
+
+ if (scan->numberOfOrderBys > 0)
+ {
+ /* Must fetch tuples in strict distance order */
+ return getNextNearest(scan);
+ }
+ else
+ {
+ /* Fetch tuples index-page-at-a-time */
+ for (;;)
+ {
+ if (so->curPageData < so->nPageData)
+ {
+ if (scan->kill_prior_tuple && so->curPageData > 0)
+ {
+
+ if (so->killedItems == NULL)
+ {
+ MemoryContext oldCxt =
+ MemoryContextSwitchTo(so->giststate->scanCxt);
+
+ so->killedItems =
+ (OffsetNumber *) palloc(MaxIndexTuplesPerPage
+ * sizeof(OffsetNumber));
+
+ MemoryContextSwitchTo(oldCxt);
+ }
+ if (so->numKilled < MaxIndexTuplesPerPage)
+ so->killedItems[so->numKilled++] =
+ so->pageData[so->curPageData - 1].offnum;
+ }
+ /* continuing to return tuples from a leaf page */
+ scan->xs_heaptid = so->pageData[so->curPageData].heapPtr;
+ scan->xs_recheck = so->pageData[so->curPageData].recheck;
+
+ /* in an index-only scan, also return the reconstructed tuple */
+ if (scan->xs_want_itup)
+ scan->xs_hitup = so->pageData[so->curPageData].recontup;
+
+ so->curPageData++;
+
+ return true;
+ }
+
+ /*
+ * Check the last returned tuple and add it to killedItems if
+ * necessary
+ */
+ if (scan->kill_prior_tuple
+ && so->curPageData > 0
+ && so->curPageData == so->nPageData)
+ {
+
+ if (so->killedItems == NULL)
+ {
+ MemoryContext oldCxt =
+ MemoryContextSwitchTo(so->giststate->scanCxt);
+
+ so->killedItems =
+ (OffsetNumber *) palloc(MaxIndexTuplesPerPage
+ * sizeof(OffsetNumber));
+
+ MemoryContextSwitchTo(oldCxt);
+ }
+ if (so->numKilled < MaxIndexTuplesPerPage)
+ so->killedItems[so->numKilled++] =
+ so->pageData[so->curPageData - 1].offnum;
+ }
+ /* find and process the next index page */
+ do
+ {
+ GISTSearchItem *item;
+
+ if ((so->curBlkno != InvalidBlockNumber) && (so->numKilled > 0))
+ gistkillitems(scan);
+
+ item = getNextGISTSearchItem(so);
+
+ if (!item)
+ return false;
+
+ CHECK_FOR_INTERRUPTS();
+
+ /* save current item BlockNumber for next gistkillitems() call */
+ so->curBlkno = item->blkno;
+
+ /*
+ * While scanning a leaf page, ItemPointers of matching heap
+ * tuples are stored in so->pageData. If there are any on
+ * this page, we fall out of the inner "do" and loop around to
+ * return them.
+ */
+ gistScanPage(scan, item, item->distances, NULL, NULL);
+
+ pfree(item);
+ } while (so->nPageData == 0);
+ }
+ }
+}
+
+/*
+ * gistgetbitmap() -- Get a bitmap of all heap tuple locations
+ */
+int64
+gistgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
+{
+ GISTScanOpaque so = (GISTScanOpaque) scan->opaque;
+ int64 ntids = 0;
+ GISTSearchItem fakeItem;
+
+ if (!so->qual_ok)
+ return 0;
+
+ pgstat_count_index_scan(scan->indexRelation);
+
+ /* Begin the scan by processing the root page */
+ so->curPageData = so->nPageData = 0;
+ scan->xs_hitup = NULL;
+ if (so->pageDataCxt)
+ MemoryContextReset(so->pageDataCxt);
+
+ fakeItem.blkno = GIST_ROOT_BLKNO;
+ memset(&fakeItem.data.parentlsn, 0, sizeof(GistNSN));
+ gistScanPage(scan, &fakeItem, NULL, tbm, &ntids);
+
+ /*
+ * While scanning a leaf page, ItemPointers of matching heap tuples will
+ * be stored directly into tbm, so we don't need to deal with them here.
+ */
+ for (;;)
+ {
+ GISTSearchItem *item = getNextGISTSearchItem(so);
+
+ if (!item)
+ break;
+
+ CHECK_FOR_INTERRUPTS();
+
+ gistScanPage(scan, item, item->distances, tbm, &ntids);
+
+ pfree(item);
+ }
+
+ return ntids;
+}
+
+/*
+ * Can we do index-only scans on the given index column?
+ *
+ * Opclasses that implement a fetch function support index-only scans.
+ * Opclasses without compression functions also support index-only scans.
+ * Included attributes always can be fetched for index-only scans.
+ */
+bool
+gistcanreturn(Relation index, int attno)
+{
+ if (attno > IndexRelationGetNumberOfKeyAttributes(index) ||
+ OidIsValid(index_getprocid(index, attno, GIST_FETCH_PROC)) ||
+ !OidIsValid(index_getprocid(index, attno, GIST_COMPRESS_PROC)))
+ return true;
+ else
+ return false;
+}