ginfast.c

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/*-------------------------------------------------------------------------
 *
 * ginfast.c
 *    Fast insert routines for the Postgres inverted index access method.
 *    Pending entries are stored in linear list of pages.  Later on
 *    (typically during VACUUM), ginInsertCleanup() will be invoked to
 *    transfer pending entries into the regular index structure.  This
 *    wins because bulk insertion is much more efficient than retail.
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *          src/backend/access/gin/ginfast.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/gin_private.h"
#include "access/ginxlog.h"
#include "access/xlog.h"
#include "access/xloginsert.h"
#include "catalog/pg_am.h"
#include "commands/vacuum.h"
#include "miscadmin.h"
#include "port/pg_bitutils.h"
#include "postmaster/autovacuum.h"
#include "storage/indexfsm.h"
#include "storage/lmgr.h"
#include "storage/predicate.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "utils/rel.h"
 
/* GUC parameter */
int         gin_pending_list_limit = 0;
 
#define GIN_PAGE_FREESIZE \
    ( BLCKSZ - MAXALIGN(SizeOfPageHeaderData) - MAXALIGN(sizeof(GinPageOpaqueData)) )
 
typedef struct KeyArray
{
    Datum      *keys;           /* expansible array */
    GinNullCategory *categories;    /* another expansible array */
    int32       nvalues;        /* current number of valid entries */
    int32       maxvalues;      /* allocated size of arrays */
} KeyArray;
 
 
/*
 * Build a pending-list page from the given array of tuples, and write it out.
 *
 * Returns amount of free space left on the page.
 */
static int32
writeListPage(Relation index, Buffer buffer,
              IndexTuple *tuples, int32 ntuples, BlockNumber rightlink)
{
    Page        page = BufferGetPage(buffer);
    int32       i,
                freesize,
                size = 0;
    OffsetNumber l,
                off;
    PGAlignedBlock workspace;
    char       *ptr;
 
    START_CRIT_SECTION();
 
    GinInitBuffer(buffer, GIN_LIST);
 
    off = FirstOffsetNumber;
    ptr = workspace.data;
 
    for (i = 0; i < ntuples; i++)
    {
        int         this_size = IndexTupleSize(tuples[i]);
 
        memcpy(ptr, tuples[i], this_size);
        ptr += this_size;
        size += this_size;
 
        l = PageAddItem(page, (Item) tuples[i], this_size, off, false, false);
 
        if (l == InvalidOffsetNumber)
            elog(ERROR, "failed to add item to index page in \"%s\"",
                 RelationGetRelationName(index));
 
        off++;
    }
 
    Assert(size <= BLCKSZ);     /* else we overran workspace */
 
    GinPageGetOpaque(page)->rightlink = rightlink;
 
    /*
     * tail page may contain only whole row(s) or final part of row placed on
     * previous pages (a "row" here meaning all the index tuples generated for
     * one heap tuple)
     */
    if (rightlink == InvalidBlockNumber)
    {
        GinPageSetFullRow(page);
        GinPageGetOpaque(page)->maxoff = 1;
    }
    else
    {
        GinPageGetOpaque(page)->maxoff = 0;
    }
 
    MarkBufferDirty(buffer);
 
    if (RelationNeedsWAL(index))
    {
        ginxlogInsertListPage data;
        XLogRecPtr  recptr;
 
        data.rightlink = rightlink;
        data.ntuples = ntuples;
 
        XLogBeginInsert();
        XLogRegisterData((char *) &data, sizeof(ginxlogInsertListPage));
 
        XLogRegisterBuffer(0, buffer, REGBUF_WILL_INIT);
        XLogRegisterBufData(0, workspace.data, size);
 
        recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_INSERT_LISTPAGE);
        PageSetLSN(page, recptr);
    }
 
    /* get free space before releasing buffer */
    freesize = PageGetExactFreeSpace(page);
 
    UnlockReleaseBuffer(buffer);
 
    END_CRIT_SECTION();
 
    return freesize;
}
 
static void
makeSublist(Relation index, IndexTuple *tuples, int32 ntuples,
            GinMetaPageData *res)
{
    Buffer      curBuffer = InvalidBuffer;
    Buffer      prevBuffer = InvalidBuffer;
    int         i,
                size = 0,
                tupsize;
    int         startTuple = 0;
 
    Assert(ntuples > 0);
 
    /*
     * Split tuples into pages
     */
    for (i = 0; i < ntuples; i++)
    {
        if (curBuffer == InvalidBuffer)
        {
            curBuffer = GinNewBuffer(index);
 
            if (prevBuffer != InvalidBuffer)
            {
                res->nPendingPages++;
                writeListPage(index, prevBuffer,
                              tuples + startTuple,
                              i - startTuple,
                              BufferGetBlockNumber(curBuffer));
            }
            else
            {
                res->head = BufferGetBlockNumber(curBuffer);
            }
 
            prevBuffer = curBuffer;
            startTuple = i;
            size = 0;
        }
 
        tupsize = MAXALIGN(IndexTupleSize(tuples[i])) + sizeof(ItemIdData);
 
        if (size + tupsize > GinListPageSize)
        {
            /* won't fit, force a new page and reprocess */
            i--;
            curBuffer = InvalidBuffer;
        }
        else
        {
            size += tupsize;
        }
    }
 
    /*
     * Write last page
     */
    res->tail = BufferGetBlockNumber(curBuffer);
    res->tailFreeSize = writeListPage(index, curBuffer,
                                      tuples + startTuple,
                                      ntuples - startTuple,
                                      InvalidBlockNumber);
    res->nPendingPages++;
    /* that was only one heap tuple */
    res->nPendingHeapTuples = 1;
}
 
/*
 * Write the index tuples contained in *collector into the index's
 * pending list.
 *
 * Function guarantees that all these tuples will be inserted consecutively,
 * preserving order
 */
void
ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
{
    Relation    index = ginstate->index;
    Buffer      metabuffer;
    Page        metapage;
    GinMetaPageData *metadata = NULL;
    Buffer      buffer = InvalidBuffer;
    Page        page = NULL;
    ginxlogUpdateMeta data;
    bool        separateList = false;
    bool        needCleanup = false;
    int         cleanupSize;
    bool        needWal;
 
    if (collector->ntuples == 0)
        return;
 
    needWal = RelationNeedsWAL(index);
 
    data.locator = index->rd_locator;
    data.ntuples = 0;
    data.newRightlink = data.prevTail = InvalidBlockNumber;
 
    metabuffer = ReadBuffer(index, GIN_METAPAGE_BLKNO);
    metapage = BufferGetPage(metabuffer);
 
    /*
     * An insertion to the pending list could logically belong anywhere in the
     * tree, so it conflicts with all serializable scans.  All scans acquire a
     * predicate lock on the metabuffer to represent that.
     */
    CheckForSerializableConflictIn(index, NULL, GIN_METAPAGE_BLKNO);
 
    if (collector->sumsize + collector->ntuples * sizeof(ItemIdData) > GinListPageSize)
    {
        /*
         * Total size is greater than one page => make sublist
         */
        separateList = true;
    }
    else
    {
        LockBuffer(metabuffer, GIN_EXCLUSIVE);
        metadata = GinPageGetMeta(metapage);
 
        if (metadata->head == InvalidBlockNumber ||
            collector->sumsize + collector->ntuples * sizeof(ItemIdData) > metadata->tailFreeSize)
        {
            /*
             * Pending list is empty or total size is greater than freespace
             * on tail page => make sublist
             *
             * We unlock metabuffer to keep high concurrency
             */
            separateList = true;
            LockBuffer(metabuffer, GIN_UNLOCK);
        }
    }
 
    if (separateList)
    {
        /*
         * We should make sublist separately and append it to the tail
         */
        GinMetaPageData sublist;
 
        memset(&sublist, 0, sizeof(GinMetaPageData));
        makeSublist(index, collector->tuples, collector->ntuples, &sublist);
 
        /*
         * metapage was unlocked, see above
         */
        LockBuffer(metabuffer, GIN_EXCLUSIVE);
        metadata = GinPageGetMeta(metapage);
 
        if (metadata->head == InvalidBlockNumber)
        {
            /*
             * Main list is empty, so just insert sublist as main list
             */
            START_CRIT_SECTION();
 
            metadata->head = sublist.head;
            metadata->tail = sublist.tail;
            metadata->tailFreeSize = sublist.tailFreeSize;
 
            metadata->nPendingPages = sublist.nPendingPages;
            metadata->nPendingHeapTuples = sublist.nPendingHeapTuples;
 
            if (needWal)
                XLogBeginInsert();
        }
        else
        {
            /*
             * Merge lists
             */
            data.prevTail = metadata->tail;
            data.newRightlink = sublist.head;
 
            buffer = ReadBuffer(index, metadata->tail);
            LockBuffer(buffer, GIN_EXCLUSIVE);
            page = BufferGetPage(buffer);
 
            Assert(GinPageGetOpaque(page)->rightlink == InvalidBlockNumber);
 
            START_CRIT_SECTION();
 
            GinPageGetOpaque(page)->rightlink = sublist.head;
 
            MarkBufferDirty(buffer);
 
            metadata->tail = sublist.tail;
            metadata->tailFreeSize = sublist.tailFreeSize;
 
            metadata->nPendingPages += sublist.nPendingPages;
            metadata->nPendingHeapTuples += sublist.nPendingHeapTuples;
 
            if (needWal)
            {
                XLogBeginInsert();
                XLogRegisterBuffer(1, buffer, REGBUF_STANDARD);
            }
        }
    }
    else
    {
        /*
         * Insert into tail page.  Metapage is already locked
         */
        OffsetNumber l,
                    off;
        int         i,
                    tupsize;
        char       *ptr;
        char       *collectordata;
 
        buffer = ReadBuffer(index, metadata->tail);
        LockBuffer(buffer, GIN_EXCLUSIVE);
        page = BufferGetPage(buffer);
 
        off = (PageIsEmpty(page)) ? FirstOffsetNumber :
            OffsetNumberNext(PageGetMaxOffsetNumber(page));
 
        collectordata = ptr = (char *) palloc(collector->sumsize);
 
        data.ntuples = collector->ntuples;
 
        START_CRIT_SECTION();
 
        if (needWal)
            XLogBeginInsert();
 
        /*
         * Increase counter of heap tuples
         */
        Assert(GinPageGetOpaque(page)->maxoff <= metadata->nPendingHeapTuples);
        GinPageGetOpaque(page)->maxoff++;
        metadata->nPendingHeapTuples++;
 
        for (i = 0; i < collector->ntuples; i++)
        {
            tupsize = IndexTupleSize(collector->tuples[i]);
            l = PageAddItem(page, (Item) collector->tuples[i], tupsize, off, false, false);
 
            if (l == InvalidOffsetNumber)
                elog(ERROR, "failed to add item to index page in \"%s\"",
                     RelationGetRelationName(index));
 
            memcpy(ptr, collector->tuples[i], tupsize);
            ptr += tupsize;
 
            off++;
        }
 
        Assert((ptr - collectordata) <= collector->sumsize);
        if (needWal)
        {
            XLogRegisterBuffer(1, buffer, REGBUF_STANDARD);
            XLogRegisterBufData(1, collectordata, collector->sumsize);
        }
 
        metadata->tailFreeSize = PageGetExactFreeSpace(page);
 
        MarkBufferDirty(buffer);
    }
 
    /*
     * Set pd_lower just past the end of the metadata.  This is essential,
     * because without doing so, metadata will be lost if xlog.c compresses
     * the page.  (We must do this here because pre-v11 versions of PG did not
     * set the metapage's pd_lower correctly, so a pg_upgraded index might
     * contain the wrong value.)
     */
    ((PageHeader) metapage)->pd_lower =
        ((char *) metadata + sizeof(GinMetaPageData)) - (char *) metapage;
 
    /*
     * Write metabuffer, make xlog entry
     */
    MarkBufferDirty(metabuffer);
 
    if (needWal)
    {
        XLogRecPtr  recptr;
 
        memcpy(&data.metadata, metadata, sizeof(GinMetaPageData));
 
        XLogRegisterBuffer(0, metabuffer, REGBUF_WILL_INIT | REGBUF_STANDARD);
        XLogRegisterData((char *) &data, sizeof(ginxlogUpdateMeta));
 
        recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_UPDATE_META_PAGE);
        PageSetLSN(metapage, recptr);
 
        if (buffer != InvalidBuffer)
        {
            PageSetLSN(page, recptr);
        }
    }
 
    if (buffer != InvalidBuffer)
        UnlockReleaseBuffer(buffer);
 
    /*
     * Force pending list cleanup when it becomes too long. And,
     * ginInsertCleanup could take significant amount of time, so we prefer to
     * call it when it can do all the work in a single collection cycle. In
     * non-vacuum mode, it shouldn't require maintenance_work_mem, so fire it
     * while pending list is still small enough to fit into
     * gin_pending_list_limit.
     *
     * ginInsertCleanup() should not be called inside our CRIT_SECTION.
     */
    cleanupSize = GinGetPendingListCleanupSize(index);
    if (metadata->nPendingPages * GIN_PAGE_FREESIZE > cleanupSize * 1024L)
        needCleanup = true;
 
    UnlockReleaseBuffer(metabuffer);
 
    END_CRIT_SECTION();
 
    /*
     * Since it could contend with concurrent cleanup process we cleanup
     * pending list not forcibly.
     */
    if (needCleanup)
        ginInsertCleanup(ginstate, false, true, false, NULL);
}
 
/*
 * Create temporary index tuples for a single indexable item (one index column
 * for the heap tuple specified by ht_ctid), and append them to the array
 * in *collector.  They will subsequently be written out using
 * ginHeapTupleFastInsert.  Note that to guarantee consistent state, all
 * temp tuples for a given heap tuple must be written in one call to
 * ginHeapTupleFastInsert.
 */
void
ginHeapTupleFastCollect(GinState *ginstate,
                        GinTupleCollector *collector,
                        OffsetNumber attnum, Datum value, bool isNull,
                        ItemPointer ht_ctid)
{
    Datum      *entries;
    GinNullCategory *categories;
    int32       i,
                nentries;
 
    /*
     * Extract the key values that need to be inserted in the index
     */
    entries = ginExtractEntries(ginstate, attnum, value, isNull,
                                &nentries, &categories);
 
    /*
     * Protect against integer overflow in allocation calculations
     */
    if (nentries < 0 ||
        collector->ntuples + nentries > MaxAllocSize / sizeof(IndexTuple))
        elog(ERROR, "too many entries for GIN index");
 
    /*
     * Allocate/reallocate memory for storing collected tuples
     */
    if (collector->tuples == NULL)
    {
        /*
         * Determine the number of elements to allocate in the tuples array
         * initially.  Make it a power of 2 to avoid wasting memory when
         * resizing (since palloc likes powers of 2).
         */
        collector->lentuples = pg_nextpower2_32(Max(16, nentries));
        collector->tuples = palloc_array(IndexTuple, collector->lentuples);
    }
    else if (collector->lentuples < collector->ntuples + nentries)
    {
        /*
         * Advance lentuples to the next suitable power of 2.  This won't
         * overflow, though we could get to a value that exceeds
         * MaxAllocSize/sizeof(IndexTuple), causing an error in repalloc.
         */
        collector->lentuples = pg_nextpower2_32(collector->ntuples + nentries);
        collector->tuples = repalloc_array(collector->tuples,
                                           IndexTuple, collector->lentuples);
    }
 
    /*
     * Build an index tuple for each key value, and add to array.  In pending
     * tuples we just stick the heap TID into t_tid.
     */
    for (i = 0; i < nentries; i++)
    {
        IndexTuple  itup;
 
        itup = GinFormTuple(ginstate, attnum, entries[i], categories[i],
                            NULL, 0, 0, true);
        itup->t_tid = *ht_ctid;
        collector->tuples[collector->ntuples++] = itup;
        collector->sumsize += IndexTupleSize(itup);
    }
}
 
/*
 * Deletes pending list pages up to (not including) newHead page.
 * If newHead == InvalidBlockNumber then function drops the whole list.
 *
 * metapage is pinned and exclusive-locked throughout this function.
 */
static void
shiftList(Relation index, Buffer metabuffer, BlockNumber newHead,
          bool fill_fsm, IndexBulkDeleteResult *stats)
{
    Page        metapage;
    GinMetaPageData *metadata;
    BlockNumber blknoToDelete;
 
    metapage = BufferGetPage(metabuffer);
    metadata = GinPageGetMeta(metapage);
    blknoToDelete = metadata->head;
 
    do
    {
        Page        page;
        int         i;
        int64       nDeletedHeapTuples = 0;
        ginxlogDeleteListPages data;
        Buffer      buffers[GIN_NDELETE_AT_ONCE];
        BlockNumber freespace[GIN_NDELETE_AT_ONCE];
 
        data.ndeleted = 0;
        while (data.ndeleted < GIN_NDELETE_AT_ONCE && blknoToDelete != newHead)
        {
            freespace[data.ndeleted] = blknoToDelete;
            buffers[data.ndeleted] = ReadBuffer(index, blknoToDelete);
            LockBuffer(buffers[data.ndeleted], GIN_EXCLUSIVE);
            page = BufferGetPage(buffers[data.ndeleted]);
 
            data.ndeleted++;
 
            Assert(!GinPageIsDeleted(page));
 
            nDeletedHeapTuples += GinPageGetOpaque(page)->maxoff;
            blknoToDelete = GinPageGetOpaque(page)->rightlink;
        }
 
        if (stats)
            stats->pages_deleted += data.ndeleted;
 
        /*
         * This operation touches an unusually large number of pages, so
         * prepare the XLogInsert machinery for that before entering the
         * critical section.
         */
        if (RelationNeedsWAL(index))
            XLogEnsureRecordSpace(data.ndeleted, 0);
 
        START_CRIT_SECTION();
 
        metadata->head = blknoToDelete;
 
        Assert(metadata->nPendingPages >= data.ndeleted);
        metadata->nPendingPages -= data.ndeleted;
        Assert(metadata->nPendingHeapTuples >= nDeletedHeapTuples);
        metadata->nPendingHeapTuples -= nDeletedHeapTuples;
 
        if (blknoToDelete == InvalidBlockNumber)
        {
            metadata->tail = InvalidBlockNumber;
            metadata->tailFreeSize = 0;
            metadata->nPendingPages = 0;
            metadata->nPendingHeapTuples = 0;
        }
 
        /*
         * Set pd_lower just past the end of the metadata.  This is essential,
         * because without doing so, metadata will be lost if xlog.c
         * compresses the page.  (We must do this here because pre-v11
         * versions of PG did not set the metapage's pd_lower correctly, so a
         * pg_upgraded index might contain the wrong value.)
         */
        ((PageHeader) metapage)->pd_lower =
            ((char *) metadata + sizeof(GinMetaPageData)) - (char *) metapage;
 
        MarkBufferDirty(metabuffer);
 
        for (i = 0; i < data.ndeleted; i++)
        {
            page = BufferGetPage(buffers[i]);
            GinPageGetOpaque(page)->flags = GIN_DELETED;
            MarkBufferDirty(buffers[i]);
        }
 
        if (RelationNeedsWAL(index))
        {
            XLogRecPtr  recptr;
 
            XLogBeginInsert();
            XLogRegisterBuffer(0, metabuffer,
                               REGBUF_WILL_INIT | REGBUF_STANDARD);
            for (i = 0; i < data.ndeleted; i++)
                XLogRegisterBuffer(i + 1, buffers[i], REGBUF_WILL_INIT);
 
            memcpy(&data.metadata, metadata, sizeof(GinMetaPageData));
 
            XLogRegisterData((char *) &data,
                             sizeof(ginxlogDeleteListPages));
 
            recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_DELETE_LISTPAGE);
            PageSetLSN(metapage, recptr);
 
            for (i = 0; i < data.ndeleted; i++)
            {
                page = BufferGetPage(buffers[i]);
                PageSetLSN(page, recptr);
            }
        }
 
        for (i = 0; i < data.ndeleted; i++)
            UnlockReleaseBuffer(buffers[i]);
 
        END_CRIT_SECTION();
 
        for (i = 0; fill_fsm && i < data.ndeleted; i++)
            RecordFreeIndexPage(index, freespace[i]);
 
    } while (blknoToDelete != newHead);
}
 
/* Initialize empty KeyArray */
static void
initKeyArray(KeyArray *keys, int32 maxvalues)
{
    keys->keys = palloc_array(Datum, maxvalues);
    keys->categories = palloc_array(GinNullCategory, maxvalues);
    keys->nvalues = 0;
    keys->maxvalues = maxvalues;
}
 
/* Add datum to KeyArray, resizing if needed */
static void
addDatum(KeyArray *keys, Datum datum, GinNullCategory category)
{
    if (keys->nvalues >= keys->maxvalues)
    {
        keys->maxvalues *= 2;
        keys->keys = repalloc_array(keys->keys, Datum, keys->maxvalues);
        keys->categories = repalloc_array(keys->categories, GinNullCategory, keys->maxvalues);
    }
 
    keys->keys[keys->nvalues] = datum;
    keys->categories[keys->nvalues] = category;
    keys->nvalues++;
}
 
/*
 * Collect data from a pending-list page in preparation for insertion into
 * the main index.
 *
 * Go through all tuples >= startoff on page and collect values in accum
 *
 * Note that ka is just workspace --- it does not carry any state across
 * calls.
 */
static void
processPendingPage(BuildAccumulator *accum, KeyArray *ka,
                   Page page, OffsetNumber startoff)
{
    ItemPointerData heapptr;
    OffsetNumber i,
                maxoff;
    OffsetNumber attrnum;
 
    /* reset *ka to empty */
    ka->nvalues = 0;
 
    maxoff = PageGetMaxOffsetNumber(page);
    Assert(maxoff >= FirstOffsetNumber);
    ItemPointerSetInvalid(&heapptr);
    attrnum = 0;
 
    for (i = startoff; i <= maxoff; i = OffsetNumberNext(i))
    {
        IndexTuple  itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, i));
        OffsetNumber curattnum;
        Datum       curkey;
        GinNullCategory curcategory;
 
        /* Check for change of heap TID or attnum */
        curattnum = gintuple_get_attrnum(accum->ginstate, itup);
 
        if (!ItemPointerIsValid(&heapptr))
        {
            heapptr = itup->t_tid;
            attrnum = curattnum;
        }
        else if (!(ItemPointerEquals(&heapptr, &itup->t_tid) &&
                   curattnum == attrnum))
        {
            /*
             * ginInsertBAEntries can insert several datums per call, but only
             * for one heap tuple and one column.  So call it at a boundary,
             * and reset ka.
             */
            ginInsertBAEntries(accum, &heapptr, attrnum,
                               ka->keys, ka->categories, ka->nvalues);
            ka->nvalues = 0;
            heapptr = itup->t_tid;
            attrnum = curattnum;
        }
 
        /* Add key to KeyArray */
        curkey = gintuple_get_key(accum->ginstate, itup, &curcategory);
        addDatum(ka, curkey, curcategory);
    }
 
    /* Dump out all remaining keys */
    ginInsertBAEntries(accum, &heapptr, attrnum,
                       ka->keys, ka->categories, ka->nvalues);
}
 
/*
 * Move tuples from pending pages into regular GIN structure.
 *
 * On first glance it looks completely not crash-safe. But if we crash
 * after posting entries to the main index and before removing them from the
 * pending list, it's okay because when we redo the posting later on, nothing
 * bad will happen.
 *
 * fill_fsm indicates that ginInsertCleanup should add deleted pages
 * to FSM otherwise caller is responsible to put deleted pages into
 * FSM.
 *
 * If stats isn't null, we count deleted pending pages into the counts.
 */
void
ginInsertCleanup(GinState *ginstate, bool full_clean,
                 bool fill_fsm, bool forceCleanup,
                 IndexBulkDeleteResult *stats)
{
    Relation    index = ginstate->index;
    Buffer      metabuffer,
                buffer;
    Page        metapage,
                page;
    GinMetaPageData *metadata;
    MemoryContext opCtx,
                oldCtx;
    BuildAccumulator accum;
    KeyArray    datums;
    BlockNumber blkno,
                blknoFinish;
    bool        cleanupFinish = false;
    bool        fsm_vac = false;
    Size        workMemory;
 
    /*
     * We would like to prevent concurrent cleanup process. For that we will
     * lock metapage in exclusive mode using LockPage() call. Nobody other
     * will use that lock for metapage, so we keep possibility of concurrent
     * insertion into pending list
     */
 
    if (forceCleanup)
    {
        /*
         * We are called from [auto]vacuum/analyze or gin_clean_pending_list()
         * and we would like to wait concurrent cleanup to finish.
         */
        LockPage(index, GIN_METAPAGE_BLKNO, ExclusiveLock);
        workMemory =
            (IsAutoVacuumWorkerProcess() && autovacuum_work_mem != -1) ?
            autovacuum_work_mem : maintenance_work_mem;
    }
    else
    {
        /*
         * We are called from regular insert and if we see concurrent cleanup
         * just exit in hope that concurrent process will clean up pending
         * list.
         */
        if (!ConditionalLockPage(index, GIN_METAPAGE_BLKNO, ExclusiveLock))
            return;
        workMemory = work_mem;
    }
 
    metabuffer = ReadBuffer(index, GIN_METAPAGE_BLKNO);
    LockBuffer(metabuffer, GIN_SHARE);
    metapage = BufferGetPage(metabuffer);
    metadata = GinPageGetMeta(metapage);
 
    if (metadata->head == InvalidBlockNumber)
    {
        /* Nothing to do */
        UnlockReleaseBuffer(metabuffer);
        UnlockPage(index, GIN_METAPAGE_BLKNO, ExclusiveLock);
        return;
    }
 
    /*
     * Remember a tail page to prevent infinite cleanup if other backends add
     * new tuples faster than we can cleanup.
     */
    blknoFinish = metadata->tail;
 
    /*
     * Read and lock head of pending list
     */
    blkno = metadata->head;
    buffer = ReadBuffer(index, blkno);
    LockBuffer(buffer, GIN_SHARE);
    page = BufferGetPage(buffer);
 
    LockBuffer(metabuffer, GIN_UNLOCK);
 
    /*
     * Initialize.  All temporary space will be in opCtx
     */
    opCtx = AllocSetContextCreate(CurrentMemoryContext,
                                  "GIN insert cleanup temporary context",
                                  ALLOCSET_DEFAULT_SIZES);
 
    oldCtx = MemoryContextSwitchTo(opCtx);
 
    initKeyArray(&datums, 128);
    ginInitBA(&accum);
    accum.ginstate = ginstate;
 
    /*
     * At the top of this loop, we have pin and lock on the current page of
     * the pending list.  However, we'll release that before exiting the loop.
     * Note we also have pin but not lock on the metapage.
     */
    for (;;)
    {
        Assert(!GinPageIsDeleted(page));
 
        /*
         * Are we walk through the page which as we remember was a tail when
         * we start our cleanup?  But if caller asks us to clean up whole
         * pending list then ignore old tail, we will work until list becomes
         * empty.
         */
        if (blkno == blknoFinish && full_clean == false)
            cleanupFinish = true;
 
        /*
         * read page's datums into accum
         */
        processPendingPage(&accum, &datums, page, FirstOffsetNumber);
 
        vacuum_delay_point();
 
        /*
         * Is it time to flush memory to disk?  Flush if we are at the end of
         * the pending list, or if we have a full row and memory is getting
         * full.
         */
        if (GinPageGetOpaque(page)->rightlink == InvalidBlockNumber ||
            (GinPageHasFullRow(page) &&
             (accum.allocatedMemory >= workMemory * 1024L)))
        {
            ItemPointerData *list;
            uint32      nlist;
            Datum       key;
            GinNullCategory category;
            OffsetNumber maxoff,
                        attnum;
 
            /*
             * Unlock current page to increase performance. Changes of page
             * will be checked later by comparing maxoff after completion of
             * memory flush.
             */
            maxoff = PageGetMaxOffsetNumber(page);
            LockBuffer(buffer, GIN_UNLOCK);
 
            /*
             * Moving collected data into regular structure can take
             * significant amount of time - so, run it without locking pending
             * list.
             */
            ginBeginBAScan(&accum);
            while ((list = ginGetBAEntry(&accum,
                                         &attnum, &key, &category, &nlist)) != NULL)
            {
                ginEntryInsert(ginstate, attnum, key, category,
                               list, nlist, NULL);
                vacuum_delay_point();
            }
 
            /*
             * Lock the whole list to remove pages
             */
            LockBuffer(metabuffer, GIN_EXCLUSIVE);
            LockBuffer(buffer, GIN_SHARE);
 
            Assert(!GinPageIsDeleted(page));
 
            /*
             * While we left the page unlocked, more stuff might have gotten
             * added to it.  If so, process those entries immediately.  There
             * shouldn't be very many, so we don't worry about the fact that
             * we're doing this with exclusive lock. Insertion algorithm
             * guarantees that inserted row(s) will not continue on next page.
             * NOTE: intentionally no vacuum_delay_point in this loop.
             */
            if (PageGetMaxOffsetNumber(page) != maxoff)
            {
                ginInitBA(&accum);
                processPendingPage(&accum, &datums, page, maxoff + 1);
 
                ginBeginBAScan(&accum);
                while ((list = ginGetBAEntry(&accum,
                                             &attnum, &key, &category, &nlist)) != NULL)
                    ginEntryInsert(ginstate, attnum, key, category,
                                   list, nlist, NULL);
            }
 
            /*
             * Remember next page - it will become the new list head
             */
            blkno = GinPageGetOpaque(page)->rightlink;
            UnlockReleaseBuffer(buffer);    /* shiftList will do exclusive
                                             * locking */
 
            /*
             * remove read pages from pending list, at this point all content
             * of read pages is in regular structure
             */
            shiftList(index, metabuffer, blkno, fill_fsm, stats);
 
            /* At this point, some pending pages have been freed up */
            fsm_vac = true;
 
            Assert(blkno == metadata->head);
            LockBuffer(metabuffer, GIN_UNLOCK);
 
            /*
             * if we removed the whole pending list or we cleanup tail (which
             * we remembered on start our cleanup process) then just exit
             */
            if (blkno == InvalidBlockNumber || cleanupFinish)
                break;
 
            /*
             * release memory used so far and reinit state
             */
            MemoryContextReset(opCtx);
            initKeyArray(&datums, datums.maxvalues);
            ginInitBA(&accum);
        }
        else
        {
            blkno = GinPageGetOpaque(page)->rightlink;
            UnlockReleaseBuffer(buffer);
        }
 
        /*
         * Read next page in pending list
         */
        vacuum_delay_point();
        buffer = ReadBuffer(index, blkno);
        LockBuffer(buffer, GIN_SHARE);
        page = BufferGetPage(buffer);
    }
 
    UnlockPage(index, GIN_METAPAGE_BLKNO, ExclusiveLock);
    ReleaseBuffer(metabuffer);
 
    /*
     * As pending list pages can have a high churn rate, it is desirable to
     * recycle them immediately to the FreeSpaceMap when ordinary backends
     * clean the list.
     */
    if (fsm_vac && fill_fsm)
        IndexFreeSpaceMapVacuum(index);
 
    /* Clean up temporary space */
    MemoryContextSwitchTo(oldCtx);
    MemoryContextDelete(opCtx);
}
 
/*
 * SQL-callable function to clean the insert pending list
 */
Datum
gin_clean_pending_list(PG_FUNCTION_ARGS)
{
    Oid         indexoid = PG_GETARG_OID(0);
    Relation    indexRel = index_open(indexoid, RowExclusiveLock);
    IndexBulkDeleteResult stats;
    GinState    ginstate;
 
    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is in progress"),
                 errhint("GIN pending list cannot be cleaned up during recovery.")));
 
    /* Must be a GIN index */
    if (indexRel->rd_rel->relkind != RELKIND_INDEX ||
        indexRel->rd_rel->relam != GIN_AM_OID)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a GIN index",
                        RelationGetRelationName(indexRel))));
 
    /*
     * Reject attempts to read non-local temporary relations; we would be
     * likely to get wrong data since we have no visibility into the owning
     * session's local buffers.
     */
    if (RELATION_IS_OTHER_TEMP(indexRel))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot access temporary indexes of other sessions")));
 
    /* User must own the index (comparable to privileges needed for VACUUM) */
    if (!object_ownercheck(RelationRelationId, indexoid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_INDEX,
                       RelationGetRelationName(indexRel));
 
    memset(&stats, 0, sizeof(stats));
    initGinState(&ginstate, indexRel);
    ginInsertCleanup(&ginstate, true, true, true, &stats);
 
    index_close(indexRel, RowExclusiveLock);
 
    PG_RETURN_INT64((int64) stats.pages_deleted);
}