spgxlog.c

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/*-------------------------------------------------------------------------
 *
 * spgxlog.c
 *    WAL replay logic for SP-GiST
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *           src/backend/access/spgist/spgxlog.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/bufmask.h"
#include "access/spgist_private.h"
#include "access/spgxlog.h"
#include "access/xlogutils.h"
#include "storage/standby.h"
#include "utils/memutils.h"
 
 
static MemoryContext opCtx;     /* working memory for operations */
 
 
/*
 * Prepare a dummy SpGistState, with just the minimum info needed for replay.
 *
 * At present, all we need is enough info to support spgFormDeadTuple(),
 * plus the isBuild flag.
 */
static void
fillFakeState(SpGistState *state, spgxlogState stateSrc)
{
    memset(state, 0, sizeof(*state));
 
    state->redirectXid = stateSrc.redirectXid;
    state->isBuild = stateSrc.isBuild;
    state->deadTupleStorage = palloc0(SGDTSIZE);
}
 
/*
 * Add a leaf tuple, or replace an existing placeholder tuple.  This is used
 * to replay SpGistPageAddNewItem() operations.  If the offset points at an
 * existing tuple, it had better be a placeholder tuple.
 */
static void
addOrReplaceTuple(Page page, Item tuple, int size, OffsetNumber offset)
{
    if (offset <= PageGetMaxOffsetNumber(page))
    {
        SpGistDeadTuple dt = (SpGistDeadTuple) PageGetItem(page,
                                                           PageGetItemId(page, offset));
 
        if (dt->tupstate != SPGIST_PLACEHOLDER)
            elog(ERROR, "SPGiST tuple to be replaced is not a placeholder");
 
        Assert(SpGistPageGetOpaque(page)->nPlaceholder > 0);
        SpGistPageGetOpaque(page)->nPlaceholder--;
 
        PageIndexTupleDelete(page, offset);
    }
 
    Assert(offset <= PageGetMaxOffsetNumber(page) + 1);
 
    if (PageAddItem(page, tuple, size, offset, false, false) != offset)
        elog(ERROR, "failed to add item of size %u to SPGiST index page",
             size);
}
 
static void
spgRedoAddLeaf(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    char       *ptr = XLogRecGetData(record);
    spgxlogAddLeaf *xldata = (spgxlogAddLeaf *) ptr;
    char       *leafTuple;
    SpGistLeafTupleData leafTupleHdr;
    Buffer      buffer;
    Page        page;
    XLogRedoAction action;
 
    ptr += sizeof(spgxlogAddLeaf);
    leafTuple = ptr;
    /* the leaf tuple is unaligned, so make a copy to access its header */
    memcpy(&leafTupleHdr, leafTuple, sizeof(SpGistLeafTupleData));
 
    /*
     * In normal operation we would have both current and parent pages locked
     * simultaneously; but in WAL replay it should be safe to update the leaf
     * page before updating the parent.
     */
    if (xldata->newPage)
    {
        buffer = XLogInitBufferForRedo(record, 0);
        SpGistInitBuffer(buffer,
                         SPGIST_LEAF | (xldata->storesNulls ? SPGIST_NULLS : 0));
        action = BLK_NEEDS_REDO;
    }
    else
        action = XLogReadBufferForRedo(record, 0, &buffer);
 
    if (action == BLK_NEEDS_REDO)
    {
        page = BufferGetPage(buffer);
 
        /* insert new tuple */
        if (xldata->offnumLeaf != xldata->offnumHeadLeaf)
        {
            /* normal cases, tuple was added by SpGistPageAddNewItem */
            addOrReplaceTuple(page, (Item) leafTuple, leafTupleHdr.size,
                              xldata->offnumLeaf);
 
            /* update head tuple's chain link if needed */
            if (xldata->offnumHeadLeaf != InvalidOffsetNumber)
            {
                SpGistLeafTuple head;
 
                head = (SpGistLeafTuple) PageGetItem(page,
                                                     PageGetItemId(page, xldata->offnumHeadLeaf));
                Assert(SGLT_GET_NEXTOFFSET(head) == SGLT_GET_NEXTOFFSET(&leafTupleHdr));
                SGLT_SET_NEXTOFFSET(head, xldata->offnumLeaf);
            }
        }
        else
        {
            /* replacing a DEAD tuple */
            PageIndexTupleDelete(page, xldata->offnumLeaf);
            if (PageAddItem(page,
                            (Item) leafTuple, leafTupleHdr.size,
                            xldata->offnumLeaf, false, false) != xldata->offnumLeaf)
                elog(ERROR, "failed to add item of size %u to SPGiST index page",
                     leafTupleHdr.size);
        }
 
        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);
 
    /* update parent downlink if necessary */
    if (xldata->offnumParent != InvalidOffsetNumber)
    {
        if (XLogReadBufferForRedo(record, 1, &buffer) == BLK_NEEDS_REDO)
        {
            SpGistInnerTuple tuple;
            BlockNumber blknoLeaf;
 
            XLogRecGetBlockTag(record, 0, NULL, NULL, &blknoLeaf);
 
            page = BufferGetPage(buffer);
 
            tuple = (SpGistInnerTuple) PageGetItem(page,
                                                   PageGetItemId(page, xldata->offnumParent));
 
            spgUpdateNodeLink(tuple, xldata->nodeI,
                              blknoLeaf, xldata->offnumLeaf);
 
            PageSetLSN(page, lsn);
            MarkBufferDirty(buffer);
        }
        if (BufferIsValid(buffer))
            UnlockReleaseBuffer(buffer);
    }
}
 
static void
spgRedoMoveLeafs(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    char       *ptr = XLogRecGetData(record);
    spgxlogMoveLeafs *xldata = (spgxlogMoveLeafs *) ptr;
    SpGistState state;
    OffsetNumber *toDelete;
    OffsetNumber *toInsert;
    int         nInsert;
    Buffer      buffer;
    Page        page;
    XLogRedoAction action;
    BlockNumber blknoDst;
 
    XLogRecGetBlockTag(record, 1, NULL, NULL, &blknoDst);
 
    fillFakeState(&state, xldata->stateSrc);
 
    nInsert = xldata->replaceDead ? 1 : xldata->nMoves + 1;
 
    ptr += SizeOfSpgxlogMoveLeafs;
    toDelete = (OffsetNumber *) ptr;
    ptr += sizeof(OffsetNumber) * xldata->nMoves;
    toInsert = (OffsetNumber *) ptr;
    ptr += sizeof(OffsetNumber) * nInsert;
 
    /* now ptr points to the list of leaf tuples */
 
    /*
     * In normal operation we would have all three pages (source, dest, and
     * parent) locked simultaneously; but in WAL replay it should be safe to
     * update them one at a time, as long as we do it in the right order.
     */
 
    /* Insert tuples on the dest page (do first, so redirect is valid) */
    if (xldata->newPage)
    {
        buffer = XLogInitBufferForRedo(record, 1);
        SpGistInitBuffer(buffer,
                         SPGIST_LEAF | (xldata->storesNulls ? SPGIST_NULLS : 0));
        action = BLK_NEEDS_REDO;
    }
    else
        action = XLogReadBufferForRedo(record, 1, &buffer);
 
    if (action == BLK_NEEDS_REDO)
    {
        int         i;
 
        page = BufferGetPage(buffer);
 
        for (i = 0; i < nInsert; i++)
        {
            char       *leafTuple;
            SpGistLeafTupleData leafTupleHdr;
 
            /*
             * the tuples are not aligned, so must copy to access the size
             * field.
             */
            leafTuple = ptr;
            memcpy(&leafTupleHdr, leafTuple,
                   sizeof(SpGistLeafTupleData));
 
            addOrReplaceTuple(page, (Item) leafTuple,
                              leafTupleHdr.size, toInsert[i]);
            ptr += leafTupleHdr.size;
        }
 
        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);
 
    /* Delete tuples from the source page, inserting a redirection pointer */
    if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
    {
        page = BufferGetPage(buffer);
 
        spgPageIndexMultiDelete(&state, page, toDelete, xldata->nMoves,
                                state.isBuild ? SPGIST_PLACEHOLDER : SPGIST_REDIRECT,
                                SPGIST_PLACEHOLDER,
                                blknoDst,
                                toInsert[nInsert - 1]);
 
        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);
 
    /* And update the parent downlink */
    if (XLogReadBufferForRedo(record, 2, &buffer) == BLK_NEEDS_REDO)
    {
        SpGistInnerTuple tuple;
 
        page = BufferGetPage(buffer);
 
        tuple = (SpGistInnerTuple) PageGetItem(page,
                                               PageGetItemId(page, xldata->offnumParent));
 
        spgUpdateNodeLink(tuple, xldata->nodeI,
                          blknoDst, toInsert[nInsert - 1]);
 
        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);
}
 
static void
spgRedoAddNode(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    char       *ptr = XLogRecGetData(record);
    spgxlogAddNode *xldata = (spgxlogAddNode *) ptr;
    char       *innerTuple;
    SpGistInnerTupleData innerTupleHdr;
    SpGistState state;
    Buffer      buffer;
    Page        page;
    XLogRedoAction action;
 
    ptr += sizeof(spgxlogAddNode);
    innerTuple = ptr;
    /* the tuple is unaligned, so make a copy to access its header */
    memcpy(&innerTupleHdr, innerTuple, sizeof(SpGistInnerTupleData));
 
    fillFakeState(&state, xldata->stateSrc);
 
    if (!XLogRecHasBlockRef(record, 1))
    {
        /* update in place */
        Assert(xldata->parentBlk == -1);
        if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
        {
            page = BufferGetPage(buffer);
 
            PageIndexTupleDelete(page, xldata->offnum);
            if (PageAddItem(page, (Item) innerTuple, innerTupleHdr.size,
                            xldata->offnum,
                            false, false) != xldata->offnum)
                elog(ERROR, "failed to add item of size %u to SPGiST index page",
                     innerTupleHdr.size);
 
            PageSetLSN(page, lsn);
            MarkBufferDirty(buffer);
        }
        if (BufferIsValid(buffer))
            UnlockReleaseBuffer(buffer);
    }
    else
    {
        BlockNumber blkno;
        BlockNumber blknoNew;
 
        XLogRecGetBlockTag(record, 0, NULL, NULL, &blkno);
        XLogRecGetBlockTag(record, 1, NULL, NULL, &blknoNew);
 
        /*
         * In normal operation we would have all three pages (source, dest,
         * and parent) locked simultaneously; but in WAL replay it should be
         * safe to update them one at a time, as long as we do it in the right
         * order. We must insert the new tuple before replacing the old tuple
         * with the redirect tuple.
         */
 
        /* Install new tuple first so redirect is valid */
        if (xldata->newPage)
        {
            /* AddNode is not used for nulls pages */
            buffer = XLogInitBufferForRedo(record, 1);
            SpGistInitBuffer(buffer, 0);
            action = BLK_NEEDS_REDO;
        }
        else
            action = XLogReadBufferForRedo(record, 1, &buffer);
        if (action == BLK_NEEDS_REDO)
        {
            page = BufferGetPage(buffer);
 
            addOrReplaceTuple(page, (Item) innerTuple,
                              innerTupleHdr.size, xldata->offnumNew);
 
            /*
             * If parent is in this same page, update it now.
             */
            if (xldata->parentBlk == 1)
            {
                SpGistInnerTuple parentTuple;
 
                parentTuple = (SpGistInnerTuple) PageGetItem(page,
                                                             PageGetItemId(page, xldata->offnumParent));
 
                spgUpdateNodeLink(parentTuple, xldata->nodeI,
                                  blknoNew, xldata->offnumNew);
            }
            PageSetLSN(page, lsn);
            MarkBufferDirty(buffer);
        }
        if (BufferIsValid(buffer))
            UnlockReleaseBuffer(buffer);
 
        /* Delete old tuple, replacing it with redirect or placeholder tuple */
        if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
        {
            SpGistDeadTuple dt;
 
            page = BufferGetPage(buffer);
 
            if (state.isBuild)
                dt = spgFormDeadTuple(&state, SPGIST_PLACEHOLDER,
                                      InvalidBlockNumber,
                                      InvalidOffsetNumber);
            else
                dt = spgFormDeadTuple(&state, SPGIST_REDIRECT,
                                      blknoNew,
                                      xldata->offnumNew);
 
            PageIndexTupleDelete(page, xldata->offnum);
            if (PageAddItem(page, (Item) dt, dt->size,
                            xldata->offnum,
                            false, false) != xldata->offnum)
                elog(ERROR, "failed to add item of size %u to SPGiST index page",
                     dt->size);
 
            if (state.isBuild)
                SpGistPageGetOpaque(page)->nPlaceholder++;
            else
                SpGistPageGetOpaque(page)->nRedirection++;
 
            /*
             * If parent is in this same page, update it now.
             */
            if (xldata->parentBlk == 0)
            {
                SpGistInnerTuple parentTuple;
 
                parentTuple = (SpGistInnerTuple) PageGetItem(page,
                                                             PageGetItemId(page, xldata->offnumParent));
 
                spgUpdateNodeLink(parentTuple, xldata->nodeI,
                                  blknoNew, xldata->offnumNew);
            }
            PageSetLSN(page, lsn);
            MarkBufferDirty(buffer);
        }
        if (BufferIsValid(buffer))
            UnlockReleaseBuffer(buffer);
 
        /*
         * Update parent downlink (if we didn't do it as part of the source or
         * destination page update already).
         */
        if (xldata->parentBlk == 2)
        {
            if (XLogReadBufferForRedo(record, 2, &buffer) == BLK_NEEDS_REDO)
            {
                SpGistInnerTuple parentTuple;
 
                page = BufferGetPage(buffer);
 
                parentTuple = (SpGistInnerTuple) PageGetItem(page,
                                                             PageGetItemId(page, xldata->offnumParent));
 
                spgUpdateNodeLink(parentTuple, xldata->nodeI,
                                  blknoNew, xldata->offnumNew);
 
                PageSetLSN(page, lsn);
                MarkBufferDirty(buffer);
            }
            if (BufferIsValid(buffer))
                UnlockReleaseBuffer(buffer);
        }
    }
}
 
static void
spgRedoSplitTuple(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    char       *ptr = XLogRecGetData(record);
    spgxlogSplitTuple *xldata = (spgxlogSplitTuple *) ptr;
    char       *prefixTuple;
    SpGistInnerTupleData prefixTupleHdr;
    char       *postfixTuple;
    SpGistInnerTupleData postfixTupleHdr;
    Buffer      buffer;
    Page        page;
    XLogRedoAction action;
 
    ptr += sizeof(spgxlogSplitTuple);
    prefixTuple = ptr;
    /* the prefix tuple is unaligned, so make a copy to access its header */
    memcpy(&prefixTupleHdr, prefixTuple, sizeof(SpGistInnerTupleData));
    ptr += prefixTupleHdr.size;
    postfixTuple = ptr;
    /* postfix tuple is also unaligned */
    memcpy(&postfixTupleHdr, postfixTuple, sizeof(SpGistInnerTupleData));
 
    /*
     * In normal operation we would have both pages locked simultaneously; but
     * in WAL replay it should be safe to update them one at a time, as long
     * as we do it in the right order.
     */
 
    /* insert postfix tuple first to avoid dangling link */
    if (!xldata->postfixBlkSame)
    {
        if (xldata->newPage)
        {
            buffer = XLogInitBufferForRedo(record, 1);
            /* SplitTuple is not used for nulls pages */
            SpGistInitBuffer(buffer, 0);
            action = BLK_NEEDS_REDO;
        }
        else
            action = XLogReadBufferForRedo(record, 1, &buffer);
        if (action == BLK_NEEDS_REDO)
        {
            page = BufferGetPage(buffer);
 
            addOrReplaceTuple(page, (Item) postfixTuple,
                              postfixTupleHdr.size, xldata->offnumPostfix);
 
            PageSetLSN(page, lsn);
            MarkBufferDirty(buffer);
        }
        if (BufferIsValid(buffer))
            UnlockReleaseBuffer(buffer);
    }
 
    /* now handle the original page */
    if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
    {
        page = BufferGetPage(buffer);
 
        PageIndexTupleDelete(page, xldata->offnumPrefix);
        if (PageAddItem(page, (Item) prefixTuple, prefixTupleHdr.size,
                        xldata->offnumPrefix, false, false) != xldata->offnumPrefix)
            elog(ERROR, "failed to add item of size %u to SPGiST index page",
                 prefixTupleHdr.size);
 
        if (xldata->postfixBlkSame)
            addOrReplaceTuple(page, (Item) postfixTuple,
                              postfixTupleHdr.size,
                              xldata->offnumPostfix);
 
        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);
}
 
static void
spgRedoPickSplit(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    char       *ptr = XLogRecGetData(record);
    spgxlogPickSplit *xldata = (spgxlogPickSplit *) ptr;
    char       *innerTuple;
    SpGistInnerTupleData innerTupleHdr;
    SpGistState state;
    OffsetNumber *toDelete;
    OffsetNumber *toInsert;
    uint8      *leafPageSelect;
    Buffer      srcBuffer;
    Buffer      destBuffer;
    Buffer      innerBuffer;
    Page        srcPage;
    Page        destPage;
    Page        page;
    int         i;
    BlockNumber blknoInner;
    XLogRedoAction action;
 
    XLogRecGetBlockTag(record, 2, NULL, NULL, &blknoInner);
 
    fillFakeState(&state, xldata->stateSrc);
 
    ptr += SizeOfSpgxlogPickSplit;
    toDelete = (OffsetNumber *) ptr;
    ptr += sizeof(OffsetNumber) * xldata->nDelete;
    toInsert = (OffsetNumber *) ptr;
    ptr += sizeof(OffsetNumber) * xldata->nInsert;
    leafPageSelect = (uint8 *) ptr;
    ptr += sizeof(uint8) * xldata->nInsert;
 
    innerTuple = ptr;
    /* the inner tuple is unaligned, so make a copy to access its header */
    memcpy(&innerTupleHdr, innerTuple, sizeof(SpGistInnerTupleData));
    ptr += innerTupleHdr.size;
 
    /* now ptr points to the list of leaf tuples */
 
    if (xldata->isRootSplit)
    {
        /* when splitting root, we touch it only in the guise of new inner */
        srcBuffer = InvalidBuffer;
        srcPage = NULL;
    }
    else if (xldata->initSrc)
    {
        /* just re-init the source page */
        srcBuffer = XLogInitBufferForRedo(record, 0);
        srcPage = (Page) BufferGetPage(srcBuffer);
 
        SpGistInitBuffer(srcBuffer,
                         SPGIST_LEAF | (xldata->storesNulls ? SPGIST_NULLS : 0));
        /* don't update LSN etc till we're done with it */
    }
    else
    {
        /*
         * Delete the specified tuples from source page.  (In case we're in
         * Hot Standby, we need to hold lock on the page till we're done
         * inserting leaf tuples and the new inner tuple, else the added
         * redirect tuple will be a dangling link.)
         */
        srcPage = NULL;
        if (XLogReadBufferForRedo(record, 0, &srcBuffer) == BLK_NEEDS_REDO)
        {
            srcPage = BufferGetPage(srcBuffer);
 
            /*
             * We have it a bit easier here than in doPickSplit(), because we
             * know the inner tuple's location already, so we can inject the
             * correct redirection tuple now.
             */
            if (!state.isBuild)
                spgPageIndexMultiDelete(&state, srcPage,
                                        toDelete, xldata->nDelete,
                                        SPGIST_REDIRECT,
                                        SPGIST_PLACEHOLDER,
                                        blknoInner,
                                        xldata->offnumInner);
            else
                spgPageIndexMultiDelete(&state, srcPage,
                                        toDelete, xldata->nDelete,
                                        SPGIST_PLACEHOLDER,
                                        SPGIST_PLACEHOLDER,
                                        InvalidBlockNumber,
                                        InvalidOffsetNumber);
 
            /* don't update LSN etc till we're done with it */
        }
    }
 
    /* try to access dest page if any */
    if (!XLogRecHasBlockRef(record, 1))
    {
        destBuffer = InvalidBuffer;
        destPage = NULL;
    }
    else if (xldata->initDest)
    {
        /* just re-init the dest page */
        destBuffer = XLogInitBufferForRedo(record, 1);
        destPage = (Page) BufferGetPage(destBuffer);
 
        SpGistInitBuffer(destBuffer,
                         SPGIST_LEAF | (xldata->storesNulls ? SPGIST_NULLS : 0));
        /* don't update LSN etc till we're done with it */
    }
    else
    {
        /*
         * We could probably release the page lock immediately in the
         * full-page-image case, but for safety let's hold it till later.
         */
        if (XLogReadBufferForRedo(record, 1, &destBuffer) == BLK_NEEDS_REDO)
            destPage = (Page) BufferGetPage(destBuffer);
        else
            destPage = NULL;    /* don't do any page updates */
    }
 
    /* restore leaf tuples to src and/or dest page */
    for (i = 0; i < xldata->nInsert; i++)
    {
        char       *leafTuple;
        SpGistLeafTupleData leafTupleHdr;
 
        /* the tuples are not aligned, so must copy to access the size field. */
        leafTuple = ptr;
        memcpy(&leafTupleHdr, leafTuple, sizeof(SpGistLeafTupleData));
        ptr += leafTupleHdr.size;
 
        page = leafPageSelect[i] ? destPage : srcPage;
        if (page == NULL)
            continue;           /* no need to touch this page */
 
        addOrReplaceTuple(page, (Item) leafTuple, leafTupleHdr.size,
                          toInsert[i]);
    }
 
    /* Now update src and dest page LSNs if needed */
    if (srcPage != NULL)
    {
        PageSetLSN(srcPage, lsn);
        MarkBufferDirty(srcBuffer);
    }
    if (destPage != NULL)
    {
        PageSetLSN(destPage, lsn);
        MarkBufferDirty(destBuffer);
    }
 
    /* restore new inner tuple */
    if (xldata->initInner)
    {
        innerBuffer = XLogInitBufferForRedo(record, 2);
        SpGistInitBuffer(innerBuffer, (xldata->storesNulls ? SPGIST_NULLS : 0));
        action = BLK_NEEDS_REDO;
    }
    else
        action = XLogReadBufferForRedo(record, 2, &innerBuffer);
 
    if (action == BLK_NEEDS_REDO)
    {
        page = BufferGetPage(innerBuffer);
 
        addOrReplaceTuple(page, (Item) innerTuple, innerTupleHdr.size,
                          xldata->offnumInner);
 
        /* if inner is also parent, update link while we're here */
        if (xldata->innerIsParent)
        {
            SpGistInnerTuple parent;
 
            parent = (SpGistInnerTuple) PageGetItem(page,
                                                    PageGetItemId(page, xldata->offnumParent));
            spgUpdateNodeLink(parent, xldata->nodeI,
                              blknoInner, xldata->offnumInner);
        }
 
        PageSetLSN(page, lsn);
        MarkBufferDirty(innerBuffer);
    }
    if (BufferIsValid(innerBuffer))
        UnlockReleaseBuffer(innerBuffer);
 
    /*
     * Now we can release the leaf-page locks.  It's okay to do this before
     * updating the parent downlink.
     */
    if (BufferIsValid(srcBuffer))
        UnlockReleaseBuffer(srcBuffer);
    if (BufferIsValid(destBuffer))
        UnlockReleaseBuffer(destBuffer);
 
    /* update parent downlink, unless we did it above */
    if (XLogRecHasBlockRef(record, 3))
    {
        Buffer      parentBuffer;
 
        if (XLogReadBufferForRedo(record, 3, &parentBuffer) == BLK_NEEDS_REDO)
        {
            SpGistInnerTuple parent;
 
            page = BufferGetPage(parentBuffer);
 
            parent = (SpGistInnerTuple) PageGetItem(page,
                                                    PageGetItemId(page, xldata->offnumParent));
            spgUpdateNodeLink(parent, xldata->nodeI,
                              blknoInner, xldata->offnumInner);
 
            PageSetLSN(page, lsn);
            MarkBufferDirty(parentBuffer);
        }
        if (BufferIsValid(parentBuffer))
            UnlockReleaseBuffer(parentBuffer);
    }
    else
        Assert(xldata->innerIsParent || xldata->isRootSplit);
}
 
static void
spgRedoVacuumLeaf(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    char       *ptr = XLogRecGetData(record);
    spgxlogVacuumLeaf *xldata = (spgxlogVacuumLeaf *) ptr;
    OffsetNumber *toDead;
    OffsetNumber *toPlaceholder;
    OffsetNumber *moveSrc;
    OffsetNumber *moveDest;
    OffsetNumber *chainSrc;
    OffsetNumber *chainDest;
    SpGistState state;
    Buffer      buffer;
    Page        page;
    int         i;
 
    fillFakeState(&state, xldata->stateSrc);
 
    ptr += SizeOfSpgxlogVacuumLeaf;
    toDead = (OffsetNumber *) ptr;
    ptr += sizeof(OffsetNumber) * xldata->nDead;
    toPlaceholder = (OffsetNumber *) ptr;
    ptr += sizeof(OffsetNumber) * xldata->nPlaceholder;
    moveSrc = (OffsetNumber *) ptr;
    ptr += sizeof(OffsetNumber) * xldata->nMove;
    moveDest = (OffsetNumber *) ptr;
    ptr += sizeof(OffsetNumber) * xldata->nMove;
    chainSrc = (OffsetNumber *) ptr;
    ptr += sizeof(OffsetNumber) * xldata->nChain;
    chainDest = (OffsetNumber *) ptr;
 
    if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
    {
        page = BufferGetPage(buffer);
 
        spgPageIndexMultiDelete(&state, page,
                                toDead, xldata->nDead,
                                SPGIST_DEAD, SPGIST_DEAD,
                                InvalidBlockNumber,
                                InvalidOffsetNumber);
 
        spgPageIndexMultiDelete(&state, page,
                                toPlaceholder, xldata->nPlaceholder,
                                SPGIST_PLACEHOLDER, SPGIST_PLACEHOLDER,
                                InvalidBlockNumber,
                                InvalidOffsetNumber);
 
        /* see comments in vacuumLeafPage() */
        for (i = 0; i < xldata->nMove; i++)
        {
            ItemId      idSrc = PageGetItemId(page, moveSrc[i]);
            ItemId      idDest = PageGetItemId(page, moveDest[i]);
            ItemIdData  tmp;
 
            tmp = *idSrc;
            *idSrc = *idDest;
            *idDest = tmp;
        }
 
        spgPageIndexMultiDelete(&state, page,
                                moveSrc, xldata->nMove,
                                SPGIST_PLACEHOLDER, SPGIST_PLACEHOLDER,
                                InvalidBlockNumber,
                                InvalidOffsetNumber);
 
        for (i = 0; i < xldata->nChain; i++)
        {
            SpGistLeafTuple lt;
 
            lt = (SpGistLeafTuple) PageGetItem(page,
                                               PageGetItemId(page, chainSrc[i]));
            Assert(lt->tupstate == SPGIST_LIVE);
            SGLT_SET_NEXTOFFSET(lt, chainDest[i]);
        }
 
        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);
}
 
static void
spgRedoVacuumRoot(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    char       *ptr = XLogRecGetData(record);
    spgxlogVacuumRoot *xldata = (spgxlogVacuumRoot *) ptr;
    OffsetNumber *toDelete;
    Buffer      buffer;
    Page        page;
 
    toDelete = xldata->offsets;
 
    if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
    {
        page = BufferGetPage(buffer);
 
        /* The tuple numbers are in order */
        PageIndexMultiDelete(page, toDelete, xldata->nDelete);
 
        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);
}
 
static void
spgRedoVacuumRedirect(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    char       *ptr = XLogRecGetData(record);
    spgxlogVacuumRedirect *xldata = (spgxlogVacuumRedirect *) ptr;
    OffsetNumber *itemToPlaceholder;
    Buffer      buffer;
 
    itemToPlaceholder = xldata->offsets;
 
    /*
     * If any redirection tuples are being removed, make sure there are no
     * live Hot Standby transactions that might need to see them.
     */
    if (InHotStandby)
    {
        RelFileLocator locator;
 
        XLogRecGetBlockTag(record, 0, &locator, NULL, NULL);
        ResolveRecoveryConflictWithSnapshot(xldata->snapshotConflictHorizon,
                                            xldata->isCatalogRel,
                                            locator);
    }
 
    if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
    {
        Page        page = BufferGetPage(buffer);
        SpGistPageOpaque opaque = SpGistPageGetOpaque(page);
        int         i;
 
        /* Convert redirect pointers to plain placeholders */
        for (i = 0; i < xldata->nToPlaceholder; i++)
        {
            SpGistDeadTuple dt;
 
            dt = (SpGistDeadTuple) PageGetItem(page,
                                               PageGetItemId(page, itemToPlaceholder[i]));
            Assert(dt->tupstate == SPGIST_REDIRECT);
            dt->tupstate = SPGIST_PLACEHOLDER;
            ItemPointerSetInvalid(&dt->pointer);
        }
 
        Assert(opaque->nRedirection >= xldata->nToPlaceholder);
        opaque->nRedirection -= xldata->nToPlaceholder;
        opaque->nPlaceholder += xldata->nToPlaceholder;
 
        /* Remove placeholder tuples at end of page */
        if (xldata->firstPlaceholder != InvalidOffsetNumber)
        {
            int         max = PageGetMaxOffsetNumber(page);
            OffsetNumber *toDelete;
 
            toDelete = palloc(sizeof(OffsetNumber) * max);
 
            for (i = xldata->firstPlaceholder; i <= max; i++)
                toDelete[i - xldata->firstPlaceholder] = i;
 
            i = max - xldata->firstPlaceholder + 1;
            Assert(opaque->nPlaceholder >= i);
            opaque->nPlaceholder -= i;
 
            /* The array is sorted, so can use PageIndexMultiDelete */
            PageIndexMultiDelete(page, toDelete, i);
 
            pfree(toDelete);
        }
 
        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);
}
 
void
spg_redo(XLogReaderState *record)
{
    uint8       info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
    MemoryContext oldCxt;
 
    oldCxt = MemoryContextSwitchTo(opCtx);
    switch (info)
    {
        case XLOG_SPGIST_ADD_LEAF:
            spgRedoAddLeaf(record);
            break;
        case XLOG_SPGIST_MOVE_LEAFS:
            spgRedoMoveLeafs(record);
            break;
        case XLOG_SPGIST_ADD_NODE:
            spgRedoAddNode(record);
            break;
        case XLOG_SPGIST_SPLIT_TUPLE:
            spgRedoSplitTuple(record);
            break;
        case XLOG_SPGIST_PICKSPLIT:
            spgRedoPickSplit(record);
            break;
        case XLOG_SPGIST_VACUUM_LEAF:
            spgRedoVacuumLeaf(record);
            break;
        case XLOG_SPGIST_VACUUM_ROOT:
            spgRedoVacuumRoot(record);
            break;
        case XLOG_SPGIST_VACUUM_REDIRECT:
            spgRedoVacuumRedirect(record);
            break;
        default:
            elog(PANIC, "spg_redo: unknown op code %u", info);
    }
 
    MemoryContextSwitchTo(oldCxt);
    MemoryContextReset(opCtx);
}
 
void
spg_xlog_startup(void)
{
    opCtx = AllocSetContextCreate(CurrentMemoryContext,
                                  "SP-GiST temporary context",
                                  ALLOCSET_DEFAULT_SIZES);
}
 
void
spg_xlog_cleanup(void)
{
    MemoryContextDelete(opCtx);
    opCtx = NULL;
}
 
/*
 * Mask a SpGist page before performing consistency checks on it.
 */
void
spg_mask(char *pagedata, BlockNumber blkno)
{
    Page        page = (Page) pagedata;
    PageHeader  pagehdr = (PageHeader) page;
 
    mask_page_lsn_and_checksum(page);
 
    mask_page_hint_bits(page);
 
    /*
     * Mask the unused space, but only if the page's pd_lower appears to have
     * been set correctly.
     */
    if (pagehdr->pd_lower >= SizeOfPageHeaderData)
        mask_unused_space(page);
}