nbtxlog.c

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/*-------------------------------------------------------------------------
 *
 * nbtxlog.c
 *    WAL replay logic for btrees.
 *
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/access/nbtree/nbtxlog.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/bufmask.h"
#include "access/nbtree.h"
#include "access/nbtxlog.h"
#include "access/transam.h"
#include "access/xlog.h"
#include "access/xlogutils.h"
#include "miscadmin.h"
#include "storage/procarray.h"
#include "utils/memutils.h"

static MemoryContext opCtx;     /* working memory for operations */

/*
 * _bt_restore_page -- re-enter all the index tuples on a page
 *
 * The page is freshly init'd, and *from (length len) is a copy of what
 * had been its upper part (pd_upper to pd_special).  We assume that the
 * tuples had been added to the page in item-number order, and therefore
 * the one with highest item number appears first (lowest on the page).
 */
static void
_bt_restore_page(Page page, char *from, int len)
{
    IndexTupleData itupdata;
    Size        itemsz;
    char       *end = from + len;
    Item        items[MaxIndexTuplesPerPage];
    uint16      itemsizes[MaxIndexTuplesPerPage];
    int         i;
    int         nitems;

    /*
     * To get the items back in the original order, we add them to the page in
     * reverse.  To figure out where one tuple ends and another begins, we
     * have to scan them in forward order first.
     */
    i = 0;
    while (from < end)
    {
        /*
         * As we step through the items, 'from' won't always be properly
         * aligned, so we need to use memcpy().  Further, we use Item (which
         * is just a char*) here for our items array for the same reason;
         * wouldn't want the compiler or anyone thinking that an item is
         * aligned when it isn't.
         */
        memcpy(&itupdata, from, sizeof(IndexTupleData));
        itemsz = IndexTupleSize(&itupdata);
        itemsz = MAXALIGN(itemsz);

        items[i] = (Item) from;
        itemsizes[i] = itemsz;
        i++;

        from += itemsz;
    }
    nitems = i;

    for (i = nitems - 1; i >= 0; i--)
    {
        if (PageAddItem(page, items[i], itemsizes[i], nitems - i,
                        false, false) == InvalidOffsetNumber)
            elog(PANIC, "_bt_restore_page: cannot add item to page");
        from += itemsz;
    }
}

static void
_bt_restore_meta(XLogReaderState *record, uint8 block_id)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    Buffer      metabuf;
    Page        metapg;
    BTMetaPageData *md;
    BTPageOpaque pageop;
    xl_btree_metadata *xlrec;
    char       *ptr;
    Size        len;

    metabuf = XLogInitBufferForRedo(record, block_id);
    ptr = XLogRecGetBlockData(record, block_id, &len);

    Assert(len == sizeof(xl_btree_metadata));
    Assert(BufferGetBlockNumber(metabuf) == BTREE_METAPAGE);
    xlrec = (xl_btree_metadata *) ptr;
    metapg = BufferGetPage(metabuf);

    _bt_pageinit(metapg, BufferGetPageSize(metabuf));

    md = BTPageGetMeta(metapg);
    md->btm_magic = BTREE_MAGIC;
    md->btm_version = xlrec->version;
    md->btm_root = xlrec->root;
    md->btm_level = xlrec->level;
    md->btm_fastroot = xlrec->fastroot;
    md->btm_fastlevel = xlrec->fastlevel;
    /* Cannot log BTREE_MIN_VERSION index metapage without upgrade */
    Assert(md->btm_version >= BTREE_NOVAC_VERSION);
    md->btm_oldest_btpo_xact = xlrec->oldest_btpo_xact;
    md->btm_last_cleanup_num_heap_tuples = xlrec->last_cleanup_num_heap_tuples;
    md->btm_allequalimage = xlrec->allequalimage;

    pageop = (BTPageOpaque) PageGetSpecialPointer(metapg);
    pageop->btpo_flags = BTP_META;

    /*
     * 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.
     */
    ((PageHeader) metapg)->pd_lower =
        ((char *) md + sizeof(BTMetaPageData)) - (char *) metapg;

    PageSetLSN(metapg, lsn);
    MarkBufferDirty(metabuf);
    UnlockReleaseBuffer(metabuf);
}

/*
 * _bt_clear_incomplete_split -- clear INCOMPLETE_SPLIT flag on a page
 *
 * This is a common subroutine of the redo functions of all the WAL record
 * types that can insert a downlink: insert, split, and newroot.
 */
static void
_bt_clear_incomplete_split(XLogReaderState *record, uint8 block_id)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    Buffer      buf;

    if (XLogReadBufferForRedo(record, block_id, &buf) == BLK_NEEDS_REDO)
    {
        Page        page = (Page) BufferGetPage(buf);
        BTPageOpaque pageop = (BTPageOpaque) PageGetSpecialPointer(page);

        Assert(P_INCOMPLETE_SPLIT(pageop));
        pageop->btpo_flags &= ~BTP_INCOMPLETE_SPLIT;

        PageSetLSN(page, lsn);
        MarkBufferDirty(buf);
    }
    if (BufferIsValid(buf))
        UnlockReleaseBuffer(buf);
}

static void
btree_xlog_insert(bool isleaf, bool ismeta, bool posting,
                  XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    xl_btree_insert *xlrec = (xl_btree_insert *) XLogRecGetData(record);
    Buffer      buffer;
    Page        page;

    /*
     * Insertion to an internal page finishes an incomplete split at the child
     * level.  Clear the incomplete-split flag in the child.  Note: during
     * normal operation, the child and parent pages are locked at the same
     * time, so that clearing the flag and inserting the downlink appear
     * atomic to other backends.  We don't bother with that during replay,
     * because readers don't care about the incomplete-split flag and there
     * cannot be updates happening.
     */
    if (!isleaf)
        _bt_clear_incomplete_split(record, 1);
    if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
    {
        Size        datalen;
        char       *datapos = XLogRecGetBlockData(record, 0, &datalen);

        page = BufferGetPage(buffer);

        if (!posting)
        {
            /* Simple retail insertion */
            if (PageAddItem(page, (Item) datapos, datalen, xlrec->offnum,
                            false, false) == InvalidOffsetNumber)
                elog(PANIC, "failed to add new item");
        }
        else
        {
            ItemId      itemid;
            IndexTuple  oposting,
                        newitem,
                        nposting;
            uint16      postingoff;

            /*
             * A posting list split occurred during leaf page insertion.  WAL
             * record data will start with an offset number representing the
             * point in an existing posting list that a split occurs at.
             *
             * Use _bt_swap_posting() to repeat posting list split steps from
             * primary.  Note that newitem from WAL record is 'orignewitem',
             * not the final version of newitem that is actually inserted on
             * page.
             */
            postingoff = *((uint16 *) datapos);
            datapos += sizeof(uint16);
            datalen -= sizeof(uint16);

            itemid = PageGetItemId(page, OffsetNumberPrev(xlrec->offnum));
            oposting = (IndexTuple) PageGetItem(page, itemid);

            /* Use mutable, aligned newitem copy in _bt_swap_posting() */
            Assert(isleaf && postingoff > 0);
            newitem = CopyIndexTuple((IndexTuple) datapos);
            nposting = _bt_swap_posting(newitem, oposting, postingoff);

            /* Replace existing posting list with post-split version */
            memcpy(oposting, nposting, MAXALIGN(IndexTupleSize(nposting)));

            /* Insert "final" new item (not orignewitem from WAL stream) */
            Assert(IndexTupleSize(newitem) == datalen);
            if (PageAddItem(page, (Item) newitem, datalen, xlrec->offnum,
                            false, false) == InvalidOffsetNumber)
                elog(PANIC, "failed to add posting split new item");
        }

        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);

    /*
     * Note: in normal operation, we'd update the metapage while still holding
     * lock on the page we inserted into.  But during replay it's not
     * necessary to hold that lock, since no other index updates can be
     * happening concurrently, and readers will cope fine with following an
     * obsolete link from the metapage.
     */
    if (ismeta)
        _bt_restore_meta(record, 2);
}

static void
btree_xlog_split(bool newitemonleft, XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    xl_btree_split *xlrec = (xl_btree_split *) XLogRecGetData(record);
    bool        isleaf = (xlrec->level == 0);
    Buffer      lbuf;
    Buffer      rbuf;
    Page        rpage;
    BTPageOpaque ropaque;
    char       *datapos;
    Size        datalen;
    BlockNumber leftsib;
    BlockNumber rightsib;
    BlockNumber rnext;

    XLogRecGetBlockTag(record, 0, NULL, NULL, &leftsib);
    XLogRecGetBlockTag(record, 1, NULL, NULL, &rightsib);
    if (!XLogRecGetBlockTag(record, 2, NULL, NULL, &rnext))
        rnext = P_NONE;

    /*
     * Clear the incomplete split flag on the left sibling of the child page
     * this is a downlink for.  (Like in btree_xlog_insert, this can be done
     * before locking the other pages)
     */
    if (!isleaf)
        _bt_clear_incomplete_split(record, 3);

    /* Reconstruct right (new) sibling page from scratch */
    rbuf = XLogInitBufferForRedo(record, 1);
    datapos = XLogRecGetBlockData(record, 1, &datalen);
    rpage = (Page) BufferGetPage(rbuf);

    _bt_pageinit(rpage, BufferGetPageSize(rbuf));
    ropaque = (BTPageOpaque) PageGetSpecialPointer(rpage);

    ropaque->btpo_prev = leftsib;
    ropaque->btpo_next = rnext;
    ropaque->btpo.level = xlrec->level;
    ropaque->btpo_flags = isleaf ? BTP_LEAF : 0;
    ropaque->btpo_cycleid = 0;

    _bt_restore_page(rpage, datapos, datalen);

    PageSetLSN(rpage, lsn);
    MarkBufferDirty(rbuf);

    /* Now reconstruct left (original) sibling page */
    if (XLogReadBufferForRedo(record, 0, &lbuf) == BLK_NEEDS_REDO)
    {
        /*
         * To retain the same physical order of the tuples that they had, we
         * initialize a temporary empty page for the left page and add all the
         * items to that in item number order.  This mirrors how _bt_split()
         * works.  Retaining the same physical order makes WAL consistency
         * checking possible.  See also _bt_restore_page(), which does the
         * same for the right page.
         */
        Page        lpage = (Page) BufferGetPage(lbuf);
        BTPageOpaque lopaque = (BTPageOpaque) PageGetSpecialPointer(lpage);
        OffsetNumber off;
        IndexTuple  newitem = NULL,
                    left_hikey = NULL,
                    nposting = NULL;
        Size        newitemsz = 0,
                    left_hikeysz = 0;
        Page        newlpage;
        OffsetNumber leftoff,
                    replacepostingoff = InvalidOffsetNumber;

        datapos = XLogRecGetBlockData(record, 0, &datalen);

        if (newitemonleft || xlrec->postingoff != 0)
        {
            newitem = (IndexTuple) datapos;
            newitemsz = MAXALIGN(IndexTupleSize(newitem));
            datapos += newitemsz;
            datalen -= newitemsz;

            if (xlrec->postingoff != 0)
            {
                ItemId      itemid;
                IndexTuple  oposting;

                /* Posting list must be at offset number before new item's */
                replacepostingoff = OffsetNumberPrev(xlrec->newitemoff);

                /* Use mutable, aligned newitem copy in _bt_swap_posting() */
                newitem = CopyIndexTuple(newitem);
                itemid = PageGetItemId(lpage, replacepostingoff);
                oposting = (IndexTuple) PageGetItem(lpage, itemid);
                nposting = _bt_swap_posting(newitem, oposting,
                                            xlrec->postingoff);
            }
        }

        /*
         * Extract left hikey and its size.  We assume that 16-bit alignment
         * is enough to apply IndexTupleSize (since it's fetching from a
         * uint16 field).
         */
        left_hikey = (IndexTuple) datapos;
        left_hikeysz = MAXALIGN(IndexTupleSize(left_hikey));
        datapos += left_hikeysz;
        datalen -= left_hikeysz;

        Assert(datalen == 0);

        newlpage = PageGetTempPageCopySpecial(lpage);

        /* Set high key */
        leftoff = P_HIKEY;
        if (PageAddItem(newlpage, (Item) left_hikey, left_hikeysz,
                        P_HIKEY, false, false) == InvalidOffsetNumber)
            elog(PANIC, "failed to add high key to left page after split");
        leftoff = OffsetNumberNext(leftoff);

        for (off = P_FIRSTDATAKEY(lopaque); off < xlrec->firstrightoff; off++)
        {
            ItemId      itemid;
            Size        itemsz;
            IndexTuple  item;

            /* Add replacement posting list when required */
            if (off == replacepostingoff)
            {
                Assert(newitemonleft ||
                       xlrec->firstrightoff == xlrec->newitemoff);
                if (PageAddItem(newlpage, (Item) nposting,
                                MAXALIGN(IndexTupleSize(nposting)), leftoff,
                                false, false) == InvalidOffsetNumber)
                    elog(ERROR, "failed to add new posting list item to left page after split");
                leftoff = OffsetNumberNext(leftoff);
                continue;       /* don't insert oposting */
            }

            /* add the new item if it was inserted on left page */
            else if (newitemonleft && off == xlrec->newitemoff)
            {
                if (PageAddItem(newlpage, (Item) newitem, newitemsz, leftoff,
                                false, false) == InvalidOffsetNumber)
                    elog(ERROR, "failed to add new item to left page after split");
                leftoff = OffsetNumberNext(leftoff);
            }

            itemid = PageGetItemId(lpage, off);
            itemsz = ItemIdGetLength(itemid);
            item = (IndexTuple) PageGetItem(lpage, itemid);
            if (PageAddItem(newlpage, (Item) item, itemsz, leftoff,
                            false, false) == InvalidOffsetNumber)
                elog(ERROR, "failed to add old item to left page after split");
            leftoff = OffsetNumberNext(leftoff);
        }

        /* cope with possibility that newitem goes at the end */
        if (newitemonleft && off == xlrec->newitemoff)
        {
            if (PageAddItem(newlpage, (Item) newitem, newitemsz, leftoff,
                            false, false) == InvalidOffsetNumber)
                elog(ERROR, "failed to add new item to left page after split");
            leftoff = OffsetNumberNext(leftoff);
        }

        PageRestoreTempPage(newlpage, lpage);

        /* Fix opaque fields */
        lopaque->btpo_flags = BTP_INCOMPLETE_SPLIT;
        if (isleaf)
            lopaque->btpo_flags |= BTP_LEAF;
        lopaque->btpo_next = rightsib;
        lopaque->btpo_cycleid = 0;

        PageSetLSN(lpage, lsn);
        MarkBufferDirty(lbuf);
    }

    /*
     * We no longer need the buffers.  They must be released together, so that
     * readers cannot observe two inconsistent halves.
     */
    if (BufferIsValid(lbuf))
        UnlockReleaseBuffer(lbuf);
    UnlockReleaseBuffer(rbuf);

    /*
     * Fix left-link of the page to the right of the new right sibling.
     *
     * Note: in normal operation, we do this while still holding lock on the
     * two split pages.  However, that's not necessary for correctness in WAL
     * replay, because no other index update can be in progress, and readers
     * will cope properly when following an obsolete left-link.
     */
    if (rnext != P_NONE)
    {
        Buffer      buffer;

        if (XLogReadBufferForRedo(record, 2, &buffer) == BLK_NEEDS_REDO)
        {
            Page        page = (Page) BufferGetPage(buffer);
            BTPageOpaque pageop = (BTPageOpaque) PageGetSpecialPointer(page);

            pageop->btpo_prev = rightsib;

            PageSetLSN(page, lsn);
            MarkBufferDirty(buffer);
        }
        if (BufferIsValid(buffer))
            UnlockReleaseBuffer(buffer);
    }
}

static void
btree_xlog_dedup(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    xl_btree_dedup *xlrec = (xl_btree_dedup *) XLogRecGetData(record);
    Buffer      buf;

    if (XLogReadBufferForRedo(record, 0, &buf) == BLK_NEEDS_REDO)
    {
        char       *ptr = XLogRecGetBlockData(record, 0, NULL);
        Page        page = (Page) BufferGetPage(buf);
        BTPageOpaque opaque = (BTPageOpaque) PageGetSpecialPointer(page);
        OffsetNumber offnum,
                    minoff,
                    maxoff;
        BTDedupState state;
        BTDedupInterval *intervals;
        Page        newpage;

        state = (BTDedupState) palloc(sizeof(BTDedupStateData));
        state->deduplicate = true;  /* unused */
        state->nmaxitems = 0;   /* unused */
        /* Conservatively use larger maxpostingsize than primary */
        state->maxpostingsize = BTMaxItemSize(page);
        state->base = NULL;
        state->baseoff = InvalidOffsetNumber;
        state->basetupsize = 0;
        state->htids = palloc(state->maxpostingsize);
        state->nhtids = 0;
        state->nitems = 0;
        state->phystupsize = 0;
        state->nintervals = 0;

        minoff = P_FIRSTDATAKEY(opaque);
        maxoff = PageGetMaxOffsetNumber(page);
        newpage = PageGetTempPageCopySpecial(page);

        if (!P_RIGHTMOST(opaque))
        {
            ItemId      itemid = PageGetItemId(page, P_HIKEY);
            Size        itemsz = ItemIdGetLength(itemid);
            IndexTuple  item = (IndexTuple) PageGetItem(page, itemid);

            if (PageAddItem(newpage, (Item) item, itemsz, P_HIKEY,
                            false, false) == InvalidOffsetNumber)
                elog(ERROR, "deduplication failed to add highkey");
        }

        intervals = (BTDedupInterval *) ptr;
        for (offnum = minoff;
             offnum <= maxoff;
             offnum = OffsetNumberNext(offnum))
        {
            ItemId      itemid = PageGetItemId(page, offnum);
            IndexTuple  itup = (IndexTuple) PageGetItem(page, itemid);

            if (offnum == minoff)
                _bt_dedup_start_pending(state, itup, offnum);
            else if (state->nintervals < xlrec->nintervals &&
                     state->baseoff == intervals[state->nintervals].baseoff &&
                     state->nitems < intervals[state->nintervals].nitems)
            {
                if (!_bt_dedup_save_htid(state, itup))
                    elog(ERROR, "deduplication failed to add heap tid to pending posting list");
            }
            else
            {
                _bt_dedup_finish_pending(newpage, state);
                _bt_dedup_start_pending(state, itup, offnum);
            }
        }

        _bt_dedup_finish_pending(newpage, state);
        Assert(state->nintervals == xlrec->nintervals);
        Assert(memcmp(state->intervals, intervals,
                      state->nintervals * sizeof(BTDedupInterval)) == 0);

        if (P_HAS_GARBAGE(opaque))
        {
            BTPageOpaque nopaque = (BTPageOpaque) PageGetSpecialPointer(newpage);

            nopaque->btpo_flags &= ~BTP_HAS_GARBAGE;
        }

        PageRestoreTempPage(newpage, page);
        PageSetLSN(page, lsn);
        MarkBufferDirty(buf);
    }

    if (BufferIsValid(buf))
        UnlockReleaseBuffer(buf);
}

static void
btree_xlog_vacuum(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    xl_btree_vacuum *xlrec = (xl_btree_vacuum *) XLogRecGetData(record);
    Buffer      buffer;
    Page        page;
    BTPageOpaque opaque;

    /*
     * We need to take a cleanup lock here, just like btvacuumpage(). However,
     * it isn't necessary to exhaustively get a cleanup lock on every block in
     * the index during recovery (just getting a cleanup lock on pages with
     * items to kill suffices).  See nbtree/README for details.
     */
    if (XLogReadBufferForRedoExtended(record, 0, RBM_NORMAL, true, &buffer)
        == BLK_NEEDS_REDO)
    {
        char       *ptr = XLogRecGetBlockData(record, 0, NULL);

        page = (Page) BufferGetPage(buffer);

        if (xlrec->nupdated > 0)
        {
            OffsetNumber *updatedoffsets;
            xl_btree_update *updates;

            updatedoffsets = (OffsetNumber *)
                (ptr + xlrec->ndeleted * sizeof(OffsetNumber));
            updates = (xl_btree_update *) ((char *) updatedoffsets +
                                           xlrec->nupdated *
                                           sizeof(OffsetNumber));

            for (int i = 0; i < xlrec->nupdated; i++)
            {
                BTVacuumPosting vacposting;
                IndexTuple  origtuple;
                ItemId      itemid;
                Size        itemsz;

                itemid = PageGetItemId(page, updatedoffsets[i]);
                origtuple = (IndexTuple) PageGetItem(page, itemid);

                vacposting = palloc(offsetof(BTVacuumPostingData, deletetids) +
                                    updates->ndeletedtids * sizeof(uint16));
                vacposting->updatedoffset = updatedoffsets[i];
                vacposting->itup = origtuple;
                vacposting->ndeletedtids = updates->ndeletedtids;
                memcpy(vacposting->deletetids,
                       (char *) updates + SizeOfBtreeUpdate,
                       updates->ndeletedtids * sizeof(uint16));

                _bt_update_posting(vacposting);

                /* Overwrite updated version of tuple */
                itemsz = MAXALIGN(IndexTupleSize(vacposting->itup));
                if (!PageIndexTupleOverwrite(page, updatedoffsets[i],
                                             (Item) vacposting->itup, itemsz))
                    elog(PANIC, "failed to update partially dead item");

                pfree(vacposting->itup);
                pfree(vacposting);

                /* advance to next xl_btree_update from array */
                updates = (xl_btree_update *)
                    ((char *) updates + SizeOfBtreeUpdate +
                     updates->ndeletedtids * sizeof(uint16));
            }
        }

        if (xlrec->ndeleted > 0)
            PageIndexMultiDelete(page, (OffsetNumber *) ptr, xlrec->ndeleted);

        /*
         * Mark the page as not containing any LP_DEAD items --- see comments
         * in _bt_delitems_vacuum().
         */
        opaque = (BTPageOpaque) PageGetSpecialPointer(page);
        opaque->btpo_flags &= ~BTP_HAS_GARBAGE;

        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);
}

static void
btree_xlog_delete(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    xl_btree_delete *xlrec = (xl_btree_delete *) XLogRecGetData(record);
    Buffer      buffer;
    Page        page;
    BTPageOpaque opaque;

    /*
     * If we have any conflict processing to do, it must happen before we
     * update the page
     */
    if (InHotStandby)
    {
        RelFileNode rnode;

        XLogRecGetBlockTag(record, 0, &rnode, NULL, NULL);

        ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid, rnode);
    }

    /*
     * We don't need to take a cleanup lock to apply these changes. See
     * nbtree/README for details.
     */
    if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
    {
        char       *ptr = XLogRecGetBlockData(record, 0, NULL);

        page = (Page) BufferGetPage(buffer);

        PageIndexMultiDelete(page, (OffsetNumber *) ptr, xlrec->ndeleted);

        /* Mark the page as not containing any LP_DEAD items */
        opaque = (BTPageOpaque) PageGetSpecialPointer(page);
        opaque->btpo_flags &= ~BTP_HAS_GARBAGE;

        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);
}

static void
btree_xlog_mark_page_halfdead(uint8 info, XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    xl_btree_mark_page_halfdead *xlrec = (xl_btree_mark_page_halfdead *) XLogRecGetData(record);
    Buffer      buffer;
    Page        page;
    BTPageOpaque pageop;
    IndexTupleData trunctuple;

    /*
     * In normal operation, we would lock all the pages this WAL record
     * touches before changing any of them.  In WAL replay, it should be okay
     * to lock just one page at a time, since no concurrent index updates can
     * be happening, and readers should not care whether they arrive at the
     * target page or not (since it's surely empty).
     */

    /* to-be-deleted subtree's parent page */
    if (XLogReadBufferForRedo(record, 1, &buffer) == BLK_NEEDS_REDO)
    {
        OffsetNumber poffset;
        ItemId      itemid;
        IndexTuple  itup;
        OffsetNumber nextoffset;
        BlockNumber rightsib;

        page = (Page) BufferGetPage(buffer);
        pageop = (BTPageOpaque) PageGetSpecialPointer(page);

        poffset = xlrec->poffset;

        nextoffset = OffsetNumberNext(poffset);
        itemid = PageGetItemId(page, nextoffset);
        itup = (IndexTuple) PageGetItem(page, itemid);
        rightsib = BTreeTupleGetDownLink(itup);

        itemid = PageGetItemId(page, poffset);
        itup = (IndexTuple) PageGetItem(page, itemid);
        BTreeTupleSetDownLink(itup, rightsib);
        nextoffset = OffsetNumberNext(poffset);
        PageIndexTupleDelete(page, nextoffset);

        PageSetLSN(page, lsn);
        MarkBufferDirty(buffer);
    }
    if (BufferIsValid(buffer))
        UnlockReleaseBuffer(buffer);

    /* Rewrite the leaf page as a halfdead page */
    buffer = XLogInitBufferForRedo(record, 0);
    page = (Page) BufferGetPage(buffer);

    _bt_pageinit(page, BufferGetPageSize(buffer));
    pageop = (BTPageOpaque) PageGetSpecialPointer(page);

    pageop->btpo_prev = xlrec->leftblk;
    pageop->btpo_next = xlrec->rightblk;
    pageop->btpo.level = 0;
    pageop->btpo_flags = BTP_HALF_DEAD | BTP_LEAF;
    pageop->btpo_cycleid = 0;

    /*
     * Construct a dummy high key item that points to top parent page (value
     * is InvalidBlockNumber when the top parent page is the leaf page itself)
     */
    MemSet(&trunctuple, 0, sizeof(IndexTupleData));
    trunctuple.t_info = sizeof(IndexTupleData);
    BTreeTupleSetTopParent(&trunctuple, xlrec->topparent);

    if (PageAddItem(page, (Item) &trunctuple, sizeof(IndexTupleData), P_HIKEY,
                    false, false) == InvalidOffsetNumber)
        elog(ERROR, "could not add dummy high key to half-dead page");

    PageSetLSN(page, lsn);
    MarkBufferDirty(buffer);
    UnlockReleaseBuffer(buffer);
}


static void
btree_xlog_unlink_page(uint8 info, XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    xl_btree_unlink_page *xlrec = (xl_btree_unlink_page *) XLogRecGetData(record);
    BlockNumber leftsib;
    BlockNumber rightsib;
    Buffer      leftbuf;
    Buffer      target;
    Buffer      rightbuf;
    Page        page;
    BTPageOpaque pageop;

    leftsib = xlrec->leftsib;
    rightsib = xlrec->rightsib;

    /*
     * In normal operation, we would lock all the pages this WAL record
     * touches before changing any of them.  In WAL replay, we at least lock
     * the pages in the same standard left-to-right order (leftsib, target,
     * rightsib), and don't release the sibling locks until the target is
     * marked deleted.
     *
     * btree_xlog_split() can get away with fixing its right sibling page's
     * left link last of all, after dropping all other locks.  We prefer to
     * avoid dropping locks on same-level pages early compared to normal
     * operation.  This keeps things simple for backwards scans.  See
     * nbtree/README.
     */

    /* Fix right-link of left sibling, if any */
    if (leftsib != P_NONE)
    {
        if (XLogReadBufferForRedo(record, 1, &leftbuf) == BLK_NEEDS_REDO)
        {
            page = (Page) BufferGetPage(leftbuf);
            pageop = (BTPageOpaque) PageGetSpecialPointer(page);
            pageop->btpo_next = rightsib;

            PageSetLSN(page, lsn);
            MarkBufferDirty(leftbuf);
        }
    }
    else
        leftbuf = InvalidBuffer;

    /* Rewrite target page as empty deleted page */
    target = XLogInitBufferForRedo(record, 0);
    page = (Page) BufferGetPage(target);

    _bt_pageinit(page, BufferGetPageSize(target));
    pageop = (BTPageOpaque) PageGetSpecialPointer(page);

    pageop->btpo_prev = leftsib;
    pageop->btpo_next = rightsib;
    pageop->btpo.xact = xlrec->btpo_xact;
    pageop->btpo_flags = BTP_DELETED;
    pageop->btpo_cycleid = 0;

    PageSetLSN(page, lsn);
    MarkBufferDirty(target);

    /* Fix left-link of right sibling */
    if (XLogReadBufferForRedo(record, 2, &rightbuf) == BLK_NEEDS_REDO)
    {
        page = (Page) BufferGetPage(rightbuf);
        pageop = (BTPageOpaque) PageGetSpecialPointer(page);
        pageop->btpo_prev = leftsib;

        PageSetLSN(page, lsn);
        MarkBufferDirty(rightbuf);
    }

    /* Release siblings */
    if (BufferIsValid(leftbuf))
        UnlockReleaseBuffer(leftbuf);
    if (BufferIsValid(rightbuf))
        UnlockReleaseBuffer(rightbuf);

    /* Release target */
    UnlockReleaseBuffer(target);

    /*
     * If we deleted a parent of the targeted leaf page, instead of the leaf
     * itself, update the leaf to point to the next remaining child in the
     * to-be-deleted subtree
     */
    if (XLogRecHasBlockRef(record, 3))
    {
        /*
         * There is no real data on the page, so we just re-create it from
         * scratch using the information from the WAL record.
         *
         * Note that we don't end up here when the target page is also the
         * leafbuf page.  There is no need to add a dummy hikey item with a
         * top parent link when deleting leafbuf because it's the last page
         * we'll delete in the subtree undergoing deletion.
         */
        Buffer              leafbuf;
        IndexTupleData      trunctuple;

        leafbuf = XLogInitBufferForRedo(record, 3);
        page = (Page) BufferGetPage(leafbuf);

        _bt_pageinit(page, BufferGetPageSize(leafbuf));
        pageop = (BTPageOpaque) PageGetSpecialPointer(page);

        pageop->btpo_flags = BTP_HALF_DEAD | BTP_LEAF;
        pageop->btpo_prev = xlrec->leafleftsib;
        pageop->btpo_next = xlrec->leafrightsib;
        pageop->btpo.level = 0;
        pageop->btpo_cycleid = 0;

        /* Add a dummy hikey item */
        MemSet(&trunctuple, 0, sizeof(IndexTupleData));
        trunctuple.t_info = sizeof(IndexTupleData);
        BTreeTupleSetTopParent(&trunctuple, xlrec->topparent);

        if (PageAddItem(page, (Item) &trunctuple, sizeof(IndexTupleData), P_HIKEY,
                        false, false) == InvalidOffsetNumber)
            elog(ERROR, "could not add dummy high key to half-dead page");

        PageSetLSN(page, lsn);
        MarkBufferDirty(leafbuf);
        UnlockReleaseBuffer(leafbuf);
    }

    /* Update metapage if needed */
    if (info == XLOG_BTREE_UNLINK_PAGE_META)
        _bt_restore_meta(record, 4);
}

static void
btree_xlog_newroot(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    xl_btree_newroot *xlrec = (xl_btree_newroot *) XLogRecGetData(record);
    Buffer      buffer;
    Page        page;
    BTPageOpaque pageop;
    char       *ptr;
    Size        len;

    buffer = XLogInitBufferForRedo(record, 0);
    page = (Page) BufferGetPage(buffer);

    _bt_pageinit(page, BufferGetPageSize(buffer));
    pageop = (BTPageOpaque) PageGetSpecialPointer(page);

    pageop->btpo_flags = BTP_ROOT;
    pageop->btpo_prev = pageop->btpo_next = P_NONE;
    pageop->btpo.level = xlrec->level;
    if (xlrec->level == 0)
        pageop->btpo_flags |= BTP_LEAF;
    pageop->btpo_cycleid = 0;

    if (xlrec->level > 0)
    {
        ptr = XLogRecGetBlockData(record, 0, &len);
        _bt_restore_page(page, ptr, len);

        /* Clear the incomplete-split flag in left child */
        _bt_clear_incomplete_split(record, 1);
    }

    PageSetLSN(page, lsn);
    MarkBufferDirty(buffer);
    UnlockReleaseBuffer(buffer);

    _bt_restore_meta(record, 2);
}

static void
btree_xlog_reuse_page(XLogReaderState *record)
{
    xl_btree_reuse_page *xlrec = (xl_btree_reuse_page *) XLogRecGetData(record);

    /*
     * Btree reuse_page records exist to provide a conflict point when we
     * reuse pages in the index via the FSM.  That's all they do though.
     *
     * latestRemovedXid was the page's btpo.xact.  The btpo.xact <
     * RecentGlobalXmin test in _bt_page_recyclable() conceptually mirrors the
     * pgxact->xmin > limitXmin test in GetConflictingVirtualXIDs().
     * Consequently, one XID value achieves the same exclusion effect on
     * primary and standby.
     */
    if (InHotStandby)
    {
        ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid,
                                            xlrec->node);
    }
}

void
btree_redo(XLogReaderState *record)
{
    uint8       info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
    MemoryContext oldCtx;

    oldCtx = MemoryContextSwitchTo(opCtx);
    switch (info)
    {
        case XLOG_BTREE_INSERT_LEAF:
            btree_xlog_insert(true, false, false, record);
            break;
        case XLOG_BTREE_INSERT_UPPER:
            btree_xlog_insert(false, false, false, record);
            break;
        case XLOG_BTREE_INSERT_META:
            btree_xlog_insert(false, true, false, record);
            break;
        case XLOG_BTREE_SPLIT_L:
            btree_xlog_split(true, record);
            break;
        case XLOG_BTREE_SPLIT_R:
            btree_xlog_split(false, record);
            break;
        case XLOG_BTREE_INSERT_POST:
            btree_xlog_insert(true, false, true, record);
            break;
        case XLOG_BTREE_DEDUP:
            btree_xlog_dedup(record);
            break;
        case XLOG_BTREE_VACUUM:
            btree_xlog_vacuum(record);
            break;
        case XLOG_BTREE_DELETE:
            btree_xlog_delete(record);
            break;
        case XLOG_BTREE_MARK_PAGE_HALFDEAD:
            btree_xlog_mark_page_halfdead(info, record);
            break;
        case XLOG_BTREE_UNLINK_PAGE:
        case XLOG_BTREE_UNLINK_PAGE_META:
            btree_xlog_unlink_page(info, record);
            break;
        case XLOG_BTREE_NEWROOT:
            btree_xlog_newroot(record);
            break;
        case XLOG_BTREE_REUSE_PAGE:
            btree_xlog_reuse_page(record);
            break;
        case XLOG_BTREE_META_CLEANUP:
            _bt_restore_meta(record, 0);
            break;
        default:
            elog(PANIC, "btree_redo: unknown op code %u", info);
    }
    MemoryContextSwitchTo(oldCtx);
    MemoryContextReset(opCtx);
}

void
btree_xlog_startup(void)
{
    opCtx = AllocSetContextCreate(CurrentMemoryContext,
                                  "Btree recovery temporary context",
                                  ALLOCSET_DEFAULT_SIZES);
}

void
btree_xlog_cleanup(void)
{
    MemoryContextDelete(opCtx);
    opCtx = NULL;
}

/*
 * Mask a btree page before performing consistency checks on it.
 */
void
btree_mask(char *pagedata, BlockNumber blkno)
{
    Page        page = (Page) pagedata;
    BTPageOpaque maskopaq;

    mask_page_lsn_and_checksum(page);

    mask_page_hint_bits(page);
    mask_unused_space(page);

    maskopaq = (BTPageOpaque) PageGetSpecialPointer(page);

    if (P_ISDELETED(maskopaq))
    {
        /*
         * Mask page content on a DELETED page since it will be re-initialized
         * during replay. See btree_xlog_unlink_page() for details.
         */
        mask_page_content(page);
    }
    else if (P_ISLEAF(maskopaq))
    {
        /*
         * In btree leaf pages, it is possible to modify the LP_FLAGS without
         * emitting any WAL record. Hence, mask the line pointer flags. See
         * _bt_killitems(), _bt_check_unique() for details.
         */
        mask_lp_flags(page);
    }

    /*
     * BTP_HAS_GARBAGE is just an un-logged hint bit. So, mask it. See
     * _bt_killitems(), _bt_check_unique() for details.
     */
    maskopaq->btpo_flags &= ~BTP_HAS_GARBAGE;

    /*
     * During replay of a btree page split, we don't set the BTP_SPLIT_END
     * flag of the right sibling and initialize the cycle_id to 0 for the same
     * page. See btree_xlog_split() for details.
     */
    maskopaq->btpo_flags &= ~BTP_SPLIT_END;
    maskopaq->btpo_cycleid = 0;
}