path: root/src/backend/access/nbtree/nbtxlog.c

/*-------------------------------------------------------------------------
 *
 * nbtxlog.c
 *	  WAL replay logic for btrees.
 *
 *
 * Portions Copyright (c) 1996-2021, 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");
	}
}

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_last_cleanup_num_delpages = xlrec->last_cleanup_num_delpages;
	md->btm_last_cleanup_num_heap_tuples = -1.0;
	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 (the locks are coupled), 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		buf;
	Buffer		rbuf;
	Page		rpage;
	BTPageOpaque ropaque;
	char	   *datapos;
	Size		datalen;
	BlockNumber origpagenumber;
	BlockNumber rightpagenumber;
	BlockNumber spagenumber;

	XLogRecGetBlockTag(record, 0, NULL, NULL, &origpagenumber);
	XLogRecGetBlockTag(record, 1, NULL, NULL, &rightpagenumber);
	if (!XLogRecGetBlockTag(record, 2, NULL, NULL, &spagenumber))
		spagenumber = P_NONE;

	/*
	 * Clear the incomplete split flag on the appropriate child page one level
	 * down when origpage/buf is an internal page (there must have been
	 * cascading page splits during original execution in the event of an
	 * internal page split).  This is like the corresponding btree_xlog_insert
	 * call for internal pages.  We're not clearing the incomplete split flag
	 * for the current page split here (you can think of this as part of the
	 * insert of newitem that the page split action needs to perform in
	 * passing).
	 *
	 * Like in btree_xlog_insert, this can be done before locking other pages.
	 * We never need to couple cross-level locks in REDO routines.
	 */
	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 = origpagenumber;
	ropaque->btpo_next = spagenumber;
	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 original page (left half of split) */
	if (XLogReadBufferForRedo(record, 0, &buf) == 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		origpage = (Page) BufferGetPage(buf);
		BTPageOpaque oopaque = (BTPageOpaque) PageGetSpecialPointer(origpage);
		OffsetNumber off;
		IndexTuple	newitem = NULL,
					left_hikey = NULL,
					nposting = NULL;
		Size		newitemsz = 0,
					left_hikeysz = 0;
		Page		leftpage;
		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(origpage, replacepostingoff);
				oposting = (IndexTuple) PageGetItem(origpage, 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);

		leftpage = PageGetTempPageCopySpecial(origpage);

		/* Add high key tuple from WAL record to temp page */
		leftoff = P_HIKEY;
		if (PageAddItem(leftpage, (Item) left_hikey, left_hikeysz, P_HIKEY,
						false, false) == InvalidOffsetNumber)
			elog(ERROR, "failed to add high key to left page after split");
		leftoff = OffsetNumberNext(leftoff);

		for (off = P_FIRSTDATAKEY(oopaque); 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(leftpage, (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(leftpage, (Item) newitem, newitemsz, leftoff,
								false, false) == InvalidOffsetNumber)
					elog(ERROR, "failed to add new item to left page after split");
				leftoff = OffsetNumberNext(leftoff);
			}

			itemid = PageGetItemId(origpage, off);
			itemsz = ItemIdGetLength(itemid);
			item = (IndexTuple) PageGetItem(origpage, itemid);
			if (PageAddItem(leftpage, (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(leftpage, (Item) newitem, newitemsz, leftoff,
							false, false) == InvalidOffsetNumber)
				elog(ERROR, "failed to add new item to left page after split");
			leftoff = OffsetNumberNext(leftoff);
		}

		PageRestoreTempPage(leftpage, origpage);

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

		PageSetLSN(origpage, lsn);
		MarkBufferDirty(buf);
	}

	/* Fix left-link of the page to the right of the new right sibling */
	if (spagenumber != P_NONE)
	{
		Buffer		sbuf;

		if (XLogReadBufferForRedo(record, 2, &sbuf) == BLK_NEEDS_REDO)
		{
			Page		spage = (Page) BufferGetPage(sbuf);
			BTPageOpaque spageop = (BTPageOpaque) PageGetSpecialPointer(spage);

			spageop->btpo_prev = rightpagenumber;

			PageSetLSN(spage, lsn);
			MarkBufferDirty(sbuf);
		}
		if (BufferIsValid(sbuf))
			UnlockReleaseBuffer(sbuf);
	}

	/*
	 * Finally, release the remaining buffers.  sbuf, rbuf, and buf must be
	 * released together, so that readers cannot observe inconsistencies.
	 */
	UnlockReleaseBuffer(rbuf);
	if (BufferIsValid(buf))
		UnlockReleaseBuffer(buf);
}

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_updates(Page page, OffsetNumber *updatedoffsets,
				   xl_btree_update *updates, int nupdated)
{
	BTVacuumPosting vacposting;
	IndexTuple	origtuple;
	ItemId		itemid;
	Size		itemsz;

	for (int i = 0; i < nupdated; i++)
	{
		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));
	}
}

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));

			btree_xlog_updates(page, updatedoffsets, updates, xlrec->nupdated);
		}

		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);

		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));

			btree_xlog_updates(page, updatedoffsets, updates, xlrec->nupdated);
		}

		if (xlrec->ndeleted > 0)
			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);
	}

	/*
	 * Don't need to couple cross-level locks in REDO routines, so release
	 * lock on internal page immediately
	 */
	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;
	uint32		level;
	bool		isleaf;
	FullTransactionId safexid;
	Buffer		leftbuf;
	Buffer		target;
	Buffer		rightbuf;
	Page		page;
	BTPageOpaque pageop;

	leftsib = xlrec->leftsib;
	rightsib = xlrec->rightsib;
	level = xlrec->level;
	isleaf = (level == 0);
	safexid = xlrec->safexid;

	/* No leaftopparent for level 0 (leaf page) or level 1 target */
	Assert(!BlockNumberIsValid(xlrec->leaftopparent) || level > 1);

	/*
	 * 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.
	 */

	/* 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_level = level;
	BTPageSetDeleted(page, safexid);
	if (isleaf)
		pageop->btpo_flags |= BTP_LEAF;
	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;

		Assert(!isleaf);

		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->leaftopparent);

		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);
}

/*
 * In general VACUUM must defer recycling as a way of avoiding certain race
 * conditions.  Deleted pages contain a safexid value that is used by VACUUM
 * to determine whether or not it's safe to place a page that was deleted by
 * VACUUM earlier into the FSM now.  See nbtree/README.
 *
 * As far as any backend operating during original execution is concerned, the
 * FSM is a cache of recycle-safe pages; the mere presence of the page in the
 * FSM indicates that the page must already be safe to recycle (actually,
 * _bt_getbuf() verifies it's safe using BTPageIsRecyclable(), but that's just
 * because it would be unwise to completely trust the FSM, given its current
 * limitations).
 *
 * This isn't sufficient to prevent similar concurrent recycling race
 * conditions during Hot Standby, though.  For that we need to log a
 * xl_btree_reuse_page record at the point that a page is actually recycled
 * and reused for an entirely unrelated page inside _bt_split().  These
 * records include the same safexid value from the original deleted page,
 * stored in the record's latestRemovedFullXid field.
 *
 * The GlobalVisCheckRemovableFullXid() test in BTPageIsRecyclable() is used
 * to determine if it's safe to recycle a page.  This mirrors our own test:
 * the PGPROC->xmin > limitXmin test inside GetConflictingVirtualXIDs().
 * Consequently, one XID value achieves the same exclusion effect on primary
 * and standby.
 */
static void
btree_xlog_reuse_page(XLogReaderState *record)
{
	xl_btree_reuse_page *xlrec = (xl_btree_reuse_page *) XLogRecGetData(record);

	if (InHotStandby)
		ResolveRecoveryConflictWithSnapshotFullXid(xlrec->latestRemovedFullXid,
												   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_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_delete_or_dedup_one_page(), _bt_killitems(), and _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;
}