postgres/src/backend/access/nbtree/nbtxlog.c

/*-------------------------------------------------------------------------
 *
 * nbtxlog.c
 *	  WAL replay logic for btrees.
 *
 *
 * Portions Copyright (c) 1996-2014, 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/heapam_xlog.h"
#include "access/nbtree.h"
#include "access/transam.h"
#include "storage/procarray.h"
#include "miscadmin.h"

/*
 * _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)
	{
		/* Need to copy tuple header due to alignment considerations */
		memcpy(&itupdata, from, sizeof(IndexTupleData));
		itemsz = IndexTupleDSize(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(RelFileNode rnode, XLogRecPtr lsn,
				 BlockNumber root, uint32 level,
				 BlockNumber fastroot, uint32 fastlevel)
{
	Buffer		metabuf;
	Page		metapg;
	BTMetaPageData *md;
	BTPageOpaque pageop;

	metabuf = XLogReadBuffer(rnode, BTREE_METAPAGE, true);
	Assert(BufferIsValid(metabuf));
	metapg = BufferGetPage(metabuf);

	_bt_pageinit(metapg, BufferGetPageSize(metabuf));

	md = BTPageGetMeta(metapg);
	md->btm_magic = BTREE_MAGIC;
	md->btm_version = BTREE_VERSION;
	md->btm_root = root;
	md->btm_level = level;
	md->btm_fastroot = fastroot;
	md->btm_fastlevel = fastlevel;

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

	/*
	 * Set pd_lower just past the end of the metadata.  This is not essential
	 * but it makes the page look compressible to xlog.c.
	 */
	((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(XLogRecPtr lsn, XLogRecord *record,
						   RelFileNode rnode, BlockNumber cblock)
{
	Buffer		buf;

	buf = XLogReadBuffer(rnode, cblock, false);
	if (BufferIsValid(buf))
	{
		Page		page = (Page) BufferGetPage(buf);

		if (lsn > PageGetLSN(page))
		{
			BTPageOpaque pageop = (BTPageOpaque) PageGetSpecialPointer(page);

			Assert((pageop->btpo_flags & BTP_INCOMPLETE_SPLIT) != 0);
			pageop->btpo_flags &= ~BTP_INCOMPLETE_SPLIT;

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

static void
btree_xlog_insert(bool isleaf, bool ismeta,
				  XLogRecPtr lsn, XLogRecord *record)
{
	xl_btree_insert *xlrec = (xl_btree_insert *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;
	char	   *datapos;
	int			datalen;
	xl_btree_metadata md;
	BlockNumber cblkno = 0;
	int			main_blk_index;

	datapos = (char *) xlrec + SizeOfBtreeInsert;
	datalen = record->xl_len - SizeOfBtreeInsert;

	/*
	 * if this insert finishes a split at lower level, extract the block
	 * number of the (left) child.
	 */
	if (!isleaf && (record->xl_info & XLR_BKP_BLOCK(0)) == 0)
	{
		memcpy(&cblkno, datapos, sizeof(BlockNumber));
		Assert(cblkno != 0);
		datapos += sizeof(BlockNumber);
		datalen -= sizeof(BlockNumber);
	}
	if (ismeta)
	{
		memcpy(&md, datapos, sizeof(xl_btree_metadata));
		datapos += sizeof(xl_btree_metadata);
		datalen -= sizeof(xl_btree_metadata);
	}

	/*
	 * 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)
	{
		if (record->xl_info & XLR_BKP_BLOCK(0))
			(void) RestoreBackupBlock(lsn, record, 0, false, false);
		else
			_bt_clear_incomplete_split(lsn, record, xlrec->target.node, cblkno);
		main_blk_index = 1;
	}
	else
		main_blk_index = 0;

	if (record->xl_info & XLR_BKP_BLOCK(main_blk_index))
		(void) RestoreBackupBlock(lsn, record, main_blk_index, false, false);
	else
	{
		buffer = XLogReadBuffer(xlrec->target.node,
							 ItemPointerGetBlockNumber(&(xlrec->target.tid)),
								false);
		if (BufferIsValid(buffer))
		{
			page = (Page) BufferGetPage(buffer);

			if (lsn > PageGetLSN(page))
			{
				if (PageAddItem(page, (Item) datapos, datalen,
							ItemPointerGetOffsetNumber(&(xlrec->target.tid)),
								false, false) == InvalidOffsetNumber)
					elog(PANIC, "btree_insert_redo: failed to add item");

				PageSetLSN(page, lsn);
				MarkBufferDirty(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(xlrec->target.node, lsn,
						 md.root, md.level,
						 md.fastroot, md.fastlevel);
}

static void
btree_xlog_split(bool onleft, bool isroot,
				 XLogRecPtr lsn, XLogRecord *record)
{
	xl_btree_split *xlrec = (xl_btree_split *) XLogRecGetData(record);
	bool		isleaf = (xlrec->level == 0);
	Buffer		lbuf;
	Buffer		rbuf;
	Page		rpage;
	BTPageOpaque ropaque;
	char	   *datapos;
	int			datalen;
	OffsetNumber newitemoff = 0;
	Item		newitem = NULL;
	Size		newitemsz = 0;
	Item		left_hikey = NULL;
	Size		left_hikeysz = 0;
	BlockNumber cblkno = InvalidBlockNumber;

	datapos = (char *) xlrec + SizeOfBtreeSplit;
	datalen = record->xl_len - SizeOfBtreeSplit;

	/* Extract newitemoff and newitem, if present */
	if (onleft)
	{
		memcpy(&newitemoff, datapos, sizeof(OffsetNumber));
		datapos += sizeof(OffsetNumber);
		datalen -= sizeof(OffsetNumber);
	}
	if (onleft && !(record->xl_info & XLR_BKP_BLOCK(0)))
	{
		/*
		 * We assume that 16-bit alignment is enough to apply IndexTupleSize
		 * (since it's fetching from a uint16 field) and also enough for
		 * PageAddItem to insert the tuple.
		 */
		newitem = (Item) datapos;
		newitemsz = MAXALIGN(IndexTupleSize(newitem));
		datapos += newitemsz;
		datalen -= newitemsz;
	}

	/* Extract left hikey and its size (still assuming 16-bit alignment) */
	if (!isleaf && !(record->xl_info & XLR_BKP_BLOCK(0)))
	{
		left_hikey = (Item) datapos;
		left_hikeysz = MAXALIGN(IndexTupleSize(left_hikey));
		datapos += left_hikeysz;
		datalen -= left_hikeysz;
	}

	/*
	 * If this insertion finishes an incomplete split, get the block number of
	 * the child.
	 */
	if (!isleaf && !(record->xl_info & XLR_BKP_BLOCK(1)))
	{
		memcpy(&cblkno, datapos, sizeof(BlockNumber));
		datapos += sizeof(BlockNumber);
		datalen -= sizeof(BlockNumber);
	}

	/*
	 * 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)
	{
		if (record->xl_info & XLR_BKP_BLOCK(2))
			(void) RestoreBackupBlock(lsn, record, 2, false, false);
		else
			_bt_clear_incomplete_split(lsn, record, xlrec->node, cblkno);
	}

	/* Reconstruct right (new) sibling page from scratch */
	rbuf = XLogReadBuffer(xlrec->node, xlrec->rightsib, true);
	Assert(BufferIsValid(rbuf));
	rpage = (Page) BufferGetPage(rbuf);

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

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

	_bt_restore_page(rpage, datapos, datalen);

	/*
	 * On leaf level, the high key of the left page is equal to the first key
	 * on the right page.
	 */
	if (isleaf)
	{
		ItemId		hiItemId = PageGetItemId(rpage, P_FIRSTDATAKEY(ropaque));

		left_hikey = PageGetItem(rpage, hiItemId);
		left_hikeysz = ItemIdGetLength(hiItemId);
	}

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

	/* don't release the buffer yet; we touch right page's first item below */

	/* Now reconstruct left (original) sibling page */
	if (record->xl_info & XLR_BKP_BLOCK(0))
		lbuf = RestoreBackupBlock(lsn, record, 0, false, true);
	else
	{
		lbuf = XLogReadBuffer(xlrec->node, xlrec->leftsib, false);

		if (BufferIsValid(lbuf))
		{
			/*
			 * 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.  It's not strictly required to retain the
			 * same physical order, as long as the items are in the correct
			 * item number order, but it helps debugging.  See also
			 * _bt_restore_page(), which does the same for the right page.
			 */
			Page		lpage = (Page) BufferGetPage(lbuf);
			BTPageOpaque lopaque = (BTPageOpaque) PageGetSpecialPointer(lpage);

			if (lsn > PageGetLSN(lpage))
			{
				OffsetNumber off;
				Page		newlpage;
				OffsetNumber leftoff;

				newlpage = PageGetTempPageCopySpecial(lpage);

				/* Set high key */
				leftoff = P_HIKEY;
				if (PageAddItem(newlpage, 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->firstright; off++)
				{
					ItemId		itemid;
					Size		itemsz;
					Item		item;

					/* add the new item if it was inserted on left page */
					if (onleft && off == newitemoff)
					{
						if (PageAddItem(newlpage, 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 = PageGetItem(lpage, itemid);
					if (PageAddItem(newlpage, 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 (onleft && off == newitemoff)
				{
					if (PageAddItem(newlpage, 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 = xlrec->rightsib;
				lopaque->btpo_cycleid = 0;

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

	/* We no longer need the buffers */
	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 (xlrec->rnext != P_NONE)
	{
		/*
		 * the backup block containing right sibling is 2 or 3, depending
		 * whether this was a leaf or internal page.
		 */
		int			rnext_index = isleaf ? 2 : 3;

		if (record->xl_info & XLR_BKP_BLOCK(rnext_index))
			(void) RestoreBackupBlock(lsn, record, rnext_index, false, false);
		else
		{
			Buffer		buffer;

			buffer = XLogReadBuffer(xlrec->node, xlrec->rnext, false);

			if (BufferIsValid(buffer))
			{
				Page		page = (Page) BufferGetPage(buffer);

				if (lsn > PageGetLSN(page))
				{
					BTPageOpaque pageop = (BTPageOpaque) PageGetSpecialPointer(page);

					pageop->btpo_prev = xlrec->rightsib;

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

static void
btree_xlog_vacuum(XLogRecPtr lsn, XLogRecord *record)
{
	xl_btree_vacuum *xlrec = (xl_btree_vacuum *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;
	BTPageOpaque opaque;

	/*
	 * If queries might be active then we need to ensure every leaf page is
	 * unpinned between the lastBlockVacuumed and the current block, if there
	 * are any.  This prevents replay of the VACUUM from reaching the stage of
	 * removing heap tuples while there could still be indexscans "in flight"
	 * to those particular tuples (see nbtree/README).
	 *
	 * It might be worth checking if there are actually any backends running;
	 * if not, we could just skip this.
	 *
	 * Since VACUUM can visit leaf pages out-of-order, it might issue records
	 * with lastBlockVacuumed >= block; that's not an error, it just means
	 * nothing to do now.
	 *
	 * Note: since we touch all pages in the range, we will lock non-leaf
	 * pages, and also any empty (all-zero) pages that may be in the index. It
	 * doesn't seem worth the complexity to avoid that.  But it's important
	 * that HotStandbyActiveInReplay() will not return true if the database
	 * isn't yet consistent; so we need not fear reading still-corrupt blocks
	 * here during crash recovery.
	 */
	if (HotStandbyActiveInReplay())
	{
		BlockNumber blkno;

		for (blkno = xlrec->lastBlockVacuumed + 1; blkno < xlrec->block; blkno++)
		{
			/*
			 * We use RBM_NORMAL_NO_LOG mode because it's not an error
			 * condition to see all-zero pages.  The original btvacuumpage
			 * scan would have skipped over all-zero pages, noting them in FSM
			 * but not bothering to initialize them just yet; so we mustn't
			 * throw an error here.  (We could skip acquiring the cleanup lock
			 * if PageIsNew, but it's probably not worth the cycles to test.)
			 *
			 * XXX we don't actually need to read the block, we just need to
			 * confirm it is unpinned. If we had a special call into the
			 * buffer manager we could optimise this so that if the block is
			 * not in shared_buffers we confirm it as unpinned.
			 */
			buffer = XLogReadBufferExtended(xlrec->node, MAIN_FORKNUM, blkno,
											RBM_NORMAL_NO_LOG);
			if (BufferIsValid(buffer))
			{
				LockBufferForCleanup(buffer);
				UnlockReleaseBuffer(buffer);
			}
		}
	}

	/*
	 * If we have a full-page image, restore it (using a cleanup lock) and
	 * we're done.
	 */
	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		(void) RestoreBackupBlock(lsn, record, 0, true, false);
		return;
	}

	/*
	 * Like in btvacuumpage(), we need to take a cleanup lock on every leaf
	 * page. See nbtree/README for details.
	 */
	buffer = XLogReadBufferExtended(xlrec->node, MAIN_FORKNUM, xlrec->block, RBM_NORMAL);
	if (!BufferIsValid(buffer))
		return;
	LockBufferForCleanup(buffer);
	page = (Page) BufferGetPage(buffer);

	if (lsn <= PageGetLSN(page))
	{
		UnlockReleaseBuffer(buffer);
		return;
	}

	if (record->xl_len > SizeOfBtreeVacuum)
	{
		OffsetNumber *unused;
		OffsetNumber *unend;

		unused = (OffsetNumber *) ((char *) xlrec + SizeOfBtreeVacuum);
		unend = (OffsetNumber *) ((char *) xlrec + record->xl_len);

		if ((unend - unused) > 0)
			PageIndexMultiDelete(page, unused, unend - unused);
	}

	/*
	 * 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);
	UnlockReleaseBuffer(buffer);
}

/*
 * Get the latestRemovedXid from the heap pages pointed at by the index
 * tuples being deleted. This puts the work for calculating latestRemovedXid
 * into the recovery path rather than the primary path.
 *
 * It's possible that this generates a fair amount of I/O, since an index
 * block may have hundreds of tuples being deleted. Repeat accesses to the
 * same heap blocks are common, though are not yet optimised.
 *
 * XXX optimise later with something like XLogPrefetchBuffer()
 */
static TransactionId
btree_xlog_delete_get_latestRemovedXid(xl_btree_delete *xlrec)
{
	OffsetNumber *unused;
	Buffer		ibuffer,
				hbuffer;
	Page		ipage,
				hpage;
	ItemId		iitemid,
				hitemid;
	IndexTuple	itup;
	HeapTupleHeader htuphdr;
	BlockNumber hblkno;
	OffsetNumber hoffnum;
	TransactionId latestRemovedXid = InvalidTransactionId;
	int			i;

	/*
	 * If there's nothing running on the standby we don't need to derive a
	 * full latestRemovedXid value, so use a fast path out of here.  This
	 * returns InvalidTransactionId, and so will conflict with all HS
	 * transactions; but since we just worked out that that's zero people,
	 * it's OK.
	 *
	 * XXX There is a race condition here, which is that a new backend might
	 * start just after we look.  If so, it cannot need to conflict, but this
	 * coding will result in throwing a conflict anyway.
	 */
	if (CountDBBackends(InvalidOid) == 0)
		return latestRemovedXid;

	/*
	 * In what follows, we have to examine the previous state of the index
	 * page, as well as the heap page(s) it points to.  This is only valid if
	 * WAL replay has reached a consistent database state; which means that
	 * the preceding check is not just an optimization, but is *necessary*. We
	 * won't have let in any user sessions before we reach consistency.
	 */
	if (!reachedConsistency)
		elog(PANIC, "btree_xlog_delete_get_latestRemovedXid: cannot operate with inconsistent data");

	/*
	 * Get index page.  If the DB is consistent, this should not fail, nor
	 * should any of the heap page fetches below.  If one does, we return
	 * InvalidTransactionId to cancel all HS transactions.  That's probably
	 * overkill, but it's safe, and certainly better than panicking here.
	 */
	ibuffer = XLogReadBuffer(xlrec->node, xlrec->block, false);
	if (!BufferIsValid(ibuffer))
		return InvalidTransactionId;
	ipage = (Page) BufferGetPage(ibuffer);

	/*
	 * Loop through the deleted index items to obtain the TransactionId from
	 * the heap items they point to.
	 */
	unused = (OffsetNumber *) ((char *) xlrec + SizeOfBtreeDelete);

	for (i = 0; i < xlrec->nitems; i++)
	{
		/*
		 * Identify the index tuple about to be deleted
		 */
		iitemid = PageGetItemId(ipage, unused[i]);
		itup = (IndexTuple) PageGetItem(ipage, iitemid);

		/*
		 * Locate the heap page that the index tuple points at
		 */
		hblkno = ItemPointerGetBlockNumber(&(itup->t_tid));
		hbuffer = XLogReadBuffer(xlrec->hnode, hblkno, false);
		if (!BufferIsValid(hbuffer))
		{
			UnlockReleaseBuffer(ibuffer);
			return InvalidTransactionId;
		}
		hpage = (Page) BufferGetPage(hbuffer);

		/*
		 * Look up the heap tuple header that the index tuple points at by
		 * using the heap node supplied with the xlrec. We can't use
		 * heap_fetch, since it uses ReadBuffer rather than XLogReadBuffer.
		 * Note that we are not looking at tuple data here, just headers.
		 */
		hoffnum = ItemPointerGetOffsetNumber(&(itup->t_tid));
		hitemid = PageGetItemId(hpage, hoffnum);

		/*
		 * Follow any redirections until we find something useful.
		 */
		while (ItemIdIsRedirected(hitemid))
		{
			hoffnum = ItemIdGetRedirect(hitemid);
			hitemid = PageGetItemId(hpage, hoffnum);
			CHECK_FOR_INTERRUPTS();
		}

		/*
		 * If the heap item has storage, then read the header and use that to
		 * set latestRemovedXid.
		 *
		 * Some LP_DEAD items may not be accessible, so we ignore them.
		 */
		if (ItemIdHasStorage(hitemid))
		{
			htuphdr = (HeapTupleHeader) PageGetItem(hpage, hitemid);

			HeapTupleHeaderAdvanceLatestRemovedXid(htuphdr, &latestRemovedXid);
		}
		else if (ItemIdIsDead(hitemid))
		{
			/*
			 * Conjecture: if hitemid is dead then it had xids before the xids
			 * marked on LP_NORMAL items. So we just ignore this item and move
			 * onto the next, for the purposes of calculating
			 * latestRemovedxids.
			 */
		}
		else
			Assert(!ItemIdIsUsed(hitemid));

		UnlockReleaseBuffer(hbuffer);
	}

	UnlockReleaseBuffer(ibuffer);

	/*
	 * If all heap tuples were LP_DEAD then we will be returning
	 * InvalidTransactionId here, which avoids conflicts. This matches
	 * existing logic which assumes that LP_DEAD tuples must already be older
	 * than the latestRemovedXid on the cleanup record that set them as
	 * LP_DEAD, hence must already have generated a conflict.
	 */
	return latestRemovedXid;
}

static void
btree_xlog_delete(XLogRecPtr lsn, XLogRecord *record)
{
	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.
	 *
	 * Btree delete records can conflict with standby queries.  You might
	 * think that vacuum records would conflict as well, but we've handled
	 * that already.  XLOG_HEAP2_CLEANUP_INFO records provide the highest xid
	 * cleaned by the vacuum of the heap and so we can resolve any conflicts
	 * just once when that arrives.  After that we know that no conflicts
	 * exist from individual btree vacuum records on that index.
	 */
	if (InHotStandby)
	{
		TransactionId latestRemovedXid = btree_xlog_delete_get_latestRemovedXid(xlrec);

		ResolveRecoveryConflictWithSnapshot(latestRemovedXid, xlrec->node);
	}

	/* If we have a full-page image, restore it and we're done */
	if (record->xl_info & XLR_BKP_BLOCK(0))
	{
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
		return;
	}

	/*
	 * We don't need to take a cleanup lock to apply these changes. See
	 * nbtree/README for details.
	 */
	buffer = XLogReadBuffer(xlrec->node, xlrec->block, false);
	if (!BufferIsValid(buffer))
		return;
	page = (Page) BufferGetPage(buffer);

	if (lsn <= PageGetLSN(page))
	{
		UnlockReleaseBuffer(buffer);
		return;
	}

	if (record->xl_len > SizeOfBtreeDelete)
	{
		OffsetNumber *unused;

		unused = (OffsetNumber *) ((char *) xlrec + SizeOfBtreeDelete);

		PageIndexMultiDelete(page, unused, xlrec->nitems);
	}

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

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

static void
btree_xlog_mark_page_halfdead(uint8 info, XLogRecPtr lsn, XLogRecord *record)
{
	xl_btree_mark_page_halfdead *xlrec = (xl_btree_mark_page_halfdead *) XLogRecGetData(record);
	BlockNumber parent;
	Buffer		buffer;
	Page		page;
	BTPageOpaque pageop;
	IndexTupleData trunctuple;

	parent = ItemPointerGetBlockNumber(&(xlrec->target.tid));

	/*
	 * 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).
	 */

	/* parent page */
	if (record->xl_info & XLR_BKP_BLOCK(0))
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
	else
	{
		buffer = XLogReadBuffer(xlrec->target.node, parent, false);
		if (BufferIsValid(buffer))
		{
			page = (Page) BufferGetPage(buffer);
			pageop = (BTPageOpaque) PageGetSpecialPointer(page);
			if (lsn > PageGetLSN(page))
			{
				OffsetNumber poffset;
				ItemId		itemid;
				IndexTuple	itup;
				OffsetNumber nextoffset;
				BlockNumber rightsib;

				poffset = ItemPointerGetOffsetNumber(&(xlrec->target.tid));

				nextoffset = OffsetNumberNext(poffset);
				itemid = PageGetItemId(page, nextoffset);
				itup = (IndexTuple) PageGetItem(page, itemid);
				rightsib = ItemPointerGetBlockNumber(&itup->t_tid);

				itemid = PageGetItemId(page, poffset);
				itup = (IndexTuple) PageGetItem(page, itemid);
				ItemPointerSet(&(itup->t_tid), rightsib, P_HIKEY);
				nextoffset = OffsetNumberNext(poffset);
				PageIndexTupleDelete(page, nextoffset);

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

	/* Rewrite the leaf page as a halfdead page */
	buffer = XLogReadBuffer(xlrec->target.node, xlrec->leafblk, true);
	Assert(BufferIsValid(buffer));
	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 hikey item that points to the next parent to be
	 * deleted (if any).
	 */
	MemSet(&trunctuple, 0, sizeof(IndexTupleData));
	trunctuple.t_info = sizeof(IndexTupleData);
	if (xlrec->topparent != InvalidBlockNumber)
		ItemPointerSet(&trunctuple.t_tid, xlrec->topparent, P_HIKEY);
	else
		ItemPointerSetInvalid(&trunctuple.t_tid);
	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, XLogRecPtr lsn, XLogRecord *record)
{
	xl_btree_unlink_page *xlrec = (xl_btree_unlink_page *) XLogRecGetData(record);
	BlockNumber target;
	BlockNumber leftsib;
	BlockNumber rightsib;
	Buffer		buffer;
	Page		page;
	BTPageOpaque pageop;

	target = xlrec->deadblk;
	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, 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).
	 */

	/* Fix left-link of right sibling */
	if (record->xl_info & XLR_BKP_BLOCK(0))
		(void) RestoreBackupBlock(lsn, record, 0, false, false);
	else
	{
		buffer = XLogReadBuffer(xlrec->node, rightsib, false);
		if (BufferIsValid(buffer))
		{
			page = (Page) BufferGetPage(buffer);
			if (lsn <= PageGetLSN(page))
			{
				UnlockReleaseBuffer(buffer);
			}
			else
			{
				pageop = (BTPageOpaque) PageGetSpecialPointer(page);
				pageop->btpo_prev = leftsib;

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

	/* Fix right-link of left sibling, if any */
	if (record->xl_info & XLR_BKP_BLOCK(1))
		(void) RestoreBackupBlock(lsn, record, 1, false, false);
	else
	{
		if (leftsib != P_NONE)
		{
			buffer = XLogReadBuffer(xlrec->node, leftsib, false);
			if (BufferIsValid(buffer))
			{
				page = (Page) BufferGetPage(buffer);
				if (lsn <= PageGetLSN(page))
				{
					UnlockReleaseBuffer(buffer);
				}
				else
				{
					pageop = (BTPageOpaque) PageGetSpecialPointer(page);
					pageop->btpo_next = rightsib;

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

	/* Rewrite target page as empty deleted page */
	buffer = XLogReadBuffer(xlrec->node, target, true);
	Assert(BufferIsValid(buffer));
	page = (Page) BufferGetPage(buffer);

	_bt_pageinit(page, BufferGetPageSize(buffer));
	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(buffer);
	UnlockReleaseBuffer(buffer);

	/*
	 * 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
	 * branch.
	 */
	if (target != xlrec->leafblk)
	{
		/*
		 * There is no real data on the page, so we just re-create it from
		 * scratch using the information from the WAL record.
		 */
		IndexTupleData trunctuple;

		buffer = XLogReadBuffer(xlrec->node, xlrec->leafblk, true);
		Assert(BufferIsValid(buffer));
		page = (Page) BufferGetPage(buffer);
		pageop = (BTPageOpaque) PageGetSpecialPointer(page);

		_bt_pageinit(page, BufferGetPageSize(buffer));
		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);
		if (xlrec->topparent != InvalidBlockNumber)
			ItemPointerSet(&trunctuple.t_tid, xlrec->topparent, P_HIKEY);
		else
			ItemPointerSetInvalid(&trunctuple.t_tid);
		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);
	}

	/* Update metapage if needed */
	if (info == XLOG_BTREE_UNLINK_PAGE_META)
	{
		xl_btree_metadata md;

		memcpy(&md, (char *) xlrec + SizeOfBtreeUnlinkPage,
			   sizeof(xl_btree_metadata));
		_bt_restore_meta(xlrec->node, lsn,
						 md.root, md.level,
						 md.fastroot, md.fastlevel);
	}
}

static void
btree_xlog_newroot(XLogRecPtr lsn, XLogRecord *record)
{
	xl_btree_newroot *xlrec = (xl_btree_newroot *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;
	BTPageOpaque pageop;

	buffer = XLogReadBuffer(xlrec->node, xlrec->rootblk, true);
	Assert(BufferIsValid(buffer));
	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 (record->xl_len > SizeOfBtreeNewroot)
	{
		IndexTuple	itup;
		BlockNumber cblkno;

		_bt_restore_page(page,
						 (char *) xlrec + SizeOfBtreeNewroot,
						 record->xl_len - SizeOfBtreeNewroot);
		/* extract block number of the left-hand split page */
		itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, P_HIKEY));
		cblkno = ItemPointerGetBlockNumber(&(itup->t_tid));
		Assert(ItemPointerGetOffsetNumber(&(itup->t_tid)) == P_HIKEY);

		/* Clear the incomplete-split flag in left child */
		if (record->xl_info & XLR_BKP_BLOCK(0))
			(void) RestoreBackupBlock(lsn, record, 0, false, false);
		else
			_bt_clear_incomplete_split(lsn, record, xlrec->node, cblkno);
	}

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

	_bt_restore_meta(xlrec->node, lsn,
					 xlrec->rootblk, xlrec->level,
					 xlrec->rootblk, xlrec->level);
}

static void
btree_xlog_reuse_page(XLogRecPtr lsn, XLogRecord *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
	 * master and standby.
	 */
	if (InHotStandby)
	{
		ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid,
											xlrec->node);
	}

	/* Backup blocks are not used in reuse_page records */
	Assert(!(record->xl_info & XLR_BKP_BLOCK_MASK));
}


void
btree_redo(XLogRecPtr lsn, XLogRecord *record)
{
	uint8		info = record->xl_info & ~XLR_INFO_MASK;

	switch (info)
	{
		case XLOG_BTREE_INSERT_LEAF:
			btree_xlog_insert(true, false, lsn, record);
			break;
		case XLOG_BTREE_INSERT_UPPER:
			btree_xlog_insert(false, false, lsn, record);
			break;
		case XLOG_BTREE_INSERT_META:
			btree_xlog_insert(false, true, lsn, record);
			break;
		case XLOG_BTREE_SPLIT_L:
			btree_xlog_split(true, false, lsn, record);
			break;
		case XLOG_BTREE_SPLIT_R:
			btree_xlog_split(false, false, lsn, record);
			break;
		case XLOG_BTREE_SPLIT_L_ROOT:
			btree_xlog_split(true, true, lsn, record);
			break;
		case XLOG_BTREE_SPLIT_R_ROOT:
			btree_xlog_split(false, true, lsn, record);
			break;
		case XLOG_BTREE_VACUUM:
			btree_xlog_vacuum(lsn, record);
			break;
		case XLOG_BTREE_DELETE:
			btree_xlog_delete(lsn, record);
			break;
		case XLOG_BTREE_MARK_PAGE_HALFDEAD:
			btree_xlog_mark_page_halfdead(info, lsn, record);
			break;
		case XLOG_BTREE_UNLINK_PAGE:
		case XLOG_BTREE_UNLINK_PAGE_META:
			btree_xlog_unlink_page(info, lsn, record);
			break;
		case XLOG_BTREE_NEWROOT:
			btree_xlog_newroot(lsn, record);
			break;
		case XLOG_BTREE_REUSE_PAGE:
			btree_xlog_reuse_page(lsn, record);
			break;
		default:
			elog(PANIC, "btree_redo: unknown op code %u", info);
	}
}