示例#1
0
文件: brin_xlog.c 项目: Brar/postgres
/*
 * Update a tuple on a single page.
 */
static void
brin_xlog_samepage_update(XLogReaderState *record)
{
	XLogRecPtr	lsn = record->EndRecPtr;
	xl_brin_samepage_update *xlrec;
	Buffer		buffer;
	XLogRedoAction action;

	xlrec = (xl_brin_samepage_update *) XLogRecGetData(record);
	action = XLogReadBufferForRedo(record, 0, &buffer);
	if (action == BLK_NEEDS_REDO)
	{
		Size		tuplen;
		BrinTuple  *brintuple;
		Page		page;
		OffsetNumber offnum;

		brintuple = (BrinTuple *) XLogRecGetBlockData(record, 0, &tuplen);

		page = (Page) BufferGetPage(buffer);

		offnum = xlrec->offnum;

		if (!PageIndexTupleOverwrite(page, offnum, (Item) brintuple, tuplen))
			elog(PANIC, "brin_xlog_samepage_update: failed to replace tuple");

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

	/* XXX no FSM updates here ... */
}
示例#2
0
/*
 * redo any page update (except page split)
 */
static void
gistRedoPageUpdateRecord(XLogReaderState *record)
{
	XLogRecPtr	lsn = record->EndRecPtr;
	gistxlogPageUpdate *xldata = (gistxlogPageUpdate *) XLogRecGetData(record);
	Buffer		buffer;
	Page		page;

	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
	{
		char	   *begin;
		char	   *data;
		Size		datalen;
		int			ninserted = 0;

		data = begin = XLogRecGetBlockData(record, 0, &datalen);

		page = (Page) BufferGetPage(buffer);

		if (xldata->ntodelete == 1 && xldata->ntoinsert == 1)
		{
			/*
			 * When replacing one tuple with one other tuple, we must use
			 * PageIndexTupleOverwrite for consistency with gistplacetopage.
			 */
			OffsetNumber offnum = *((OffsetNumber *) data);
			IndexTuple	itup;
			Size		itupsize;

			data += sizeof(OffsetNumber);
			itup = (IndexTuple) data;
			itupsize = IndexTupleSize(itup);
			if (!PageIndexTupleOverwrite(page, offnum, (Item) itup, itupsize))
				elog(ERROR, "failed to add item to GiST index page, size %d bytes",
					 (int) itupsize);
			data += itupsize;
			/* should be nothing left after consuming 1 tuple */
			Assert(data - begin == datalen);
			/* update insertion count for assert check below */
			ninserted++;
		}
		else if (xldata->ntodelete > 0)
		{
			/* Otherwise, delete old tuples if any */
			OffsetNumber *todelete = (OffsetNumber *) data;

			data += sizeof(OffsetNumber) * xldata->ntodelete;

			PageIndexMultiDelete(page, todelete, xldata->ntodelete);
			if (GistPageIsLeaf(page))
				GistMarkTuplesDeleted(page);
		}

		/* Add new tuples if any */
		if (data - begin < datalen)
		{
			OffsetNumber off = (PageIsEmpty(page)) ? FirstOffsetNumber :
			OffsetNumberNext(PageGetMaxOffsetNumber(page));

			while (data - begin < datalen)
			{
				IndexTuple	itup = (IndexTuple) data;
				Size		sz = IndexTupleSize(itup);
				OffsetNumber l;

				data += sz;

				l = PageAddItem(page, (Item) itup, sz, off, false, false);
				if (l == InvalidOffsetNumber)
					elog(ERROR, "failed to add item to GiST index page, size %d bytes",
						 (int) sz);
				off++;
				ninserted++;
			}
		}

		/* Check that XLOG record contained expected number of tuples */
		Assert(ninserted == xldata->ntoinsert);

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

	/*
	 * Fix follow-right data on left child page
	 *
	 * This must be done while still holding the lock on the target page. Note
	 * that even if the target page no longer exists, we still attempt to
	 * replay the change on the child page.
	 */
	if (XLogRecHasBlockRef(record, 1))
		gistRedoClearFollowRight(record, 1);

	if (BufferIsValid(buffer))
		UnlockReleaseBuffer(buffer);
}
示例#3
0
/*
 * Update tuple origtup (size origsz), located in offset oldoff of buffer
 * oldbuf, to newtup (size newsz) as summary tuple for the page range starting
 * at heapBlk.  oldbuf must not be locked on entry, and is not locked at exit.
 *
 * If samepage is true, attempt to put the new tuple in the same page, but if
 * there's no room, use some other one.
 *
 * If the update is successful, return true; the revmap is updated to point to
 * the new tuple.  If the update is not done for whatever reason, return false.
 * Caller may retry the update if this happens.
 */
bool
brin_doupdate(Relation idxrel, BlockNumber pagesPerRange,
			  BrinRevmap *revmap, BlockNumber heapBlk,
			  Buffer oldbuf, OffsetNumber oldoff,
			  const BrinTuple *origtup, Size origsz,
			  const BrinTuple *newtup, Size newsz,
			  bool samepage)
{
	Page		oldpage;
	ItemId		oldlp;
	BrinTuple  *oldtup;
	Size		oldsz;
	Buffer		newbuf;
	bool		extended;

	Assert(newsz == MAXALIGN(newsz));

	/* If the item is oversized, don't bother. */
	if (newsz > BrinMaxItemSize)
	{
		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
			errmsg("index row size %lu exceeds maximum %lu for index \"%s\"",
				   (unsigned long) newsz,
				   (unsigned long) BrinMaxItemSize,
				   RelationGetRelationName(idxrel))));
		return false;			/* keep compiler quiet */
	}

	/* make sure the revmap is long enough to contain the entry we need */
	brinRevmapExtend(revmap, heapBlk);

	if (!samepage)
	{
		/* need a page on which to put the item */
		newbuf = brin_getinsertbuffer(idxrel, oldbuf, newsz, &extended);
		if (!BufferIsValid(newbuf))
		{
			Assert(!extended);
			return false;
		}

		/*
		 * Note: it's possible (though unlikely) that the returned newbuf is
		 * the same as oldbuf, if brin_getinsertbuffer determined that the old
		 * buffer does in fact have enough space.
		 */
		if (newbuf == oldbuf)
		{
			Assert(!extended);
			newbuf = InvalidBuffer;
		}
	}
	else
	{
		LockBuffer(oldbuf, BUFFER_LOCK_EXCLUSIVE);
		newbuf = InvalidBuffer;
		extended = false;
	}
	oldpage = BufferGetPage(oldbuf);
	oldlp = PageGetItemId(oldpage, oldoff);

	/*
	 * Check that the old tuple wasn't updated concurrently: it might have
	 * moved someplace else entirely ...
	 */
	if (!ItemIdIsNormal(oldlp))
	{
		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);

		/*
		 * If this happens, and the new buffer was obtained by extending the
		 * relation, then we need to ensure we don't leave it uninitialized or
		 * forget about it.
		 */
		if (BufferIsValid(newbuf))
		{
			if (extended)
				brin_initialize_empty_new_buffer(idxrel, newbuf);
			UnlockReleaseBuffer(newbuf);
			if (extended)
				FreeSpaceMapVacuum(idxrel);
		}
		return false;
	}

	oldsz = ItemIdGetLength(oldlp);
	oldtup = (BrinTuple *) PageGetItem(oldpage, oldlp);

	/*
	 * ... or it might have been updated in place to different contents.
	 */
	if (!brin_tuples_equal(oldtup, oldsz, origtup, origsz))
	{
		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
		if (BufferIsValid(newbuf))
		{
			if (extended)
				brin_initialize_empty_new_buffer(idxrel, newbuf);
			UnlockReleaseBuffer(newbuf);
			if (extended)
				FreeSpaceMapVacuum(idxrel);
		}
		return false;
	}

	/*
	 * Great, the old tuple is intact.  We can proceed with the update.
	 *
	 * If there's enough room in the old page for the new tuple, replace it.
	 *
	 * Note that there might now be enough space on the page even though the
	 * caller told us there isn't, if a concurrent update moved another tuple
	 * elsewhere or replaced a tuple with a smaller one.
	 */
	if (((BrinPageFlags(oldpage) & BRIN_EVACUATE_PAGE) == 0) &&
		brin_can_do_samepage_update(oldbuf, origsz, newsz))
	{
		if (BufferIsValid(newbuf))
		{
			/* as above */
			if (extended)
				brin_initialize_empty_new_buffer(idxrel, newbuf);
			UnlockReleaseBuffer(newbuf);
		}

		START_CRIT_SECTION();
		if (!PageIndexTupleOverwrite(oldpage, oldoff, (Item) newtup, newsz))
			elog(ERROR, "failed to replace BRIN tuple");
		MarkBufferDirty(oldbuf);

		/* XLOG stuff */
		if (RelationNeedsWAL(idxrel))
		{
			xl_brin_samepage_update xlrec;
			XLogRecPtr	recptr;
			uint8		info = XLOG_BRIN_SAMEPAGE_UPDATE;

			xlrec.offnum = oldoff;

			XLogBeginInsert();
			XLogRegisterData((char *) &xlrec, SizeOfBrinSamepageUpdate);

			XLogRegisterBuffer(0, oldbuf, REGBUF_STANDARD);
			XLogRegisterBufData(0, (char *) newtup, newsz);

			recptr = XLogInsert(RM_BRIN_ID, info);

			PageSetLSN(oldpage, recptr);
		}

		END_CRIT_SECTION();

		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);

		if (extended)
			FreeSpaceMapVacuum(idxrel);

		return true;
	}
	else if (newbuf == InvalidBuffer)
	{
		/*
		 * Not enough space, but caller said that there was. Tell them to
		 * start over.
		 */
		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
		return false;
	}
	else
	{
		/*
		 * Not enough free space on the oldpage. Put the new tuple on the new
		 * page, and update the revmap.
		 */
		Page		newpage = BufferGetPage(newbuf);
		Buffer		revmapbuf;
		ItemPointerData newtid;
		OffsetNumber newoff;
		BlockNumber newblk = InvalidBlockNumber;
		Size		freespace = 0;

		revmapbuf = brinLockRevmapPageForUpdate(revmap, heapBlk);

		START_CRIT_SECTION();

		/*
		 * We need to initialize the page if it's newly obtained.  Note we
		 * will WAL-log the initialization as part of the update, so we don't
		 * need to do that here.
		 */
		if (extended)
			brin_page_init(BufferGetPage(newbuf), BRIN_PAGETYPE_REGULAR);

		PageIndexTupleDeleteNoCompact(oldpage, oldoff);
		newoff = PageAddItem(newpage, (Item) newtup, newsz,
							 InvalidOffsetNumber, false, false);
		if (newoff == InvalidOffsetNumber)
			elog(ERROR, "failed to add BRIN tuple to new page");
		MarkBufferDirty(oldbuf);
		MarkBufferDirty(newbuf);

		/* needed to update FSM below */
		if (extended)
		{
			newblk = BufferGetBlockNumber(newbuf);
			freespace = br_page_get_freespace(newpage);
		}

		ItemPointerSet(&newtid, BufferGetBlockNumber(newbuf), newoff);
		brinSetHeapBlockItemptr(revmapbuf, pagesPerRange, heapBlk, newtid);
		MarkBufferDirty(revmapbuf);

		/* XLOG stuff */
		if (RelationNeedsWAL(idxrel))
		{
			xl_brin_update xlrec;
			XLogRecPtr	recptr;
			uint8		info;

			info = XLOG_BRIN_UPDATE | (extended ? XLOG_BRIN_INIT_PAGE : 0);

			xlrec.insert.offnum = newoff;
			xlrec.insert.heapBlk = heapBlk;
			xlrec.insert.pagesPerRange = pagesPerRange;
			xlrec.oldOffnum = oldoff;

			XLogBeginInsert();

			/* new page */
			XLogRegisterData((char *) &xlrec, SizeOfBrinUpdate);

			XLogRegisterBuffer(0, newbuf, REGBUF_STANDARD | (extended ? REGBUF_WILL_INIT : 0));
			XLogRegisterBufData(0, (char *) newtup, newsz);

			/* revmap page */
			XLogRegisterBuffer(1, revmapbuf, 0);

			/* old page */
			XLogRegisterBuffer(2, oldbuf, REGBUF_STANDARD);

			recptr = XLogInsert(RM_BRIN_ID, info);

			PageSetLSN(oldpage, recptr);
			PageSetLSN(newpage, recptr);
			PageSetLSN(BufferGetPage(revmapbuf), recptr);
		}

		END_CRIT_SECTION();

		LockBuffer(revmapbuf, BUFFER_LOCK_UNLOCK);
		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
		UnlockReleaseBuffer(newbuf);

		if (extended)
		{
			Assert(BlockNumberIsValid(newblk));
			RecordPageWithFreeSpace(idxrel, newblk, freespace);
			FreeSpaceMapVacuum(idxrel);
		}

		return true;
	}
}
示例#4
0
文件: gist.c 项目: Tao-Ma/postgres
/*
 * Place tuples from 'itup' to 'buffer'. If 'oldoffnum' is valid, the tuple
 * at that offset is atomically removed along with inserting the new tuples.
 * This is used to replace a tuple with a new one.
 *
 * If 'leftchildbuf' is valid, we're inserting the downlink for the page
 * to the right of 'leftchildbuf', or updating the downlink for 'leftchildbuf'.
 * F_FOLLOW_RIGHT flag on 'leftchildbuf' is cleared and NSN is set.
 *
 * If 'markfollowright' is true and the page is split, the left child is
 * marked with F_FOLLOW_RIGHT flag. That is the normal case. During buffered
 * index build, however, there is no concurrent access and the page splitting
 * is done in a slightly simpler fashion, and false is passed.
 *
 * If there is not enough room on the page, it is split. All the split
 * pages are kept pinned and locked and returned in *splitinfo, the caller
 * is responsible for inserting the downlinks for them. However, if
 * 'buffer' is the root page and it needs to be split, gistplacetopage()
 * performs the split as one atomic operation, and *splitinfo is set to NIL.
 * In that case, we continue to hold the root page locked, and the child
 * pages are released; note that new tuple(s) are *not* on the root page
 * but in one of the new child pages.
 *
 * If 'newblkno' is not NULL, returns the block number of page the first
 * new/updated tuple was inserted to. Usually it's the given page, but could
 * be its right sibling if the page was split.
 *
 * Returns 'true' if the page was split, 'false' otherwise.
 */
bool
gistplacetopage(Relation rel, Size freespace, GISTSTATE *giststate,
				Buffer buffer,
				IndexTuple *itup, int ntup, OffsetNumber oldoffnum,
				BlockNumber *newblkno,
				Buffer leftchildbuf,
				List **splitinfo,
				bool markfollowright)
{
	BlockNumber blkno = BufferGetBlockNumber(buffer);
	Page		page = BufferGetPage(buffer);
	bool		is_leaf = (GistPageIsLeaf(page)) ? true : false;
	XLogRecPtr	recptr;
	int			i;
	bool		is_split;

	/*
	 * Refuse to modify a page that's incompletely split. This should not
	 * happen because we finish any incomplete splits while we walk down the
	 * tree. However, it's remotely possible that another concurrent inserter
	 * splits a parent page, and errors out before completing the split. We
	 * will just throw an error in that case, and leave any split we had in
	 * progress unfinished too. The next insert that comes along will clean up
	 * the mess.
	 */
	if (GistFollowRight(page))
		elog(ERROR, "concurrent GiST page split was incomplete");

	*splitinfo = NIL;

	/*
	 * if isupdate, remove old key: This node's key has been modified, either
	 * because a child split occurred or because we needed to adjust our key
	 * for an insert in a child node. Therefore, remove the old version of
	 * this node's key.
	 *
	 * for WAL replay, in the non-split case we handle this by setting up a
	 * one-element todelete array; in the split case, it's handled implicitly
	 * because the tuple vector passed to gistSplit won't include this tuple.
	 */
	is_split = gistnospace(page, itup, ntup, oldoffnum, freespace);

	/*
	 * If leaf page is full, try at first to delete dead tuples. And then
	 * check again.
	 */
	if (is_split && GistPageIsLeaf(page) && GistPageHasGarbage(page))
	{
		gistvacuumpage(rel, page, buffer);
		is_split = gistnospace(page, itup, ntup, oldoffnum, freespace);
	}

	if (is_split)
	{
		/* no space for insertion */
		IndexTuple *itvec;
		int			tlen;
		SplitedPageLayout *dist = NULL,
				   *ptr;
		BlockNumber oldrlink = InvalidBlockNumber;
		GistNSN		oldnsn = 0;
		SplitedPageLayout rootpg;
		bool		is_rootsplit;
		int			npage;

		is_rootsplit = (blkno == GIST_ROOT_BLKNO);

		/*
		 * Form index tuples vector to split. If we're replacing an old tuple,
		 * remove the old version from the vector.
		 */
		itvec = gistextractpage(page, &tlen);
		if (OffsetNumberIsValid(oldoffnum))
		{
			/* on inner page we should remove old tuple */
			int			pos = oldoffnum - FirstOffsetNumber;

			tlen--;
			if (pos != tlen)
				memmove(itvec + pos, itvec + pos + 1, sizeof(IndexTuple) * (tlen - pos));
		}
		itvec = gistjoinvector(itvec, &tlen, itup, ntup);
		dist = gistSplit(rel, page, itvec, tlen, giststate);

		/*
		 * Check that split didn't produce too many pages.
		 */
		npage = 0;
		for (ptr = dist; ptr; ptr = ptr->next)
			npage++;
		/* in a root split, we'll add one more page to the list below */
		if (is_rootsplit)
			npage++;
		if (npage > GIST_MAX_SPLIT_PAGES)
			elog(ERROR, "GiST page split into too many halves (%d, maximum %d)",
				 npage, GIST_MAX_SPLIT_PAGES);

		/*
		 * Set up pages to work with. Allocate new buffers for all but the
		 * leftmost page. The original page becomes the new leftmost page, and
		 * is just replaced with the new contents.
		 *
		 * For a root-split, allocate new buffers for all child pages, the
		 * original page is overwritten with new root page containing
		 * downlinks to the new child pages.
		 */
		ptr = dist;
		if (!is_rootsplit)
		{
			/* save old rightlink and NSN */
			oldrlink = GistPageGetOpaque(page)->rightlink;
			oldnsn = GistPageGetNSN(page);

			dist->buffer = buffer;
			dist->block.blkno = BufferGetBlockNumber(buffer);
			dist->page = PageGetTempPageCopySpecial(BufferGetPage(buffer));

			/* clean all flags except F_LEAF */
			GistPageGetOpaque(dist->page)->flags = (is_leaf) ? F_LEAF : 0;

			ptr = ptr->next;
		}
		for (; ptr; ptr = ptr->next)
		{
			/* Allocate new page */
			ptr->buffer = gistNewBuffer(rel);
			GISTInitBuffer(ptr->buffer, (is_leaf) ? F_LEAF : 0);
			ptr->page = BufferGetPage(ptr->buffer);
			ptr->block.blkno = BufferGetBlockNumber(ptr->buffer);
		}

		/*
		 * Now that we know which blocks the new pages go to, set up downlink
		 * tuples to point to them.
		 */
		for (ptr = dist; ptr; ptr = ptr->next)
		{
			ItemPointerSetBlockNumber(&(ptr->itup->t_tid), ptr->block.blkno);
			GistTupleSetValid(ptr->itup);
		}

		/*
		 * If this is a root split, we construct the new root page with the
		 * downlinks here directly, instead of requiring the caller to insert
		 * them. Add the new root page to the list along with the child pages.
		 */
		if (is_rootsplit)
		{
			IndexTuple *downlinks;
			int			ndownlinks = 0;
			int			i;

			rootpg.buffer = buffer;
			rootpg.page = PageGetTempPageCopySpecial(BufferGetPage(rootpg.buffer));
			GistPageGetOpaque(rootpg.page)->flags = 0;

			/* Prepare a vector of all the downlinks */
			for (ptr = dist; ptr; ptr = ptr->next)
				ndownlinks++;
			downlinks = palloc(sizeof(IndexTuple) * ndownlinks);
			for (i = 0, ptr = dist; ptr; ptr = ptr->next)
				downlinks[i++] = ptr->itup;

			rootpg.block.blkno = GIST_ROOT_BLKNO;
			rootpg.block.num = ndownlinks;
			rootpg.list = gistfillitupvec(downlinks, ndownlinks,
										  &(rootpg.lenlist));
			rootpg.itup = NULL;

			rootpg.next = dist;
			dist = &rootpg;
		}
		else
		{
			/* Prepare split-info to be returned to caller */
			for (ptr = dist; ptr; ptr = ptr->next)
			{
				GISTPageSplitInfo *si = palloc(sizeof(GISTPageSplitInfo));

				si->buf = ptr->buffer;
				si->downlink = ptr->itup;
				*splitinfo = lappend(*splitinfo, si);
			}
		}

		/*
		 * Fill all pages. All the pages are new, ie. freshly allocated empty
		 * pages, or a temporary copy of the old page.
		 */
		for (ptr = dist; ptr; ptr = ptr->next)
		{
			char	   *data = (char *) (ptr->list);

			for (i = 0; i < ptr->block.num; i++)
			{
				IndexTuple	thistup = (IndexTuple) data;

				if (PageAddItem(ptr->page, (Item) data, IndexTupleSize(thistup), i + FirstOffsetNumber, false, false) == InvalidOffsetNumber)
					elog(ERROR, "failed to add item to index page in \"%s\"", RelationGetRelationName(rel));

				/*
				 * If this is the first inserted/updated tuple, let the caller
				 * know which page it landed on.
				 */
				if (newblkno && ItemPointerEquals(&thistup->t_tid, &(*itup)->t_tid))
					*newblkno = ptr->block.blkno;

				data += IndexTupleSize(thistup);
			}

			/* Set up rightlinks */
			if (ptr->next && ptr->block.blkno != GIST_ROOT_BLKNO)
				GistPageGetOpaque(ptr->page)->rightlink =
					ptr->next->block.blkno;
			else
				GistPageGetOpaque(ptr->page)->rightlink = oldrlink;

			/*
			 * Mark the all but the right-most page with the follow-right
			 * flag. It will be cleared as soon as the downlink is inserted
			 * into the parent, but this ensures that if we error out before
			 * that, the index is still consistent. (in buffering build mode,
			 * any error will abort the index build anyway, so this is not
			 * needed.)
			 */
			if (ptr->next && !is_rootsplit && markfollowright)
				GistMarkFollowRight(ptr->page);
			else
				GistClearFollowRight(ptr->page);

			/*
			 * Copy the NSN of the original page to all pages. The
			 * F_FOLLOW_RIGHT flags ensure that scans will follow the
			 * rightlinks until the downlinks are inserted.
			 */
			GistPageSetNSN(ptr->page, oldnsn);
		}

		/*
		 * gistXLogSplit() needs to WAL log a lot of pages, prepare WAL
		 * insertion for that. NB: The number of pages and data segments
		 * specified here must match the calculations in gistXLogSplit()!
		 */
		if (RelationNeedsWAL(rel))
			XLogEnsureRecordSpace(npage, 1 + npage * 2);

		START_CRIT_SECTION();

		/*
		 * Must mark buffers dirty before XLogInsert, even though we'll still
		 * be changing their opaque fields below.
		 */
		for (ptr = dist; ptr; ptr = ptr->next)
			MarkBufferDirty(ptr->buffer);
		if (BufferIsValid(leftchildbuf))
			MarkBufferDirty(leftchildbuf);

		/*
		 * The first page in the chain was a temporary working copy meant to
		 * replace the old page. Copy it over the old page.
		 */
		PageRestoreTempPage(dist->page, BufferGetPage(dist->buffer));
		dist->page = BufferGetPage(dist->buffer);

		/* Write the WAL record */
		if (RelationNeedsWAL(rel))
			recptr = gistXLogSplit(is_leaf,
								   dist, oldrlink, oldnsn, leftchildbuf,
								   markfollowright);
		else
			recptr = gistGetFakeLSN(rel);

		for (ptr = dist; ptr; ptr = ptr->next)
		{
			PageSetLSN(ptr->page, recptr);
		}

		/*
		 * Return the new child buffers to the caller.
		 *
		 * If this was a root split, we've already inserted the downlink
		 * pointers, in the form of a new root page. Therefore we can release
		 * all the new buffers, and keep just the root page locked.
		 */
		if (is_rootsplit)
		{
			for (ptr = dist->next; ptr; ptr = ptr->next)
				UnlockReleaseBuffer(ptr->buffer);
		}
	}
	else
	{
		/*
		 * Enough space.  We always get here if ntup==0.
		 */
		START_CRIT_SECTION();

		/*
		 * Delete old tuple if any, then insert new tuple(s) if any.  If
		 * possible, use the fast path of PageIndexTupleOverwrite.
		 */
		if (OffsetNumberIsValid(oldoffnum))
		{
			if (ntup == 1)
			{
				/* One-for-one replacement, so use PageIndexTupleOverwrite */
				if (!PageIndexTupleOverwrite(page, oldoffnum, (Item) *itup,
											 IndexTupleSize(*itup)))
					elog(ERROR, "failed to add item to index page in \"%s\"",
						 RelationGetRelationName(rel));
			}
			else
			{
				/* Delete old, then append new tuple(s) to page */
				PageIndexTupleDelete(page, oldoffnum);
				gistfillbuffer(page, itup, ntup, InvalidOffsetNumber);
			}
		}
		else
		{
			/* Just append new tuples at the end of the page */
			gistfillbuffer(page, itup, ntup, InvalidOffsetNumber);
		}

		MarkBufferDirty(buffer);

		if (BufferIsValid(leftchildbuf))
			MarkBufferDirty(leftchildbuf);

		if (RelationNeedsWAL(rel))
		{
			OffsetNumber ndeloffs = 0,
						deloffs[1];

			if (OffsetNumberIsValid(oldoffnum))
			{
				deloffs[0] = oldoffnum;
				ndeloffs = 1;
			}

			recptr = gistXLogUpdate(buffer,
									deloffs, ndeloffs, itup, ntup,
									leftchildbuf);

			PageSetLSN(page, recptr);
		}
		else
		{
			recptr = gistGetFakeLSN(rel);
			PageSetLSN(page, recptr);
		}

		if (newblkno)
			*newblkno = blkno;
	}

	/*
	 * If we inserted the downlink for a child page, set NSN and clear
	 * F_FOLLOW_RIGHT flag on the left child, so that concurrent scans know to
	 * follow the rightlink if and only if they looked at the parent page
	 * before we inserted the downlink.
	 *
	 * Note that we do this *after* writing the WAL record. That means that
	 * the possible full page image in the WAL record does not include these
	 * changes, and they must be replayed even if the page is restored from
	 * the full page image. There's a chicken-and-egg problem: if we updated
	 * the child pages first, we wouldn't know the recptr of the WAL record
	 * we're about to write.
	 */
	if (BufferIsValid(leftchildbuf))
	{
		Page		leftpg = BufferGetPage(leftchildbuf);

		GistPageSetNSN(leftpg, recptr);
		GistClearFollowRight(leftpg);

		PageSetLSN(leftpg, recptr);
	}

	END_CRIT_SECTION();

	return is_split;
}