nbtinsert.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

	/*
	 * Determine exactly where new item will go.
	 */
	if (afteritem > 0)
		newitemoff = afteritem + 1;
	else
	{
		/*----------
		 * If we will need to split the page to put the item here,
		 * check whether we can put the tuple somewhere to the right,
		 * instead.  Keep scanning right until we
		 *		(a) find a page with enough free space,
		 *		(b) reach the last page where the tuple can legally go, or
		 *		(c) get tired of searching.
		 * (c) is not flippant; it is important because if there are many
		 * pages' worth of equal keys, it's better to split one of the early
		 * pages than to scan all the way to the end of the run of equal keys
		 * on every insert.  We implement "get tired" as a random choice,
		 * since stopping after scanning a fixed number of pages wouldn't work
		 * well (we'd never reach the right-hand side of previously split
		 * pages).	Currently the probability of moving right is set at 0.99,
		 * which may seem too high to change the behavior much, but it does an
		 * excellent job of preventing O(N^2) behavior with many equal keys.
		 *----------
		 */
		bool		movedright = false;

		while (PageGetFreeSpace(page) < itemsz &&
			   !P_RIGHTMOST(lpageop) &&
			   _bt_compare(rel, keysz, scankey, page, P_HIKEY) == 0 &&
			   random() > (MAX_RANDOM_VALUE / 100))
		{
			/*
			 * step right to next non-dead page
			 *
			 * must write-lock that page before releasing write lock on
			 * current page; else someone else's _bt_check_unique scan could
			 * fail to see our insertion.  write locks on intermediate dead
			 * pages won't do because we don't know when they will get
			 * de-linked from the tree.
			 */
			Buffer		rbuf = InvalidBuffer;

			for (;;)
			{
				BlockNumber rblkno = lpageop->btpo_next;

				rbuf = _bt_relandgetbuf(rel, rbuf, rblkno, BT_WRITE);
				page = BufferGetPage(rbuf);
				lpageop = (BTPageOpaque) PageGetSpecialPointer(page);
				if (!P_IGNORE(lpageop))
					break;
				if (P_RIGHTMOST(lpageop))
					elog(ERROR, "fell off the end of \"%s\"",
						 RelationGetRelationName(rel));
			}
			_bt_relbuf(rel, buf);
			buf = rbuf;
			movedright = true;
		}

		/*
		 * Now we are on the right page, so find the insert position. If we
		 * moved right at all, we know we should insert at the start of the
		 * page, else must find the position by searching.
		 */
		if (movedright)
			newitemoff = P_FIRSTDATAKEY(lpageop);
		else
			newitemoff = _bt_binsrch(rel, buf, keysz, scankey, false);
	}

	/*
	 * Do we need to split the page to fit the item on it?
	 *
	 * Note: PageGetFreeSpace() subtracts sizeof(ItemIdData) from its result,
	 * so this comparison is correct even though we appear to be accounting
	 * only for the item and not for its line pointer.
	 */
	if (PageGetFreeSpace(page) < itemsz)
	{
		bool		is_root = P_ISROOT(lpageop);
		bool		is_only = P_LEFTMOST(lpageop) && P_RIGHTMOST(lpageop);
		bool		newitemonleft;
		Buffer		rbuf;

		/* Choose the split point */
		firstright = _bt_findsplitloc(rel, page,
									  newitemoff, itemsz,
									  &newitemonleft);

		/* split the buffer into left and right halves */
		rbuf = _bt_split(rel, buf, firstright,
						 newitemoff, itemsz, btitem, newitemonleft);

		/*----------
		 * By here,
		 *
		 *		+  our target page has been split;
		 *		+  the original tuple has been inserted;
		 *		+  we have write locks on both the old (left half)
		 *		   and new (right half) buffers, after the split; and
		 *		+  we know the key we want to insert into the parent
		 *		   (it's the "high key" on the left child page).
		 *
		 * We're ready to do the parent insertion.  We need to hold onto the
		 * locks for the child pages until we locate the parent, but we can
		 * release them before doing the actual insertion (see Lehman and Yao
		 * for the reasoning).
		 *----------
		 */
		_bt_insert_parent(rel, buf, rbuf, stack, is_root, is_only);
	}
	else
	{
		Buffer		metabuf = InvalidBuffer;
		Page		metapg = NULL;
		BTMetaPageData *metad = NULL;
		OffsetNumber itup_off;
		BlockNumber itup_blkno;

		itup_off = newitemoff;
		itup_blkno = BufferGetBlockNumber(buf);

		/*
		 * If we are doing this insert because we split a page that was the
		 * only one on its tree level, but was not the root, it may have been
		 * the "fast root".  We need to ensure that the fast root link points
		 * at or above the current page.  We can safely acquire a lock on the
		 * metapage here --- see comments for _bt_newroot().
		 */
		if (split_only_page)
		{
			metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_WRITE);
			metapg = BufferGetPage(metabuf);
			metad = BTPageGetMeta(metapg);

			if (metad->btm_fastlevel >= lpageop->btpo.level)
			{
				/* no update wanted */
				_bt_relbuf(rel, metabuf);
				metabuf = InvalidBuffer;
			}
		}

		/* Do the update.  No ereport(ERROR) until changes are logged */
		START_CRIT_SECTION();

		_bt_pgaddtup(rel, page, itemsz, btitem, newitemoff, "page");

		if (BufferIsValid(metabuf))
		{
			metad->btm_fastroot = itup_blkno;
			metad->btm_fastlevel = lpageop->btpo.level;
		}

		/* XLOG stuff */
		if (!rel->rd_istemp)
		{
			xl_btree_insert xlrec;
			xl_btree_metadata xlmeta;
			uint8		xlinfo;
			XLogRecPtr	recptr;
			XLogRecData rdata[3];
			XLogRecData *nextrdata;
			BTItemData	truncitem;

			xlrec.target.node = rel->rd_node;
			ItemPointerSet(&(xlrec.target.tid), itup_blkno, itup_off);

			rdata[0].data = (char *) &xlrec;
			rdata[0].len = SizeOfBtreeInsert;
			rdata[0].buffer = InvalidBuffer;
			rdata[0].next = nextrdata = &(rdata[1]);

			if (BufferIsValid(metabuf))
			{
				xlmeta.root = metad->btm_root;
				xlmeta.level = metad->btm_level;
				xlmeta.fastroot = metad->btm_fastroot;
				xlmeta.fastlevel = metad->btm_fastlevel;

				nextrdata->data = (char *) &xlmeta;
				nextrdata->len = sizeof(xl_btree_metadata);
				nextrdata->buffer = InvalidBuffer;
				nextrdata->next = nextrdata + 1;
				nextrdata++;
				xlinfo = XLOG_BTREE_INSERT_META;
			}
			else if (P_ISLEAF(lpageop))
				xlinfo = XLOG_BTREE_INSERT_LEAF;
			else
				xlinfo = XLOG_BTREE_INSERT_UPPER;

			/* Read comments in _bt_pgaddtup */
			if (!P_ISLEAF(lpageop) && newitemoff == P_FIRSTDATAKEY(lpageop))
			{
				truncitem = *btitem;
				truncitem.bti_itup.t_info = sizeof(BTItemData);
				nextrdata->data = (char *) &truncitem;
				nextrdata->len = sizeof(BTItemData);
			}
			else
			{
				nextrdata->data = (char *) btitem;
				nextrdata->len = IndexTupleDSize(btitem->bti_itup) +
					(sizeof(BTItemData) - sizeof(IndexTupleData));
			}
			nextrdata->buffer = buf;
			nextrdata->buffer_std = true;
			nextrdata->next = NULL;

			recptr = XLogInsert(RM_BTREE_ID, xlinfo, rdata);

			if (BufferIsValid(metabuf))
			{
				PageSetLSN(metapg, recptr);
				PageSetTLI(metapg, ThisTimeLineID);
			}

			PageSetLSN(page, recptr);
			PageSetTLI(page, ThisTimeLineID);
		}

		END_CRIT_SECTION();

		/* Write out the updated page and release pin/lock */
		if (BufferIsValid(metabuf))
			_bt_wrtbuf(rel, metabuf);

		_bt_wrtbuf(rel, buf);
	}
}

/*
 *	_bt_split() -- split a page in the btree.
 *
 *		On entry, buf is the page to split, and is write-locked and pinned.
 *		firstright is the item index of the first item to be moved to the
 *		new right page.  newitemoff etc. tell us about the new item that
 *		must be inserted along with the data from the old page.
 *
 *		Returns the new right sibling of buf, pinned and write-locked.
 *		The pin and lock on buf are maintained.
 */
static Buffer
_bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
		  OffsetNumber newitemoff, Size newitemsz, BTItem newitem,
		  bool newitemonleft)
{
	Buffer		rbuf;
	Page		origpage;
	Page		leftpage,
				rightpage;
	BTPageOpaque ropaque,
				lopaque,
				oopaque;
	Buffer		sbuf = InvalidBuffer;
	Page		spage = NULL;
	BTPageOpaque sopaque = NULL;
	OffsetNumber itup_off = 0;
	BlockNumber itup_blkno = 0;
	Size		itemsz;
	ItemId		itemid;
	BTItem		item;
	OffsetNumber leftoff,
				rightoff;
	OffsetNumber maxoff;
	OffsetNumber i;

	rbuf = _bt_getbuf(rel, P_NEW, BT_WRITE);
	origpage = BufferGetPage(buf);
	leftpage = PageGetTempPage(origpage, sizeof(BTPageOpaqueData));
	rightpage = BufferGetPage(rbuf);

	_bt_pageinit(leftpage, BufferGetPageSize(buf));
	_bt_pageinit(rightpage, BufferGetPageSize(rbuf));

	/* init btree private data */
	oopaque = (BTPageOpaque) PageGetSpecialPointer(origpage);
	lopaque = (BTPageOpaque) PageGetSpecialPointer(leftpage);
	ropaque = (BTPageOpaque) PageGetSpecialPointer(rightpage);

	/* if we're splitting this page, it won't be the root when we're done */
	lopaque->btpo_flags = oopaque->btpo_flags;
	lopaque->btpo_flags &= ~BTP_ROOT;
	ropaque->btpo_flags = lopaque->btpo_flags;
	lopaque->btpo_prev = oopaque->btpo_prev;
	lopaque->btpo_next = BufferGetBlockNumber(rbuf);
	ropaque->btpo_prev = BufferGetBlockNumber(buf);
	ropaque->btpo_next = oopaque->btpo_next;
	lopaque->btpo.level = ropaque->btpo.level = oopaque->btpo.level;

	/*
	 * If the page we're splitting is not the rightmost page at its level in
	 * the tree, then the first entry on the page is the high key for the
	 * page.  We need to copy that to the right half.  Otherwise (meaning the
	 * rightmost page case), all the items on the right half will be user
	 * data.
	 */
	rightoff = P_HIKEY;

	if (!P_RIGHTMOST(oopaque))
	{
		itemid = PageGetItemId(origpage, P_HIKEY);
		itemsz = ItemIdGetLength(itemid);
		item = (BTItem) PageGetItem(origpage, itemid);
		if (PageAddItem(rightpage, (Item) item, itemsz, rightoff,
						LP_USED) == InvalidOffsetNumber)
			elog(PANIC, "failed to add hikey to the right sibling");
		rightoff = OffsetNumberNext(rightoff);
	}

	/*
	 * The "high key" for the new left page will be the first key that's going
	 * to go into the new right page.  This might be either the existing data
	 * item at position firstright, or the incoming tuple.
	 */
	leftoff = P_HIKEY;
	if (!newitemonleft && newitemoff == firstright)
	{
		/* incoming tuple will become first on right page */
		itemsz = newitemsz;
		item = newitem;
	}
	else
	{
		/* existing item at firstright will become first on right page */
		itemid = PageGetItemId(origpage, firstright);
		itemsz = ItemIdGetLength(itemid);
		item = (BTItem) PageGetItem(origpage, itemid);
	}
	if (PageAddItem(leftpage, (Item) item, itemsz, leftoff,
					LP_USED) == InvalidOffsetNumber)
		elog(PANIC, "failed to add hikey to the left sibling");
	leftoff = OffsetNumberNext(leftoff);

	/*
	 * Now transfer all the data items to the appropriate page
	 */
	maxoff = PageGetMaxOffsetNumber(origpage);

	for (i = P_FIRSTDATAKEY(oopaque); i <= maxoff; i = OffsetNumberNext(i))
	{
		itemid = PageGetItemId(origpage, i);
		itemsz = ItemIdGetLength(itemid);
		item = (BTItem) PageGetItem(origpage, itemid);

		/* does new item belong before this one? */
		if (i == newitemoff)
		{
			if (newitemonleft)
			{
				_bt_pgaddtup(rel, leftpage, newitemsz, newitem, leftoff,
							 "left sibling");
				itup_off = leftoff;
				itup_blkno = BufferGetBlockNumber(buf);
				leftoff = OffsetNumberNext(leftoff);
			}
			else
			{
				_bt_pgaddtup(rel, rightpage, newitemsz, newitem, rightoff,
							 "right sibling");
				itup_off = rightoff;
				itup_blkno = BufferGetBlockNumber(rbuf);
				rightoff = OffsetNumberNext(rightoff);
			}
		}

		/* decide which page to put it on */
		if (i < firstright)
		{
			_bt_pgaddtup(rel, leftpage, itemsz, item, leftoff,
						 "left sibling");
			leftoff = OffsetNumberNext(leftoff);
		}
		else
		{
			_bt_pgaddtup(rel, rightpage, itemsz, item, rightoff,
						 "right sibling");
			rightoff = OffsetNumberNext(rightoff);
		}
	}

	/* cope with possibility that newitem goes at the end */
	if (i <= newitemoff)
	{
		if (newitemonleft)
		{
			_bt_pgaddtup(rel, leftpage, newitemsz, newitem, leftoff,
						 "left sibling");
			itup_off = leftoff;
			itup_blkno = BufferGetBlockNumber(buf);
			leftoff = OffsetNumberNext(leftoff);
		}
		else
		{
			_bt_pgaddtup(rel, rightpage, newitemsz, newitem, rightoff,