コード例 #1
0
ファイル: hio.c プロジェクト: adunstan/postgresql-dev
/*
 * RelationGetBufferForTuple
 *
 *	Returns pinned and exclusive-locked buffer of a page in given relation
 *	with free space >= given len.
 *
 *	If otherBuffer is not InvalidBuffer, then it references a previously
 *	pinned buffer of another page in the same relation; on return, this
 *	buffer will also be exclusive-locked.  (This case is used by heap_update;
 *	the otherBuffer contains the tuple being updated.)
 *
 *	The reason for passing otherBuffer is that if two backends are doing
 *	concurrent heap_update operations, a deadlock could occur if they try
 *	to lock the same two buffers in opposite orders.  To ensure that this
 *	can't happen, we impose the rule that buffers of a relation must be
 *	locked in increasing page number order.  This is most conveniently done
 *	by having RelationGetBufferForTuple lock them both, with suitable care
 *	for ordering.
 *
 *	NOTE: it is unlikely, but not quite impossible, for otherBuffer to be the
 *	same buffer we select for insertion of the new tuple (this could only
 *	happen if space is freed in that page after heap_update finds there's not
 *	enough there).	In that case, the page will be pinned and locked only once.
 *
 *	For the vmbuffer and vmbuffer_other arguments, we avoid deadlock by
 *	locking them only after locking the corresponding heap page, and taking
 *	no further lwlocks while they are locked.
 *
 *	We normally use FSM to help us find free space.  However,
 *	if HEAP_INSERT_SKIP_FSM is specified, we just append a new empty page to
 *	the end of the relation if the tuple won't fit on the current target page.
 *	This can save some cycles when we know the relation is new and doesn't
 *	contain useful amounts of free space.
 *
 *	HEAP_INSERT_SKIP_FSM is also useful for non-WAL-logged additions to a
 *	relation, if the caller holds exclusive lock and is careful to invalidate
 *	relation's smgr_targblock before the first insertion --- that ensures that
 *	all insertions will occur into newly added pages and not be intermixed
 *	with tuples from other transactions.  That way, a crash can't risk losing
 *	any committed data of other transactions.  (See heap_insert's comments
 *	for additional constraints needed for safe usage of this behavior.)
 *
 *	The caller can also provide a BulkInsertState object to optimize many
 *	insertions into the same relation.	This keeps a pin on the current
 *	insertion target page (to save pin/unpin cycles) and also passes a
 *	BULKWRITE buffer selection strategy object to the buffer manager.
 *	Passing NULL for bistate selects the default behavior.
 *
 *	We always try to avoid filling existing pages further than the fillfactor.
 *	This is OK since this routine is not consulted when updating a tuple and
 *	keeping it on the same page, which is the scenario fillfactor is meant
 *	to reserve space for.
 *
 *	ereport(ERROR) is allowed here, so this routine *must* be called
 *	before any (unlogged) changes are made in buffer pool.
 */
Buffer
RelationGetBufferForTuple(Relation relation, Size len,
						  Buffer otherBuffer, int options,
						  BulkInsertState bistate,
						  Buffer *vmbuffer, Buffer *vmbuffer_other)
{
	bool		use_fsm = !(options & HEAP_INSERT_SKIP_FSM);
	Buffer		buffer = InvalidBuffer;
	Page		page;
	Size		pageFreeSpace,
				saveFreeSpace;
	BlockNumber targetBlock,
				otherBlock;
	bool		needLock;

	len = MAXALIGN(len);		/* be conservative */

	/* Bulk insert is not supported for updates, only inserts. */
	Assert(otherBuffer == InvalidBuffer || !bistate);

	/*
	 * If we're gonna fail for oversize tuple, do it right away
	 */
	if (len > MaxHeapTupleSize)
		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
				 errmsg("row is too big: size %lu, maximum size %lu",
						(unsigned long) len,
						(unsigned long) MaxHeapTupleSize)));

	/* Compute desired extra freespace due to fillfactor option */
	saveFreeSpace = RelationGetTargetPageFreeSpace(relation,
												   HEAP_DEFAULT_FILLFACTOR);

	if (otherBuffer != InvalidBuffer)
		otherBlock = BufferGetBlockNumber(otherBuffer);
	else
		otherBlock = InvalidBlockNumber;		/* just to keep compiler quiet */

	/*
	 * We first try to put the tuple on the same page we last inserted a tuple
	 * on, as cached in the BulkInsertState or relcache entry.	If that
	 * doesn't work, we ask the Free Space Map to locate a suitable page.
	 * Since the FSM's info might be out of date, we have to be prepared to
	 * loop around and retry multiple times. (To insure this isn't an infinite
	 * loop, we must update the FSM with the correct amount of free space on
	 * each page that proves not to be suitable.)  If the FSM has no record of
	 * a page with enough free space, we give up and extend the relation.
	 *
	 * When use_fsm is false, we either put the tuple onto the existing target
	 * page or extend the relation.
	 */
	if (len + saveFreeSpace > MaxHeapTupleSize)
	{
		/* can't fit, don't bother asking FSM */
		targetBlock = InvalidBlockNumber;
		use_fsm = false;
	}
	else if (bistate && bistate->current_buf != InvalidBuffer)
		targetBlock = BufferGetBlockNumber(bistate->current_buf);
	else
		targetBlock = RelationGetTargetBlock(relation);

	if (targetBlock == InvalidBlockNumber && use_fsm)
	{
		/*
		 * We have no cached target page, so ask the FSM for an initial
		 * target.
		 */
		targetBlock = GetPageWithFreeSpace(relation, len + saveFreeSpace);

		/*
		 * If the FSM knows nothing of the rel, try the last page before we
		 * give up and extend.	This avoids one-tuple-per-page syndrome during
		 * bootstrapping or in a recently-started system.
		 */
		if (targetBlock == InvalidBlockNumber)
		{
			BlockNumber nblocks = RelationGetNumberOfBlocks(relation);

			if (nblocks > 0)
				targetBlock = nblocks - 1;
		}
	}

	while (targetBlock != InvalidBlockNumber)
	{
		/*
		 * Read and exclusive-lock the target block, as well as the other
		 * block if one was given, taking suitable care with lock ordering and
		 * the possibility they are the same block.
		 *
		 * If the page-level all-visible flag is set, caller will need to
		 * clear both that and the corresponding visibility map bit.  However,
		 * by the time we return, we'll have x-locked the buffer, and we don't
		 * want to do any I/O while in that state.	So we check the bit here
		 * before taking the lock, and pin the page if it appears necessary.
		 * Checking without the lock creates a risk of getting the wrong
		 * answer, so we'll have to recheck after acquiring the lock.
		 */
		if (otherBuffer == InvalidBuffer)
		{
			/* easy case */
			buffer = ReadBufferBI(relation, targetBlock, bistate);
			if (PageIsAllVisible(BufferGetPage(buffer)))
				visibilitymap_pin(relation, targetBlock, vmbuffer);
			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
		}
		else if (otherBlock == targetBlock)
		{
			/* also easy case */
			buffer = otherBuffer;
			if (PageIsAllVisible(BufferGetPage(buffer)))
				visibilitymap_pin(relation, targetBlock, vmbuffer);
			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
		}
		else if (otherBlock < targetBlock)
		{
			/* lock other buffer first */
			buffer = ReadBuffer(relation, targetBlock);
			if (PageIsAllVisible(BufferGetPage(buffer)))
				visibilitymap_pin(relation, targetBlock, vmbuffer);
			LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE);
			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
		}
		else
		{
			/* lock target buffer first */
			buffer = ReadBuffer(relation, targetBlock);
			if (PageIsAllVisible(BufferGetPage(buffer)))
				visibilitymap_pin(relation, targetBlock, vmbuffer);
			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
			LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE);
		}

		/*
		 * We now have the target page (and the other buffer, if any) pinned
		 * and locked.	However, since our initial PageIsAllVisible checks
		 * were performed before acquiring the lock, the results might now be
		 * out of date, either for the selected victim buffer, or for the
		 * other buffer passed by the caller.  In that case, we'll need to
		 * give up our locks, go get the pin(s) we failed to get earlier, and
		 * re-lock.  That's pretty painful, but hopefully shouldn't happen
		 * often.
		 *
		 * Note that there's a small possibility that we didn't pin the page
		 * above but still have the correct page pinned anyway, either because
		 * we've already made a previous pass through this loop, or because
		 * caller passed us the right page anyway.
		 *
		 * Note also that it's possible that by the time we get the pin and
		 * retake the buffer locks, the visibility map bit will have been
		 * cleared by some other backend anyway.  In that case, we'll have
		 * done a bit of extra work for no gain, but there's no real harm
		 * done.
		 */
		if (otherBuffer == InvalidBuffer || buffer <= otherBuffer)
			GetVisibilityMapPins(relation, buffer, otherBuffer,
								 targetBlock, otherBlock, vmbuffer,
								 vmbuffer_other);
		else
			GetVisibilityMapPins(relation, otherBuffer, buffer,
								 otherBlock, targetBlock, vmbuffer_other,
								 vmbuffer);

		/*
		 * Now we can check to see if there's enough free space here. If so,
		 * we're done.
		 */
		page = BufferGetPage(buffer);
		pageFreeSpace = PageGetHeapFreeSpace(page);
		if (len + saveFreeSpace <= pageFreeSpace)
		{
			/* use this page as future insert target, too */
			RelationSetTargetBlock(relation, targetBlock);
			return buffer;
		}

		/*
		 * Not enough space, so we must give up our page locks and pin (if
		 * any) and prepare to look elsewhere.	We don't care which order we
		 * unlock the two buffers in, so this can be slightly simpler than the
		 * code above.
		 */
		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
		if (otherBuffer == InvalidBuffer)
			ReleaseBuffer(buffer);
		else if (otherBlock != targetBlock)
		{
			LockBuffer(otherBuffer, BUFFER_LOCK_UNLOCK);
			ReleaseBuffer(buffer);
		}

		/* Without FSM, always fall out of the loop and extend */
		if (!use_fsm)
			break;

		/*
		 * Update FSM as to condition of this page, and ask for another page
		 * to try.
		 */
		targetBlock = RecordAndGetPageWithFreeSpace(relation,
													targetBlock,
													pageFreeSpace,
													len + saveFreeSpace);
	}

	/*
	 * Have to extend the relation.
	 *
	 * We have to use a lock to ensure no one else is extending the rel at the
	 * same time, else we will both try to initialize the same new page.  We
	 * can skip locking for new or temp relations, however, since no one else
	 * could be accessing them.
	 */
	needLock = !RELATION_IS_LOCAL(relation);

	if (needLock)
		LockRelationForExtension(relation, ExclusiveLock);

	/*
	 * XXX This does an lseek - rather expensive - but at the moment it is the
	 * only way to accurately determine how many blocks are in a relation.	Is
	 * it worth keeping an accurate file length in shared memory someplace,
	 * rather than relying on the kernel to do it for us?
	 */
	buffer = ReadBufferBI(relation, P_NEW, bistate);

	/*
	 * We can be certain that locking the otherBuffer first is OK, since it
	 * must have a lower page number.
	 */
	if (otherBuffer != InvalidBuffer)
		LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE);

	/*
	 * Now acquire lock on the new page.
	 */
	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

	/*
	 * Release the file-extension lock; it's now OK for someone else to extend
	 * the relation some more.	Note that we cannot release this lock before
	 * we have buffer lock on the new page, or we risk a race condition
	 * against vacuumlazy.c --- see comments therein.
	 */
	if (needLock)
		UnlockRelationForExtension(relation, ExclusiveLock);

	/*
	 * We need to initialize the empty new page.  Double-check that it really
	 * is empty (this should never happen, but if it does we don't want to
	 * risk wiping out valid data).
	 */
	page = BufferGetPage(buffer);

	if (!PageIsNew(page))
		elog(ERROR, "page %u of relation \"%s\" should be empty but is not",
			 BufferGetBlockNumber(buffer),
			 RelationGetRelationName(relation));

	PageInit(page, BufferGetPageSize(buffer), 0);

	if (len > PageGetHeapFreeSpace(page))
	{
		/* We should not get here given the test at the top */
		elog(PANIC, "tuple is too big: size %lu", (unsigned long) len);
	}

	/*
	 * Remember the new page as our target for future insertions.
	 *
	 * XXX should we enter the new page into the free space map immediately,
	 * or just keep it for this backend's exclusive use in the short run
	 * (until VACUUM sees it)?	Seems to depend on whether you expect the
	 * current backend to make more insertions or not, which is probably a
	 * good bet most of the time.  So for now, don't add it to FSM yet.
	 */
	RelationSetTargetBlock(relation, BufferGetBlockNumber(buffer));

	return buffer;
}
コード例 #2
0
ファイル: brin_pageops.c プロジェクト: dreamsxin/postgresql-1
/*
 * Return a pinned and exclusively locked buffer which can be used to insert an
 * index item of size itemsz (caller must ensure not to request sizes
 * impossible to fulfill).  If oldbuf is a valid buffer, it is also locked (in
 * an order determined to avoid deadlocks.)
 *
 * If we find that the old page is no longer a regular index page (because
 * of a revmap extension), the old buffer is unlocked and we return
 * InvalidBuffer.
 *
 * If there's no existing page with enough free space to accommodate the new
 * item, the relation is extended.  If this happens, *extended is set to true,
 * and it is the caller's responsibility to initialize the page (and WAL-log
 * that fact) prior to use.
 *
 * Note that in some corner cases it is possible for this routine to extend the
 * relation and then not return the buffer.  It is this routine's
 * responsibility to WAL-log the page initialization and to record the page in
 * FSM if that happens.  Such a buffer may later be reused by this routine.
 */
static Buffer
brin_getinsertbuffer(Relation irel, Buffer oldbuf, Size itemsz,
					 bool *extended)
{
	BlockNumber oldblk;
	BlockNumber newblk;
	Page		page;
	int			freespace;

	/* callers must have checked */
	Assert(itemsz <= BrinMaxItemSize);

	*extended = false;

	if (BufferIsValid(oldbuf))
		oldblk = BufferGetBlockNumber(oldbuf);
	else
		oldblk = InvalidBlockNumber;

	/*
	 * Loop until we find a page with sufficient free space.  By the time we
	 * return to caller out of this loop, both buffers are valid and locked;
	 * if we have to restart here, neither buffer is locked and buf is not a
	 * pinned buffer.
	 */
	newblk = RelationGetTargetBlock(irel);
	if (newblk == InvalidBlockNumber)
		newblk = GetPageWithFreeSpace(irel, itemsz);
	for (;;)
	{
		Buffer		buf;
		bool		extensionLockHeld = false;

		CHECK_FOR_INTERRUPTS();

		if (newblk == InvalidBlockNumber)
		{
			/*
			 * There's not enough free space in any existing index page,
			 * according to the FSM: extend the relation to obtain a shiny new
			 * page.
			 */
			if (!RELATION_IS_LOCAL(irel))
			{
				LockRelationForExtension(irel, ExclusiveLock);
				extensionLockHeld = true;
			}
			buf = ReadBuffer(irel, P_NEW);
			newblk = BufferGetBlockNumber(buf);
			*extended = true;

			BRIN_elog((DEBUG2, "brin_getinsertbuffer: extending to page %u",
					   BufferGetBlockNumber(buf)));
		}
		else if (newblk == oldblk)
		{
			/*
			 * There's an odd corner-case here where the FSM is out-of-date,
			 * and gave us the old page.
			 */
			buf = oldbuf;
		}
		else
		{
			buf = ReadBuffer(irel, newblk);
		}

		/*
		 * We lock the old buffer first, if it's earlier than the new one; but
		 * before we do, we need to check that it hasn't been turned into a
		 * revmap page concurrently; if we detect that it happened, give up
		 * and tell caller to start over.
		 */
		if (BufferIsValid(oldbuf) && oldblk < newblk)
		{
			LockBuffer(oldbuf, BUFFER_LOCK_EXCLUSIVE);
			if (!BRIN_IS_REGULAR_PAGE(BufferGetPage(oldbuf)))
			{
				LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);

				/*
				 * It is possible that the new page was obtained from
				 * extending the relation.  In that case, we must be sure to
				 * record it in the FSM before leaving, because otherwise the
				 * space would be lost forever.  However, we cannot let an
				 * uninitialized page get in the FSM, so we need to initialize
				 * it first.
				 */
				if (*extended)
				{
					brin_initialize_empty_new_buffer(irel, buf);
					/* shouldn't matter, but don't confuse caller */
					*extended = false;
				}

				if (extensionLockHeld)
					UnlockRelationForExtension(irel, ExclusiveLock);

				ReleaseBuffer(buf);
				return InvalidBuffer;
			}
		}

		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);

		if (extensionLockHeld)
			UnlockRelationForExtension(irel, ExclusiveLock);

		page = BufferGetPage(buf);

		/*
		 * We have a new buffer to insert into.  Check that the new page has
		 * enough free space, and return it if it does; otherwise start over.
		 * Note that we allow for the FSM to be out of date here, and in that
		 * case we update it and move on.
		 *
		 * (br_page_get_freespace also checks that the FSM didn't hand us a
		 * page that has since been repurposed for the revmap.)
		 */
		freespace = *extended ?
			BrinMaxItemSize : br_page_get_freespace(page);
		if (freespace >= itemsz)
		{
			RelationSetTargetBlock(irel, BufferGetBlockNumber(buf));

			/*
			 * Since the target block specification can get lost on cache
			 * invalidations, make sure we update the more permanent FSM with
			 * data about it before going away.
			 */
			if (*extended)
				RecordPageWithFreeSpace(irel, BufferGetBlockNumber(buf),
										freespace);

			/*
			 * Lock the old buffer if not locked already.  Note that in this
			 * case we know for sure it's a regular page: it's later than the
			 * new page we just got, which is not a revmap page, and revmap
			 * pages are always consecutive.
			 */
			if (BufferIsValid(oldbuf) && oldblk > newblk)
			{
				LockBuffer(oldbuf, BUFFER_LOCK_EXCLUSIVE);
				Assert(BRIN_IS_REGULAR_PAGE(BufferGetPage(oldbuf)));
			}

			return buf;
		}

		/* This page is no good. */

		/*
		 * If an entirely new page does not contain enough free space for the
		 * new item, then surely that item is oversized.  Complain loudly; but
		 * first make sure we initialize the page and record it as free, for
		 * next time.
		 */
		if (*extended)
		{
			brin_initialize_empty_new_buffer(irel, buf);

			ereport(ERROR,
					(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
			errmsg("index row size %lu exceeds maximum %lu for index \"%s\"",
				   (unsigned long) itemsz,
				   (unsigned long) freespace,
				   RelationGetRelationName(irel))));
			return InvalidBuffer;		/* keep compiler quiet */
		}

		if (newblk != oldblk)
			UnlockReleaseBuffer(buf);
		if (BufferIsValid(oldbuf) && oldblk <= newblk)
			LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);

		newblk = RecordAndGetPageWithFreeSpace(irel, newblk, freespace, itemsz);
	}
}