Extend relations multiple blocks at a time to improve scalability.

Contention on the relation extension lock can become quite fierce when
multiple processes are inserting data into the same relation at the same
time at a high rate.  Experimentation shows the extending the relation
multiple blocks at a time improves scalability.

Dilip Kumar, reviewed by Petr Jelinek, Amit Kapila, and me.

Author: robertmhaas

src/backend/access/heap/hio.c

@@ -168,6 +168,75 @@ GetVisibilityMapPins(Relation relation, Buffer buffer1, Buffer buffer2,
 	}
 }
 
+/*
+ * Extend a relation by multiple blocks to avoid future contention on the
+ * relation extension lock.  Our goal is to pre-extend the relation by an
+ * amount which ramps up as the degree of contention ramps up, but limiting
+ * the result to some sane overall value.
+ */
+static void
+RelationAddExtraBlocks(Relation relation, BulkInsertState bistate)
+{
+	Page		page;
+	BlockNumber	blockNum = InvalidBlockNumber,
+				firstBlock = InvalidBlockNumber;
+	int			extraBlocks = 0;
+	int			lockWaiters = 0;
+	Size		freespace = 0;
+	Buffer		buffer;
+
+	/* Use the length of the lock wait queue to judge how much to extend. */
+	lockWaiters = RelationExtensionLockWaiterCount(relation);
+	if (lockWaiters <= 0)
+		return;
+
+	/*
+	 * It might seem like multiplying the number of lock waiters by as much
+	 * as 20 is too aggressive, but benchmarking revealed that smaller numbers
+	 * were insufficient.  512 is just an arbitrary cap to prevent pathological
+	 * results.
+	 */
+	extraBlocks = Min(512, lockWaiters * 20);
+
+	while (extraBlocks-- >= 0)
+	{
+		/* Ouch - an unnecessary lseek() each time through the loop! */
+		buffer = ReadBufferBI(relation, P_NEW, bistate);
+
+		/* Extend by one page. */
+		LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+		page = BufferGetPage(buffer);
+		PageInit(page, BufferGetPageSize(buffer), 0);
+		MarkBufferDirty(buffer);
+		blockNum = BufferGetBlockNumber(buffer);
+		freespace = PageGetHeapFreeSpace(page);
+		UnlockReleaseBuffer(buffer);
+
+		/* Remember first block number thus added. */
+		if (firstBlock == InvalidBlockNumber)
+			firstBlock = blockNum;
+
+		/*
+		 * Immediately update the bottom level of the FSM.  This has a good
+		 * chance of making this page visible to other concurrently inserting
+		 * backends, and we want that to happen without delay.
+		 */
+		RecordPageWithFreeSpace(relation, blockNum, freespace);
+	}
+
+	/*
+	 * Updating the upper levels of the free space map is too expensive
+	 * to do for every block, but it's worth doing once at the end to make
+	 * sure that subsequent insertion activity sees all of those nifty free
+	 * pages we just inserted.
+	 *
+	 * Note that we're using the freespace value that was reported for the
+	 * last block we added as if it were the freespace value for every block
+	 * we added.  That's actually true, because they're all equally empty.
+	 */
+	UpdateFreeSpaceMap(relation, firstBlock, blockNum, freespace);
+}
+
 /*
  * RelationGetBufferForTuple
  *
@@ -233,8 +302,8 @@ RelationGetBufferForTuple(Relation relation, Size len,
 	bool		use_fsm = !(options & HEAP_INSERT_SKIP_FSM);
 	Buffer		buffer = InvalidBuffer;
 	Page		page;
-	Size		pageFreeSpace,
-				saveFreeSpace;
+	Size		pageFreeSpace = 0,
+				saveFreeSpace = 0;
 	BlockNumber targetBlock,
 				otherBlock;
 	bool		needLock;
@@ -308,6 +377,7 @@ RelationGetBufferForTuple(Relation relation, Size len,
 		}
 	}
 
+loop:
 	while (targetBlock != InvalidBlockNumber)
 	{
 		/*
@@ -440,10 +510,46 @@ RelationGetBufferForTuple(Relation relation, Size len,
 	 */
 	needLock = !RELATION_IS_LOCAL(relation);
 
+	/*
+	 * If we need the lock but are not able to acquire it immediately, we'll
+	 * consider extending the relation by multiple blocks at a time to manage
+	 * contention on the relation extension lock.  However, this only makes
+	 * sense if we're using the FSM; otherwise, there's no point.
+	 */
 	if (needLock)
-		LockRelationForExtension(relation, ExclusiveLock);
+	{
+		if (!use_fsm)
+			LockRelationForExtension(relation, ExclusiveLock);
+		else if (!ConditionalLockRelationForExtension(relation, ExclusiveLock))
+		{
+			/* Couldn't get the lock immediately; wait for it. */
+			LockRelationForExtension(relation, ExclusiveLock);
+
+			/*
+			 * Check if some other backend has extended a block for us while
+			 * we were waiting on the lock.
+			 */
+			targetBlock = GetPageWithFreeSpace(relation, len + saveFreeSpace);
+
+			/*
+			 * If some other waiter has already extended the relation, we
+			 * don't need to do so; just use the existing freespace.
+			 */
+			if (targetBlock != InvalidBlockNumber)
+			{
+				UnlockRelationForExtension(relation, ExclusiveLock);
+				goto loop;
+			}
+
+			/* Time to bulk-extend. */
+			RelationAddExtraBlocks(relation, bistate);
+		}
+	}
 
 	/*
+	 * In addition to whatever extension we performed above, we always add
+	 * at least one block to satisfy our own request.
+	 *
 	 * 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,

src/backend/storage/freespace/freespace.c

@@ -109,6 +109,8 @@ static int fsm_set_and_search(Relation rel, FSMAddress addr, uint16 slot,
 				   uint8 newValue, uint8 minValue);
 static BlockNumber fsm_search(Relation rel, uint8 min_cat);
 static uint8 fsm_vacuum_page(Relation rel, FSMAddress addr, bool *eof);
+static BlockNumber fsm_get_lastblckno(Relation rel, FSMAddress addr);
+static void fsm_update_recursive(Relation rel, FSMAddress addr, uint8 new_cat);
 
 
 /******** Public API ********/
@@ -188,6 +190,46 @@ RecordPageWithFreeSpace(Relation rel, BlockNumber heapBlk, Size spaceAvail)
 	fsm_set_and_search(rel, addr, slot, new_cat, 0);
 }
 
+/*
+ * Update the upper levels of the free space map all the way up to the root
+ * to make sure we don't lose track of new blocks we just inserted.  This is
+ * intended to be used after adding many new blocks to the relation; we judge
+ * it not worth updating the upper levels of the tree every time data for
+ * a single page changes, but for a bulk-extend it's worth it.
+ */
+void
+UpdateFreeSpaceMap(Relation rel, BlockNumber startBlkNum,
+					BlockNumber endBlkNum, Size freespace)
+{
+	int			new_cat = fsm_space_avail_to_cat(freespace);
+	FSMAddress	addr;
+	uint16		slot;
+	BlockNumber	blockNum;
+	BlockNumber	lastBlkOnPage;
+
+	blockNum = startBlkNum;
+
+	while (blockNum <= endBlkNum)
+	{
+		/*
+		 * Find FSM address for this block; update tree all the way to the
+		 * root.
+		 */
+		addr = fsm_get_location(blockNum, &slot);
+		fsm_update_recursive(rel, addr, new_cat);
+
+		/*
+		 * Get the last block number on this FSM page.  If that's greater
+		 * than or equal to our endBlkNum, we're done.  Otherwise, advance
+		 * to the first block on the next page.
+		 */
+		lastBlkOnPage = fsm_get_lastblckno(rel, addr);
+		if (lastBlkOnPage >= endBlkNum)
+			break;
+		blockNum = lastBlkOnPage + 1;
+	}
+}
+
 /*
  * XLogRecordPageWithFreeSpace - like RecordPageWithFreeSpace, for use in
  *		WAL replay
@@ -788,3 +830,42 @@ fsm_vacuum_page(Relation rel, FSMAddress addr, bool *eof_p)
 
 	return max_avail;
 }
+
+/*
+ * This function will return the last block number stored on given
+ * FSM page address.
+ */
+static BlockNumber
+fsm_get_lastblckno(Relation rel, FSMAddress addr)
+{
+	int			slot;
+
+	/*
+	 * Get the last slot number on the given address and convert that to
+	 * block number
+	 */
+	slot = SlotsPerFSMPage - 1;
+	return fsm_get_heap_blk(addr, slot);
+}
+
+/*
+ * Recursively update the FSM tree from given address to
+ * all the way up to root.
+ */
+static void
+fsm_update_recursive(Relation rel, FSMAddress addr, uint8 new_cat)
+{
+	uint16		parentslot;
+	FSMAddress	parent;
+
+	if (addr.level == FSM_ROOT_LEVEL)
+		return;
+
+	/*
+	 * Get the parent page and our slot in the parent page, and
+	 * update the information in that.
+	 */
+	parent = fsm_get_parent(addr, &parentslot);
+	fsm_set_and_search(rel, parent, parentslot, new_cat, 0);
+	fsm_update_recursive(rel, parent, new_cat);
+}

src/backend/storage/lmgr/lmgr.c

@@ -340,6 +340,41 @@ LockRelationForExtension(Relation relation, LOCKMODE lockmode)
 	(void) LockAcquire(&tag, lockmode, false, false);
 }
 
+/*
+ *		ConditionalLockRelationForExtension
+ *
+ * As above, but only lock if we can get the lock without blocking.
+ * Returns TRUE iff the lock was acquired.
+ */
+bool
+ConditionalLockRelationForExtension(Relation relation, LOCKMODE lockmode)
+{
+	LOCKTAG		tag;
+
+	SET_LOCKTAG_RELATION_EXTEND(tag,
+								relation->rd_lockInfo.lockRelId.dbId,
+								relation->rd_lockInfo.lockRelId.relId);
+
+	return (LockAcquire(&tag, lockmode, false, true) != LOCKACQUIRE_NOT_AVAIL);
+}
+
+/*
+ *		RelationExtensionLockWaiterCount
+ *
+ * Count the number of processes waiting for the given relation extension lock.
+ */
+int
+RelationExtensionLockWaiterCount(Relation relation)
+{
+	LOCKTAG		tag;
+
+	SET_LOCKTAG_RELATION_EXTEND(tag,
+								relation->rd_lockInfo.lockRelId.dbId,
+								relation->rd_lockInfo.lockRelId.relId);
+
+	return LockWaiterCount(&tag);
+}
+
 /*
  *		UnlockRelationForExtension
  */

src/backend/storage/lmgr/lock.c

@@ -4380,3 +4380,40 @@ VirtualXactLock(VirtualTransactionId vxid, bool wait)
 	LockRelease(&tag, ShareLock, false);
 	return true;
 }
+
+/*
+ * LockWaiterCount
+ *
+ * Find the number of lock requester on this locktag
+ */
+int
+LockWaiterCount(const LOCKTAG *locktag)
+{
+	LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid;
+	LOCK	   *lock;
+	bool		found;
+	uint32		hashcode;
+	LWLock	   *partitionLock;
+	int			waiters = 0;
+
+	if (lockmethodid <= 0 || lockmethodid >= lengthof(LockMethods))
+		elog(ERROR, "unrecognized lock method: %d", lockmethodid);
+
+	hashcode = LockTagHashCode(locktag);
+	partitionLock = LockHashPartitionLock(hashcode);
+	LWLockAcquire(partitionLock, LW_EXCLUSIVE);
+
+	lock = (LOCK *) hash_search_with_hash_value(LockMethodLockHash,
+												(const void *) locktag,
+												hashcode,
+												HASH_FIND,
+												&found);
+	if (found)
+	{
+		Assert(lock != NULL);
+		waiters = lock->nRequested;
+	}
+	LWLockRelease(partitionLock);
+
+	return waiters;
+}

src/include/storage/freespace.h

@@ -32,5 +32,9 @@ extern void XLogRecordPageWithFreeSpace(RelFileNode rnode, BlockNumber heapBlk,
 
 extern void FreeSpaceMapTruncateRel(Relation rel, BlockNumber nblocks);
 extern void FreeSpaceMapVacuum(Relation rel);
+extern void UpdateFreeSpaceMap(Relation rel,
+							BlockNumber firtsBlkNum,
+							BlockNumber lastBlkNum,
+							Size freespace);
 
 #endif   /* FREESPACE_H_ */

src/include/storage/lmgr.h

@@ -53,6 +53,9 @@ extern void UnlockRelationIdForSession(LockRelId *relid, LOCKMODE lockmode);
 /* Lock a relation for extension */
 extern void LockRelationForExtension(Relation relation, LOCKMODE lockmode);
 extern void UnlockRelationForExtension(Relation relation, LOCKMODE lockmode);
+extern bool ConditionalLockRelationForExtension(Relation relation,
+									LOCKMODE lockmode);
+extern int	RelationExtensionLockWaiterCount(Relation relation);
 
 /* Lock a page (currently only used within indexes) */
 extern void LockPage(Relation relation, BlockNumber blkno, LOCKMODE lockmode);

src/include/storage/lock.h

@@ -574,6 +574,8 @@ extern void RememberSimpleDeadLock(PGPROC *proc1,
 					   PGPROC *proc2);
 extern void InitDeadLockChecking(void);
 
+extern int	LockWaiterCount(const LOCKTAG *locktag);
+
 #ifdef LOCK_DEBUG
 extern void DumpLocks(PGPROC *proc);
 extern void DumpAllLocks(void);