Optimize iteration over PGPROC for fast-path lock searches.

MasaoFujii · MasaoFujii · commit e80171d57c25 · 2025-03-14T22:49:29.000+09:00
This commit improves efficiency in FastPathTransferRelationLocks() and GetLockConflicts(), which iterate over PGPROCs to search for fast-path locks. Previously, these functions recalculated the fast-path group during every loop iteration, even though it remained constant. This update optimizes the process by calculating the group once and reusing it throughout the loop. The functions also now skip empty fast-path groups, avoiding unnecessary scans of their slots. Additionally, groups belonging to inactive backends (with pid=0) are always empty, so checking the group is sufficient to bypass these backends, further enhancing performance. Author: Fujii Masao <masao.fujii@gmail.com> Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi> Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> Discussion: https://postgr.es/m/07d5fd6a-71f1-4ce8-8602-4cc6883f4bd1@oss.nttdata.com
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
@@ -2774,6 +2774,9 @@ FastPathTransferRelationLocks(LockMethod lockMethodTable, const LOCKTAG *locktag
 	Oid			relid = locktag->locktag_field2;
 	uint32		i;
 
+	/* fast-path group the lock belongs to */
+	uint32		group = FAST_PATH_REL_GROUP(relid);
+
 	/*
 	 * Every PGPROC that can potentially hold a fast-path lock is present in
 	 * ProcGlobal->allProcs.  Prepared transactions are not, but any
@@ -2783,8 +2786,7 @@ FastPathTransferRelationLocks(LockMethod lockMethodTable, const LOCKTAG *locktag
 	for (i = 0; i < ProcGlobal->allProcCount; i++)
 	{
 		PGPROC	   *proc = &ProcGlobal->allProcs[i];
-		uint32		j,
-					group;
+		uint32		j;
 
 		LWLockAcquire(&proc->fpInfoLock, LW_EXCLUSIVE);
 
@@ -2802,16 +2804,16 @@ FastPathTransferRelationLocks(LockMethod lockMethodTable, const LOCKTAG *locktag
 		 * less clear that our backend is certain to have performed a memory
 		 * fencing operation since the other backend set proc->databaseId.  So
 		 * for now, we test it after acquiring the LWLock just to be safe.
+		 *
+		 * Also skip groups without any registered fast-path locks.
 		 */
-		if (proc->databaseId != locktag->locktag_field1)
+		if (proc->databaseId != locktag->locktag_field1 ||
+			proc->fpLockBits[group] == 0)
 		{
 			LWLockRelease(&proc->fpInfoLock);
 			continue;
 		}
 
-		/* fast-path group the lock belongs to */
-		group = FAST_PATH_REL_GROUP(relid);
-
 		for (j = 0; j < FP_LOCK_SLOTS_PER_GROUP; j++)
 		{
 			uint32		lockmode;
@@ -3027,6 +3029,9 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 		Oid			relid = locktag->locktag_field2;
 		VirtualTransactionId vxid;
 
+		/* fast-path group the lock belongs to */
+		uint32		group = FAST_PATH_REL_GROUP(relid);
+
 		/*
 		 * Iterate over relevant PGPROCs.  Anything held by a prepared
 		 * transaction will have been transferred to the primary lock table,
@@ -3040,8 +3045,7 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 		for (i = 0; i < ProcGlobal->allProcCount; i++)
 		{
 			PGPROC	   *proc = &ProcGlobal->allProcs[i];
-			uint32		j,
-						group;
+			uint32		j;
 
 			/* A backend never blocks itself */
 			if (proc == MyProc)
@@ -3056,16 +3060,16 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 			 *
 			 * See FastPathTransferRelationLocks() for discussion of why we do
 			 * this test after acquiring the lock.
+			 *
+			 * Also skip groups without any registered fast-path locks.
 			 */
-			if (proc->databaseId != locktag->locktag_field1)
+			if (proc->databaseId != locktag->locktag_field1 ||
+				proc->fpLockBits[group] == 0)
 			{
 				LWLockRelease(&proc->fpInfoLock);
 				continue;
 			}
 
-			/* fast-path group the lock belongs to */
-			group = FAST_PATH_REL_GROUP(relid);
-
 			for (j = 0; j < FP_LOCK_SLOTS_PER_GROUP; j++)
 			{
 				uint32		lockmask;
