Remove AELs from subxids correctly on standby

Issues relate only to subtransactions that hold AccessExclusiveLocks
when replayed on standby.

Prior to PG10, aborting subtransactions that held an
AccessExclusiveLock failed to release the lock until top level commit or
abort. 49bff530 fixed that.

However, 49bff530 also introduced a similar bug where subtransaction
commit would fail to release an AccessExclusiveLock, leaving the lock to
be removed sometimes early and sometimes late. This commit fixes
that bug also. Backpatch to PG10 needed.

Tested by observation. Note need for multi-node isolationtester to improve
test coverage for this and other HS cases.

Reported-by: Simon Riggs
Author: Simon Riggs

src/backend/access/transam/xact.c

@@ -5602,12 +5602,10 @@ xact_redo_commit(xl_xact_parsed_commit *parsed,
 		/*
 		 * Release locks, if any. We do this for both two phase and normal one
 		 * phase transactions. In effect we are ignoring the prepare phase and
-		 * just going straight to lock release. At commit we release all locks
-		 * via their top-level xid only, so no need to provide subxact list,
-		 * which will save time when replaying commits.
+		 * just going straight to lock release.
 		 */
 		if (parsed->xinfo & XACT_XINFO_HAS_AE_LOCKS)
-			StandbyReleaseLockTree(xid, 0, NULL);
+			StandbyReleaseLockTree(xid, parsed->nsubxacts, parsed->subxacts);
 	}
 
 	if (parsed->xinfo & XACT_XINFO_HAS_ORIGIN)

src/backend/storage/ipc/procarray.c

@@ -684,11 +684,8 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
 
 	/*
 	 * Remove stale locks, if any.
-	 *
-	 * Locks are always assigned to the toplevel xid so we don't need to care
-	 * about subxcnt/subxids (and by extension not about ->suboverflowed).
 	 */
-	StandbyReleaseOldLocks(running->xcnt, running->xids);
+	StandbyReleaseOldLocks(running->oldestRunningXid);
 
 	/*
 	 * If our snapshot is already valid, nothing else to do...

src/backend/storage/ipc/standby.c

@@ -722,7 +722,7 @@ StandbyReleaseAllLocks(void)
  *		as long as they're not prepared transactions.
  */
 void
-StandbyReleaseOldLocks(int nxids, TransactionId *xids)
+StandbyReleaseOldLocks(TransactionId oldxid)
 {
 	ListCell   *cell,
 			   *prev,
@@ -741,26 +741,8 @@ StandbyReleaseOldLocks(int nxids, TransactionId *xids)
 
 		if (StandbyTransactionIdIsPrepared(lock->xid))
 			remove = false;
-		else
-		{
-			int			i;
-			bool		found = false;
-
-			for (i = 0; i < nxids; i++)
-			{
-				if (lock->xid == xids[i])
-				{
-					found = true;
-					break;
-				}
-			}
-
-			/*
-			 * If its not a running transaction, remove it.
-			 */
-			if (!found)
+		else if (TransactionIdPrecedes(lock->xid, oldxid))
 			remove = true;
-		}
 
 		if (remove)
 		{

src/include/storage/standby.h

@@ -50,7 +50,7 @@ extern void StandbyAcquireAccessExclusiveLock(TransactionId xid, Oid dbOid, Oid
 extern void StandbyReleaseLockTree(TransactionId xid,
 					   int nsubxids, TransactionId *subxids);
 extern void StandbyReleaseAllLocks(void);
-extern void StandbyReleaseOldLocks(int nxids, TransactionId *xids);
+extern void StandbyReleaseOldLocks(TransactionId oldxid);
 
 #define MinSizeOfXactRunningXacts offsetof(xl_running_xacts, xids)