2pc_remove_prepXacts.v1.patch

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 2251b02..e196a55 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -114,6 +114,7 @@ int			max_prepared_xacts = 0;
 typedef struct GlobalTransactionData
 {
 	GlobalTransaction next;		/* list link for free list */
+	int			prepXactId		/* array offset within prepXacts */
 	int			pgprocno;		/* ID of associated dummy PGPROC */
 	BackendId	dummyBackendId; /* similar to backend id for backends */
 	TimestampTz prepared_at;	/* time of preparation */
@@ -407,7 +408,8 @@ MarkAsPreparing(TransactionId xid, const char *gid,
 
 	/* And insert it into the active array */
 	Assert(TwoPhaseState->numPrepXacts < max_prepared_xacts);
-	TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts++] = gxact;
+	TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts] = gxact;
+	gxact->prepXactId = TwoPhaseState->numPrepXacts++;
 
 	/*
 	 * Remember that we have this GlobalTransaction entry locked for us. If we
@@ -551,31 +553,25 @@ LockGXact(const char *gid, Oid user)
 static void
 RemoveGXact(GlobalTransaction gxact)
 {
-	int			i;
-
-	LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
+	int			i = gxact->prepXactId;
+	GlobalTransaction	last_gxact;
 
-	for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
-	{
-		if (gxact == TwoPhaseState->prepXacts[i])
-		{
-			/* remove from the active array */
-			TwoPhaseState->numPrepXacts--;
-			TwoPhaseState->prepXacts[i] = TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts];
+	Assert(gxact->prepXactId >= 0);
 
-			/* and put it back in the freelist */
-			gxact->next = TwoPhaseState->freeGXacts;
-			TwoPhaseState->freeGXacts = gxact;
+	LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
 
-			LWLockRelease(TwoPhaseStateLock);
+	/* remove from the active array */
+	TwoPhaseState->numPrepXacts--;
+	last_gxact = TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts];
+	TwoPhaseState->prepXacts[i] = last_gxact;
+	last_gxact->prepXactId = i;
+	gxact->prepXactId = -1;
 
-			return;
-		}
-	}
+	/* and put it back in the freelist */
+	gxact->next = TwoPhaseState->freeGXacts;
+	TwoPhaseState->freeGXacts = gxact;
 
 	LWLockRelease(TwoPhaseStateLock);
-
-	elog(ERROR, "failed to find %p in GlobalTransaction array", gxact);
 }
 
 /*