From 436af241c88a2f9b971dbe248e6ec6360438033c Mon Sep 17 00:00:00 2001
From: Simon Riggs <simon@2ndQuadrant.com>
Date: Sat, 12 May 2012 13:25:34 +0100
Subject: [PATCH] Ensure backwards compatibility for
 GetStableLatestTransactionId()

---
 src/backend/access/transam/xact.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index be4905181e0..b34b418fd98 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -392,11 +392,10 @@ GetCurrentTransactionIdIfAny(void)
 	return CurrentTransactionState->transactionId;
 }
 
-
 /*
- *	GetStableLatestTransactionIdIfAny
+ *	GetStableLatestTransactionId
  *
- * Get the latest XID once and then return same value for rest of transaction.
+ * Get the XID once and then return same value for rest of transaction.
  * Acts as a useful reference point for maintenance tasks.
  */
 TransactionId
@@ -405,13 +404,16 @@ GetStableLatestTransactionId(void)
 	static LocalTransactionId lxid = InvalidLocalTransactionId;
 	static TransactionId stablexid = InvalidTransactionId;
 
-	if (lxid != MyProc->lxid ||
-		!TransactionIdIsValid(stablexid))
+	if (lxid != MyProc->lxid)
 	{
 		lxid = MyProc->lxid;
-		stablexid = ReadNewTransactionId();
+		stablexid = GetTopTransactionIdIfAny();
+		if (!TransactionIdIsValid(stablexid))
+			stablexid = ReadNewTransactionId();
 	}
 
+	Assert(TransactionIdIsValid(stablexid));
+
 	return stablexid;
 }