From 1a4bc2db6cb80a6e52aed8f5a68b895231653d6c Mon Sep 17 00:00:00 2001
From: Simon Riggs <simon@2ndQuadrant.com>
Date: Fri, 11 May 2012 14:38:11 +0100
Subject: Ensure age() returns a stable value rather than the latest value

---
 src/backend/access/transam/xact.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

(limited to 'src/backend/access/transam/xact.c')

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 901fff059a1..be4905181e0 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -393,6 +393,28 @@ GetCurrentTransactionIdIfAny(void)
 }
 
 
+/*
+ *	GetStableLatestTransactionIdIfAny
+ *
+ * Get the latest XID once and then return same value for rest of transaction.
+ * Acts as a useful reference point for maintenance tasks.
+ */
+TransactionId
+GetStableLatestTransactionId(void)
+{
+	static LocalTransactionId lxid = InvalidLocalTransactionId;
+	static TransactionId stablexid = InvalidTransactionId;
+
+	if (lxid != MyProc->lxid ||
+		!TransactionIdIsValid(stablexid))
+	{
+		lxid = MyProc->lxid;
+		stablexid = ReadNewTransactionId();
+	}
+
+	return stablexid;
+}
+
 /*
  * AssignTransactionId
  *
-- 
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