Avoid hot standby cancels from VAC FREEZE

alvherre · alvherre · commit 6537a48c5521 · 2016-05-25T19:39:49.000-04:00
VACUUM FREEZE generated false cancelations of standby queries on an otherwise idle master. Caused by an off-by-one error on cutoff_xid which goes back to original commit. Analysis and report by Marco Nenciarini Bug fix by Simon Riggs This is a correct backpatch of commit 66fbcb0 to branches 9.1 through 9.4. That commit was backpatched to 9.0 originally, but it was immediately reverted in 9.0-9.4 because it didn't compile.
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
@@ -6928,7 +6928,13 @@ heap_xlog_freeze(XLogRecPtr lsn, XLogRecord *record)
 	 * consider the frozen xids as running.
 	 */
 	if (InHotStandby)
-		ResolveRecoveryConflictWithSnapshot(cutoff_xid, xlrec->node);
+	{
+		TransactionId latestRemovedXid = cutoff_xid;
+
+		TransactionIdRetreat(latestRemovedXid);
+
+		ResolveRecoveryConflictWithSnapshot(latestRemovedXid, xlrec->node);
+	}
 
 	/* If we have a full-page image, restore it and we're done */
 	if (record->xl_info & XLR_BKP_BLOCK(0))
@@ -7103,7 +7109,13 @@ heap_xlog_freeze_page(XLogRecPtr lsn, XLogRecord *record)
 	 * consider the frozen xids as running.
 	 */
 	if (InHotStandby)
-		ResolveRecoveryConflictWithSnapshot(cutoff_xid, xlrec->node);
+	{
+		TransactionId latestRemovedXid = cutoff_xid;
+
+		TransactionIdRetreat(latestRemovedXid);
+
+		ResolveRecoveryConflictWithSnapshot(latestRemovedXid, xlrec->node);
+	}
 
 	/* If we have a full-page image, restore it and we're done */
 	if (record->xl_info & XLR_BKP_BLOCK(0))
