Avoid hot standby cancels from VAC FREEZE

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 66fbcb0d2e 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
index 78746d15b9525170999d4e76d741059e68278542..1f1bac5c6be070e17fc4dcce4db19c411706a319 100644 (file)
--- 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))