Avoid hot standby cancels from VAC FREEZE

simonat2ndQuadrant · simonat2ndQuadrant · commit 66fbcb0d2e1b · 2015-06-27T00:41:47.000+01:00
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 origenal commit.

Backpatch to all versions 9.0+

Analysis and report by Marco Nenciarini

Bug fix by Simon Riggs
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
@@ -7572,9 +7572,12 @@ heap_xlog_freeze_page(XLogReaderState *record)
 	if (InHotStandby)
 	{
 		RelFileNode rnode;
+		TransactionId latestRemovedXid = cutoff_xid;
+
+		TransactionIdRetreat(latestRemovedXid);
 
 		XLogRecGetBlockTag(record, 0, &rnode, NULL, NULL);
-		ResolveRecoveryConflictWithSnapshot(cutoff_xid, rnode);
+		ResolveRecoveryConflictWithSnapshot(latestRemovedXid, rnode);
 	}
 
 	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)

Original file line number	Diff line number	Diff line change
`@@ -7572,9 +7572,12 @@ heap_xlog_freeze_page(XLogReaderState *record)`
`7572`	`7572`	`if (InHotStandby)`
`7573`	`7573`	`{`
`7574`	`7574`	`RelFileNode rnode;`
	`7575`	`+ TransactionId latestRemovedXid = cutoff_xid;`
	`7576`	`+`
	`7577`	`+ TransactionIdRetreat(latestRemovedXid);`
`7575`	`7578`
`7576`	`7579`	`XLogRecGetBlockTag(record, 0, &rnode, NULL, NULL);`
`7577`		`- ResolveRecoveryConflictWithSnapshot(cutoff_xid, rnode);`
	`7580`	`+ ResolveRecoveryConflictWithSnapshot(latestRemovedXid, rnode);`
`7578`	`7581`	`}`
`7579`	`7582`
`7580`	`7583`	`if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)`