From c994b9211fd0cf7a5b680ae115330117604b9f7c Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Tue, 22 May 2012 19:42:28 -0400 Subject: [PATCH] Ensure that seqscans check for interrupts at least once per page. If a seqscan encounters many consecutive pages containing only dead tuples, it can remain in the loop in heapgettup for a long time, and there was no CHECK_FOR_INTERRUPTS anywhere in that loop. This meant there were real-world situations where a query would be effectively uncancelable for long stretches. Add a check placed to occur once per page, which should be enough to provide reasonable response time without adding any measurable overhead. Report and patch by Merlin Moncure (though I tweaked it a bit). Back-patch to all supported branches. --- src/backend/access/heap/heapam.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index 10644c7d8f..0dc6611d8d 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -206,6 +206,13 @@ heapgetpage(HeapScanDesc scan, BlockNumber page) scan->rs_cbuf = InvalidBuffer; } + /* + * Be sure to check for interrupts at least once per page. Checks at + * higher code levels won't be able to stop a seqscan that encounters + * many pages' worth of consecutive dead tuples. + */ + CHECK_FOR_INTERRUPTS(); + /* read page using selected strategy */ scan->rs_cbuf = ReadBufferWithStrategy(scan->rs_rd, page, -- 2.50.0