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authorTom Lane <tgl@sss.pgh.pa.us>2012-05-22 19:42:12 -0400
committerTom Lane <tgl@sss.pgh.pa.us>2012-05-22 19:42:12 -0400
commit276bea211f08a3b0d6d5753b654322c8efb781d1 (patch)
tree5963c42ce69afbadd0827fbbdcecb07c5512063e /src
parentae7c8b290f525504978c01d77366a753505d10d5 (diff)
downloadpostgresql-276bea211f08a3b0d6d5753b654322c8efb781d1.tar.gz
postgresql-276bea211f08a3b0d6d5753b654322c8efb781d1.zip
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.
Diffstat (limited to 'src')
-rw-r--r--src/backend/access/heap/heapam.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index cc8b45fd489..197067d4a1d 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -219,6 +219,13 @@ 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 = ReadBufferExtended(scan->rs_rd, MAIN_FORKNUM, page,
RBM_NORMAL, scan->rs_strategy);