postgres.git / summary / log / commit / refs

commit    3ce6fa5568a3d554551cfec4167a9f55510a9468
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Tue May 22 23:42:23 2012 +0000
First released in: 9.2.0, 8.3.19, 8.4.12, 9.0.8, 9.1.4

    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 5294f30016f..89cf249447a 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -217,6 +217,13 @@ 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);


[parent: 6e088424e2d4]