Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly
Appearance settings

Commit 317de9c

Browse filesBrowse files
david-rowleydavid-rowley
committed
Fix hypothetical bug in heap backward scans
Both heapgettup() and heapgettup_pagemode() incorrectly set the first page to scan in a backward scan in which the number of pages to scan was specified by heap_setscanlimits(). The code incorrectly started the scan at the end of the relation when startBlk was 0, or otherwise at startBlk - 1, neither of which is correct when only scanning a subset of pages. The fix here checks if heap_setscanlimits() has changed the number of pages to scan and if so we set the first page to scan as the final page in the specified range during backward scans. Proper adjustment of this code was forgotten when heap_setscanlimits() was added in 7516f52 back in 9.5. However, practice, nowhere in core code performs backward scans after having used heap_setscanlimits(), yet, it is possible an extension uses the heap functions in this way, hence backpatch. An upcoming patch does use heap_setscanlimits() with backward scans, so this must be fixed before that can go in. Author: David Rowley Discussion: https://postgr.es/m/CAApHDvpGc9h0_oVD2CtgBcxCS1N-qDYZSeBRnUh+0CWJA9cMaA@mail.gmail.com Backpatch-through: 9.5, all supported versions
1 parent 7e07867 commit 317de9c
Copy full SHA for 317de9c

File tree

Expand file treeCollapse file tree

1 file changed

+16
-4
lines changed
Filter options
Expand file treeCollapse file tree

1 file changed

+16
-4
lines changed

‎src/backend/access/heap/heapam.c

Copy file name to clipboardExpand all lines: src/backend/access/heap/heapam.c
+16-4Lines changed: 16 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -569,8 +569,14 @@ heapgettup(HeapScanDesc scan,
569569
* forward scanners.
570570
*/
571571
scan->rs_syncscan = false;
572-
/* start from last page of the scan */
573-
if (scan->rs_startblock > 0)
572+
573+
/*
574+
* Start from last page of the scan. Ensure we take into account
575+
* rs_numblocks if it's been adjusted by heap_setscanlimits().
576+
*/
577+
if (scan->rs_numblocks != InvalidBlockNumber)
578+
page = (scan->rs_startblock + scan->rs_numblocks - 1) % scan->rs_nblocks;
579+
else if (scan->rs_startblock > 0)
574580
page = scan->rs_startblock - 1;
575581
else
576582
page = scan->rs_nblocks - 1;
@@ -868,8 +874,14 @@ heapgettup_pagemode(HeapScanDesc scan,
868874
* forward scanners.
869875
*/
870876
scan->rs_syncscan = false;
871-
/* start from last page of the scan */
872-
if (scan->rs_startblock > 0)
877+
878+
/*
879+
* Start from last page of the scan. Ensure we take into account
880+
* rs_numblocks if it's been adjusted by heap_setscanlimits().
881+
*/
882+
if (scan->rs_numblocks != InvalidBlockNumber)
883+
page = (scan->rs_startblock + scan->rs_numblocks - 1) % scan->rs_nblocks;
884+
else if (scan->rs_startblock > 0)
873885
page = scan->rs_startblock - 1;
874886
else
875887
page = scan->rs_nblocks - 1;

0 commit comments

Comments
0 (0)
Morty Proxy This is a proxified and sanitized view of the page, visit original site.