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David Rowley 712ce074a8 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 7516f5259 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
2021-01-25 20:00:16 +13:00
..
backend Fix hypothetical bug in heap backward scans 2021-01-25 20:00:16 +13:00
bin Fix pg_dump for GRANT OPTION among initial privileges. 2021-01-16 12:21:39 -08:00
common Replace use of sys_siglist[] with strsignal(). 2020-07-15 22:05:12 -04:00
fe_utils Fix translation of special characters in psql's LaTeX output modes. 2018-11-26 17:32:51 -05:00
include Prevent excess SimpleLruTruncate() deletion. 2021-01-16 12:21:39 -08:00
interfaces Stamp 10.15. 2020-11-09 17:29:52 -05:00
makefiles Select CFLAGS_SL at configure time, not in platform-specific Makefiles. 2019-10-21 12:32:36 -04:00
pl Translation updates 2020-11-09 12:42:39 +01:00
port Stamp 10.15. 2020-11-09 17:29:52 -05:00
template Further tweaking of PG_SYSROOT heuristics for macOS. 2021-01-20 12:07:46 -05:00
test Fix ALTER DEFAULT PRIVILEGES with duplicated objects 2021-01-20 11:39:24 +09:00
timezone Update time zone data files to tzdata release 2021a. 2021-01-24 16:29:48 -05:00
tools Sync our copy of the timezone library with IANA release tzcode2020c. 2020-10-16 21:40:16 -04:00
tutorial Phase 2 of pgindent updates. 2017-06-21 15:19:25 -04:00
.gitignore Convert cvsignore to gitignore, and add .gitignore for build targets. 2010-09-22 12:57:04 +02:00
DEVELOPERS Replace a couple of references to files that no longer exist in the source 2009-05-04 08:08:47 +00:00
Makefile Build src/test/isolation during "make" and "make install". 2017-11-22 20:18:52 -08:00
Makefile.global.in Select CFLAGS_SL at configure time, not in platform-specific Makefiles. 2019-10-21 12:32:36 -04:00
Makefile.shlib makefile: use proper linker flags for C++ compiles 2020-03-31 22:26:11 -04:00
nls-global.mk nls-global.mk: search build dir for source files, too 2016-06-07 18:55:18 -04:00