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Heikki Linnakangas dcd9c06a42 Fix OldestMemberMXactId and OldestVisibleMXactId array usage 
Commit ab355e3a88 changed how the OldestMemberMXactId array is
indexed. It's no longer indexed by synthetic dummyBackendId, but with
ProcNumber. The PGPROC entries for prepared xacts come after auxiliary
processes in the allProcs array, which rendered the calculation for
MaxOldestSlot and the indexes into the array incorrect.  (The
OldestVisibleMXactId array is not used for prepared xacts, and thus
never accessed with ProcNumber's greater than MaxBackends, so this
only affects the OldestMemberMXactId array.)

As a result, a prepared xact would store its value past the end of the
OldestMemberMXactId array, overflowing into the OldestVisibleMXactId
array. That could cause a transaction's row lock to appear invisible
to other backends, or other such visibility issues. With a very small
max_connections setting, the store could even go beyond the
OldestVisibleMXactId array, stomping over the first element in the
BufferDescriptor array.

To fix, calculate the array sizes more precisely, and introduce helper
functions to calculate the array indexes correctly.

Author: Yura Sokolov <y.sokolov@postgrespro.ru>
Reviewed-by: Sami Imseih <samimseih@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://www.postgresql.org/message-id/7acc94b0-ea82-4657-b1b0-77842cb7a60c@postgrespro.ru
Backpatch-through: 17
2026-03-02 19:19:29 +02:00
config Allow PG_PRINTF_ATTRIBUTE to be different in C and C++ code. 2026-02-25 11:57:26 -05:00
contrib postgres_fdw: Fix thinko in comment for UserMappingPasswordRequired(). 2026-02-27 17:05:03 +09:00
doc doc: Clarify INCLUDING COMMENTS behavior in CREATE TABLE LIKE. 2026-02-26 09:02:53 +09:00
src Fix OldestMemberMXactId and OldestVisibleMXactId array usage 2026-03-02 19:19:29 +02:00
.abi-compliance-history Placate ABI checker. 2026-02-07 11:48:14 +13:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:02:42 -04:00
.cirrus.tasks.yml Fix typo 2026-01-07 15:48:54 +01:00
.cirrus.yml ci: Per-repo configuration for manually trigger tasks 2025-08-14 11:33:47 -04:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Add .editorconfig 2019-12-18 09:13:13 +01:00
.git-blame-ignore-revs Add previous commit to .git-blame-ignore-revs. 2025-10-21 10:02:19 -05:00
.gitattributes Fix git whitespace warning 2025-08-15 10:32:07 +02:00
.gitignore Update top-level .gitignore. 2022-12-04 15:23:00 -05:00
aclocal.m4 autoconf: Move export_dynamic determination to configure 2022-12-06 18:55:28 -08:00
configure Allow PG_PRINTF_ATTRIBUTE to be different in C and C++ code. 2026-02-25 11:57:26 -05:00
configure.ac Allow PG_PRINTF_ATTRIBUTE to be different in C and C++ code. 2026-02-25 11:57:26 -05:00
COPYRIGHT Update copyright for 2026 2026-01-01 13:24:10 -05:00
GNUmakefile.in Allow selecting the git revision to be packaged by "make dist". 2024-05-03 11:08:50 -04:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Adapt REL_17_STABLE to its new status as a stable branch 2024-07-01 08:05:35 +09:00
meson.build Allow PG_PRINTF_ATTRIBUTE to be different in C and C++ code. 2026-02-25 11:57:26 -05:00
meson_options.txt Allow selecting the git revision to be packaged by "make dist". 2024-05-03 11:08:50 -04:00
README.md Adapt REL_17_STABLE to its new status as a stable branch 2024-07-01 08:05:35 +09:00

README.md

PostgreSQL Database Management System

This directory contains the source code distribution of the PostgreSQL database management system.

PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.

Copyright and license information can be found in the file COPYRIGHT.

General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/17/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/17/installation.html.

The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.