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Michael Paquier bf3dba508e Fix regression with slot invalidation checks
This commit reverts 818fefd8fd, that has been introduced to address a
an instability in some of the TAP tests due to the presence of random
standby snapshot WAL records, when slots are invalidated by
InvalidatePossiblyObsoleteSlot().

Anyway, this commit had also the consequence of introducing a behavior
regression.  After 818fefd8fd, the code may determine that a slot needs
to be invalidated while it may not require one: the slot may have moved
from a conflicting state to a non-conflicting state between the moment
when the mutex is released and the moment when we recheck the slot, in
InvalidatePossiblyObsoleteSlot().  Hence, the invalidations may be more
aggressive than they actually have to.

105b2cb336 has tackled the test instability in a way that should be
hopefully sufficient for the buildfarm, even for slow members:
- In v18, the test relies on an injection point that bypasses the
creation of the random records generated for standby snapshots,
eliminating the random factor that impacted the test.  This option was
not available when 818fefd8fd was discussed.
- In v16 and v17, the problem was bypassed by disallowing a slot to
become active in some of the scenarios tested.

While on it, this commit adds a comment to document that it is fine for
a recheck to use xmin and LSN values stored in the slot, without storing
and reusing them across multiple checks.

Reported-by: "suyu.cmj" <mengjuan.cmj@alibaba-inc.com>
Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://postgr.es/m/f492465f-657e-49af-8317-987460cb68b0.mengjuan.cmj@alibaba-inc.com
Backpatch-through: 16
2025-10-30 13:13:31 +09:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config Don't put library-supplied -L/-I switches before user-supplied ones. 2025-07-29 15:17:40 -04:00
contrib pg_stat_statements: Fix handling of duplicate constant locations 2025-10-29 12:35:02 +01:00
doc doc: Remove mention of Git protocol support 2025-10-23 21:26:15 +02:00
src Fix regression with slot invalidation checks 2025-10-30 13:13:31 +09:00
.abi-compliance-history Update .abi-compliance-history file. 2025-10-21 12:23:23 -05:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:09:53 -04:00
.cirrus.tasks.yml ci: Simplify ci-os-only handling 2025-08-14 12:09:53 -04:00
.cirrus.yml ci: Per-repo configuration for manually trigger tasks 2025-08-14 11:33:44 -04:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Add script to keep .editorconfig in sync with .gitattributes 2025-02-01 10:09:45 +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 10:32:22 +02:00
.gitignore Update top-level .gitignore. 2022-12-04 15:23:00 -05:00
.mailmap Add a Git .mailmap file 2024-11-05 13:56:02 +01:00
aclocal.m4 autoconf: Move export_dynamic determination to configure 2022-12-06 18:55:28 -08:00
configure Stamp 18.0. 2025-09-22 16:11:33 -04:00
configure.ac Stamp 18.0. 2025-09-22 16:11:33 -04:00
COPYRIGHT Align organization wording in copyright statement 2025-05-16 11:20:07 -04:00
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_18_STABLE to its new status as a stable branch 2025-06-29 23:00:00 -04:00
meson.build Fix meson build with -Duuid=ossp when using version older than 0.60 2025-09-24 08:00:09 +09:00
meson_options.txt Add support for basic NUMA awareness 2025-04-07 23:08:17 +02:00
README.md Adapt REL_18_STABLE to its new status as a stable branch 2025-06-29 23:00:00 -04:00

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/18/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/18/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/.