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Michael Paquier e3714dc059 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 13:13:37 +09:00
config Don't put library-supplied -L/-I switches before user-supplied ones. 2025-07-29 15:17:41 -04:00
contrib Allow role created by new test to log in on Windows. 2025-10-18 18:36:21 -04:00
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 13:13:37 +09:00
.abi-compliance-history Add .abi-compliance-history to back-branches. 2025-10-21 16:37:29 -05:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:03:27 -04:00
.cirrus.tasks.yml ci: Simplify ci-os-only handling 2025-08-14 12:03:27 -04:00
.cirrus.yml ci: Per-repo configuration for manually trigger tasks 2025-08-14 11:33:50 -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 10:31:52 +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 Stamp 16.10. 2025-08-11 17:06:43 -04:00
configure.ac Stamp 16.10. 2025-08-11 17:06:43 -04:00
COPYRIGHT Align organization wording in copyright statement 2025-05-16 11:20:07 -04:00
GNUmakefile.in Integrate pg_bsd_indent into our build/test infrastructure. 2023-02-12 12:22:21 -05:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Dynamically find correct installation docs in Makefile. 2022-01-19 14:48:25 +01:00
meson.build Fix meson build with -Duuid=ossp when using version older than 0.60 2025-09-22 08:03:31 +09:00
meson_options.txt meson: Attach colon to keyword argument 2023-06-29 12:53:41 +02:00
README Canonicalize some URLs 2020-02-10 20:47:50 +01:00
README.git Canonicalize some URLs 2020-02-10 20:47:50 +01:00

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.

PostgreSQL has many language interfaces, many of which are listed here:

	https://www.postgresql.org/download/

See the file INSTALL for instructions on how to build and install
PostgreSQL.  That file also lists supported operating systems and
hardware platforms and contains information regarding any other
software packages that are required to build or run the PostgreSQL
system.  Copyright and license information can be found in the
file COPYRIGHT.  A comprehensive documentation set is included in this
distribution; it can be read as described in the installation
instructions.

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