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Andres Freund ce5d489166 Fix bug due to confusion about what IsMVCCSnapshot means 
In 0b96e734c5 I (Andres) relied on page_collect_tuples() being called only
with an MVCC snapshot, and added assertions to that end, but did not realize
that IsMVCCSnapshot() allows both proper MVCC snapshots and historical
snapshots, which behave quite similarly to MVCC snapshots.

Unfortunately that can lead to incorrect visibility results during logical
decoding, as a historical snapshot is interpreted as a plain MVCC
snapshot. The only reason this wasn't noticed earlier is that it's hard to
reach as most of the time there are no sequential scans during logical
decoding.

To fix the bug and avoid issues like this in the future, split
IsMVCCSnapshot() into IsMVCCSnapshot() and IsMVCCLikeSnapshot(), where now
only the latter includes historic snapshots.

One effect of this is that during logical decoding no page-at-a-time snapshots
are used, as otherwise runtime branches to handle historic snapshots would be
needed in some performance critical paths. Given how uncommon sequential scans
are during logical decoding, that seems acceptable.

Author: Antonin Houska <ah@cybertec.at>
Reported-by: Antonin Houska <ah@cybertec.at>
Discussion: https://postgr.es/m/61812.1770637345@localhost
2026-03-13 13:53:19 -04:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config Change copyObject() to use typeof_unqual 2026-03-13 07:06:57 +01:00
contrib Initialize variable to placate compiler. 2026-03-13 11:32:14 -05:00
doc Add stats_reset column to pg_stat_database_conflicts. 2026-03-13 22:17:14 +09:00
src Fix bug due to confusion about what IsMVCCSnapshot means 2026-03-13 13:53:19 -04:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:09:34 -04:00
.cirrus.tasks.yml Revert "Change default value of default_toast_compression to "lz4"" 2026-03-05 08:25:35 +09:00
.cirrus.yml ci: Per-repo configuration for manually trigger tasks 2025-08-14 11:54:03 -04:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Update .editorconfig and .gitattributes for postgresql.conf.sample. 2025-11-18 10:28:36 -06:00
.git-blame-ignore-revs Add commit b6eb8dde6b to .git-blame-ignore-revs. 2026-03-13 11:45:34 -05:00
.gitattributes Update .editorconfig and .gitattributes for postgresql.conf.sample. 2025-11-18 10:28:36 -06:00
.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 Change copyObject() to use typeof_unqual 2026-03-13 07:06:57 +01:00
configure.ac Change copyObject() to use typeof_unqual 2026-03-13 07:06:57 +01:00
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 Restore AIX support. 2026-02-23 13:34:22 -05:00
meson.build Change copyObject() to use typeof_unqual 2026-03-13 07:06:57 +01:00
meson_options.txt Update copyright for 2026 2026-01-01 13:24:10 -05:00
README.md Revise the style of a paragraph in README.md. 2024-03-21 10:16:41 -05:00

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