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Andres Freund 333f586372 bufmgr: Allow conditionally locking of already locked buffer 
In fcb9c977aa I included an assertion in BufferLockConditional() to detect if
a conditional lock acquisition is done on a buffer that we already have
locked. The assertion was added in the course of adding other assertions.
Unfortunately I failed to realize that some of our code relies on such lock
acquisitions to silently fail. E.g. spgist and nbtree may try to conditionally
lock an already locked buffer when acquiring a empty buffer.

LWLockAcquireConditional(), which was previously used to implement
ConditionalLockBuffer(), does not have such an assert.

Instead of just removing the assert, and relying on the lock acquisition to
fail due to the buffer already locked, this commit changes the behaviour of
conditional content lock acquisition to fail if the current backend has any
pre-existing lock on the buffer, even if the lock modes would not
conflict. The reason for that is that we currently do not have space to track
multiple lock acquisitions on a single buffer. Allowing multiple locks on the
same buffer by a backend also seems likely to lead to bugs.

There is only one non-self-exclusive conditional content lock acquisition, in
GetVictimBuffer(), but it only is used if the target buffer is not pinned and
thus can't already be locked by the current backend.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/90bd2cbb-49ce-4092-9f61-5ac2ab782c94@gmail.com
2026-01-29 16:49:01 -05:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config Update copyright for 2026 2026-01-01 13:24:10 -05:00
contrib Standardize replication origin naming to use "ReplOrigin". 2026-01-28 11:03:29 -08:00
doc Add support for "mcv" in pg_restore_extended_stats() 2026-01-29 12:14:08 +09:00
src bufmgr: Allow conditionally locking of already locked buffer 2026-01-29 16:49:01 -05:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:09:34 -04:00
.cirrus.tasks.yml ci: Configure g++ with 32-bit for 32-bit build 2026-01-09 08:58:50 +01:00
.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 a couple of recent commits to .git-blame-ignore-revs. 2026-01-28 15:56:48 -06:00
.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 Detect if flags are needed for C++11 support 2026-01-22 09:09:25 +01:00
configure.ac Detect if flags are needed for C++11 support 2026-01-22 09:09:25 +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 Remove AIX support 2024-02-28 15:17:23 +04:00
meson.build Detect if flags are needed for C++11 support 2026-01-22 09:09:25 +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/.