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Melanie Plageman da6874635d Make local buffers pin limit more conservative 
GetLocalPinLimit() and GetAdditionalLocalPinLimit(), currently in use
only by the read stream, previously allowed a backend to pin all
num_temp_buffers local buffers. This meant that the read stream could
use every available local buffer for read-ahead, leaving none for other
concurrent pin-holders like other read streams and related buffers like
the visibility map buffer needed during on-access pruning.

This became more noticeable since b46e1e54d0, which allows on-access
pruning to set the visibility map, which meant that some scans also
needed to pin a page of the VM. It caused a test in
src/test/regress/sql/temp.sql to fail in some cases.

Cap the local pin limit to num_temp_buffers / 4, providing some
headroom. This doesn't guarantee that all needed pins will be available
— for example, a backend can still open more cursors than there are
buffers — but it makes it less likely that read-ahead will exhaust the
pool.

Note that these functions are not limited by definition to use in the
read stream; however, this cap should be appropriate in other contexts.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/97529f5a-ec10-46b1-ab50-4653126c6889%40gmail.com
2026-04-21 11:03:05 -04:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config Update config.guess and config.sub 2026-04-09 11:26:14 +02:00
contrib Fix a set of typos and grammar issues across the tree 2026-04-21 14:46:22 +09:00
doc Fix a set of typos and grammar issues across the tree 2026-04-21 14:46:22 +09:00
src Make local buffers pin limit more conservative 2026-04-21 11:03:05 -04:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:09:34 -04:00
.cirrus.tasks.yml Enable test_cplusplusext with MSVC 2026-04-01 07:48:47 +02:00
.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 commits to .git-blame-ignore-revs. 2026-04-08 13:41:22 -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 Add errdetail() with PID and UID about source of termination signal. 2026-04-07 10:22:33 -04:00
configure.ac Add errdetail() with PID and UID about source of termination signal. 2026-04-07 10:22:33 -04:00
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 Meson: Fix check_header() for readline and gssapi 2026-04-20 12:36:14 +09:00
meson_options.txt Revert "Add built-in fuzzing harnesses for security testing." 2026-04-10 09:53:58 -04:00
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/.