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Tom Lane 21fddb3d76 Don't treat EINVAL from semget() as a hard failure. 
It turns out that on some platforms (at least current macOS, NetBSD,
OpenBSD) semget(2) will return EINVAL if there is a pre-existing
semaphore set with the same key and too few semaphores.  Our code
expects EEXIST in that case and treats EINVAL as a hard failure,
resulting in failure during initdb or postmaster start.

POSIX does document EINVAL for too-few-semaphores-in-set, and is
silent on its priority relative to EEXIST, so this behavior arguably
conforms to spec.  Nonetheless it's quite problematic because EINVAL
is also documented to mean that nsems is greater than the system's
limit on the number of semaphores per set (SEMMSL).  If that is
where the problem lies, retrying would just become an infinite loop.

To resolve this contradiction, retry after EINVAL, but also install a
loop limit that will make us give up regardless of the specific errno
after trying 1000 different keys.  (1000 is a pretty arbitrary number,
but it seems like it should be sufficient.)  I like this better than
the previous infinite-looping behavior, since it will also keep us out
of trouble if (say) we get EACCES due to a system-level permissions
problem rather than anything to do with a specific semaphore set.

This problem has only been observed in the field in PG 17, which uses
a higher nsems value than other branches (cf. 38da05346, 810a8b1c8).
That makes it possible to get the failure if a new v17 postmaster
has a key collision with an existing postmaster of another branch.
In principle though, we might see such a collision against a semaphore
set created by some other application, in which case all branches are
vulnerable on these platforms.  Hence, backpatch.

Reported-by: Gavin Panella <gavinpanella@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CALL7chmzY3eXHA7zHnODUVGZLSvK3wYCSP0RmcDFHJY8f28Q3g@mail.gmail.com
Backpatch-through: 13
2025-08-13 12:00:03 -04:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config Improve prep_buildtree 2025-08-04 14:06:58 +02:00
contrib postgres_fdw: Fix tests with ANALYZE and remote sampling 2025-08-13 13:11:19 +09:00
doc Adjust some table column widths in PDF 2025-08-13 17:40:13 +02:00
src Don't treat EINVAL from semget() as a hard failure. 2025-08-13 12:00:03 -04:00
.cirrus.star Remove duplicate words in docs and code comments. 2023-10-09 09:18:47 +05:30
.cirrus.tasks.yml Hide ICU C++ APIs from pg_locale.h 2025-07-09 14:20:22 +07:00
.cirrus.yml ci: Test NetBSD and OpenBSD 2025-02-12 09:40:07 -05:00
.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 commit 1d1612aec7 to .git-blame-ignore-revs. 2025-07-29 10:32:53 -05:00
.gitattributes Add script to keep .editorconfig in sync with .gitattributes 2025-02-01 10:09:45 +01:00
.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 Fix ./configure checks with __cpuidex() and __cpuid() 2025-07-30 11:55:42 +09:00
configure.ac Fix ./configure checks with __cpuidex() and __cpuid() 2025-07-30 11:55:42 +09:00
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 Remove AIX support 2024-02-28 15:17:23 +04:00
meson.build meson: add and use stamp files for generated headers 2025-08-11 15:18:23 -04:00
meson_options.txt Add support for basic NUMA awareness 2025-04-07 23:08:17 +02:00
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/.