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Jacob Champion 4966bd3ed9 libpq: Grease the protocol by default
Send PG_PROTOCOL_GREASE and _pq_.test_protocol_negotiation, which were
introduced in commit d8d7c5dc8, by default, and fail the connection if
the server attempts to claim support for them. The hope is to provide
feedback to noncompliant implementations and gain confidence in our
ability to advance the protocol. (See the other commit for details.)

To help end users navigate the situation, a link to our documentation
that explains the behavior is displayed. We append this to the error
message when the NegotiateProtocolVersion response is incorrect, or when
the peer sends an error during startup that appears to be grease-
related.

It's still possible for users to connect to servers that don't support
protocol negotiation, by adding max_protocol_version=3.0 to their
connection strings. Only the default connection behavior is impacted.

This commit is tracked as a PG19 open item and will be reverted before
RC1. (The implementation here doesn't handle negotiation with later
server versions, so it can't be released into the wild as a
five-year-supported feature. But an improved implementation might be
able to do so, in the future...)

Author: Jelte Fennema-Nio <postgres@jeltef.nl>
Co-authored-by: Jacob Champion <jacob.champion@enterprisedb.com>
Discussion: https://postgr.es/m/DDPR5BPWH1RJ.1LWAK6QAURVAY%40jeltef.nl
2026-02-23 10:48:20 -08:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config Restore AIX support. 2026-02-23 13:34:22 -05:00
contrib Fix additional fallthrough warnings from clang 2026-02-23 07:40:19 +01:00
doc libpq: Grease the protocol by default 2026-02-23 10:48:20 -08:00
src libpq: Grease the protocol by default 2026-02-23 10:48:20 -08:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:09:34 -04:00
.cirrus.tasks.yml meson: allow disabling building/installation of static libraries. 2026-02-23 16:45:40 +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 Restore AIX support. 2026-02-23 13:34:22 -05:00
configure.ac Restore AIX support. 2026-02-23 13:34:22 -05:00
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 Restore AIX support. 2026-02-23 13:34:22 -05:00
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

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/.