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Alexander Korotkov e85662df44 Fix false reports in pg_visibility 
Currently, pg_visibility computes its xid horizon using the
GetOldestNonRemovableTransactionId().  The problem is that this horizon can
sometimes go backward.  That can lead to reporting false errors.

In order to fix that, this commit implements a new function
GetStrictOldestNonRemovableTransactionId().  This function computes the xid
horizon, which would be guaranteed to be newer or equal to any xid horizon
computed before.

We have to do the following to achieve this.

1. Ignore processes xmin's, because they consider connection to other databases
   that were ignored before.
2. Ignore KnownAssignedXids, because they are not database-aware. At the same
   time, the primary could compute its horizons database-aware.
3. Ignore walsender xmin, because it could go backward if some replication
   connections don't use replication slots.

As a result, we're using only currently running xids to compute the horizon.
Surely these would significantly sacrifice accuracy.  But we have to do so to
avoid reporting false errors.

Inspired by earlier patch by Daniel Shelepanov and the following discussion
with Robert Haas and Tom Lane.

Discussion: https://postgr.es/m/1649062270.289865713%40f403.i.mail.ru
Reviewed-by: Alexander Lakhin, Dmitry Koval
 		2024-03-14 13:12:05 +02:00
config Remove AIX support 2024-02-28 15:17:23 +04:00
contrib Fix false reports in pg_visibility 2024-03-14 13:12:05 +02:00
doc Introduce "builtin" collation provider. 2024-03-13 23:33:44 -07:00
src Fix false reports in pg_visibility 2024-03-14 13:12:05 +02:00
.cirrus.star Remove duplicate words in docs and code comments. 2023-10-09 09:18:47 +05:30
.cirrus.tasks.yml ci: Use a RAM disk and more CPUs on FreeBSD. 2024-03-13 14:58:27 +13:00
.cirrus.yml ci: Make compute resources for CI configurable 2023-08-23 15:15:28 -07:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Add .editorconfig 2019-12-18 09:13:13 +01:00
.git-blame-ignore-revs Add a few recent commits to .git-blame-ignore-revs. 2024-03-05 14:15:06 -06:00
.gitattributes Remove non-existing file from .gitattributes 2024-02-16 11:39:09 +01:00
.gitignore Update top-level .gitignore. 2022-12-04 15:23:00 -05:00
COPYRIGHT Update copyright for 2024 2024-01-03 20:49:05 -05:00
GNUmakefile.in Combine headerscheck and cpluspluscheck scripts 2024-03-10 07:56:17 +01:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Remove AIX support 2024-02-28 15:17:23 +04:00
README.md Convert README to Markdown. 2024-02-28 14:53:52 -06:00
aclocal.m4 autoconf: Move export_dynamic determination to configure 2022-12-06 18:55:28 -08:00
configure Add --copy-file-range option to pg_upgrade. 2024-03-06 12:01:01 +13:00
configure.ac Add --copy-file-range option to pg_upgrade. 2024-03-06 12:01:01 +13:00
meson.build meson: macos: Avoid warnings on Sonoma 2024-03-13 01:40:53 -07:00
meson_options.txt Add backend support for injection points 2024-01-22 10:15:50 +09:00

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/.