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Michael Paquier 2b8e5273e9 Fix handling of shared statistics with dropped databases
Dropping a database while a connection is attempted on it was able to
lead to the presence of valid database entries in shared statistics.
The issue is that MyDatabaseId was getting set too early than it should,
as, if the connection attempted on the dropped database fails when
renamed or dropped, the shutdown callback of the shared statistics would
finish by re-inserting a correct entry related to the database already
dropped.

As analyzed by the bug reporters, this issue could lead to phantom
entries in the database list maintained by the autovacuum launcher
(in rebuild_database_list()) if the database dropped was part of the
database list when it was still valid.  After the database was dropped,
it would remain the highest on the list of databases to considered by
the autovacuum worker as things to process.  This would prevent
autovacuum jobs to happen on all the other databases still present.

The commit fixes this issue by delaying setting MyDatabaseId until the
database existence has been re-checked with the second scan on
pg_database after getting a shared lock on it, and by switching
pgstat_update_dbstats() so as nothing happens if MyDatabaseId is not
valid.

Issue introduced by 5891c7a8ed, so backpatch down to 15.

Reported-by: Will Mortensen, Jacob Speidel
Analyzed-by: Will Mortensen, Jacob Speidel
Author: Andres Freund
Discussion: https://postgr.es/m/17973-bca1f7d5c14f601e@postgresql.org
Backpatch-through: 15
2023-09-04 08:04:22 +09:00
config Use native CRC instructions on 64-bit LoongArch 2023-08-10 11:36:15 +07:00
contrib postgres_fdw: Fix test for parameterized foreign scan. 2023-08-30 17:15:00 +09:00
doc Doc: Improve documentation for creating custom scan paths. 2023-08-30 17:45:00 +09:00
src Fix handling of shared statistics with dropped databases 2023-09-04 08:04:22 +09:00
.cirrus.star ci: Prepare to make compute resources for CI configurable 2023-08-23 15:15:28 -07:00
.cirrus.tasks.yml Use "template" data directory in tests 2023-08-24 14:38:02 -07:00
.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
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.git-blame-ignore-revs Add bc6041b61f to .git-blame-ignore-revs. 2023-08-30 16:06:12 +09:00
.gitattributes gitattributes: Ignore imported pg_bsd_indent code for whitespace checks 2023-02-22 09:00:28 +01:00
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aclocal.m4 autoconf: Move export_dynamic determination to configure 2022-12-06 18:55:28 -08:00
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COPYRIGHT Update copyright for 2023 2023-01-02 15:00:37 -05:00
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HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
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meson_options.txt meson: Attach colon to keyword argument 2023-06-29 12:53:41 +02:00
meson.build Generate a locale-agnostic initdb template 2023-08-29 18:06:55 +02:00
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README.git Canonicalize some URLs 2020-02-10 20:47:50 +01:00

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.

PostgreSQL has many language interfaces, many of which are listed here:

	https://www.postgresql.org/download/

See the file INSTALL for instructions on how to build and install
PostgreSQL.  That file also lists supported operating systems and
hardware platforms and contains information regarding any other
software packages that are required to build or run the PostgreSQL
system.  Copyright and license information can be found in the
file COPYRIGHT.  A comprehensive documentation set is included in this
distribution; it can be read as described in the installation
instructions.

The latest version of this software may be obtained at
https://www.postgresql.org/download/.  For more information look at our
web site located at https://www.postgresql.org/.