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Michael Paquier ccfbd9287d Replace existing durable_rename_excl() calls with durable_rename() 
durable_rename_excl() attempts to avoid overwriting any existing files
by using link() and unlink(), falling back to rename() on some platforms
(e.g., Windows where link() followed by unlink() is not concurrent-safe,
see 909b449).  Most callers of durable_rename_excl() use it just in case
there is an existing file, but it happens that for all of them we never
expect a target file to exist (WAL segment recycling, creation of
timeline history file and basic_archive).

basic_archive used durable_rename_excl() to avoid overwriting an archive
concurrently created by another server.  Now, there is a stat() call to
avoid overwriting an existing archive a couple of lines above, so note
that this change opens a small TOCTOU window in this module between the
stat() call and durable_rename().

Furthermore, as mentioned in the top comment of durable_rename_excl(),
this routine can result in multiple hard links to the same file and data
corruption, with two or more links to the same file in pg_wal/ if a
crash happens before the unlink() call during WAL recycling.
Specifically, this would produce links to the same file for the current
WAL file and the next one because the half-recycled WAL file was
re-recycled during crash recovery of a follow-up cluster restart.

This change replaces all calls to durable_rename_excl() with
durable_rename().  This removes the protection against accidentally
overwriting an existing file, but some platforms are already living
without it, and all those code paths never expect an existing file (a
couple of assertions are added to check after that, in case).

This is a bug fix, but knowing the unlikeliness of the problem involving
one of more crashes at an exceptionally bad moment, no backpatch is
done.  This could be revisited in the future.

Author: Nathan Bossart
Reviewed-by: Robert Haas, Kyotaro Horiguchi, Michael Paquier
Discussion: https://postgr.es/m/20220407182954.GA1231544@nathanxps13
2022-04-28 10:11:45 +09:00
config Update config.guess and config.sub 2022-04-07 07:45:25 +02:00
contrib Replace existing durable_rename_excl() calls with durable_rename() 2022-04-28 10:11:45 +09:00
doc doc: Add links to tables 2022-04-22 11:19:17 +02:00
src Replace existing durable_rename_excl() calls with durable_rename() 2022-04-28 10:11:45 +09:00
.cirrus.yml Make upgradecheck a no-op in MSVC's vcregress.pl 2022-04-02 12:06:11 +09:00
.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 and not so recent revs to git-blame-ignore-revs. 2022-03-19 12:37:28 -07:00
.gitattributes Remove trailing whitespace from *.sgml files. 2022-04-20 11:04:49 -04:00
.gitignore Support for optimizing and emitting code in LLVM JIT provider. 2018-03-22 11:05:22 -07:00
aclocal.m4 Probe $PROVE not $PERL while checking for modules needed by TAP tests. 2021-11-22 12:54:52 -05:00
configure Set minimum required version of zstd as 1.4.0. 2022-04-01 11:05:52 -04:00
configure.ac Set minimum required version of zstd as 1.4.0. 2022-04-01 11:05:52 -04:00
COPYRIGHT Update copyright for 2022 2022-01-07 19:04:57 -05:00
GNUmakefile.in add missing tag from commit b8c4261e5e 2021-07-01 15:47:46 -04:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Dynamically find correct installation docs in Makefile. 2022-01-19 14:48:25 +01:00
README Canonicalize some URLs 2020-02-10 20:47:50 +01:00
README.git Canonicalize some URLs 2020-02-10 20:47:50 +01:00

README 

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/.