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Thomas Munro ae632f7a31 Fix race in SERIALIZABLE READ ONLY. 
Commit bdaabb9b started skipping doomed transactions when building the
list of possible conflicts for SERIALIZABLE READ ONLY.  That makes
sense, because doomed transactions won't commit, but a couple of subtle
things broke:

1.  If all uncommitted r/w transactions are doomed, a READ ONLY
transaction would arbitrarily not benefit from the safe snapshot
optimization.  It would not be taken immediately, and yet no other
transaction would set SXACT_FLAG_RO_SAFE later.

2.  In the same circumstances but with DEFERRABLE, GetSafeSnapshot()
would correctly exit its wait loop without sleeping and then take the
optimization in non-assert builds, but assert builds would fail a sanity
check that SXACT_FLAG_RO_SAFE had been set by another transaction.

This is similar to the case for PredXact->WritableSxactCount == 0.  We
should opt out immediately if our possibleUnsafeConflicts list is empty
after filtering.

The code to maintain the serializable global xmin is moved down below
the new opt out site, because otherwise we'd have to reverse its effects
before returning.

Back-patch to all supported releases.  Bug #17368.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/17116-d6ca217acc180e30%40postgresql.org
Discussion: https://postgr.es/m/20110707212159.GF76634%40csail.mit.edu
 		2023-03-09 17:09:57 +13:00
config Suppress warning about stack_base_ptr with late-model GCC. 2022-02-17 22:45:34 -05:00
contrib Fix calculation of which GENERATED columns need to be updated. 2023-01-05 14:12:17 -05:00
doc Stop recommending auto-download of DTD files, and indeed disable it. 2023-02-08 17:15:23 -05:00
src Fix race in SERIALIZABLE READ ONLY. 2023-03-09 17:09:57 +13:00
.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 Backpatch addition of .git-blame-ignore-revs 2022-08-05 19:36:24 +02:00
.gitattributes gitattributes: Add new file 2019-11-12 08:13:55 +01:00
.gitignore Add portlock directory to .gitignore 2022-11-26 07:47:16 -05:00
COPYRIGHT Update copyright for 2023 2023-01-02 15:00:36 -05:00
GNUmakefile.in Remove temporary portlock directory during make [dist]clean. 2022-11-26 10:30:58 -05:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Don't unset MAKEFLAGS in non-GNU Makefile. 2019-06-25 09:36:21 +12:00
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
aclocal.m4 Probe $PROVE not $PERL while checking for modules needed by TAP tests. 2021-11-22 12:54:52 -05:00
configure Fix handling of SCRAM-SHA-256's channel binding with RSA-PSS certificates 2023-02-15 10:12:36 +09:00
configure.in Fix handling of SCRAM-SHA-256's channel binding with RSA-PSS certificates 2023-02-15 10:12:36 +09:00

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/.