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Robert Haas 5bbac7ec1b Advance the stop point for multixact offset creation only at checkpoint. 
Commit b69bf30b9b advanced the stop point
at vacuum time, but this has subsequently been shown to be unsafe as a
result of analysis by myself and Thomas Munro and testing by Thomas
Munro.  The crux of the problem is that the SLRU deletion logic may
get confused about what to remove if, at exactly the right time during
the checkpoint process, the head of the SLRU crosses what used to be
the tail.

This patch, by me, fixes the problem by advancing the stop point only
following a checkpoint.  This has the additional advantage of making
the removal logic work during recovery more like the way it works during
normal running, which is probably good.

At least one of the calls to DetermineSafeOldestOffset which this patch
removes was already dead, because MultiXactAdvanceOldest is called only
during recovery and DetermineSafeOldestOffset was set up to do nothing
during recovery.  That, however, is inconsistent with the principle that
recovery and normal running should work similarly, and was confusing to
boot.

Along the way, fix some comments that previous patches in this area
neglected to update.  It's not clear to me whether there's any
concrete basis for the decision to use only half of the multixact ID
space, but it's neither necessary nor sufficient to prevent multixact
member wraparound, so the comments should not say otherwise.
2015-05-10 22:45:42 -04:00
config On OS X, link libpython normally, ignoring the "framework" framework. 2014-05-30 18:19:14 -04:00
contrib Fix incorrect declaration of citext's regexp_matches() functions. 2015-05-05 15:50:53 -04:00
doc Recommend include_realm=1 in docs 2015-05-08 19:40:06 -04:00
src Advance the stop point for multixact offset creation only at checkpoint. 2015-05-10 22:45:42 -04:00
.gitignore Add pkg-config files for libpq and ecpg libraries 2013-03-31 16:58:40 -04:00
aclocal.m4 Remove cvs keywords from all files. 2010-09-20 22:08:53 +02:00
configure Suppress clang's unhelpful gripes about -pthread switch being unused. 2015-04-05 13:01:55 -04:00
configure.in Suppress clang's unhelpful gripes about -pthread switch being unused. 2015-04-05 13:01:55 -04:00
COPYRIGHT Update copyright for 2015 2015-01-06 11:43:46 -05:00
GNUmakefile.in Don't generate plain-text HISTORY and src/test/regress/README anymore. 2014-02-10 20:48:12 -05:00
HISTORY Improve text of stub HISTORY file. 2014-02-12 18:16:27 -05:00
Makefile Allow make check in PL directories 2011-02-15 06:52:12 +02:00
README Don't generate plain-text HISTORY and src/test/regress/README anymore. 2014-02-10 20:48:12 -05:00
README.git Don't generate plain-text HISTORY and src/test/regress/README anymore. 2014-02-10 20:48:12 -05:00

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:

	http://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
http://www.postgresql.org/download/.  For more information look at our
web site located at http://www.postgresql.org/.