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Alvaro Herrera 8e9a16ab8f Rework tuple freezing protocol 
Tuple freezing was broken in connection to MultiXactIds; commit
8e53ae025d tried to fix it, but didn't go far enough.  As noted by
Noah Misch, freezing a tuple whose Xmax is a multi containing an aborted
update might cause locks in the multi to go ignored by later
transactions.  This is because the code depended on a multixact above
their cutoff point not having any lock-only member older than the cutoff
point for Xids, which is easily defeated in READ COMMITTED transactions.

The fix for this involves creating a new MultiXactId when necessary.
But this cannot be done during WAL replay, and moreover multixact
examination requires using CLOG access routines which are not supposed
to be used during WAL replay either; so tuple freezing cannot be done
with the old freeze WAL record.  Therefore, separate the freezing
computation from its execution, and change the WAL record to carry all
necessary information.  At WAL replay time, it's easy to re-execute
freezing because we don't need to re-compute the new infomask/Xmax
values but just take them from the WAL record.

While at it, restructure the coding to ensure all page changes occur in
a single critical section without much room for failures.  The previous
coding wasn't using a critical section, without any explanation as to
why this was acceptable.

In replication scenarios using the 9.3 branch, standby servers must be
upgraded before their master, so that they are prepared to deal with the
new WAL record once the master is upgraded; failure to do so will cause
WAL replay to die with a PANIC message.  Later upgrade of the standby
will allow the process to continue where it left off, so there's no
disruption of the data in the standby in any case.  Standbys know how to
deal with the old WAL record, so it's okay to keep the master running
the old code for a while.

In master, the old freeze WAL record is gone, for cleanliness' sake;
there's no compatibility concern there.

Backpatch to 9.3, where the original bug was introduced and where the
previous fix was backpatched.

Álvaro Herrera and Andres Freund
 		2013-12-16 11:29:51 -03:00
config Compiler optimizations for page checksum code. 2013-04-30 06:59:26 +01:00
contrib Fix progress logging when scale factor is large. 2013-12-12 19:07:53 +09:00
doc Fix ancient docs/comments thinko: XID comparison is mod 2^32, not 2^31. 2013-12-12 12:39:54 -05:00
src Rework tuple freezing protocol 2013-12-16 11:29:51 -03:00
.gitignore Add pkg-config files for libpq and ecpg libraries 2013-03-31 16:58:40 -04:00
COPYRIGHT Update copyrights for 2013 2013-01-01 17:15:01 -05:00
GNUmakefile.in Make init-po and update-po recursive make targets 2012-06-29 14:01:54 +03:00
Makefile Allow make check in PL directories 2011-02-15 06:52:12 +02:00
README Remove useless whitespace at end of lines 2010-11-23 22:34:55 +02:00
README.git Fix doc links in README file to work with new website layout 2013-11-12 12:54:09 +01:00
aclocal.m4 Remove cvs keywords from all files. 2010-09-20 22:08:53 +02:00
configure Stamp 9.3.2. 2013-12-02 15:57:48 -05:00
configure.in Stamp 9.3.2. 2013-12-02 15:57:48 -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.  Changes between all PostgreSQL releases are recorded in the
file HISTORY.  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/.