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Remove docs for "Incrementally Updated Backups" because it was of 

questionable reliability;  information moved to a wiki:

	http://wiki.postgresql.org/wiki/Incrementally_Updated_Backups

Backpatch to 9.0.
This commit is contained in:
Bruce Momjian 2010-08-25 23:55:54 +00:00
parent 9389ac8928
commit 13e6d6c5da
1 changed files with 1 additions and 92 deletions
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doc/src/sgml/high-availability.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.80 2010/08/24 15:22:12 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.81 2010/08/25 23:55:54 momjian Exp $ -->
<chapter id="high-availability">
<title>High Availability, Load Balancing, and Replication</title>
@ -1890,95 +1890,4 @@ LOG: database system is ready to accept read only connections
</sect1>
<sect1 id="backup-incremental-updated">
<title>Incrementally Updated Backups</title>
<indexterm zone="high-availability">
<primary>incrementally updated backups</primary>
</indexterm>
<indexterm zone="high-availability">
<primary>change accumulation</primary>
</indexterm>
<para>
In a standby configuration, it is possible to offload the expense of
taking periodic base backups from the primary server; instead base backups
can be made by backing
up a standby server's files. This concept is generally known as
incrementally updated backups, log change accumulation, or more simply,
change accumulation.
</para>
<para>
If we take a file system backup of the standby server's data
directory while it is processing
logs shipped from the primary, we will be able to reload that backup and
restart the standby's recovery process from the last restart point.
We no longer need to keep WAL files from before the standby's restart point.
If recovery is needed, it will be faster to recover from the incrementally
updated backup than from the original base backup.
</para>
<para>
The procedure for taking a file system backup of the standby server's
data directory while it's processing logs shipped from the primary is:
<orderedlist>
<listitem>
<para>
Perform the backup, without using <function>pg_start_backup</> and
<function>pg_stop_backup</>. Note that the <filename>pg_control</>
file must be backed up <emphasis>first</>, as in:
<programlisting>
cp /var/lib/pgsql/data/global/pg_control /tmp
cp -r /var/lib/pgsql/data /path/to/backup
mv /tmp/pg_control /path/to/backup/data/global
</programlisting>
<filename>pg_control</> contains the location where WAL replay will
begin after restoring from the backup; backing it up first ensures
that it points to the last restartpoint when the backup started, not
some later restartpoint that happened while files were copied to the
backup.
</para>
</listitem>
<listitem>
<para>
Make note of the backup ending WAL location by calling the <function>
pg_last_xlog_replay_location</> function at the end of the backup,
and keep it with the backup.
<programlisting>
psql -c "select pg_last_xlog_replay_location();" > /path/to/backup/end_location
</programlisting>
When recovering from the incrementally updated backup, the server
can begin accepting connections and complete the recovery successfully
before the database has become consistent. To avoid that, you must
ensure the database is consistent before users try to connect to the
server and when the recovery ends. You can do that by comparing the
progress of the recovery with the stored backup ending WAL location:
the server is not consistent until recovery has reached the backup end
location. The progress of the recovery can also be observed with the
<function>pg_last_xlog_replay_location</> function, though that requires
connecting to the server while it might not be consistent yet, so
care should be taken with that method.
</para>
<para>
</para>
</listitem>
</orderedlist>
</para>
<para>
Since the standby server is not <quote>live</>, it is not possible to
use <function>pg_start_backup()</> and <function>pg_stop_backup()</>
to manage the backup process; it will be up to you to determine how
far back you need to keep WAL segment files to have a recoverable
backup. That is determined by the last restartpoint when the backup
was taken, any WAL older than that can be deleted from the archive
once the backup is complete. You can determine the last restartpoint
by running <application>pg_controldata</> on the standby server before
taking the backup, or by using the <varname>log_checkpoints</> option
to print values to the standby's server log.
</para>
</sect1>
</chapter>