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Update recovery documentation.
Simon Riggs
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<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.88 2006/09/19 19:04:51 neilc Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.89 2006/10/02 22:33:02 momjian Exp $ -->
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<chapter id="backup">
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<title>Backup and Restore</title>
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@ -1167,6 +1167,48 @@ restore_command = 'copy /mnt/server/archivedir/%f "%p"' # Windows
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</para>
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</sect2>
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<sect2 id="backup-incremental-updated">
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<title>Incrementally Updated Backups</title>
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<indexterm zone="backup">
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<primary>incrementally updated backups</primary>
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</indexterm>
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<indexterm zone="backup">
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<primary>change accumulation</primary>
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</indexterm>
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<para>
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Restartable Recovery can also be utilised to offload the expense of
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taking periodic base backups from a main server, by instead backing
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up a Standby server's files. This concept is also generally known as
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incrementally updated backups, log change accumulation or more simply,
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change accumulation.
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</para>
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<para>
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If we take a backup of the server files whilst a recovery is in progress,
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we will be able to restart the recovery from the last restartpoint.
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That backup now has many of the changes from previous WAL archive files,
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so this version is now an updated version of the original base backup.
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If we need to recover, it will be faster to recover from the
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incrementally updated backup than from the base backup.
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</para>
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<para>
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To make use of this capability you will need to set up a Standby database
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on a second system, as described in <xref linkend="warm-standby">. By
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taking a backup of the Standby server while it is running you will
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have produced an incrementally updated backup. Once this configuration
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has been implemented you will no longer need to produce regular base
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backups of the Primary server: all base backups can be performed on the
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Standby server. If you wish to do this, it is not a requirement that you
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also implement the failover features of a Warm Standby configuration,
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though you may find it desirable to do both.
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</para>
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</sect2>
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<sect2 id="continuous-archiving-caveats">
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<title>Caveats</title>
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@ -1317,6 +1359,14 @@ restore_command = 'copy /mnt/server/archivedir/%f "%p"' # Windows
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really offers a solution for Disaster Recovery, not HA.
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</para>
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<para>
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When running a Standby Server, backups can be performed on the Standby
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rather than the Primary, thereby offloading the expense of
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taking periodic base backups. (See
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<xref linkend="backup-incremental-updated">)
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</para>
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<para>
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Other mechanisms for High Availability replication are available, both
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commercially and as open-source software.
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