<sect2 id="backup-incremental-updated">

<title>Incrementally Updated Backups</title>

<indexterm zone="backup">

<primary>incrementally updated backups</primary>

</indexterm>

<indexterm zone="backup">

<primary>change accumulation</primary>

</indexterm>

<para>

In a warm 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 backup of the standby server's data directory while it is processing

logs shipped from the primary, we will be able to reload that data and

restart the standby's recovery process from the last restart point.

We no longer need to keep WAL files from before the restart point.

If we need to recover, it will be faster to recover from the incrementally

updated backup than from the original base backup.

</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. You can do this by running <application>pg_controldata</>

on the standby server to inspect the control file and determine the

current checkpoint WAL location, or by using the

<varname>log_restartpoints</> option to print values to the server log.

</para>

</sect2>