Incrementally Updated Backup

Way past feature freeze, but this small change allows a powerful new
feature utilising the Restartable Recovery capability. Very useful for
very large database backups...

Includes full documentation.

Perhaps a bit rushed, but inclusion in 8.2 would be great. (Ouch, don't
shout back, read the patch first....)

-----------------------------
Docs copied here as better explanation:

   <title>Incrementally Updated Backups</title>

   <para>
    Restartable Recovery can also be utilised to avoid the need to take
    regular complete base backups, thus improving backup performance in
    situations where the server is heavily loaded or the database is
    very large.  This concept is known as incrementally updated backups.
   </para>

   <para>
    If we take a backup of the server files after a recovery is
partially
    completed, we will be able to restart the recovery from the last
    restartpoint. This backup is now further forward along the timeline
    than the original base backup, so we can refer to it as an
incrementally
    updated backup. If we need to recover, it will be faster to recover
from
    the incrementally updated backup than from the base backup.
   </para>

   <para>
    The <xref linkend="startup-after-recovery"> option in the
recovery.conf
    file is provided to allow the recovery to complete up to the current
last
    WAL segment, yet without starting the database. This option allows
us
    to stop the server and take a backup of the partially recovered
server
    files: this is the incrementally updated backup.
   </para>

   <para>
    We can use the incrementally updated backup concept to come up with
a
    streamlined backup schedule. For example:
  <orderedlist>
   <listitem>
    <para>
     Set up continuous archiving
    </para>
   </listitem>
   <listitem>
    <para>
     Take weekly base backup
    </para>
   </listitem>
   <listitem>
    <para>
     After 24 hours, restore base backup to another server, then run a
     partial recovery and take a backup of the latest database state to
     produce an incrmentally updated backup.
    </para>
   </listitem>
   <listitem>
    <para>
     After next 24 hours, restore the incrementally updated backup to
the
     second server, then run a partial recovery, at the end, take a
backup
     of the partially recovered files.
    </para>
   </listitem>
   <listitem>
    <para>
     Repeat previous step each day, until the end of the week.
    </para>
   </listitem>
  </orderedlist>
   </para>

   <para>
    A weekly backup need only be taken once per week, yet the same level
of
    protection is offered as if base backups were taken nightly.
   </para>

  </sect2>

--
  Simon Riggs
  EnterpriseDB   http://www.enterprisedb.com