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Online Backup and WAL archives

From: Morus Walter <morus(dot)walter(at)tanto(dot)de>
To: pgsql-admin(at)postgresql(dot)org
Subject: Online Backup and WAL archives
Date: 2005-02-01 12:59:15
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-admin

I'm currently considering to use postgresql 8.0 online backups.

The documentation says 
' To make use of this backup, you will need to keep around all the 
WAL segment files generated at or after the starting time of the backup. '

Now I'm wondering how much of these WAL segment files do I really need
in order to recover the databases to a consistent state.

Let's say I cannot write the WAL segments to tape dynamically when they
are archived. Then a complete disk failure would mean, that I loose WAL 
segments also.
Therefore I would like to save a minimum number of WAL segments at or
after the online backup that allows recovery.
Is that possible? How would I decide how much of the WAL I need?

Of course I could recover to the state of database at about the time of the 
backup only, but it would be a consistent state at least.

Or should I use the previous online backup plus all WAL segements up to
the current backup?

I expect the online backup to faster on recovery than an SQL dump, since
the latter would imply recreation of indexes during recovery.
Therefore I would prefer to use online backups.



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