Re: online tape backup

On Dienstag, 13. Februar 2007 16:34 Tom Lane wrote:
> > From what I understand, if I run a vacuum, the WAL logs will be
> > enormous, as they do not simply store the vacuum command itself,
> > but every single operation done on the db.
> > If that's true, running vacuum before the base backup could be
> > better, as there are less WAL logs to store, making the backup
> > smaller, right?
>
> You're suffering from a fundamental misconception about the nature of
> WAL. Vacuum doesn't "shrink WAL", and neither does anything else; WAL
> is a history of every action ever taken in the database, and so a
> vacuum will just add a bunch more to that history.

Seems you didn't understand me: When I make a vacuum, and then a base
backup, I do not need to include the WAL records anymore. But when I do
a base backup and afterwards vacuum, the WAL will be huge already, also
making restore much longer.

Is there a simple way to turn on/off WAL? I'd like to use it, but then
switch it off, make vacuum, turn WAL on again and make a base backup.
That should save a reasonable amount of time and backup space.
Databases are about 40GB now (test phase) and will be considerable more
once in production (we're using dbmail.org as mailserver then).

mfg zmi
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