Re: PITR, checkpoint, and local relations

Tom Lane wrote:
> "J. R. Nield" <jrnield@usol.com> writes:
> >> Uh, why?  Why not just force a checkpoint and remember the exact
> >> location of the checkpoint within the current log file?
> 
> > If I do a backup with PITR and save it to tape, I need to be able to
> > restore it even if my machine is destroyed in a fire, and all the logs
> > since the end of a backup are destroyed.
> 
> And for your next trick, restore it even if the backup tape itself is
> destroyed.  C'mon, be a little reasonable here.  The backups and the
> log archive tapes are *both* critical data in any realistic view of
> the world.

Tom, just because he doesn't agree with you doesn't mean he is
unreasonable.

I think it is an admirable goal to allow the PITR backup to restore a
consistent copy of the database _without_ needing the logs.  In fact, I
consider something that _needs_ the logs to restore to a consistent
state to be broken.

If you are doing offsite backup, which people should be doing, requiring
the log tape for restore means you have to recycle the log tape _after_
the PITR backup, and to restore to a point in the future, you need two
log tapes, one that was done during the backup, and another current.

If you can restore the PITR backup without a log tape, you can take just
the PITR backup tape off site _and_ you can recyle the log tape _before_
the PITR backup, meaning you only need one tape for a restore to a point
in the future.  I think there are good reasons to have the PITR backp be
restorable on its own, if possible.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
359-1001+  If your life is a hard drive,     |  13 Roberts Road +  Christ can be your backup.        |  Newtown Square,
Pennsylvania19073