FAQ

On Thu, 2004-07-01 at 16:11, ohp@pyrenet.fr wrote:
Many thanks for your reply Simon
On Wed, 30 Jun 2004, Simon Riggs wrote:

Date: Wed, 30 Jun 2004 19:29:14 +0100
From: Simon Riggs <simon@2ndquadrant.com>
To: ohp@pyrenet.fr
Cc: pgsql-patches@postgresql.org
Subject: Re: [PATCHES] PITR Archive Recovery
On Wed, 2004-06-30 at 12:27, ohp@pyrenet.fr wrote:
Given that log files will be archieved, how can we purge them (ie know for
sure we won't need them anymore)
Good question - you're right I've not mentioned that.

The answer is straightforward. Whenever you do a backup, one of the
transaction logs will be the current one. That means any logs before the
earliest one you can see can now be purged from the archive.

So if you can see: 137,138,139 then that means anything at 136 or before
is able to be discarded.
Ok, that's clear...
BUT not very easy to put in a backup stagtegy...
It may be ok if you user tar or cpio; but surely more complicated if you
use backup software like Netvault or Tapeware
Of course, I CAN help with that, but you're right, it isn't in any
manual.
However, I'd recommend keeping more than just one backup, usually 2 or
3, so the actual purge point is dependant upon your data retention
strategy, possibly linked to tape rotation etc..
sure
if I do a backup of the DATA dir, then obviously I won't need the logs
that were taken before. I can't just delete them all because maybe a few
will be archived during the backup.
I agree
Taking a full physical backup will normally need to exclude the pg_xlog
directory, or at least the current xlog. Since it is being written to
very regularly it is almost impossible to take a clean copy using
standard utilities - though filesystem level utilities work fine.
Would it make sense to have SQL phrases (as I recall from my informix days
10 years ago)
like
START BACKUP LEVEL 0 where cluster would be archieved on whatever you
want, disallowing all writes and
SART BACKUP LEVEL 1 where cluster and logs would be archieved letting
read/write o databases possible...
These are possible in a variety of ways at operating system or device
level, so no these haven't been implemented (yet?) for PostgreSQL.

Best regards, Simon Riggs

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