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Re: Command to prune archive at restartpoints

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Command to prune archive at restartpoints
Date: 2010-03-17 10:01:44
Message-ID: 407d949e1003170301x582fe285x84ea4a94e8b7dad5@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Mar 17, 2010 at 9:37 AM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> One awkward omission in the new built-in standby mode, mainly used for
> streaming replication, is that there is no easy way to delete old
> archived files like you do with the %r parameter to restore_command.

I'm still finding this kind of narrow-minded. I'm picturing a system
with multiple replicas -- obvious no one replica can take it upon
itself to delete archived log files based only on its own
restartpoint. And besides, if you're using the archived log files for
backups you also need to take into account the backup policy and only
delete files that aren't needed for a consistent backup and aren't
needed for the replica.

What we need is a program which can take all this information from all
your slaves and backup labels into account and implement your backup
policies. It probably won't exist in time for the release and in any
case doesn't really have to ship with Postgres. There might even be
more than one.

But do we have all the information that such a program would need? Is
there a way to connect to a replica and ask it what the restart point
is? I suppose with this new command you could always just make it a
command which wakes up this demon and sends it the restart point and
the replica id and it can update its internal state and recalculate
what archives are needed. It is a bit nerve-wracking that it's
dependent on its internal state remembering the restart points it's
been given though.




-- 
greg

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