On 2013-10-15 19:29:50 +0200, Magnus Hagander wrote:
> On Tue, Oct 15, 2013 at 7:26 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> > On 2013-10-15 10:19:06 -0700, Josh Berkus wrote:
> >> On 10/15/2013 05:52 AM, Magnus Hagander wrote:
> >> > But the argument about being friendly for new users should definitely
> >> > have us change wal_level and max_wal_senders.
> >>
> >> +1 for having replication supported out-of-the-box aside from pg_hba.conf.
> >>
> >> To put it another way: users are more likely to care about replication
> >> than they are about IO overhead on a non-replicated server. And for the
> >> users who care about IO overhead, they are more likely to much about in
> >> pg.conf *anyway* in order to set a slew of performance-tuning settings.
> >
> > But it will hurt people restoring backups using pg_restore -j. I think
> > people might be rather dissapointed if that slows down by a factor of
> > three.
> >
> > I think we really need to get to the point where we increase the wal
> > level ondemand...
>
> Yeha, there are really two things.
>
> If we can increase wal_level on demand, that would solve one of them.
> Turning that into a SIGHUP parameter would be great. I have no idea
> how hard it would be. In theory, couldn't we let it be sighup and then
> just have do_pg_start_backup() block until all backends have
> acknowledged that they are on the new WAL level somehow? (Yes, I
> realize this might be a big simplification, but I'm allowed to hope,
> no?)
Depends on what you want to support. For basebackups, that should be
doable with some pullups.
It's unfortunately more complex than that for streaming rep - we really
need persistent standby registration there. Otherwise the wal_level will
fall back to minimal when the standby disconnects which will obviously
break the standby.
> The other problem is max_wal_senders. I think that's a much smaller
> problem - setting that one to 5 or so by default shouldn't have a big
> impact. But without the wal_level changes, it would also be mostly
> pointless...
Well, you currently cannot even set it when the wal_level isn't set
appropriately, but that that should be easy enough to change.
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services
