On 2013-10-15 10:36:41 -0400, Robert Haas wrote:
> On Tue, Oct 15, 2013 at 10:34 AM, Andres Freund <and...@2ndquadrant.com> 
> wrote:
> >> But I also agree that making max_wal_senders act as both a minimum and
> >> a maximum is no good.  +1 to everything Josh Berkus said.
> >
> > Josh said we should treat replication connections in a separate "pool"
> > from normal database connections, right? So you withdraw your earlier
> > objection to that?
> I don't think that's what he said.  Here's what I was referring to:
> $ Changing max_wal_senders requires a restart.  As such, we currently
> $ advise users to set the setting generously: "as many replication
> $ connections as you think you'll ever need, plus two".  If
> $ max_wal_senders is a reservation which could cause the user to run out
> $ of other connections sooner than expected, then the user is faced with a
> $ new "hard to set" parameter: they don't want to set it too high *or* too
> $ low.
> $
> $ This would result in a lot of user frustration as they try to get thier
> $ connection configuration right and have to restart the server multiple
> $ times.  I find few new features worth making it *harder* to configure
> $ PostgreSQL, and reserved replication connections certainly don't qualify.
> $
> $ If it's worth having reserved replication connections (and I can see
> $ some reasons to want it), then we need a new GUC for this:
> $ "reserved_walsender_connections"

I am referring to
> On 10/14/2013 10:51 AM, Andres Freund wrote:
> > Imo the complications around this prove my (way earlier) point that it'd
> > be much better to treat replication connections as something entirely
> > different to normal SQL connections. There's really not much overlap
> > here and while there's some philosophical point to be made about it all
> > being connections, from a practical POV treating them separately seems
> > better.
> Given that replication connections don't even appear in pg_stat_activity
> now, I'd agree with you.

I still fail to see what the point is in treating those classes of
connections together. It only serves to confuse users and makes
considerations way much more complicated. There's no need for reserved
replication connections or anything like it if would separate the pools.


Andres Freund

 Andres Freund                     http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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