Re: Perf Benchmarking and regression.

On Fri, Jun 03, 2016 at 03:17:06PM -0400, Robert Haas wrote:
> On Fri, Jun 3, 2016 at 2:20 PM, Andres Freund <andres@anarazel.de> wrote:

> >> > I'm inclined to give up and disable backend_flush_after (not the rest),
> >> > because it's new and by far the "riskiest". But I do think it's a
> >> > disservice for the majority of our users.
> >>
> >> I think that's the right course of action.  I wasn't arguing for
> >> disabling either of the other two.
> >
> > Noah was...
> 
> I know, but I'm not Noah.  :-)
> 
> We have no evidence of the other settings causing any problems yet, so
> I see no reason to second-guess the decision to leave them on by
> default at this stage.  Other people may disagree with that analysis,
> and that's fine, but my analysis is that the case for
> disable-by-default has been made for backend_flush_after but not the
> others.  I also agree that backend_flush_after is much more dangerous
> on theoretical grounds; the checkpointer is in a good position to sort
> the requests to achieve locality, but backends are not.

Disabling just backend_flush_after by default works for me, so let's do that.
Though I would not elect, on behalf of PostgreSQL, the risk of enabling
{bgwriter,checkpoint,wal_writer}_flush_after by default, a reasonable person
may choose to do so.  I doubt the community could acquire the data necessary
to ascertain which choice has more utility.