Re: Speed up Clog Access by increasing CLOG buffers

On Thu, Mar 24, 2016 at 8:08 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
wrote:
>
> On Thu, Mar 24, 2016 at 5:40 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> >
> > Even after changing to scale 500, the performance benefits on this,
> > older 2 socket, machine were minor; even though contention on the
> > ClogControlLock was the second most severe (after ProcArrayLock).
> >
>
> I have tried this patch on mainly 8 socket machine with 300 & 1000 scale
factor. I am hoping that you have tried this test on unlogged tables and
by the way at what client count, you have seen these results.
>
> > Afaics that squares with Jesper's result, which basically also didn't
> > show a difference either way?
> >
>
> One difference was that I think Jesper has done testing with
synchronous_commit mode as off whereas my tests were with synchronous
commit mode on.
>

On again looking at results posted by Jesper [1] and Mithun [2], I have one
more observation which is that in HEAD, the performance doesn't dip even at
higher client count (>75) on tests done by Jesper, whereas the results of
tests done by Mithun indicate that it dips at high client count (>64) in
HEAD and that is where the patch is helping. Now there is certainly some
difference in test environment like Jesper has done testing on 2 socket m/c
whereas mine and Mithun's tests were done 4 or 8 socket m/c. So I think
the difference in TPS due to reduced contention on CLogControlLock are
mainly visible with high socket m/c.

Can anybody having access to 4 or more socket m/c help in testing this
patch with --unlogged-tables?

[1] - http://www.postgresql.org/message-id/56E9A596.2000607@redhat.com
[2] -
http://www.postgresql.org/message-id/CAD__OujrdwQdJdoVHahQLDg-6ivu6iBCi9iJ1qPu6AtUQpL4UQ@mail.gmail.com

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com