Re: Speed up Clog Access by increasing CLOG buffers

On Thu, Mar 24, 2016 at 8:08 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Thu, Mar 24, 2016 at 5:40 AM, Andres Freund <andres@anarazel.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?