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).
> >
>

One more point, I wanted to say here which is that I think the benefit will
be shown mainly when the ClogControlLock has contention more than or near
to ProcArrayLock, otherwise even if patch reduces contention (you can see
via LWLock stats), the performance doesn't increase. From Mithun's data
[1], related to LWLocks, it seems like at 88 clients in his test, the
contention on CLOGControlLock becomes more than ProcArrayLock and that is
the point where it has started showing noticeable performance gain. I have
explained some more on that thread [2] about this point. Is it possible
for you to once test in similar situation and see the behaviour (like for
client count greater than number of cores) w.r.t locking contention and TPS.

[1] -
http://www.postgresql.org/message-id/CAD__Ouh6PahJ+q1mzzjDzLo4v9GjyufegtJNAyXc0_Lfh-4coQ@mail.gmail.com
[2] -
http://www.postgresql.org/message-id/CAA4eK1LBOQ4e3Ycge+Fe0euzVu89CqGTuGNeajOienxJR0AEKA@mail.gmail.com

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