Re: Skylake-S warning

On Thu, Oct 4, 2018 at 9:50 AM Adrien Nayrat <adrien(dot)nayrat(at)anayrat(dot)info> wrote:
>
> On 10/3/18 11:29 PM, Daniel Wood wrote:
> > If running benchmarks or you are a customer which is currently impacted by
> > GetSnapshotData() on high end multisocket systems be wary of Skylake-S.
> >
> >
> > Performance differences of nearly 2X can be seen on select only pgbench due to
> > nothing else but unlucky choices for max_connections. Scale 1000, 192 local
> > clients on a 2 socket 48 core Skylake-S(Xeon Platinum 8175M @ 2.50-GHz) system.
> > pgbench -S
>
> Could it be related to :
> https://www.postgresql.org/message-id/D2B9F2A20670C84685EF7D183F2949E2373E66%40gigant.nidsa.net
> ?

Unlikely. I understood from Daniel's email that profiling shows a
different hot-spot. In the cited .NET issue the problem was mostly due
to issuing PAUSE in a loop without attempting to grab the lock. In
PostgreSQL it's called only once per retry attempt.

Regards,
Ants Aasma
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