Re: Linux: more cores = less concurrency.

--- On Tue, 12/4/11, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:

> From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
> Subject: Re: [PERFORM] Linux: more cores = less concurrency.
> To: "Glyn Astill" <glynastill(at)yahoo(dot)co(dot)uk>
> Cc: pgsql-performance(at)postgresql(dot)org
> Date: Tuesday, 12 April, 2011, 6:55
> On Mon, Apr 11, 2011 at 7:04 AM, Glyn
> Astill <glynastill(at)yahoo(dot)co(dot)uk>
> wrote:
> > Hi Guys,
> >
> > I'm just doing some tests on a new server running one
> of our heavy select functions (the select part of a plpgsql
> function to allocate seats) concurrently.  We do use
> connection pooling and split out some selects to slony
> slaves, but the tests here are primeraly to test what an
> individual server is capable of.
> >
> > The new server uses 4 x 8 core Xeon X7550 CPUs at
> 2Ghz, our current servers are 2 x 4 core Xeon E5320 CPUs at
> 2Ghz.
> >
> > What I'm seeing is when the number of clients is
> greater than the number of cores, the new servers perform
> better on fewer cores.
>
> O man, I completely forgot the issue I ran into in my
> machines, and
> that was that zone_reclaim completely screwed postgresql
> and file
> system performance.  On machines with more CPU nodes
> and higher
> internode cost it gets turned on automagically and
> destroys
> performance for machines that use a lot of kernel cache /
> shared
> memory.
>
> Be sure and use sysctl.conf to turn it off:
>
> vm.zone_reclaim_mode = 0
>

I've made this change, not seen any immediate changes however it's good to know. Thanks Scott.