Re: Linux: more cores = less concurrency.

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