Re: Linux: more cores = less concurrency.

--- On Mon, 11/4/11, david@lang.hm <david@lang.hm> wrote:

> From: david@lang.hm <david@lang.hm>
> Subject: Re: [PERFORM] Linux: more cores = less concurrency.
> To: "Steve Clark" <sclark@netwolves.com>
> Cc: "Scott Marlowe" <scott.marlowe@gmail.com>, "Joshua D. Drake" <jd@commandprompt.com>, "Kevin Grittner"
<Kevin.Grittner@wicourts.gov>,pgsql-performance@postgresql.org, "Glyn Astill" <glynastill@yahoo.co.uk> 
> Date: Monday, 11 April, 2011, 21:04
> On Mon, 11 Apr 2011, Steve Clark
> wrote:
>
> the limit isn't 8 cores, it's that the hyperthreaded cores
> don't work well with the postgres access patterns.
>

This has nothing to do with hyperthreading. I have a hyperthreaded benchmark purely for completion, but can we please
forgetabout it. 

The issue I'm seeing is that 8 real cores outperform 16 real cores, which outperform 32 real cores under high
concurrency.

32 cores is much faster than 8 when I have relatively few clients, but as the number of clients is scaled up 8 cores
winsoutright. 

I was hoping someone had seen this sort of behaviour before, and could offer some sort of explanation or advice.