Re: Linux: more cores = less concurrency.

--- On Mon, 11/4/11, david(at)lang(dot)hm <david(at)lang(dot)hm> wrote:

> From: david(at)lang(dot)hm <david(at)lang(dot)hm>
> Subject: Re: [PERFORM] Linux: more cores = less concurrency.
> To: "Steve Clark" <sclark(at)netwolves(dot)com>
> Cc: "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com>, "Joshua D. Drake" <jd(at)commandprompt(dot)com>, "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-performance(at)postgresql(dot)org, "Glyn Astill" <glynastill(at)yahoo(dot)co(dot)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 forget about 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 wins outright.

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