Re: high user cpu, massive SELECTs, no io waiting problem

Scott, are you really moving that much data through memory, 70-80GB/sec is the limit of the new intel 7500 series in a best case scenario.

- John

-----Original Message-----
From: pgsql-performance-owner(at)postgresql(dot)org [mailto:pgsql-performance-owner(at)postgresql(dot)org] On Behalf Of Scott Marlowe
Sent: 16 February 2011 15:43
To: Marti Raudsepp
Cc: Thomas Pöhler; pgsql-performance(at)postgresql(dot)org; Felix Feinhals; Verteiler_A-Team; Björn Metzdorf
Subject: Re: [PERFORM] high user cpu, massive SELECTs, no io waiting problem

On Wed, Feb 16, 2011 at 6:44 AM, Marti Raudsepp <marti(at)juffo(dot)org> wrote:
> On Tue, Feb 15, 2011 at 20:01, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:
>> run htop and look for red.  if youi've got lots of red bar on each CPU
>> but no io wait then it's waiting for memory access.
>
> I don't think this is true. AFAICT the red bar refers to "system
> time", time that's spent in the kernel -- either in syscalls or kernel
> background threads.

My point being that if you've got a lot of RED it'll be the OS waiting
for memory access. Trust me, when we start to hit our memory
bandwidth (in the 70 to 80 GB/s range) we start to get more and more
red and more and more kernel wait time.

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