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Date: Mon, 5 Sep 2011 16:15:23 +0200
Subject: Re: Sudden drop in DBb performance
From: "Tomas Vondra" <tv@fuzzy.cz>
To: "Andy Colson" <andy@squeakycode.net>
Cc: "Tomas Vondra" <tv@fuzzy.cz>, "Gerhard Wohlgenannt" <wohlg@ai.wu.ac.at>,
	pgsql-performance@postgresql.org, "Heinz-Peter Lang" <heinz@langatium.net>,
	"Gerhard Wohlgenannt" <wohlg@ai.wu-wien.ac.at>,
	"Weichselbraun, Albert" <albert.weichselbraun@wu.ac.at>
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On 5 Září 2011, 15:51, Andy Colson wrote:
> On 09/05/2011 02:48 AM, Tomas Vondra wrote:
>> That seems a bit slow ... 27MB/s for writes and 41MB/s forreads is ait
>> slow with 8 drives.
>>
>> Tomas
>>
>>
>
> Agreed, that's really slow.  A single SATA drive will get 60 MB/s.  Did
> you run Bonnie while the VM's were up and running?
>
>    root@host:~# vmstat
>    procs -----------memory---------- ---swap-- -----io---- -system--
> ----cpu----
>     r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy
> id wa
>     0  0      0 308024 884812 40512932    0    0   464   168  353   92  4
> 2 84  9
>
>
> Only one line?  That does not help much.  Can you run it as 'vmstat 2' and
> let it run while a few slow queries are performed?  Then paste all the
> lines?

And maybe a few lines from "iostat -x 2" too.

BTW what kind of raid is it? Is it hw or sw based? Have you checked health
of the drives?

Are you sure there's nothing else using the drives (e.g. one of the VMs,
rebuild of the array or something like that)?

Tomas