From: Andy Colson <andy@squeakycode.net>
To: Scott Marlowe <scott.marlowe@gmail.com>
Cc: Gerhard Wohlgenannt <wohlg@ai.wu.ac.at>
Cc: Tomas Vondra <tv@fuzzy.cz>
Cc: pgsql-performance@postgresql.org, Heinz-Peter Lang <heinz@langatium.net>
Cc: Gerhard Wohlgenannt <wohlg@ai.wu-wien.ac.at>
Cc: Weichselbraun, Albert <albert.weichselbraun@wu.ac.at>
Subject: Re: Sudden drop in DBb performance
Date: Mon, 05 Sep 2011 14:07:42 -0500
Message-ID: <4E651DFE.805@squeakycode.net> (raw)
In-Reply-To: <CAOR=d=2fQwbTt3AoVW=pACezkWBG7r8pd4cqubyj-gbxie2MdA@mail.gmail.com>
References: <4E61D6B4.9090804@ai.wu.ac.at>
<33fadeb6ac1bade5ef01bd08d1fd7807.squirrel@sq.gransy.com>
<4E64D3D3.8000205@squeakycode.net>
<4E64D7EA.3010704@ai.wu.ac.at>
<CAOR=d=2fQwbTt3AoVW=pACezkWBG7r8pd4cqubyj-gbxie2MdA@mail.gmail.com>
On 09/05/2011 01:45 PM, Scott Marlowe wrote:
> On Mon, Sep 5, 2011 at 8:08 AM, Gerhard Wohlgenannt<wohlg@ai.wu.ac.at> wrote:
>> Below please find the results of vmstat 2 over some periode of time .. with
>> normal database / system load.
>>
2 1 1344204 240924 104156 31462484 350 0 1906 234 3687 4512 12 3 77 9
>
> Your IO Wait is actually pretty high. On an 8 core machine, 12.5%
> means one core is doing nothing but waiting for IO.
>
My server is 2-core, so these numbers looked fine by me. I need to remember core count when I look at these.
So the line above, for 2 core's would not worry me a bit, but on 8 cores, it pretty much means one core was pegged (with 9% wait? Or is it one core was pegged, and another was 72% io wait?)
I have always loved the vmstat output, but its starting to get confusing when you have to take core's into account. (And my math was never strong in the first place :-) )
Good catch, thanks Scott.
-Andy
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To: pgsql-performance@postgresql.org
Cc: andy@squeakycode.net, scott.marlowe@gmail.com, wohlg@ai.wu.ac.at, tv@fuzzy.cz, heinz@langatium.net, wohlg@ai.wu-wien.ac.at, albert.weichselbraun@wu.ac.at
Subject: Re: Sudden drop in DBb performance
In-Reply-To: <4E651DFE.805@squeakycode.net>
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