Message-ID: <4E651DFE.805@squeakycode.net>
Date: Mon, 05 Sep 2011 14:07:42 -0500
From: Andy Colson <andy@squeakycode.net>
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To: Scott Marlowe <scott.marlowe@gmail.com>
CC: Gerhard Wohlgenannt <wohlg@ai.wu.ac.at>, Tomas Vondra <tv@fuzzy.cz>,
	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>
Subject: Re: Sudden drop in DBb performance
References: <4E61D6B4.9090804@ai.wu.ac.at>
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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