| From: | Andy Colson <andy(at)squeakycode(dot)net> |
|---|---|
| To: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
| Cc: | Gerhard Wohlgenannt <wohlg(at)ai(dot)wu(dot)ac(dot)at>, Tomas Vondra <tv(at)fuzzy(dot)cz>, pgsql-performance(at)postgresql(dot)org, Heinz-Peter Lang <heinz(at)langatium(dot)net>, Gerhard Wohlgenannt <wohlg(at)ai(dot)wu-wien(dot)ac(dot)at>, "Weichselbraun, Albert" <albert(dot)weichselbraun(at)wu(dot)ac(dot)at> |
| Subject: | Re: Sudden drop in DBb performance |
| Date: | 2011-09-05 19:07:42 |
| Message-ID: | 4E651DFE.805@squeakycode.net |
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| Lists: | pgsql-performance |
On 09/05/2011 01:45 PM, Scott Marlowe wrote:
> On Mon, Sep 5, 2011 at 8:08 AM, Gerhard Wohlgenannt<wohlg(at)ai(dot)wu(dot)ac(dot)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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