| From: | "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at> |
|---|---|
| To: | "Jaime Casanova *EXTERN*" <jcasanov(at)systemguards(dot)com(dot)ec>, "psql performance list" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: measure database contention |
| Date: | 2008-12-17 07:34:23 |
| Message-ID: | D960CB61B694CF459DCFB4B0128514C202DCBE11@exadv11.host.magwien.gv.at |
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| Lists: | pgsql-performance |
Jaime Casanova wrote:
> we have a some bad queries (developers are working on that), some of
> them run in 17 secs and that is the average but when analyzing logs i
> found that from time to time some of them took upto 3 mins (the same
> query that normally runs in 17secs).
>
> so my question is: how could i look for contention problems?
A good first step is to identify the bottleneck.
Frequently, but not always, this is I/O.
Do you see a lot of I/O wait? Are the disks busy?
I don't know anything about your system, but I once experienced a
similar problem with a 2.6 Linux system where things improved considerably
after changing the I/O-scheduler to "elevator=deadline".
Yours,
Laurenz Albe
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