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Re: measure database contention

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 (view raw or flat)
Thread:
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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