From: Jaime Casanova <jcasanov@systemguards.com.ec>
To: Albe Laurenz <laurenz.albe@wien.gv.at>
Cc: psql performance list <pgsql-performance@postgresql.org>
Subject: Re: measure database contention
Date: Wed, 17 Dec 2008 10:22:04 -0500
Message-ID: <3073cc9b0812170722l75a873ffsf1dbee6c78048be7@mail.gmail.com> (raw)
In-Reply-To: <D960CB61B694CF459DCFB4B0128514C202DCBE11@exadv11.host.magwien.gv.at>
References: <3073cc9b0812161132w3ae157a8n69e2b0cccea05ca2@mail.gmail.com>
<D960CB61B694CF459DCFB4B0128514C202DCBE11@exadv11.host.magwien.gv.at>
On Wed, Dec 17, 2008 at 2:34 AM, Albe Laurenz <laurenz.albe@wien.gv.at> wrote:
> 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?
>
the disks are an RAID 10 with 4 sata disks of 15000rpm
and nop iostat reports avg of 0.12 iowait
> 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".
>
i don't understand I/O-schedulers at all... anyone knows what is the
recommended for postgres?
--
Atentamente,
Jaime Casanova
Soporte y capacitación de PostgreSQL
AsesorÃa y desarrollo de sistemas
Guayaquil - Ecuador
Cel. +59387171157
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To: pgsql-performance@postgresql.org
Cc: jcasanov@systemguards.com.ec, laurenz.albe@wien.gv.at
Subject: Re: measure database contention
In-Reply-To: <3073cc9b0812170722l75a873ffsf1dbee6c78048be7@mail.gmail.com>
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