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From: Greg Stark <gsstark@mit.edu>
Date: Thu, 5 Nov 2009 11:32:22 +0000
Message-ID: <407d949e0911050332n5ef355c1y156dcd26aa28d222@mail.gmail.com>
Subject: Re: Running some query in low priority
To: =?ISO-8859-2?Q?Grzegorz_Ja=B6kiewicz?= <gryzman@gmail.com>
Cc: S Arvind <arvindwill@gmail.com>, pgsql-performance@postgresql.org
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2009/11/5 Grzegorz Ja=C5=9Bkiewicz <gryzman@gmail.com>:
>
>
> On Thu, Nov 5, 2009 at 9:36 AM, S Arvind <arvindwill@gmail.com> wrote:
>>
>> Hi Developers and Tuners,
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Is there any way to run=
 some query in low priority and some query
>> in higher priority in pg. The main reason for this is i need my main
>> application(high priority) to be undisturbed by the sub application(low
>> priority) which is running on same DB. Is there anyother good way to ope=
rate
>> this?
>
> other than manually re-nicing back end, no.

And unfortunately this doesn't really work very well. renicing only
affects cpu priority and usually it's i/o priority you want to adjust.
Even if you can adjust i/o priority per process on your operating
system the database often does i/o work for one process in another
process or has times when a process is waiting on another process to
finish i/o. So lowering the i/o priority of the low priority process
might not have the desired effect of speeding up other processes.

Usually this isn't a problem unless you have a large batch load or
something like that happening which consumes all available i/o. In
that case you can sometimes reduce the i/o demand by just throttling
the rate at which you send data to or read data from the server.


--=20
greg