From: | Greg Stark <gsstark(at)mit(dot)edu> |
---|---|
To: | Grzegorz Jaśkiewicz <gryzman(at)gmail(dot)com> |
Cc: | S Arvind <arvindwill(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Running some query in low priority |
Date: | 2009-11-05 11:32:22 |
Message-ID: | 407d949e0911050332n5ef355c1y156dcd26aa28d222@mail.gmail.com |
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Lists: | pgsql-performance |
2009/11/5 Grzegorz Jaśkiewicz <gryzman(at)gmail(dot)com>:
>
>
> On Thu, Nov 5, 2009 at 9:36 AM, S Arvind <arvindwill(at)gmail(dot)com> wrote:
>>
>> Hi Developers and Tuners,
>> 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 operate
>> 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.
--
greg
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