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Re: random slow query

From: Mike Ivanov <mikei(at)activestate(dot)com>
To: Scott Carey <scott(at)richrelevance(dot)com>
Cc: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>, Sean Ma <seanxma(at)gmail(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: random slow query
Date: 2009-07-01 00:58:46
Message-ID: 4A4AB4C6.8070808@activestate.com (view raw or flat)
Thread:
Lists: pgsql-performance
Scott Carey wrote:
> the OS can either quickly allocate to the process or
> the page cache from the free buffers, or more slowly take from the page
> cache, or even more slowly page out a process page.
>   

Aha, now it all makes sense.

> I like to use the '5 second rule'.  dirty_background_ratio should be sized
> so that it takes about 5 seconds to flush to disk in optimal conditions.
> dirty_ratio should be 2x to 5x this depending on your application's needs --
> for a system with well tuned postgres checkpoints, smaller tends to be
> better to limit stalls while waiting for the checkpoint fsync to finish.
>   

Thanks a lot, this is invaluable information.


Regards,
Mike



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