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Re: PostgreSQL strugling during high load

From: Donald Courtney <Donald(dot)Courtney(at)Sun(dot)COM>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: PostgreSQL strugling during high load
Date: 2005-05-19 16:54:03
Message-ID: 428CC4AB.50906@sun.com (view raw or flat)
Thread:
Lists: pgsql-performance
Tom

Thanks for the post - I think I am getting this problem for
a synthetic workload at high connection loads.  The whole
system seems to stop. 

Can you give some examples on what to try out in the .conf file?

I tried
bgwriter_all_percent =  30, 10, and 3

Which I understand to mean 30%, 10% and 3% of the dirty pages should be
written out *between* checkpoints.

I didn't see any change in effect.

/regards
Don C.

Tom Lane wrote:

>"Mindaugas Riauba" <mind(at)bi(dot)lt> writes:
>  
>
>>  It looks like that not only vacuum causes our problems. vacuum_cost
>>seems to lower vacuum impact but we are still noticing slow queries "storm".
>>We are logging queries that takes >2000ms to process.
>>  And there is quiet periods and then suddenly 30+ slow queries appears in
>>log within the same second. What else could cause such behaviour?
>>    
>>
>
>Checkpoints?  You should ensure that the checkpoint settings are such
>that checkpoints don't happen too often (certainly not oftener than
>every five minutes or so), and make sure the bgwriter is configured
>to dribble out dirty pages at a reasonable rate, so that the next
>checkpoint doesn't have a whole load of stuff to write.
>
>			regards, tom lane
>
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