Re: PostgreSQL strugling during high load

What platform is this?

We had similar issue (PG 7.4.7). Raising number of checkpoint segments to 125, seperating the WAL to a different LUN helped, but it's still not completely gone.

As far as disk I/O is concerned for flushing the buffers out, I am not ruling out the combination of Dell PERC4 RAID card, and the RH AS 3.0 Update3 being a problem.

Thanks,
Anjan

-----Original Message-----
From: Donald Courtney [mailto:Donald(dot)Courtney(at)Sun(dot)COM]
Sent: Thu 5/19/2005 12:54 PM
To: Tom Lane
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: [PERFORM] PostgreSQL strugling during high load

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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