Re: PostgreSQL strugling during high load

Anjan Dave wrote:

>What platform is this?
>
>
>
Its a DELL RH 4 with the xlog on a seperate external mounted file system.
The data directory is on a external mounted file system as well.

>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. 
>
>
>
I'll try raising the number.  I guess the bg* config variables don't do
much?

thanks

>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.Courtney@Sun.COM]
>    Sent: Thu 5/19/2005 12:54 PM
>    To: Tom Lane
>    Cc: pgsql-performance@postgresql.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@bi.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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