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(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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