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 
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 

        -----Original Message----- 
        From: Donald Courtney [mailto:[EMAIL PROTECTED] 
        Sent: Thu 5/19/2005 12:54 PM 
        To: Tom Lane 
        Cc: pgsql-performance@postgresql.org 
        Subject: Re: [PERFORM] PostgreSQL strugling during high load


        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. 

        Don C. 

        Tom Lane wrote: 

        >"Mindaugas Riauba" <[EMAIL PROTECTED]> 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 
        >>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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