Re: PostgreSQL strugling during high load

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From: Matthew T. O'Connor <matthew@zeut.net>
To: Mindaugas Riauba <mind@bi.lt>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: PostgreSQL strugling during high load
Date: Sun, 15 May 2005 22:26:50 -0400
Message-ID: <428804EA.6080609@zeut.net> (raw)
In-Reply-To: <022901c557c5$73df1220$f20214ac@bite.lt>
References: <01cc01c557ba$a4fdb0b0$f20214ac@bite.lt>
	<23217.1115991763@sss.pgh.pa.us>
	<022901c557c5$73df1220$f20214ac@bite.lt>

Mindaugas Riauba wrote:

>>The "vacuum cost" parameters can be adjusted to make vacuums fired
>>by pg_autovacuum less of a burden.  I haven't got any specific numbers
>>to suggest, but perhaps someone else does.
>>    
>>
>
>  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? WAL log
>switch? One WAL file seems to last <1 minute.
>  
>

How long are these quite periods?  Do the "strom" periods correspond to 
pg_autovacuum loops?  I have heard from one person who had LOTS of 
databases and tables that caused the pg_autovacuum to create a noticable 
load just updateing all its stats.  The solution in that case was to add 
a small delay insidet the inner pg_autovacuum loop.

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