Re: [PERFORM] PostgreSQL strugling during high load

[Donald Courtney]

Anjan Dave wrote:

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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:[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
	
	

	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" <[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 "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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