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From: Glyn Astill <glynastill@yahoo.co.uk>
To: Tomas Vondra <tv@fuzzy.cz>
To: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: H800 + md1200 Performance problem
Date: Thu, 5 Apr 2012 14:10:01 +0100 (BST)
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> From: Tomas Vondra <tv@fuzzy.cz>

> But the fluctuation, that surely is strange. What are the page cache
> dirty limits, i.e.
> 
> cat /proc/sys/vm/dirty_background_ratio
> cat /proc/sys/vm/dirty_ratio
> 
> That's probably #1 source I've seen responsible for such issues (on
> machines with a lot of RAM).
> 

+1 on that.

We're running similar 32 core dell servers with H700s and 128Gb RAM.

With those at the defaults (I don't recall if it's 5 and 10 respectively) you're looking at 3.2Gb of dirty pages before pdflush flushes them and 6.4Gb before the process is forced to flush its self.


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