Message-ID: <4DC97AF0.2050204@2ndquadrant.com>
Date: Tue, 10 May 2011 13:50:40 -0400
From: Greg Smith <greg@2ndquadrant.com>
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To: Greg Smith <greg@2ndQuadrant.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Benchmarking a large server
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Greg Smith wrote:
> On 05/09/2011 11:13 PM, Shaun Thomas wrote:
>> Take a look at /proc/sys/vm/dirty_ratio and 
>> /proc/sys/vm/dirty_background_ratio if you have an older Linux 
>> system, or /proc/sys/vm/dirty_bytes, and 
>> /proc/sys/vm/dirty_background_bytes with a newer one.
>> On older systems for instance, those are set to 40 and 20 
>> respectively (recent kernels cut these in half).
>
> 1/4 actually; 10% and 5% starting in kernel 2.6.22.  The main sources 
> of this on otherwise new servers I see are RedHat Linux RHEL5 systems  
> running 2.6.18.  But as you say, even the lower defaults of the newer 
> kernels can be way too much on a system with lots of RAM.

Ugh...we're both right, sort of.  2.6.22 dropped them to 5/10:  
http://kernelnewbies.org/Linux_2_6_22 as I said.  But on the new 
Scientific Linux 6 box I installed yesterday, they're at 10/20--as you 
suggested.

Can't believe I'm going to need a table by kernel version and possibly 
distribution to keep this all straight now, what a mess.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books