Message-ID: <4CD47678.5050002@2ndquadrant.com>
Date: Fri, 05 Nov 2010 14:26:16 -0700
From: Greg Smith <greg@2ndquadrant.com>
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To: Josh Berkus <josh@agliodbs.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Major Linux performance regression; shouldn't we be
	worried about RHEL6?
References: <4CD465D8.4070007@agliodbs.com>
In-Reply-To: <4CD465D8.4070007@agliodbs.com>
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Josh Berkus wrote:
> Domas (of Facebook/Wikipedia, MySQL geek) pointed me to this report:
>
> http://www.phoronix.com/scan.php?page=article&item=linux_perf_regressions&num=1
> http://www.phoronix.com/scan.php?page=article&item=ext4_then_now&num=6
>   
The main change here was discussed back in January: 

http://archives.postgresql.org/message-id/4B512D0D.4030909@2ndquadrant.com

What I've been doing about this is the writing leading up to 
http://wiki.postgresql.org/wiki/Reliable_Writes so that when RHEL6 does 
ship, we have a place to point people toward that makes it better 
documented that the main difference here is a reliability improvement 
rather than a performance regression.  I'm not sure what else we can do 
here, other than organizing more testing for kernel bugs in this area on 
RHEL6.  The only way to regain the majority of the "lost" performance 
here is to turn off synchronous_commit in the default config.

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