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From: Greg Smith <greg@2ndQuadrant.com>
To: pgsql-performance@postgresql.org
Subject: Re: how to demonstrate the effect of direct I/O ?
Date: Tue, 07 Feb 2012 22:13:24 -0500
Message-ID: <4F31E854.7080208@2ndQuadrant.com> (raw)
In-Reply-To: <4F2DBE5A.9090102@fuzzy.cz>
References: <4F2DBE5A.9090102@fuzzy.cz>

On 02/04/2012 06:25 PM, Tomas Vondra wrote:
> What should I do to see the effect of direct I/O?

Test something other than a mainstream Linux filesystem.  The two times 
I've either measured an improvement myself for direct I/O were a) 
Veritas VxFS on Linux, which has some documented acceleration here and 
b) on Solaris.  You won't find a compelling performance improvement 
listed at 
https://ext4.wiki.kernel.org/articles/c/l/a/Clarifying_Direct_IO%27s_Semantics_fd79.html 
and Linux has generally ignored direct I/O as something important to 
optimize for.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.com




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