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To: Greg Smith <gsmith@gregsmith.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Direct I/O issues 
In-reply-to: <Pine.GSO.4.64.0611230013550.26031@westnet.com> 
References: <Pine.GSO.4.64.0611230013550.26031@westnet.com>
Comments: In-reply-to Greg Smith <gsmith@gregsmith.com>
	message dated "Thu, 23 Nov 2006 01:30:24 -0500"
Date: Thu, 23 Nov 2006 11:45:42 -0500
Message-ID: <14171.1164300342@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Greg Smith <gsmith@gregsmith.com> writes:
> The results I get now look fishy.

There are at least two things wrong with this program:

* It does not respect the alignment requirement for O_DIRECT buffers
  (reportedly either 512 or 4096 bytes depending on filesystem).

* It does not check for errors (if it had, you might have realized the
  other problem).

			regards, tom lane