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To: Greg Smith <gsmith@gregsmith.com>
cc: Robert Haas <robertmhaas@gmail.com>,
	Gregory Stark <stark@enterprisedb.com>,
	ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp>,
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Subject: Re: posix_fadvise v22 
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Comments: In-reply-to Greg Smith <gsmith@gregsmith.com>
	message dated "Fri, 02 Jan 2009 05:08:13 -0500"
Date: Fri, 02 Jan 2009 10:33:25 -0500
Message-ID: <24481.1230910405@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Greg Smith <gsmith@gregsmith.com> writes:
> On Thu, 1 Jan 2009, Robert Haas wrote:
>> The only thing I haven't been able to do is demonstrate that this change 
>> actually produces a performance improvement.  Either I'm testing the 
>> wrong thing, or it just doesn't provide any benefit on a single-spindle 
>> system.

> When I did a round of testing on the earlier prefetch test program Greg 
> Stark put together, one of my single-spindle Linux system didn't show any 
> real benefit.  So as long as you didn't see performance degrade, your not 
> seeing any improvement isn't bad news.

ISTM that you *should* be able to see an improvement on even
single-spindle systems, due to better overlapping of CPU and I/O effort.
If the test case is either 100% CPU-bound or 100% I/O-bound then no,
but for anything in between there ought to be improvement.

			regards, tom lane