Date: Fri, 27 Apr 2007 00:50:55 -0400 (EDT)
From: Greg Smith <gsmith@gregsmith.com>
To: Postgresql list Performance <pgsql-performance@postgresql.org>
Subject: Re: Fragmentation of WAL files
In-Reply-To: <20070426080050.522ef7b5.wmoran@collaborativefusion.com>
Message-ID: <Pine.GSO.4.64.0704270019060.8684@westnet.com>
References: <3BD44C5D-E402-43EB-8FFD-1A4BC97AFD0C@decibel.org>
	<20070426080050.522ef7b5.wmoran@collaborativefusion.com>
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On Thu, 26 Apr 2007, Bill Moran wrote:

> I've seen marketing material that claims that modern NTFS doesn't suffer 
> performance problems from fragmentation.

You're only reading half of the marketing material then.  For a balanced 
picture, read the stuff generated by the companies that sell defragmenting 
tools.  A good one to start with is 
http://files.diskeeper.com/pdf/HowFileFragmentationOccursonWindowsXP.pdf

Going back to the Jim's original question, they suggest a Microsoft paper 
that talks about how the defrag report can be misleading in respect to 
open files.  See http://support.microsoft.com/kb/228198

Also, some of the most interesting details they gloss over are specific to 
which version of Windows you're using; the reference guide to the subject 
of how NTFS decides how much space to pre-allocate at a time is available 
at http://support.microsoft.com/kb/841551 (ZIP file wrapped into EXE, 
yuck!)

If you compare them, you can see that the approach they're using in NTFS 
has evolved to become more like that used by a good UNIX filesystem over 
time.  I think your typical UNIX still has a healthy lead in this area, 
but the difference isn't as big as it used to be.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD