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Filesystem fragmentation (Re: Fragmentation of WAL files)

From: Bill Moran <wmoran(at)collaborativefusion(dot)com>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: Jim Nasby <decibel(at)decibel(dot)org>, Postgresql list Performance <pgsql-performance(at)postgresql(dot)org>
Subject: Filesystem fragmentation (Re: Fragmentation of WAL files)
Date: 2007-04-26 13:14:32
Message-ID: 20070426091432.274977fe.wmoran@collaborativefusion.com (view raw or flat)
Thread:
Lists: pgsql-performance
In response to Heikki Linnakangas <heikki(at)enterprisedb(dot)com>:

[snip]

> >> Can anyone else confirm this? I don't know if this is a windows-only  
> >> issue, but I don't know of a way to check fragmentation in unix.
> > 
> > I can confirm that it's only a Windows problem.  No UNIX filesystem
> > that I'm aware of suffers from fragmentation.
> 
> What do you mean by suffering? All filesystems fragment files at some 
> point. When and how differs from filesystem to filesystem. And some 
> filesystems might be smarter than others in placing the fragments.

To clarify my viewpoint:
To my knowledge, there is no Unix filesystem that _suffers_ from
fragmentation.  Specifically, all filessytems have some degree of
fragmentation that occurs, but every Unix filesystem that I am aware of
has built-in mechanisms to mitigate this and prevent it from becoming
a performance issue.

> There's a tool for Linux in the e2fsprogs package called filefrag that 
> shows the fragmentation of a file, but I've never used it myself.

Interesting.  However, the existence of a tool does not particularly
indicated the _need_ for said tool.  It might just have been something
cool that somebody wrote.

-- 
Bill Moran
Collaborative Fusion Inc.
http://people.collaborativefusion.com/~wmoran/

wmoran(at)collaborativefusion(dot)com
Phone: 412-422-3463x4023

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