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Re: Filesystem fragmentation (Re: Fragmentation of WAL files)

From: Florian Weimer <fweimer(at)bfk(dot)de>
To: Bill Moran <wmoran(at)collaborativefusion(dot)com>
Cc: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, Jim Nasby <decibel(at)decibel(dot)org>, Postgresql list Performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Filesystem fragmentation (Re: Fragmentation of WAL files)
Date: 2007-04-27 07:39:28
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
* Bill Moran:

> 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.

One database engine tends to create a huge number of fragments because
the files are written with holes in them.  There is a significant
impact on sequential reads, but that doesn't matter much because the
engine doesn't implement fast, out-of-order B-tree scans anyway. 8-/

I still think that preallocating in reasonably sized chunks is

Florian Weimer                <fweimer(at)bfk(dot)de>
BFK edv-consulting GmbH
Kriegsstra├če 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99

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