| 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: | 82d51q9sgf.fsf@mid.bfk.de |
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| 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
beneficial.
--
Florian Weimer <fweimer(at)bfk(dot)de>
BFK edv-consulting GmbH http://www.bfk.de/
Kriegsstraße 100 tel: +49-721-96201-1
D-76133 Karlsruhe fax: +49-721-96201-99
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