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

From: Florian Weimer
Subject: Re: Filesystem fragmentation (Re: Fragmentation of WAL files)
Date: ,
Msg-id: 82d51q9sgf.fsf@mid.bfk.de
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In response to: Filesystem fragmentation (Re: Fragmentation of WAL files)  (Bill Moran)
List: pgsql-performance

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Fragmentation of WAL files  (Jim Nasby, )
 Re: Fragmentation of WAL files  (Bill Moran, )
  Re: Fragmentation of WAL files  (Heikki Linnakangas, )
   Filesystem fragmentation (Re: Fragmentation of WAL files)  (Bill Moran, )
    Re: Filesystem fragmentation (Re: Fragmentation of WAL files)  ("Craig A. James", )
     Re: Filesystem fragmentation (Re: Fragmentation of WAL files)  (Gregory Stark, )
      Re: Filesystem fragmentation (Re: Fragmentation of WAL files)  (Tom Lane, )
    Re: Filesystem fragmentation (Re: Fragmentation of WAL files)  (Florian Weimer, )
  Re: Fragmentation of WAL files  (Tom Lane, )
  Re: Fragmentation of WAL files  (Greg Smith, )

* 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                <>
BFK edv-consulting GmbH       http://www.bfk.de/
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