Date: Wed, 29 Apr 2015 10:08:54 +0200
From: Andres Freund <andres@anarazel.de>
To: Jan Gunnar Dyrset <jan.g.dyrset@cybernetica.no>
Cc: "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: PostgreSQL disk fragmentation causes performance
 problems on Windows
Message-ID: <20150429080854.GD14535@awork2.anarazel.de>
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On 2015-04-29 10:06:39 +0200, Andres Freund wrote:
> Hi,
> 
> On 2015-04-23 19:47:06 +0000, Jan Gunnar Dyrset wrote:
> > I am using PostgreSQL to log data in my application. A number of rows
> > are added periodically, but there are no updates or deletes. There are
> > several applications that log to different databases.
> > 
> > This causes terrible disk fragmentation which again causes performance
> > degradation when retrieving data from the databases. The table files
> > are getting more than 50000 fragments over time (max table size about
> > 1 GB).
> > 
> > The problem seems to be that PostgreSQL grows the database with only
> > the room it need for the new data each time it is added. Because
> > several applications are adding data to different databases, the
> > additions are never contiguous.
> 
> Which OS and filesystem is this done on? Because many halfway modern
> systems, like e.g ext4 and xfs, implement this in the background as
> 'delayed allocation'.

Oh, it's in the subject. Stupid me, sorry for that. I'd consider testing
how much better this behaves under a different operating system, as a
shorter term relief.

Greetings,

Andres Freund


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