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From: Josh Berkus <josh@agliodbs.com>
To: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: 8K recordsize bad on ZFS?
Date: Tue, 11 May 2010 18:01:48 -0700
Message-ID: <4BE9FDFC.40401@agliodbs.com> (raw)
In-Reply-To: <20100511134138.GB14663@oak.highrise.ca>
References: <4BE4ABC9.6040106@agliodbs.com>
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	<20100511134138.GB14663@oak.highrise.ca>


> Sure, but bulk load + reandom selects is going to *guarentee*
> fragmentatioon on a COW system (like ZFS, BTRFS, etc) as the selects
> start to write out all the hint-bit-dirtied blocks in random orders...
> 
> i.e. it doesn't take long to make an originally nicely continuous block
> random....

I'm testing with DD and Bonnie++, though, which create their own files.

For that matter, running an ETL procedure with a newly created database
on both recordsizes was notably (2.5x) faster on the 128K system.

So I don't think fragmentation is the difference.

-- 
                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.
                                     http://www.pgexperts.com



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