From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Gary Doades <gpd@gpdnet.co.uk>
Cc: pgsql-performance@postgresql.org
Subject: Re: Strange Create Index behaviour
Date: Wed, 15 Feb 2006 23:51:21 +0000
Message-ID: <1140047481.12131.205.camel@localhost.localdomain> (raw)
In-Reply-To: <20005.1140040283@sss.pgh.pa.us>
References: <43F38867.6010701@gpdnet.co.uk>
<19510.1140036968@sss.pgh.pa.us>
<19779.1140038874@sss.pgh.pa.us>
<43F39E53.1020009@gpdnet.co.uk>
<20005.1140040283@sss.pgh.pa.us>
On Wed, 2006-02-15 at 16:51 -0500, Tom Lane wrote:
> Gary Doades <gpd@gpdnet.co.uk> writes:
> > Interestingly, if I don't delete the table after a run, but just drop
> > and re-create the index repeatedly it stays a pretty consistent time,
> > either repeatedly good or repeatedly bad!
>
> This is consistent with the theory of a data-dependent performance
> problem in qsort. If you don't generate a fresh set of random test
> data, then you get repeatable runtimes. With a new set of test data,
> you might or might not hit the not-so-sweet-spot that we seem to have
> detected.
Agreed. Good analysis...
Best Regards, Simon Riggs
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To: pgsql-performance@postgresql.org
Cc: simon@2ndquadrant.com, tgl@sss.pgh.pa.us, gpd@gpdnet.co.uk
Subject: Re: Strange Create Index behaviour
In-Reply-To: <1140047481.12131.205.camel@localhost.localdomain>
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