From: Tom Lane <tgl@sss.pgh.pa.us>
To: Gary Doades <gpd@gpdnet.co.uk>
Cc: pgsql-performance@postgresql.org
Subject: Re: Strange Create Index behaviour
Date: Wed, 15 Feb 2006 16:51:23 -0500
Message-ID: <20005.1140040283@sss.pgh.pa.us> (raw)
In-Reply-To: <43F39E53.1020009@gpdnet.co.uk>
References: <43F38867.6010701@gpdnet.co.uk>
<19510.1140036968@sss.pgh.pa.us>
<19779.1140038874@sss.pgh.pa.us>
<43F39E53.1020009@gpdnet.co.uk>
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.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, gpd@gpdnet.co.uk
Subject: Re: Strange Create Index behaviour
In-Reply-To: <20005.1140040283@sss.pgh.pa.us>
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