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Re: BUG #5000: Optimizer does not use function-based index for an order by

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Brian Ceccarelli <ceccareb(at)talusmusic(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #5000: Optimizer does not use function-based index for an order by
Date: 2009-08-20 21:54:56
Message-ID: 407d949e0908201454v1a9e19fate65b1c5d6c3df661@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-bugs
> Description:        Optimizer does not use function-based index for an order
> by
> Details:
>
> Subject line says it all.

The optimizer makes an educated guess about whether to use indexes or
not. Without more information it's impossible to second-guess it.

You might want to ask on pgsql-general for advice on whether it's
making a good choice and how to influence it. But you'll have to
provide more information such as the actual schema and explain plans
of with and without enable_sort or enable_seqscan disabled.

Also 8.2 came out two years ago, if you're just starting with Postgres
you might as well use 8.4 which has features which will make this
easier -- including the ability to tell the planner how expensive your
function is.

-- 
greg
http://mit.edu/~gsstark/resume.pdf

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Subject: Re: BUG #4999: select 'a' < 'A' is true, but should be false . . .
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