Re: Introducing floating point cast into filter drastically changes row estimate

From: Merlin Moncure <mmoncure(at)gmail(dot)com>
To: pgsql-bugs <pgsql-bugs(at)postgresql(dot)org>
Subject: Re: Introducing floating point cast into filter drastically changes row estimate
Date: 2012-10-24 15:33:58
Message-ID: CAHyXU0xBrNk1PNQOK8o1suwMZtXweJMSvgbb6hUKdNwapK6AaQ@mail.gmail.com
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On Wed, Oct 24, 2012 at 10:06 AM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
> I was chasing down a query that ran fine in 8.1 but had an near
> infinite runtime in 9.2. It turned out to be from a bad filter
> estimate that is surprisingly simple to reproduce:

Testing some more it turns out that this isn't really a bug -- it's
just a general property of expression based filters: the planner
assumes they are very selective when in this case they are not.

merlin

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