Re: limit in subquery causes poor selectivity estimation

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Peter Eisentraut <peter_e(at)gmx(dot)net>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: limit in subquery causes poor selectivity estimation
Date: 2011-08-31 18:12:58
Message-ID: 21748.1314814378@sss.pgh.pa.us
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Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Wed, Aug 31, 2011 at 6:22 AM, Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:
>> I liked the old one better. ;-)

> AFAICS, those plans are identical, except for a minor difference in
> the cost of scanning test2.

The point is that the estimate of the result size is worse in 8.4.8.

I am not, however, convinced that 8.4.7 was actually smarter ... it
may have been getting the right answer for the wrong reason.

regards, tom lane

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