Re: RT3.4 query needed a lot more tuning with 9.2 than it did with 8.1

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Christoph Berg <christoph(dot)berg(at)credativ(dot)de>, PostgreSQL Performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: RT3.4 query needed a lot more tuning with 9.2 than it did with 8.1
Date: 2013-05-13 20:14:06
Message-ID: 11475.1368476046@sss.pgh.pa.us
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Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> The planner is estimating this the outer side of this nested loop will
> produce 33 rows and that the inner side will produce 1. One would
> assume that the row estimate for the join product couldn't be more
> than 33 * 1 = 33 rows, but the planner is estimating 62335 rows, which
> seems like nonsense.

You know, of course, that the join size estimate isn't arrived at that
way. Still, this point does make it seem more like a planner bug and
less like bad input stats. It would be nice to see a self-contained
example ...

regards, tom lane

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