Re: significant semi join overestimates (with CTEs) - Mailing list pgsql-hackers

From Robert Haas
Subject Re: significant semi join overestimates (with CTEs)
Date
Msg-id CA+TgmobgZ6_7rWUyPdjmkZKjvgjzhe0QdLONo7f=ytMcRUARnA@mail.gmail.com
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In response to significant semi join overestimates (with CTEs)  (Tomas Vondra <tomas.vondra@2ndquadrant.com>)
List pgsql-hackers
On Mon, Feb 22, 2016 at 4:32 AM, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
> Firstly, we could clamp the join cardinality estimate to the size of
> cartesian product, eliminating at least the most obvious over-estimates.
>
> Secondly, I think it'd be nice to somehow eliminate the sudden jumps in the
> estimates - I'm not quite sure why need the three different formulas in
> eqjoinsel_semi, so maybe we can get rid of some of them?

I don't have any particularly intelligent commentary on the second
point right at the moment, but I emphatically agree with you on the
first one.  I've seen that problem a number of times and it seems
completely ludicrous to me.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company



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