Too many BitmapAnds in the wild - Mailing list pgsql-general

hey,

We see a fair number of incorrectly chosen BitmapAnd plans in the wild at Faraday... enough that googling the problem
endsup at our old posts to this mailing list 😀. An attractive solution was proposed by Jeff Janes [1] 

- *cost += 0.1 * cpu_operator_cost * path->rows;
+ *cost += 6 * cpu_operator_cost * path->rows;

It appears this constant hasn't been changed for 7 years [2].

Is there any reason not to at least adjust this up by a factor of 2? 10? If Jeff is right and 6 is closer to ideal,
then0.1 must be _way_ too low? 

Thanks,
Seamus


[1]
https://www.postgresql.org/message-id/flat/CAMkU%3D1yV7WQLetrCVPqn%3DdTPdNzW3JD29ZsK0zJmgzO2tdcx-Q%40mail.gmail.com#aa3b3316cbe44fb3fd913ce019a86bb8
[2] https://github.com/postgres/postgres/blame/master/src/backend/optimizer/path/costsize.c#L1056



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Seamus Abshere, SCEA
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