From: | Seamus Abshere <seamus(at)abshere(dot)net> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Too many BitmapAnds in the wild |
Date: | 2018-09-17 19:34:31 |
Message-ID: | 1537212871.286640.1511233968.66591B19@webmail.messagingengine.com |
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Lists: | pgsql-general |
hey,
We see a fair number of incorrectly chosen BitmapAnd plans in the wild at Faraday... enough that googling the problem ends up 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, then 0.1 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
--
Seamus Abshere, SCEA
+598 9954 9954
https://www.faraday.io
https://github.com/seamusabshere
https://linkedin.com/in/seamusabshere
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