Re: Improve planner cost estimations for alternative subplans

From: Alexey Bashtanov <bashtanov(at)imap(dot)cc>
To: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Improve planner cost estimations for alternative subplans
Date: 2020-07-24 14:55:57
Message-ID: 4d85163e-e1b8-e6c2-a341-738078206eb9@imap.cc
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Hi Melanie,

Sorry for the delay.

> I've just started looking at this patch today, but I was wondering if
> you might include a test case which minimally reproduces the original
> problem you had.
I could reproduce it with an easier generated data set, please see attached.

However, to be honest with you, while searching I encountered a few
examples of the opposite behavior,
when the patched version was slower than the master branch.
So I'm not so sure whether we should use the patch, maybe we should
rather consider Tom's approach.

Best, Alex

Attachment Content-Type Size
altplan-example.sql application/sql 15.1 KB

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