Re: A problem about join ordering

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Richard Guo <guofenglinux(at)gmail(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: A problem about join ordering
Date: 2022-11-11 15:24:34
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Richard Guo <guofenglinux(at)gmail(dot)com> writes:
> I'm wondering whether we need to insist on being strict for the lower
> OJ's min_righthand. What if we instead check strictness for its whole
> syn_righthand?

Surely not. What if the only point of strictness is for a rel that
isn't part of the min_righthand? Then we could end up re-ordering
based on a condition that isn't actually strict for what we've
chosen as the join's RHS.

It might be possible to change the other part of the equation and
consider the A/B join's min_righthand instead of syn_righthand
while checking if Pcd uses A/B's RHS; but I'm not real sure about
that either.

regards, tom lane

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