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From: Tom Lane <[email protected]>
To: Alexandra Wang <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: Remove extra Sort node above a btree-compatible Index Scan
Date: Fri, 28 Feb 2025 00:43:17 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAK98qZ0MVVdV1tQKhHq=2qVkKN1rWff-YW6BGOOLoO509krv4Q@mail.gmail.com>
References: <CAK98qZ0MVVdV1tQKhHq=2qVkKN1rWff-YW6BGOOLoO509krv4Q@mail.gmail.com>

Alexandra Wang <[email protected]> writes:
> I’ve attached a patch that removes this unnecessary Sort node for
> B-tree-compatible indexes.

This does not look right at all.  You can't just ignore the opfamily
etc. while deciding whether two pathkeys represent the same sort
ordering, as you did in create_mergejoin_plan().  I don't like
pathkeys_have_same_sortop() either.  The pathkey data structures
were designed to let pointer comparison be sufficient for deciding
whether pathkeys are equivalent: see the "canonical pathkey" stuff
in pathkeys.c.  I think that this patch may be band-aiding over some
breakage of that concept, but you've not provided enough context to
figure out what the underlying problem is.

			regards, tom lane

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