From: Tom Lane <tgl@sss.pgh.pa.us>
To: Edmund Horner <ejrh00@gmail.com>
cc: David Rowley <david.rowley@2ndquadrant.com>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Tid scan improvements
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Comments: In-reply-to Edmund Horner <ejrh00@gmail.com>
	message dated "Fri, 21 Dec 2018 16:19:35 +1300"
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Date: Thu, 20 Dec 2018 22:31:16 -0500
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Edmund Horner <ejrh00@gmail.com> writes:
> For the forward scan, I seem to recall, from your merge join example,
> that it's useful to set the pathkeys even when there are no
> query_pathkeys.  We just have to unconditionally set them so that the
> larger plan can make use of them.

No.  Look at indxpath.c: it does not worry about pathkeys unless
has_useful_pathkeys is true, and it definitely does not generate
pathkeys that don't get past truncate_useless_pathkeys.  Those
functions are responsible for worrying about whether mergejoin
can use the pathkeys.  It's not tidpath.c's job to outthink them.

			regards, tom lane