| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Edmund Horner <ejrh00(at)gmail(dot)com> |
| Cc: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Tid scan improvements |
| Date: | 2018-12-21 03:31:16 |
| Message-ID: | 20220.1545363076@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Edmund Horner <ejrh00(at)gmail(dot)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
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