| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, rushabh(dot)lathia(at)gmail(dot)com |
| Subject: | Re: [PATCH] Keeps tracking the uniqueness with UniqueKey |
| Date: | 2020-04-29 00:29:20 |
| Message-ID: | CAApHDvqPN2+VTFSMCCrxiD1129rj51Rx_V74t0FM=V0es=yyAQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, 16 Apr 2020 at 14:17, Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> wrote:
> V6 also includes:
> 1. Fix the comment misleading you mentioned above.
> 2. Fixed a concern case for `relation_has_uniquekeys_for` function.
Over on [1], Richard highlights a problem in the current join removals
lack of ability to remove left joins unless the min_righthand side of
the join is a singleton rel. It's my understanding that the reason the
code checks for this is down to the fact that join removals used
unique indexed to prove the uniqueness of the relation and obviously,
those can only exist on base relations. I wondered if you might want
to look into a 0003 patch which removes that restriction? I think this
can be done now since we no longer look at unique indexes to provide
the proves that the join to be removed won't duplicate outer side
rows.
David
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