Horton

Re: Pathify RHS unique-ification for semijoin planning

Richard Guo <guofenglinux@gmail.com>

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From: Richard Guo <guofenglinux@gmail.com>
To: Alexandra Wang <alexandra.wang.oss@gmail.com>
Cc: Álvaro Herrera <alvherre@kurilemu.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Tom Lane <tgl@sss.pgh.pa.us>, Andy Fan <zhihuifan1213@163.com>, wenhui qiu <qiuwenhuifx@gmail.com>
Date: 2025-08-04T01:55:48Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Simplify relation_has_unique_index_for()

  2. Pathify RHS unique-ification for semijoin planning

  3. Convert varatt.h access macros to static inline functions.

  4. Re-export a few of createplan.c's make_xxx() functions.

On Fri, Aug 1, 2025 at 11:58 PM Alexandra Wang
<alexandra.wang.oss@gmail.com> wrote:
> While reviewing the code, the following diff concerns me:

>   if (joinrel->consider_parallel &&
> - save_jointype != JOIN_UNIQUE_OUTER &&
> - save_jointype != JOIN_FULL &&
> - save_jointype != JOIN_RIGHT &&
> - save_jointype != JOIN_RIGHT_ANTI &&
> + jointype != JOIN_FULL &&
> + jointype != JOIN_RIGHT &&
> + jointype != JOIN_RIGHT_ANTI &&
>   outerrel->partial_pathlist != NIL &&
>   bms_is_empty(joinrel->lateral_relids))
>
> What has changed that enabled JOIN_UNIQUE_OUTER to handle partial
> paths? Or is it no longer possible for the outer path to be partial?

It's the latter, as indicated by the Assert in create_unique_paths():

+       /*
+        * There shouldn't be any partial paths for the unique relation;
+        * otherwise, we won't be able to properly guarantee uniqueness.
+        */
+       Assert(unique_rel->partial_pathlist == NIL);

Thanks
Richard