Horton

Re: Properly pathify the union planner

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <guofenglinux@gmail.com>
Cc: David Rowley <dgrowleyml@gmail.com>, Alexander Lakhin <exclusion@gmail.com>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2024-03-28T02:56:35Z
Lists: pgsql-hackers 
Richard Guo <guofenglinux@gmail.com> writes:
> On Wed, Mar 27, 2024 at 6:34 PM David Rowley <dgrowleyml@gmail.com> wrote:
>> The attached is roughly what I had in mind.  I've not taken the time
>> to see what comments need to be updated, so the attached aims only to
>> assist discussion.

> I like this idea.

I haven't studied the underlying problem yet, so I'm not quite
buying into whether we need this struct at all ... but assuming
we do, I feel like "PlannerContext" is a pretty poor name.
There's basically nothing to distinguish it from "PlannerInfo",
not to mention that readers would likely assume it's a memory
context of some sort.

Perhaps "SubqueryContext" or the like would be better?  It
still has the conflict with memory contexts though.

			regards, tom lane

Commits

  1. Don't adjust ressortgroupref in generate_setop_child_grouplist()

  2. Don't zero tuple_fraction when planning UNIONs with ORDER BYs

  3. Fix assert failure when planning setop subqueries with CTEs

  4. Allow planner to use Merge Append to efficiently implement UNION

  5. Simplify PathKey checking code

  6. Clarify the 'rows' parameter in create_append_path