Horton

Re: Properly pathify the union planner

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Richard Guo <guofenglinux@gmail.com>
Cc: Alexander Lakhin <exclusion@gmail.com>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2024-03-27T10:34:09Z
Lists: pgsql-hackers

Attachments

On Wed, 27 Mar 2024 at 22:47, David Rowley <dgrowleyml@gmail.com> wrote:
> I did wonder when first working on this patch if subquery_planner()
> should grow an extra parameter, or maybe consolidate some existing
> ones by passing some struct that provides the planner with a bit more
> context about the query.  A few of the existing parameters are likely
> candidates for being in such a struct. e.g. hasRecursion and
> tuple_fraction. A SetOperationStmt could go in there too.

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.

David

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