Re: Memoize ANTI and SEMI JOIN inner

David Rowley <dgrowleyml@gmail.com>

From: David Rowley <dgrowleyml@gmail.com>

To: Alena Rybakina <a.rybakina@postgrespro.ru>

Cc: Andrei Lepikhov <lepihov@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>

Date: 2025-03-31T03:04:18Z

Lists: pgsql-hackers

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Enable use of Memoize for ANTI joins
- 0da29e4cb161 19 (unreleased) landed

On Mon, 31 Mar 2025 at 15:33, Alena Rybakina <a.rybakina@postgrespro.ru> wrote:
> I believe it's worth asserting that both inner_unique and single_mode are not true at the same time — just as a safety check.

add_paths_to_joinrel() just chooses not to populate inner_unique for
SEMI and ANTI joins because, as of today's master, it's pretty
pointless to determine that because the executor will short-circuit
and skip to the next outer tuple for those join types anyway. I don't
follow why having both these flags set would cause trouble. It seems
perfectly legitimate that add_paths_to_joinrel() could choose to set
the inner_unique flag for these join types, and if it did, the Assert
you're proposing would fail for no good reason.

David