Horton

Re: Memoize ANTI and SEMI JOIN inner

Alena Rybakina <a.rybakina@postgrespro.ru>

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From: Alena Rybakina <a.rybakina@postgrespro.ru>
To: David Rowley <dgrowleyml@gmail.com>
Cc: Andrei Lepikhov <lepihov@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2025-03-31T03:21:43Z
Lists: pgsql-hackers

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  1. Enable use of Memoize for ANTI joins

On 31.03.2025 06:04, David Rowley wrote:
> 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.
>
I tend to agree with you that someone might set this flag to true for 
these join types in the future.

However, is it necessary to check that extra->inner_unique must be false 
for SEMI/ANTI joins here, or am I missing something? It looks a little 
confusing at this point.

if(!extra->inner_unique&& (jointype== JOIN_SEMI|| jointype== JOIN_ANTI))

     single_mode= true;

--

Regards,
Alena Rybakina
Postgres Professional