Re: Memoize ANTI and SEMI JOIN inner

Andrei Lepikhov <lepihov@gmail.com>

From: Andrei Lepikhov <lepihov@gmail.com>

To: David Rowley <dgrowleyml@gmail.com>

Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>, Alena Rybakina <a.rybakina@postgrespro.ru>

Date: 2025-03-31T07:45:18Z

Lists: pgsql-hackers

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

On 3/31/25 05:33, David Rowley wrote:
> I can't say definitively that we won't find a reason in the future
> that we should set inner_unique for SEMI/ANTI joins, so I don't follow
> the need for the Assert.
> 
> Maybe you're seeing something that I'm not. What do you think will
> break if both flags are true?
I considered targeting PG 19 and July Comitfest for this feature, but 
currently, I don't see any further development needed here. What are 
your thoughts, David? Does it make sense to commit this to PG 18?

I have no reason to rush the process, but this feature seems beneficial 
for practice. When the internal structure is a bushy join tree, 
producing even a single tuple can be costly. SQL Server's Spool node 
addresses this issue, and people sometimes experience confusion 
detecting degradation during migration with specific queries.

-- 
regards, Andrei Lepikhov