Message-ID: <1b356b61-3a2a-490a-bf9a-6340a1ec004a@gmail.com>
Date: Mon, 31 Mar 2025 11:46:08 +0200
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Subject: Re: Memoize ANTI and SEMI JOIN inner
To: Richard Guo <guofenglinux@gmail.com>, David Rowley <dgrowleyml@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
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From: Andrei Lepikhov <lepihov@gmail.com>
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On 3/31/25 11:03, Richard Guo wrote:
> On Thu, Mar 20, 2025 at 3:02 PM David Rowley <dgrowleyml@gmail.com> wrote:
>> For making this work, I think the attached should be about the guts of
>> the code changes. I didn't look at the comments. Right now I can't
>> think of any reason why this can't be done, but some experimentation
>> might reveal some reason that it can't.
> 
> I reviewed this patch and I have some concerns about the following
> code:
> 
>      if (extra->inner_unique &&
>          (inner_path->param_info == NULL ||
>           bms_num_members(inner_path->param_info->ppi_serials) <
>           list_length(extra->restrictlist)))
>          return NULL;
> 
> I understand that this check is used to ensure that the entire join
> condition is parameterized in the case of unique joins, so that we can
> safely mark the cache entry as complete after reading the first tuple.
> However, ppi_clauses includes join clauses available from all outer
> rels, not just the current outer rel, while extra->restrictlist only
> includes the restriction clauses for the current join.  This means the
> check could pass even if a restriction clause isn't parameterized, as
> long as another join clause, which doesn't belong to the current join,
> is included in ppi_clauses.
Initially, I had the same concern. But if ppi_clauses contains a qual, 
it should refer to this join and, as a result, be in the 
extra->restrictlist, isn't it?
I thought about references to the other side of an OUTER JOIN, but if 
the subquery refers to LHS, it just not be transformed to the SEMI/ANTI 
join.
Anyway, if you provide an example or just a sketch, I will be happy to 
discover it.

-- 
regards, Andrei Lepikhov