On 20/3/2025 07:02, David Rowley wrote:
> On Thu, 20 Mar 2025 at 06:16, Andrei Lepikhov <lepihov@gmail.com> wrote:
>> How can we be sure that semi or anti-join needs only one tuple? I think
>> it would be enough to control the absence of join clauses and filters in
>> the join. Unfortunately, we only have such a guarantee in the plan
>> creation stage (maybe even setrefs.c). So, it seems we need to invent an
>> approach like AlternativeSubplan.
>
> I suggest looking at what 9e215378d did. You might be able to also
> allow semi and anti-joins providing the cache keys cover the entire
> join condition. I think this might be safe as Nested Loop will only
> ask its inner subnode for the first match before skipping to the next
> outer row and with anti-join, there's no reason to look for additional
> rows after the first. Semi-join and unique joins do the same thing in
> nodeNestloop.c. To save doing additional checks at run-time, the code
> does:
Thank you for the clue! I almost took the wrong direction.
I have attached the new patch, which includes corrected comments for
better clarification of the changes, as well as some additional tests.
I now feel much more confident about this version since I have resolved
that concern.
--
regards, Andrei Lepikhov
