Re: MergeJoin beats HashJoin in the case of multiple hash clauses

Tender Wang <tndrwang(at)gmail(dot)com> 于2025年4月14日周一 14:17写道：

> Hi,
>
> While I debug hashjoin codes, in estimate_multivariate_bucketsize(), I
> find that
> the list_copy(hashclauses) below is unnecessary if we have a single join
> clause.
>
> List *clauses = list_copy(hashclauses);
> ...
>
> I adjust the place of list_copy() call as the attached patch.
> This can save some overhead of function calls and memory copies.
>
> Any thoughts?
>
>
Hi Alexander,

In the last thread, I found a minor optimization for the code in
estimate_multivariate_bucketsize().
Adjust the place of list_copy() at the start of
estimate_multivariate_bucketsize, and we can avoid unnecessarily creating a
new list
and memory copy if we have only a single hash clause.

Do you think it's worth doing this?
--
Thanks,
Tender Wang