Re: MergeJoin beats HashJoin in the case of multiple hash clauses - Mailing list pgsql-hackers

Tender Wang <tndrwang@gmail.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?