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

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От	Tender Wang
Тема	Re: MergeJoin beats HashJoin in the case of multiple hash clauses
Дата	14 апреля 09:17:17
Msg-id	CAHewXNnA+5sjiZTF+4nEDNM1F-+2yP+1cpqZXwUkm6uwmPUW0w@mail.gmail.com обсуждение исходный текст
Ответ на	Re: MergeJoin beats HashJoin in the case of multiple hash clauses (Alexander Korotkov <aekorotkov@gmail.com>)
Ответы	Re: MergeJoin beats HashJoin in the case of multiple hash clauses
Список	pgsql-hackers

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?

Thanks, Tender Wang

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