| From: | Richard Guo <guofenglinux(at)gmail(dot)com> |
|---|---|
| To: | liuxy(at)gatech(dot)edu, pgsql-bugs(at)lists(dot)postgresql(dot)org |
| Subject: | Re: BUG #16889: Suboptimal behavior related to join condition |
| Date: | 2021-02-26 06:36:06 |
| Message-ID: | CAMbWs4-1wY4WZtvcb-oRwL_03KRuUE8MaNza52Ytf5GU7dEMzg@mail.gmail.com |
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| Lists: | pgsql-bugs |
Hi,
On Tue, Feb 23, 2021 at 4:15 PM PG Bug reporting form <
noreply(at)postgresql(dot)org> wrote:
>
> Expected Behavior
> Since these two queries are semantically equivalent, we were hoping that
> PostgreSQL will evaluate them in roughly the same amount of time. It looks
> to me that when evaluating the first (slower) query, the query optimizer
> does not propagate the information about "ps_suppkey" = 752 to the INNER
> JOIN condition.
>
Currently we only generate derived clauses based on equivalence classes.
So in the first query, we have 'ps_suppkey = 752' and 'p_partkey - 177 <
ps_suppkey', and we cannot deduce the clause 'p_partkey - 177 < 752'. We
do not have deduction rules to accomplish that for now.
Thanks
Richard
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