| From: | Andrei Lepikhov <lepihov(at)gmail(dot)com> |
|---|---|
| To: | Ba Jinsheng <bajinsheng(at)u(dot)nus(dot)edu> |
| Cc: | "pgsql-performance(at)lists(dot)postgresql(dot)org" <pgsql-performance(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Unexpected Performance for the Function simplify_function |
| Date: | 2024-10-25 09:38:24 |
| Message-ID: | a3d5a411-0338-4cfb-9db5-9e6baba0f011@gmail.com |
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| Thread: | |
| Lists: | pgsql-performance |
On 10/25/24 16:26, Ba Jinsheng wrote:
> >So, I wonder if you could analyse the path-choosing logic, determine the
> costs of competing paths, and explain why NestLoop wasn't chosen.
>
> To be honest, it is a bit challenging for me.
> I guess the better query plan is not considered when comparing the cost
> of paths?
I personally print all the paths (adding an elog message inside the
code) and their costs for specific JOIN. Some paths are filtered on
earlier stages and not even have a leg in pathlist.
Basically, Postgres already has some extended logging for the optimiser
paths - use -DOPTIMIZER_DEBUG compilation flag.
--
regards, Andrei Lepikhov
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