Re: Postgres 17.4 is much slower than Postgres 15.12 using RECURSIVE

Hi

po 28. 4. 2025 v 23:53 odesílatel marcos sicat <marcos(dot)sicat(at)atlasifs(dot)com>
napsal:

> Thanks, Tom.
>
> After you made your recommendation, the result returned much quicker at
> 2.62 seconds, but v15 is still faster at 1.82 seconds. No modification
> was made to the function.
>

and you look at the log file and separate query plans from there.

proposed changes just force storing query plans to the log file.

From plans we can see what is different

Regards

Pavel

>
> [image: image.png]
>
> *From: *Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
> *Date: *Monday, April 28, 2025 at 9:59 AM
> *To: *marcos sicat <marcos(dot)sicat(at)atlasifs(dot)com>
> *Cc: *Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>,
> pgsql-bugs(at)lists(dot)postgresql(dot)org <pgsql-bugs(at)lists(dot)postgresql(dot)org>
> *Subject: *Re: Postgres 17.4 is much slower than Postgres 15.12 using
> RECURSIVE
>
> marcos sicat <marcos(dot)sicat(at)atlasifs(dot)com> writes:
> > The function is the same between v15 and v17. Is there a subtle
> difference in performance for nested subqueries in v17?
>
> Your next step should be to compare the plans for the function's
> query. The auto_explain or pg_stat_statements extensions could
> be used to check that in-situ, if manually EXPLAINing that query
> doesn't yield insight.
>
> regards, tom lane
>