Re: Performance issues with v18 SQL-language-function changes

Hi

po 14. 4. 2025 v 16:38 odesílatel Robert Haas <robertmhaas(at)gmail(dot)com>
napsal:

> On Sun, Apr 13, 2025 at 3:23 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > create function fx(p_summa bigint) returns text immutable strict
> > return ltrim(to_char(p_summa, '999 999 999 999 999 999 999 999'));
> >
> > explain analyze select fx(i) from generate_series(1,1000000) as i(i);
> >
> > you arrive at the rude discovery that 0dca5d68d is about 50% slower
> > than 0dca5d68d^, because the old implementation builds a plan for fx()
> > only once and then re-uses it throughout the query.
>
> I agree that we should do something about this. I haven't reviewed
> your patches but the approach sounds broadly reasonable.
>

I can confirm that all tests passed, and patched code is about 5% faster
than the current master (tested on my slower notebook). So it should to fix
performance regression where it was it against pg17 (it was about 2%)
(tested without assertions)

Regards

Pavel

> --
> Robert Haas
> EDB: http://www.enterprisedb.com
>