| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-hackers(at)lists(dot)postgresql(dot)org, Alexander Pyhalov <a(dot)pyhalov(at)postgrespro(dot)ru>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
| Subject: | Re: Performance issues with v18 SQL-language-function changes |
| Date: | 2025-04-14 14:38:29 |
| Message-ID: | CA+Tgmobv4=R_kfdLw1ePFBr0XrCQtcK6jGFQsM=CoVeYT8Xr0Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
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.
--
Robert Haas
EDB: http://www.enterprisedb.com
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