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help / color / mirror / Atom feedFrom: Olleg Samoylov <[email protected]>
To: Tom Lane <[email protected]>
Cc: pgsql-generallists.postgresql.org <[email protected]>
Subject: Re: Interesting case of IMMUTABLE significantly hurting performance
Date: Thu, 10 Apr 2025 08:33:02 +0300
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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<CAKFQuwY51Us6LeBxtdL7MbHpJkxYpWtMOHJAhUoXXN2p5f1JfQ@mail.gmail.com>
<[email protected]>
On 10.04.2025 01:08, Tom Lane wrote:
> Yeah. The assumption is that you had a reason for marking the
> function IMMUTABLE and you want the planner to treat it that way
> even if it isn't really. (There are valid use-cases for that, for
> instance if you want calls to the function to be constant-folded.)
> regards, tom lane
Well, to_char(bigint, text) indeed not immutable, because in some
pattern it uses get information from locale. For instance,'SLDG'
patterns. But in case of
CREATE OR REPLACE FUNCTION formatted_num_immutable(p_summa bigint)
RETURNS text
LANGUAGE sql
IMMUTABLE STRICT
RETURN ltrim(to_char(p_summa, '999 999 999 999 999 999 999 999'));
to_char do not use locale information in this pattern. So it is correct
conclude that to_char is immutable with this pattern and
formatted_num_immutable too. I did not lie to the planner.
So this is looked "strange", immutable function marked as immutable
function can not be inlined, but exactly the same function marked as
volatile do.
--
Olleg
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