From: Nico Williams <nico@cryptonector.com>
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Olleg Samoylov <splarv@ya.ru>
Cc: pgsql-generallists.postgresql.org <pgsql-general@lists.postgresql.org>
Subject: Re: Interesting case of IMMUTABLE significantly hurting performance
Date: Wed, 9 Apr 2025 16:21:40 -0500
Message-ID: <Z/bk5E6pqIBWTF3j@ubby> (raw)
In-Reply-To: <8687df7d49bc4b28b41c7cf4e9ad1e15d383b2fa.camel@cybertec.at>
References: <662101e2-5ca5-4bf5-9307-2519efde8690@ya.ru>
<8687df7d49bc4b28b41c7cf4e9ad1e15d383b2fa.camel@cybertec.at>
On Wed, Apr 09, 2025 at 10:50:00PM +0200, Laurenz Albe wrote:
> The IMMUTABLE function cannot be inlined because to_char() is not IMMUTABLE.
Q: Why would to_char() not be IMMUTABLE?
A: Because it makes use of locales, and I guess the guc-timezone GUC,
which could change if the expression is ultimately used in a PlPgSQL
fragment, or if it's in a prepared statement. (I think.)
That to_char is not immutable is not documented though. Though it's
clear when looking at the docs for the `jsonb_.*_tz()` functions.
Nico
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Cc: nico@cryptonector.com, laurenz.albe@cybertec.at, splarv@ya.ru, pgsql-general@lists.postgresql.org
Subject: Re: Interesting case of IMMUTABLE significantly hurting performance
In-Reply-To: <Z/bk5E6pqIBWTF3j@ubby>
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