From: Tom Lane <tgl@sss.pgh.pa.us>
To: Laurenz Albe <laurenz.albe@cybertec.at>
cc: Thomas Michael Engelke <thomas.engelke@posteo.de>,
        pgsql-general@lists.postgresql.org
Subject: Re: ICU Collations and Collation Updates
In-reply-to: <d477c1faf35bad99fe550c8c4c1954ffa076ccfd.camel@cybertec.at>
References: <8ed41c50ba6c5322296b869e497c1b5573853b54.camel@posteo.de> <d477c1faf35bad99fe550c8c4c1954ffa076ccfd.camel@cybertec.at>
Comments: In-reply-to Laurenz Albe <laurenz.albe@cybertec.at>
	message dated "Mon, 14 Apr 2025 13:05:01 +0200"
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Date: Mon, 14 Apr 2025 10:36:40 -0400
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Laurenz Albe <laurenz.albe@cybertec.at> writes:
> On Mon, 2025-04-14 at 08:28 +0000, Thomas Michael Engelke wrote:
>> Is my understanding correct then in that this way the database
>> collations never change, unless a manual intervention reinitialises the
>> collations and reindexes the database (or appropriate indexes)? How
>> does that process compare to other RDBMS?

> When you update the C library or ICU library and the version changes,
> you get warned by PostgreSQL and have to rebuild indexes.
> So the collations can change whenever you update the respective libraries.
> You would have to build PostgreSQL yourself with a fixed version of ICU
> that you never upgrade if you want to avoid the problem.

Yeah.  AIUI there are two things that ICU does better than libc here:

1. ICU has a fairly well-defined scheme for identifying collation
versions, glibc not so much.  So the collation-changed warnings that
Laurenz mentions are a lot more trustworthy for ICU collations.

2. It's at least *possible* to use your own fixed-version ICU
library if you're desperate enough.  I don't think that would work
too well for libc; you're stuck with what the platform provides.

			regards, tom lane