Re: ICU Collations and Collation Updates

Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)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