From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@gmail.com>
cc: Rod Taylor <rbt@rbt.ca>, Jim Nasby <nasbyj@amazon.com>,
        Jeremy Schneider <schneider@ardentperf.com>,
        Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Collation version tracking for macOS
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Comments: In-reply-to Thomas Munro <thomas.munro@gmail.com>
	message dated "Wed, 08 Jun 2022 07:31:19 +1200"
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Date: Tue, 07 Jun 2022 15:43:32 -0400
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Thomas Munro <thomas.munro@gmail.com> writes:
> On Wed, Jun 8, 2022 at 3:58 AM Rod Taylor <rbt@rbt.ca> wrote:
>> Is this more involved than creating a list of all valid Unicode charact=
ers (~144 thousand), sorting them, then running crc32 over the sorted orde=
r to create the "version" for the library/collation pair? Far from free bu=
t few databases use more than a couple different collations.

> Collation rules have multiple levels and all kinds of quirks, so that
> won't work.

Yeah, and it's exactly at the level of quirks that things are likely
to change.  Nobody's going to suddenly start sorting B before A.
They might, say, change their minds about where the digram "cz"
sorts relative to single letters, in languages where special rules
for that are a thing.

The idea of fingerprinting a collation's behavior is interesting,
but I've got doubts about whether we can make a sufficiently thorough
fingerprint.

			regards, tom lane