Re: Can ICU be used for a database's default sort order?

From: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>
To: Peter Geoghegan <pg(at)bowt(dot)ie>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Can ICU be used for a database's default sort order?
Date: 2017-06-23 18:32:38
Message-ID: f689322a-4fc5-10cc-4a60-81f1ff0166c9@2ndquadrant.com
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On 6/22/17 23:10, Peter Geoghegan wrote:
> On Thu, Jun 22, 2017 at 7:10 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Is there some way I'm missing, or is this just a not-done-yet feature?
>
> It's a not-done-yet feature.

It's something I hope to address soon.

The main definitional challenge is how to associate a pg_database entry
with a collation.

What we currently effectively do is duplicate the fields of pg_collation
in pg_database. But I imagine over time we'll add more properties in
pg_collation, along with additional ALTER COLLATION commands etc., so
duplicating all of that would be a significant amount of code
complication and result in a puzzling user interface.

Ideally, I'd like to see CREATE DATABASE ... COLLATION "foo". But the
problem is of course that collations are per-database objects. Possible
solutions:

1) Associate by name only. That is, you can create a database with any
COLLATION "foo" that you want, and it's only checked when you first
connect to or do anything in the database.

2) Create shared collations. Then we'd need a way to manage having a
mix of shared and non-shared collations around.

There are significant pros and cons to all of these ideas. Some people
I talked to appeared to prefer the shared collations approach.

Other ideas?

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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