Message-ID: <606bd2baa6d65b38fee6eb23bba40c5da210255b.camel@j-davis.com>
Subject: Re: Collation version tracking for macOS
From: Jeff Davis <pgsql@j-davis.com>
To: Thomas Munro <thomas.munro@gmail.com>, Peter Eisentraut
	 <peter.eisentraut@enterprisedb.com>
Cc: Jeremy Schneider <schneider@ardentperf.com>, Peter Geoghegan
 <pg@bowt.ie>,  "Finnerty, Jim" <jfinnert@amazon.com>, "Nasby, Jim"
 <nasbyj@amazon.com>, Tom Lane <tgl@sss.pgh.pa.us>,  pgsql-hackers
 <pgsql-hackers@postgresql.org>
Date: Mon, 14 Nov 2022 16:55:25 -0800
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I looked at v6.

  * We'll need some clearer instructions on how to build/install extra
ICU versions that might not be provided by the distribution packaging.
For instance, I got a cryptic error until I used --enable-rpath, which
might not be obvious to all users.
  * Can we have a better error when the library was built with --
disable-renaming? We can just search for the plain (no suffix) symbol.
  * We should use dlerror() instead of %m to report dlopen() errors.
  * It seems like the collation version is just there to issue WARNINGs
when a user is using the non-versioned locale syntax and the library
changes underneath them (or if there is collation version change within
a single ICU major version)?
  * How are you testing this?
  * In my tests (sort, hacked so abbreviate is always false), I see a
~3% regression for ICU+UTF8. That's fine with me. I assume it's due to
the indirect function call, but that's not obvious to me from the
profile. If it's a major problem we could have a special case of
varstrfastcmp_locale() that works on the compile-time ICU version.

I realize your patch is experimental, but when there is a better
consensus on the approach, we should consider adding declarative syntax
such as:

   CREATE COLLATION (or LOCALE?) PROVIDER icu67
     TYPE icu VERSION '67' AS '/path/to/icui18n.so.67';

It will offer more opportunities to catch errors early and offer better
error messages. It would also enable it to function if the library is
built with --disable-renaming (though we'd have to trust the user).

On Sat, 2022-10-22 at 14:22 +1300, Thomas Munro wrote:
> Problem 1:=C2=A0 Suppose you're ready to start using (say) v72.=C2=A0 I g=
uess
> you'd use the REFRESH command, which would open the main linked ICU's
> collversion and stamp that into the catalogue, at which point new
> sessions would start using that, and then you'd have to rebuild all
> your indexes (with no help from PG to tell you how to find everything
> that needs to be rebuilt, as belaboured in previous reverted work).
> Aside from the possibility of getting the rebuilding job wrong (as
> belaboured elsewhere), it's not great, because there is still a
> transitional period where you can be using the wrong version for your
> data.=C2=A0 So this requires some careful planning and understanding from
> the administrator.

How is this related to the search-by-collversion design? It seems like
it's hard no matter what.


--=20
Jeff Davis
PostgreSQL Contributor Team - AWS