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Re: ICU for global collation

Peter Eisentraut <peter.eisentraut@enterprisedb.com>

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From: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
To: Daniel Verite <daniel@manitou-mail.org>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2022-01-11T11:18:58Z
Lists: pgsql-hackers 
On 10.01.22 12:49, Daniel Verite wrote:
> With the current patch, it's not possible, AFAICS, because the user
> can't tell that the collation is non-deterministic. Presumably this
> would require another option to CREATE DATABASE and another
> column to store that bit of information.

Adding this would be easy, but since pattern matching currently does not 
support nondeterministic collations, if you make a global collation 
nondeterministic, a lot of system views, psql, pg_dump queries etc. 
would break, so it's not practical.  I view this is an orthogonal 
project.  Once we can support this without breaking system views etc., 
then it's easy to enable with a new column in pg_database.

> The "daticucol" column also suggests that we don't expect to add
> other collation providers in the future. Maybe a pair of columns like
> (datcollprovider, datcolllocale) would be more future-proof,
> or a (datcollprovider, datcolllocale, datcollisdeterministic)
> triplet if non-deterministic collations are allowed.

I don't expect many new collation providers.  So I don't think an 
EAV-like storage would be helpful.  The other problem is that we don't 
know what we need.  For example, the libc provider needs both a collate 
and a ctype value, so that wouldn't fit into that scheme nicely.

> Also, pg_collation has "collversion" to detect a mismatch between
> the ICU runtime and existing indexes. I don't see that field
> for the db-wide ICU collation, so maybe we currently miss the capability
> to detect the mismatch for the db-wide collation?

Yeah, I think I need to add a datcollversion field and the associated 
checks.

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Add CHECK_FOR_INTERRUPTS while restoring changes during decoding.

  2. Improve ICU option handling in CREATE DATABASE

  3. Don't allow creation of database with ICU locale with unsupported encoding

  4. Make locale option behavior more consistent

  5. pg_dump: Dump colliculocale

  6. Remove further unwanted linker flags from perl_embed_ldflags

  7. Doc: document possible need to raise kernel's somaxconn limit.

  8. Reduce warnings with -Wshadow=compatible-local builds

  9. Remove redundant spaces in _outA_Expr() output

  10. Fix outdated --help message for postgres -f

  11. pg_upgrade: Fix version comparison for global ICU support

  12. Silence -Wmaybe-uninitialized compiler warning in dbcommands.c.

  13. Add option to use ICU as global locale provider

  14. DefineCollation() code cleanup

  15. Change collate and ctype fields to type text

  16. Call pg_newlocale_from_collation() also with default collation

  17. Use libc version as a collation version on glibc systems.

  18. Silence -Wmaybe-uninitialized compiler warnings in dbcommands.c.

  19. Make LC_COLLATE and LC_CTYPE database-level settings. Collation and