Horton

Re: Built-in CTYPE provider

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Daniel Verite <daniel@manitou-mail.org>
Cc: Robert Haas <robertmhaas@gmail.com>, Jeremy Schneider <schneider@ardentperf.com>, pgsql-hackers@postgresql.org
Date: 2023-12-28T01:26:35Z
Lists: pgsql-hackers

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On Wed, 2023-12-20 at 13:49 +0100, Daniel Verite wrote:
> 
> But C.UTF-8 is not available everywhere, and there's still the
> problem that Unicode updates through libc are not aligned
> with Postgres releases.

Attached is an implementation of a built-in provider for the "C.UTF-8"
locale. That way applications (and tests!) can count on C.UTF-8 always
being available on any platform; and it also aligns with the Postgres
Unicode updates. Documentation is sparse and the patch is a bit rough,
but feedback is welcome -- it does have some basic tests which can be
used as a guide.

The C.UTF-8 locale, briefly, is a UTF-8 locale that provides simple
collation semantics (code point order) but rich ctype semantics
(lower/upper/initcap and regexes). This locale is for users who want
proper Unicode semantics for character operations (upper/lower,
regexes), but don't need a specific natural-language string sort order
to apply to all queries and indexes in their system. One might use it
as the database default collation, and use COLLATE clauses (i.e.
COLLATE UNICODE) where more specific behavior is needed.

The builtin C.UTF-8 locale has the following advantages over using the
libc C.UTF-8 locale:

  * Collation performance: the builtin provider uses memcmp and
abbreviated keys. In libc, these advantages are only available for the
C locale.

  * Unicode version is aligned with other parts of Postgres, like
normalization.

  * Available on all platforms with exactly the same semantics.

  * Testable and documentable.

  * Avoids index corruption risks. In theory libc C.UTF-8 should also
have stable collation, but that is not 100% true. In the builtin
provider it is 100% stable.

Regards,
	Jeff Davis

Commits

  1. Support PG_UNICODE_FAST locale in the builtin collation provider.

  2. Support Unicode full case mapping and conversion.

  3. Fix test failures when language environment is not UTF-8.

  4. Add unicode_strtitle() for Unicode Default Case Conversion.

  5. Use version for builtin collations.

  6. Fix convert_case(), introduced in 5c40364dd6.

  7. Inline basic UTF-8 functions.

  8. Support C.UTF-8 locale in the new builtin collation provider.

  9. Fix another warning, introduced by 846311051e.

  10. Address more review comments on commit 2d819a08a1.

  11. Fix unreachable code warning from commit 2d819a08a1.

  12. Introduce "builtin" collation provider.

  13. Catalog changes preparing for builtin collation provider.

  14. Unicode case mapping tables and functions.

  15. Add Unicode property tables.

  16. Documentation update for Standard Collations.

  17. Cleanup for unicode-update build target and test.

  18. Shrink Unicode category table.

  19. Make some error strings more generic

  20. pg_upgrade: copy locale and encoding information to new cluster.

  21. Update Unicode data to Unicode 15.0.0

  22. Create a new type category for "internal use" types.