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Re: Order changes in PG16 since ICU introduction

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: Sandro Santilli <strk@kbt.io>, Regina Obe <lr@pcorp.us>, pgsql-hackers@lists.postgresql.org
Date: 2023-04-21T20:13:27Z
Lists: pgsql-hackers 
On Fri, 2023-04-21 at 13:28 -0400, Tom Lane wrote:
> I am wondering however whether this doesn't mean that all our
> carefully
> coded fast paths for C locale just went down the drain.

The code still exists. You can test it by using the built-in collation
"C" which is correctly specified with collprovider=libc and
collcollate=C.

For my test dataset, ICU 72, glibc 2.35:

  -- ~07s
  explain analyze select t from a order by t collate "C";

  -- ~15s
  explain analyze select t from a order by t collate "en-US-x-icu";

  -- ~21s
  explain analyze select t from a order by t collate "en-US-u-va-posix-
x-icu";

  -- ~34s
  explain analyze select t from a order by t collate "en_US";

I believe the confusion in this thread comes from:

* The syntax of CREATE DATABASE (the same as v15 but still confusing)
* The fact that you need provider=libc to get memcmp() behavior (same
as v15 but still confusing)

Regards,
	Jeff Davis

Commits

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

  1. Introduce "builtin" collation provider.

  2. ICU: do not convert locale 'C' to 'en-US-u-va-posix'.

  3. initdb: change default --locale-provider back to libc.

  4. CREATE DATABASE: make LOCALE apply to all collation providers.

  5. Remove read-only server settings lc_collate and lc_ctype

  6. ICU: use uloc_getDefault() for initdb.

  7. Doc fixes for commit 1e16af8ab5.

  8. Doc: fix some rendering problems in the PDF docs build.

  9. Doc improvements for language tags and custom ICU collations.

  10. ICU: check for U_STRING_NOT_TERMINATED_WARNING.

  11. Reduce icu_validation_level default to WARNING.

  12. Revert "ICU: do not convert locale 'C' to 'en-US-u-va-posix'."

  13. Fix initdb --no-locale.

  14. Avoid character classification in regex escape parsing.