Message-ID: <27263746746471bac876c5fae92cb21a38cde45d.camel@j-davis.com>
Subject: Re: Order changes in PG16 since ICU introduction
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: Fri, 21 Apr 2023 13:13:27 -0700
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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=3Dlibc and
collcollate=3DC.

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=3Dlibc to get memcmp() behavior (same
as v15 but still confusing)

Regards,
	Jeff Davis