Re: C locale versus en_US.UTF8. (Was: String comparision in PostgreSQL)

On Wed, Aug 29, 2012 at 12:52:50PM -0600, Scott Marlowe wrote:
> On Wed, Aug 29, 2012 at 11:43 AM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > On Wed, Aug 29, 2012 at 10:31:21AM -0700, Aleksey Tsalolikhin wrote:
> >> On Wed, Aug 29, 2012 at 9:45 AM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
> >> > citext unfortunately doesn't allow for index optimization of LIKE
> >> > queries, which IMNSHO defeats the whole purpose. to the best way
> >> > remains to use lower() ...
> >> > this will be index optimized and fast as long as you specified C
> >> > locale for your database.
> >>
> >> What is the difference between C and en_US.UTF8, please? We see that
> >> the same query (that invokes a sort) runs 15% faster under the C
> >> locale. The output between C and en_US.UTF8 is identical. We're
> >> considering moving our database from en_US.UTF8 to C, but we do deal
> >> with internationalized text.
> >
> > Well, C has reduced overhead for string comparisons, but obviously
> > doesn't work well for international characters. The single-byte
> > encodings have somewhat less overhead than UTF8. You can try using C
> > locales for databases that don't require non-ASCII characters.
>
> I think you're confusing encodings with locales. C is a locale. You

I think technically C is a non-locale.

> can have a database with a locale of C and UTF-8 encoding.
>
> create database clocale_utf8 encoding='UTF8' LC_COLLATE= 'C' template=template0;
>
> \l
> Name | Owner | Encoding | Collate | Ctype |
> Access privileges
> --------------+----------+-----------+-------------+-------------+-----------------------
> clocale_utf8 | smarlowe | UTF8 | C | en_US.UTF-8 |
>
>
> SQL_ASCII is the encoding equivalent of C locale, but it also allows
> multi-byte characters.

Yes, but what sort ordering do you get in that case?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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