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

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
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.