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

On Wed, Aug 29, 2012 at 12:43 PM, 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.

To add:
The middle ground I usually choose is to have a database encoding of
UTF8 but with the C (aka POSIX) locale. This gives you the ability to
store any unicode but indexing operations will use the faster C string
comparison operations for a significant performance boost --
especially for partial string searches on an indexed column. This is
an even more attractive option in 9.1 with the ability to specify
specific collations at runtime.

merlin