Controlling locale and impact on LIKE statements

Hi!

Background:

Using Pg8.1/8.2 on a utf-8 database, I found out that my left-anchored
LIKE clauses were forcing a full table scan instead of using the
index. After a bit of digging, I found that Pg can only use the
"normal" index for left-anchored LIKE queries if locale is 'C'.

"The optimizer can also use a B-tree index for queries involving the
pattern matching operators LIKE and ~ if the pattern is a constant and
is anchored to the beginning of the string — for example, col LIKE
'foo%' or col ~ '^foo', but not col LIKE '%bar'. However, if your
server does not use the C locale you will need to create the index
with a special operator class to support indexing of pattern-matching
queries."
http://www.postgresql.org/docs/8.1/static/indexes-types.html

What I think I need to do:

As I have a Pg install where the locale is already en_US.UTF-8, and
the database already exists, is there a DB-scoped way of controlling
the locale? I think the index usage noted above is affected by
lc_ctype but I could be wrong.

I really don't want to go down the "rebuild your pgcluster" path as
outlined here http://archives.postgresql.org/pgsql-hackers/2007-02/msg00992.php
;-)

Is there a better way? In this specific install I can create the
additional index. However, this needs a general fix for Moodle, which
has an abstract DB schema handling (we support MySQL, Pg, MSSQL,
Oracle) and the whole thing of figuring out what the locale is and
whether to add magical additional indexes just for Pg makes me look
like a loony.

See the discussion with Eloy (maintainer of the schema abstraction
layer) at http://moodle.org/mod/forum/discuss.php?d=78738#p350512
login as "guest" to avoid registration.

cheers,

martin