The udf was working fine for several days, then suddenly it stopped
executing.
In my investigation, I attempted to execute the function (named 'esp')
and I started
getting the error message: (from database named XQ)

SELECT esp(0);
Error 1305 (42000): FUNCTION XQ.esp does not exist

So from there, I attempted to re-install it:

CREATE FUNCTION esp RETURNS INTEGER SONAME 'mysqlExtension.so';

I then get this back from mysql:

FUNCTION 'esp' already exists.

I also tried in vain:

DROP FUNCTION esp;

same message comes back:

Error 1305 (42000): FUNCTION XQ.esp does not exist

Not sure where this went wrong. It was working fine then something made
it go amok. In one case it says it exists, the other it does not.

Any clues?