Kristian Waagan (of Sun's Java DB development team) has really given Java DB (Sun's distribution of Apache / Derby) a new life of its own when it comes to handling CLOBs, starting with Java DB 10.5.

Check out this thread. 

Note the following testimony from David Goulden:

The performance improvements with CLOBs are dramatic. I created a record with a CLOB containing about 10 million characters using derby 10.4. The following query took over 6(!) minutes:

       SELECT CONTENT FROM MESSAGES WHERE ID = 1

(CONTENT is the CLOB column.)

I then installed derby 10.5 and did a soft upgrade. The same query now takes less than three seconds!