Derby databases have a few limitations.
Indexes are not supported for columns defined on CLOB, BLOB, LONG VARCHAR, and XML data types.
If the length of the key columns in an index is larger than half the page size of the index, creating an index on those key columns for the table fails. For existing indexes, an insert of new rows for which the key columns are larger than half of the index page size causes the insert to fail.
Avoid creating indexes on long columns. Create indexes on small columns that provide a quick look-up to larger, unwieldy data in the row. You might not see performance improvements if you index long columns. For information about indexes, see Tuning Derby.
The system shuts down if the database log cannot allocate more disk space.
A "LogFull" error or some sort of IOException occurs in the derby.log file when the system runs out of space. If the system has no more disk space to append to the derby.log file, you might not see the error messages.