Once you create or connect to a database within a system, Derby begins outputting information and error messages to the error log.
Typically, Derby writes this information to a log called derby.log in the system directory, although you can also have Derby send messages to a stream, using the derby.stream.error.method property. By default, Derby overwrites derby.log when you start the system. You can configure Derby to append to the log with the derby.infolog.append property. For information on setting this and other properties, see Tuning Java DB.