At any time, you can transform the Derby database that has the slave role into a normal Derby database that can process transactions. This transformation from being a slave to becoming an active Derby database is called failover.
During failover, the slave applies the parts of the transaction log that have not yet been processed. It then undoes operations that belong to uncommitted transactions, resulting in a transaction-consistent state that includes all transactions whose commit log record has been sent to the slave.
You perform failover from the master system. To do so, you connect to the database on the master system using the failover=true connection URL attribute. For example, for a database named wombat, you might specify the following connection URL:
jdbc:derby:wombat;failover=true
If the network connection between the master system and the slave system is lost, you can perform failover from the slave system.
See the Derby Reference Manual for details about the failover=true attribute.
There is no automatic failover or restart of replication after one of the instances has failed.