START_TRANSACTION initiates a transaction. All the statements
    that modify records within a transaction become permanent when
    the transaction is completed, or none of them do. If you end
    the transaction with the COMMIT statement, all the statements
    within the transaction execute. If you end the transaction with a
    ROLLBACK statement, none of the statements take effect.

    To use the two-phase commit protocol for new application
    programs that invoke only Oracle Rdb databases use the
    DISTRIBUTED_TRANSACTION keyword in the START_TRANSACTION
    statement. When you do this, Oracle Rdb invokes the DECdtm system
    service calls for your application.