Enables only the modes specified, disabling all other previously
    defined modes. This is an offline operation and requires
    exclusive database access. For example, if a database is used for
    read-only access and you want to disable all other transaction
    modes, specify the following statement:

    SQL> ALTER DATABASE FILENAME mf_personnel
    cont>   SET TRANSACTION MODES (READ ONLY);

    Specifying a negated txn-mode or specifying NONE disables all
    transaction usage. Disabling all transaction usage would be
    useful when, for example, you want to perform major restructuring
    of the physical database. Execute the ALTER DATABASE statement to
    re-enable transaction modes.