The READ_ONLY option is used to change a read/write RDB$SYSTEM
    storage area (and the Oracle Rdb system relations stored in the
    area) to read-only. You might choose the READ_ONLY option if
    your database is never or rarely updated. When the RDB$SYSTEM
    storage area is changed to read-only, locking conflicts occur
    less frequently, and the automatic updating of index and relation
    cardinality is inhibited.

    No write operation can be done in a read-only storage area except
    a cardinality update. See the RMU/ANALYZE/CARDINALITY help topic
    in the RMU help file for more information and restrictions on
    updating cardinalities.

    To change a storage area other than the RDB$SYSTEM storage area
    to read-only, or to change a database to read-only, use the READ_
    ONLY option of the change-storage-area-clause.