Get the names of the fields that will change
    when this operation gets applied to a record.

def op_get_mutate_fields( op_name ):
    """
    Get the names of the fields that will change
    when this operation gets applied to a record.
    """
    global MUTATE_FIELDS

    if op_name not in MUTATE_FIELDS.keys():
        raise Exception("No such operation '%s'" % op_name)

    fields = MUTATE_FIELDS[op_name][:]
    return fields