def add_index(self, attribute, ordered=False):
return self._encode_invoke(map_add_index_codec, attribute=attribute, ordered=ordered)<EOL>
Adds an index to this map for the specified entries so that queries can run faster.

Example:
    Let's say your map values are Employee objects.
        >>> class Employee(IdentifiedDataSerializable):
        >>>     active = false
        >>>     age = None
        >>>     name = None
        >>>     #other fields
        >>>
        >>>     #methods

    If you query your values mostly based on age and active fields, you should consider indexing these.
        >>> map = self.client.get_map("employees")
        >>> map.add_index("age" , true) #ordered, since we have ranged queries for this field
        >>> map.add_index("active", false) #not ordered, because boolean field cannot have range


:param attribute: (str), index attribute of the value.
:param ordered: (bool), for ordering the index or not (optional).