':param db_name: database name (default: ``\'requests-cache\'``)
:param connection: (optional) ``pymongo.Connection``'

def __init__(self, db_name='requests-cache', **options):

    super(MongoCache, self).__init__()
    self.responses = MongoPickleDict(db_name, 'responses', options.get('connection'))
    self.keys_map = MongoDict(db_name, 'urls', self.responses.connection)
