'Retrieve the most frequently seen items in a frequency table.
Results are returned as a mapping, where the key is the key requested
and the value is a list of ``(member, score)`` tuples, ordered by the
highest (most frequent) to lowest (least frequent) score. The maximum
number of items returned is ``index capacity * rollup intervals`` if no
``limit`` is provided.'

def get_most_frequent(self, model, keys, start, end=None, rollup=None, limit=None):

    raise NotImplementedError
