Methods for fetching rows/records from Cassandra will return either a single instance of ColumnOrSuperColumn or a list
of ColumnOrSuperColumns (get_slice()).
get the token ring: a map of ranges to host addresses,
represented as a set of TokenRange instead of a map from range
to list of endpoints, because you can't use Thrift structs as
map keys:
https://issues.apache.org/jira/browse/THRIFT-162
for the same reason, we can't return a set here, even though
order is neither important nor predictable.
Get the group of columns contained by column_parent (either a ColumnFamily name or a ColumnFamily/SuperColumn name
pair) specified by the given SlicePredicate.
A SlicePredicate is similar to a mathematic predicate (see http://en.wikipedia.org/wiki/Predicate_(mathematical_logic)),
which is described as "a property that the elements of a set have in common."
SlicePredicate's in Cassandra are described with either a list of column_names or a SliceRange.