def __init__(self, cluster, table=None, sharding_key=None):
self.cluster = cluster<EOL>self.table = table<EOL>self.sharding_key = sharding_key<EOL>
:param cluster: what cluster to access data from
:param table: underlying table that actually stores data.
If you are not specifying any table here, ensure that it can be inferred
from your model's superclass (see models.DistributedModel.fix_engine_table)
:param sharding_key: how to distribute data among shards when inserting
straightly into Distributed table, optional