The best way to describe Cassandra to a newcomer is that it is a KKV store. The two Ks comprise the primary key. The first K is the partition key and is used to determine which node the data lives on and where it is found on disk. The partition contains multiple rows within it and a row within a partition is identified by the second K, which is the clustering key. The clustering key acts as both a primary key within the partition and how the rows are sorted. You can think of a partition as an ordered dictionary. These properties combined allow for very powerful data modeling.