Composite partition keys

There might be cases where a partition size might grow well beyond the disk size of a Cassandra instance, or a partition might have more than 100,000 cells, which will reduce the performance of some of the internal operations of Cassandra as well as read queries on that partition. To ensure you don't face this situation, Cassandra provides a concept of composite partition keys. Composite partition keys contain more than one column as part of the partition key. So, data is distributed based on a combination of values of both the columns. A composite partition key can split up a very large internal partition into multiple internal partitions.