Apache Cassandra Primary Key and Partition Keys

The primary key is the most important part of the Apache Cassandra data model. A table’s primary key accomplishes two tasks in Apache Cassandra:

1. Guarantees the uniqueness of the record

2. Defines placement of the record in the cluster

A table’s primary key in Cassandra comprises one or more partition keys and zero or more clustering columns. The partition key(s) always appear first in the primary key, followed by any clustering columns.

CQL data type uuid is a good option for primary keys as it guarantees uniqueness.

In Apache Cassandra, a table’s primary key cannot be altered.

Once a table has been created, it is not possible to modify the primary key. This is because in Apache Cassandra a table’s primary key dictates how the data is distributed in the cluster and how it is stored on disk.