Partition keys are the first part(s) of the primary key. Their main job is to determine which node(s) a piece of data must be written to and read from. When we talk about ensuring that a query can be served by a single node, we mean ensuring that query operates on a single partition key. When a query is processed by Cassandra, the partition key is hashed to produce a token number. This token number is then checked against the token ranges that each node is responsible for.
Partition keys
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