Kafka Streams Stateful Operations

Stateful operations, also referred to as aggregations, are used to combine multiple input values into a single output value. Kafka Streams support the following stateful operators:

• reduce: This combines multiple input values of type A into a single output A.

• aggregate: This combines multiple input values of type A into a single output B.

• count: This counts the number of events by key.

Because aggregations involve combining multiple values associated with the same key, we have to group them before applying the aggregation operator.

Grouping

Grouping may be applied both to KStream and KTable ...