8 The KTable API

This chapter covers

  • Changelog streams, the KTable, and the GlobalKTable
  • Aggregating records with a KTable
  • Enriching event streams with joins
  • Joining a KTable with another KTable

This chapter will introduce you to a new API in Kafka Streams, the Ktable. The KTable is an update or changelog stream. You’ve already used a KTable as any aggregation operations in Kafka Streams result in a KTable. The KTable is an essential abstraction for working with records with the same key. In a KStream, records with the same key are independent events. But in the KTable, a record updates the previous one with the same key.

Why is learning about an update stream necessary? Sometimes, you’ll only care about the latest entry for a given ...

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