Kafka Streams in Action

Chapter 5. The KTable API

This chapter covers

• Defining the relationship between streams and tables
• Updating records, and the KTable abstraction
• Aggregations, and windowing and joining KStreams and KTables
• Global KTables
• Queryable state stores

So far, we’ve covered the KStream API and adding state to a Kafka Streams application. In this chapter, we’re going to look deeper into adding state. Along the way, you’ll be introduced to a new abstraction, the KTable.

In discussing the KStream API, we’ve talked about individual events or an event stream. In the original ZMart example, when Jane Doe made a purchase, you considered the purchase to be an individual event. You didn’t keep track of how many purchases Jane made, or how often. In the context ...