Kafka Streams: Internal topic partitions

Question

Kafka version: 1.0.0
Let's say the stream application uses low level processor API which maintains the state and reads from a topic with 10 partitions. Please clarify if the internal topic is expected to be created with the same number of partitions OR is it per the broker default. If it's the later, if we need to increase the partitions of the internal topic, is there any option?

Answer 1

Kafka Streams will create the topic for you. And yes, it will create it with the same number of partitions as your input topic. During startup, Kafka Streams also checks if the topic has the expected number of partitions and fails if not.

The internal topic is basically a regular topic as any other and you can change the number of partitions via command line tools like for any other topic. However, this should never be required. Also note, that dropping/adding partitions, will mess up your state.