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JavaDoc description for Processor.close() in Kafka 1.0.1 says, that:
Note: Do not close any streams managed resources, like StateStores here, as they are managed by the library.
In addition, the JavaDoc description of StateStore.close() says, that:
Users only need to implement this function but should NEVER need to call this api explicitly as it will be called by the library automatically when necessary
But I've found an example in the documentation, in which a state store is being explicitly closed inside that method:
@Override
public void close() {
// close the key-value store
kvStore.close();
}
So, I'm kind of lost. Should I close the state store inside a Processor, or not?
651
State. Kafka Streams provides so-called state stores, which can be used by stream processing applications to store and query data, which is an important capability when implementing stateful operations.
To stop the application instance, call the KafkaStreams#close() method: // Stop the Kafka Streams threads streams. close();
Kafka Streams are backed by a persistent or in-memory state store, themselves being backed by Kafka changelog topics, providing full fault tolerance. The accompanying Kafka Streams Spring Boot application source code is available here.
No, you should not close the store.
The example code snippet is wrong. Thanks for pointing it out. I opened a PR to fix it: https://github.com/apache/kafka/pull/4667
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