由于状态无效，无法为 Kafka 流打开存储

Question

I am trying to work with Kafka Streams and I have created the following Topology:

    KStream<String, HistoryEvent> eventStream = builder.stream(applicationTopicName, Consumed.with(Serdes.String(),
            historyEventSerde));

    eventStream.selectKey((key, value) -> new HistoryEventKey(key, value.getIdentifier()))
            .groupByKey()
            .reduce((e1, e2) -> e2, Materialized.as(streamByKeyStoreName));

I later start the streams like this:

private void startKafkaStreams(KafkaStreams streams) {
    CompletableFuture<KafkaStreams.State> stateFuture = new CompletableFuture<>();
    streams.setStateListener((newState, oldState) -> {
        if(stateFuture.isDone()) {
            return;
        }

        if(newState == KafkaStreams.State.RUNNING || newState == KafkaStreams.State.ERROR) {
            stateFuture.complete(newState);
        }
    });

    streams.start();
    try {
        KafkaStreams.State finalState = stateFuture.get();
        if(finalState != KafkaStreams.State.RUNNING) {
            // ...
        }
    } catch (InterruptedException ex) {
        // ...
    } catch(ExecutionException ex) {
        // ...
    }
}

My Streams start without an error and they eventually get into the state of RUNNING where the future is completed. Later I am trying to access that store that I created in my topology for the KTable:

public KafkaFlowHistory createFlowHistory(String flowId) {
    ReadOnlyKeyValueStore<HistoryEventKey, HistoryEvent> store = streams.store(streamByKeyStoreName,
            QueryableStoreTypes.keyValueStore());
    return new KafkaFlowHistory(flowId, store, event -> topicProducer.send(new ProducerRecord<>(applicationTopicName, flowId, event)));
}

I have verified that the createFlowHistory is called after the initializing future is completed in RUNNING state, however I am consistently unable to do this and KafkaStreams is reporting the following error:

Exception in thread "main" org.apache.kafka.streams.errors.InvalidStateStoreException: Cannot get state store flow-event-stream-file-service-test-instance-by-key because the stream thread is PARTITIONS_ASSIGNED, not RUNNING

Apparently the state of the thread has changed. Do I need to take care of this manually when trying to query a store and wait for the internal thread of Kafka to get into the right state?

Answer 1

Older Versions ( before 2.2.0)

On startup, Kafka Streams does the following state transitions:

CREATED -> RUNNING -> REBALANCING -> RUNNING

You need to wait for the second RUNNING state before you can query.

New Version: as of 2.2.0

The state transition behavior on startup was changed (via https://issues.apache.org/jira/browse/KAFKA-7657 ) to:

CREATED -> REBALANCING -> RUNNING

Hence, you should not hit this issue any longer.