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It means that a Streams internal changelog topic does not have the expected number of topic partitions. This can happen, if you add partitions to an input topic. For more details, see FAQ "How to scale a Streams app, i.e., increase the number of input topic partitions".

I get a locking exception similar to "Caused by: java.io.IOException: Failed to lock the state directory: /tmp/kafka-streams/<app-id>/0_0". How can I resolve this?

Kafka 0.10.0 and 0.10.1 does have some bugs with regard to multi-threading. If you cannot (or don't want to) update, you can apply the following workaround:

• switch to single threaded execution
• if you want to scale your app, start multiple instances (instead of going multi-threaded with one instance)
• if you start multiple instances on the same host, use a different state directory (state.dir config parameter) for each instance (to "isolate" the instances from each other)

It might also be necessary, to delete the state directory manually before starting the application. This will not result in data loss – the state will be recreated from the underlying changelog topic.0

Producers

How should I set metadata.broker.list?

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