Kafka producers can group messages destined fordifferent partitionsintoseparate batches, and send multiple batches in one requestto optimize network usage.
FromKafka Producer Internals:
"The producer maintains buffers (batches) for each partition and can send multiple of these batches together in a single request to the broker."
* Message size is not a constraint for batching (A is false).
* Broker failures don't disable batching (B is false).
* There isno separate thread per batch(C is false).
Reference:Kafka Producer Architecture and Internals

Your Zookeeper cluster needs to have an odd number of servers, and must maintain a majority of servers up to be able to vote. Therefore, a 2N+1 zookeeper cluster can survive to N zookeeper being down, so here the right answer is N=2, 2*N+1=5

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Although any Kafka Streams application is stateless as the state is stored in Kafka, it can take a while and lots of resources to recover the state from Kafka. In order to speed up recovery, it is advised to store the Kafka Streams state on a persistent volume, so that only the missing part of the state needs to be recovered.