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  def createMessageStreams[T](topic: String, numStreams: Int,
                              decoder: Decoder[T] = new DefaultDecoder)
    : Seq[KafkaStream[T]]

The above also reveals an advantage of creating multiple streams for multiple topics at one-shot (by providing the topic-count-map). If you want to create multiple streams for multiple topics, then you would need to make a createMessageStreams call for each topic, which would trigger one rebalance for each topic. With the one-shot call, only one rebalance (for all topics) will be required.

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Advantages

• • Simpler, more intuitive API which is consistent with the createMessageStreamsByFilter API as well.
  • It may be possible to combine the createMessageStreams and createMessageStreamsByFilter calls into one API. This would need to be fleshed out in some detail, but we could have a higher-level Topic class that can either be a static topic, or a TopicFilter. Another advantage of this is that the high-level Topic class it could do things like validate topic names. However, the consumer code would need to explicitly call (new Topic(new Whitelist("white.*")) or (new Topic("topicname")) but that does not seem so bad.

Disadvantages

• • The above also reveals an advantage of creating multiple streams for multiple topics at one-shot . If you want to create multiple streams for multiple topics, then you would need to make a createMessageStreams call for each topic, which would trigger one rebalance for each topic. With the one-shot call (which receives atopic-count-map), only one rebalance (for all topics) will be required.
  • Not a disadvantage, but additional work: the consumer connector code is currently broken with respect to supporting multiple calls to createMessageStreams on the same connector object. For example, the consumerIdString is per connector object, and not per call. There are a bunch of other global variables that may need to become per-call instances. Anyway, the point is that we would need to completely fix that if we want to deprecate the option to provide a topic-count-map.

Impact to clients

Client code will need to change, since the current pattern of:

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