fantapsody commented on issue #3733: support Pattern subscribe in kafka compat 
client
URL: https://github.com/apache/pulsar/issues/3733#issuecomment-583332354
 
 
   There seems to be a few problems in the current implementations of kafka 
compact clients, I'm not sure if they have been reported:
   1. `KafkaConsumer` states its `subscribe` methods are not incremental, which 
means new subscriptions will replace the old ones. However, implementions in 
PulsarKafkaConsumer are not, and seem to create dangling consumers if 
re-subscribe to the same topics.
   
https://github.com/apache/kafka/blob/f698f3f8401845e0f73b104c0f96c54d2851b67a/clients/src/main/java/org/apache/kafka/clients/consumer/KafkaConsumer.java#L957
   
https://github.com/apache/pulsar/blob/54b39e64f361a2ed5242259e04505bcfc66c1c8a/pulsar-client-kafka-compat/pulsar-client-kafka/src/main/java/org/apache/kafka/clients/consumer/PulsarKafkaConsumer.java#L267
   2. `ConsumerRebalanceListener.onPartitionsAssigned` should be called when 
the partition becomes active.
   3. Methods in `PulsarKafkaConsumer` are not totally thread safe, although 
concurrent collections are used.

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