Kafka streams is great. But it is a processing library. It isn’t an apple-to-apple comparison to a messaging system like Pulsar. First there are already many ma

Kafka streams is great. But it is a processing library. It isn’t an apple-to-apple comparison to a messaging system like Pulsar. First there are already many mature stream processing engines and libraries (spark, flink, heron, storm). They have been in production for years and it made no sense to write a new one without a good reason. Second, kafka stream could have done a better job, not just tight with kafka. Technically kafka streams isn’t really a very specific implementation or design to kafka. If confluent has done a better job on abstraction, I would expect it is very easy to plugin different messaging systems or log storages to run "kafka streams". Although I am not sure Confluent want to see that happen. “Kafka has exactly-once delivery but messaging system x/y/z doesn’t provide it” is also confusing and misleading. Exactly-once is technically effectively-once: “at-least-once” and make the processing of the messages idempotent or “de-duplicated”. This has already been done in the industry for many decades in many mature stream processing engines like heron, flink. It isn’t a really new thing. And many messaging systems like pulsar already provides those primitives (e.g. idempotent producing, at-least-once delivery) for processing jobs to achieve effectively-once very easily. Streamlio folks did a great job about explaining exactly-once and effectively-once. It is worth checking this blog post out -- https://streaml.io/blog/exactly-once/ https://streaml.io/blog/exactly-once/ I think Pulsar itself as a distributed messaging system does provides all the three delivery semantics: at-most-once, at-least-once and effectively-once. It is very easy for people to use and integrate. I don’t think it is difficult to make kafka streams run with pulsar technically. The question is more is there a value to do that, do kafka folks wanna to do that, can the collaboration happen in the ASF? that's just my two cents.