Hi all, I'm working on a Kafka Streaming job and I've hit a case I didn't see straightforward support for. I have an input stream topic I'd like to perform two separate aggregations on, but building up two parallel sub-topologies with the same source topic at the source results in an error: "Topic <topic> has already been registered by another source."
I was wondering if the right solution here is to duplicate the stream being read off from the topic (in-memory) and then performing the aggregations on the copies of the stream. The only method on KStream I found that seems to let me generate multiple streams from a single one is the branch() method, which takes in a list of predicates. So, the workaround here seems to be to perform a flatMap that will repeat the rows N times (injecting some index for each copy) and then de-interleaving the copies with a branch. This seems like it would work, but it will require a lot of cruft: creating the intermediate data structures, the branch predicate code, etc. It seems like a natural operation to be able to fan out a stream into multiple copies for downstream aggreation/joining. Is there an easy way to do this in the current API or is it something that would be a useful addition?
