Am I using the state store appropriately?

[Jason Turim]

​We've started experimenting with Kafka to see if it can be used to
aggregate our application data. I think our use case is a match for Kafka
streams, but we aren't sure if we are using the tool correctly.  The proof
of concept we've built seems to be working as designed, I'm not sure that
we are using the APIs appropriately.

Our proof of concept is to use kafka streams to keep a running tally of
information about a program, and writes that data to an output topic, e.g.

    {
      "numberActive": 0,
      "numberInactive": 0,
      "lastLogin": "01-01-1970T00:00:00Z"
    }

Computing the tally is easy, it is essentially executing a compare and swap
(CAS) operation based on the input topic & output field.

The local state store is used to store of the most recent program for a
given key. We join an input stream against the state store and run the CAS
operation using a TransformSupplier, which explictly writes the data to the
state store using

    context.put(...)
    context.commit();

Is this an appropriate use of the local state store?  Is there another
another approach to keeping a stateful running tally in a topic?

thanks,
Jason