I don't know much about Samza, but I don't think stream processors are what we (I work with the author) are looking for. We don't really have a lot of "stream processing" to do, and aggregate functions are usually computed on-demand. Also, still have to put results from the stream process somewhere, right? Back into Kafka is something people do, but we still need indexing capabilities. As the post mentions, we use MySQL for time series storage, but we also use Kafka in front as a durable log.