title: NamedCache size() implementation is suspected to reduce performance
body: <p>We are using Kafka Streams as a stream processing engine in our application. One of our topologies aggregates the data from 30 millions devices. When the application runs on two machines, everything works fine. However, when running on one machine, the lag grows.
  Inspecting the threads showed the following:
  All threads are stuck on method size() of NamedCache, which in turn calls the method size() of ConcurrentSkipListSet. As we learn from the documentation of ConcurrentSkipListSet, size() is a very slow method since, it requires the traversal of the collection. The problem was solved by disabling the KafkaStreams cache by setting cache.max.bytes.buffering to 0 and giving more memory to RocksDB cache. </p>
  
  <p>Have you encountred such an issue too ? 
  How can i use heap memory with Kafka streams and rocks DB ? </p>