title: Kafka KStreams - how to add threads / using StreamsConfig.NUM_STREAM_THREADS_CONFIG
body: <p>I was messing about with this param and ran into some oddness. My app runs ok without it but when I added this line to the config:</p>
  <pre><code> config.put(StreamsConfig.NUM_STREAM_THREADS_CONFIG, &quot;3&quot;);
  </code></pre>
  <p>CPU usage wouldn't climb above zero. App didn't appear to be doing <em>anything</em>. No errors.</p>
  <p>Is there some advised method to increasing thread usage for a KStreams app? Or just 'trust the force' and let it all run together?</p>
  <hr />
  <h2>Edit:</h2>
  <ol>
  <li>I have two partitions</li>
  <li>Have checked the consumer lag via <code>kafka-consumer-groups</code> - lots of records available</li>
  <li>Even if there were only 1 partition - why would having multiple threads <em>do nothing</em>? 0% CPU.</li>
  </ol>