title: Purpose of statestore and changelog topic in kafka streams?
body: <p>I have a kafka stream application in which it is using stateStore (backed by RocksDB). </p>
  
  <p>All what stream thread is doing is getting data from kafka topic and putting the data into state-store. (There is other thread which read data from statestore and does business logic processing).</p>
  
  <p>I observed it creates a new kafka topic "changelog" because of stateStore. </p>
  
  <p>But I didn't get what purpose "changelog" kafka topic serves? </p>
  
  <ul>
  <li>Why is it (changelog) needed?</li>
  <li>What is relationship between statestore and "changelog" kafka topics?</li>
  <li>Who puts data into this topic? ("changelog")</li>
  </ul>