 Implementation
  <a class="anchor" href="#implementation">#</a>
</h3>
<h4 id="state-and-clean-up">
  State and Clean-up
  <a class="anchor" href="#state-and-clean-up">#</a>
</h4>
<p>In order to be able to process time windows, we need to keep track of
data belonging to the window inside of our program. To ensure that this
data is fault-tolerant and can survive failures in a distributed system,
we should store it inside of Flink-managed state. As the time
progresses, we do not need to keep all previous tran