title: Flink, basic rule for checkpointing?
body: <p>I have 2 questions regarding Flink checkpointing strategy, </p>
  
  <ol>
  <li>I know that checkpoint is related to state (right?), so if I'm not using state (ValueState sort of things) explicitly in my job code, do I need to care about checkpoint? Is it still necessary?</li>
  <li>If I need to enable the checkpointing, what should the interval be? Are there any basic rules for setting the interval? Suppose we're talking about a quite busy system (Kafka+Flink), like several billions messages per day.</li>
  </ol>
  
  <p>Many thanks.</p>