title: KafkaConsumer: what happen if committed is before beginningOffsets?
body: <p>I am debugging some kafka consuming app that is stuck. The app is running fine (up, no memory problem), but no message is processed.</p>
  
  <p>It is not my code, so I'm discovering (most of) it. However I found in some logs that the committed offset (<code>KafkaConsumer.committed</code>) is before the first offset available in the kafka partition (<code>KafkaConsumer.beginningOffset</code>). For example, I have:</p>
  
  <ul>
  <li>committed = position = 8000</li>
  <li>beginningOffset = 740.000</li>
  <li>endOffsets = 760.000</li>
  </ul>
  
  <p>We may have some bug in the way we commit offset (using <code>KafkaConsumer.commitSync</code>, and with <code>enable.auto.commit</code> false). But this is not the question here.</p>
  
  <p>However looking into the kafka code, I cannot understand what should happened in such a case, when polling messages. Will it send nothing, messages starting at beginningOffset, fails, ... ?</p>
  
  <p>Basically, is it a potential reason for the app to get stuck?</p>