title: Delete topic level config
body: <p>In order to delete all of the data in a topic I set the retention.ms config of it to 1000.</p>
  
  <pre><code>./bin/kafka-topics.sh --zookeeper $KAFKAZKHOSTS --alter --topic &lt;topic&gt; --config retention.ms=1000
  </code></pre>
  
  <p>This worked fine. All the data was deleted after a very short wait.</p>
  
  <p>Before altering the config, the retention.ms was not set on the topic and so the server default property log.retention.hours=168 was the previous retention policy. (log.retention.minutes and log.retention.ms had not been set in the server properties).</p>
  
  <p>Now I would like to remove the retention.ms config from this topic completely and go back to using the server level config.</p>
  
  <p>Commands like</p>
  
  <pre><code>./bin/kafka-topics.sh --zookeeper $KAFKAZKHOSTS --alter --topic &lt;topic&gt; --config retention.ms=
  </code></pre>
  
  <p>or</p>
  
  <pre><code>./bin/kafka-topics.sh --zookeeper $KAFKAZKHOSTS --alter --topic &lt;topic&gt; --config retention.ms=null
  </code></pre>
  
  <p>throw an error. </p>
  
  <p>I know that the delete option for kafka-topics.sh actually deletes the entire topic, so I'm not going to try play around with that.</p>
  
  <p>Question: How do I completely remove a topic level config so that the topic reverts to using the server default?</p>