title: How does kafka decides the partition if I don't mention any
body: <p>This is how I produce message :</p>
  
  <pre><code>String json = gson.toJson(msg);
  
  ProducerRecord&lt;String, String&gt; record = new ProducerRecord&lt;&gt;(kafkaProducerConfig.getTopic(), json);
  long startTime = System.currentTimeMillis();
  
  try {
      RecordMetadata meta = producer.send(record).get(5, TimeUnit.SECONDS);
  } catch (InterruptedException e) {
      e.printStackTrace();
  } catch (ExecutionException e) {
      e.printStackTrace();
  } catch (TimeoutException e) {
      e.printStackTrace();
  }
  </code></pre>
  
  <p>I have <code>15</code> partitions for this topic, I did not mention the partition key while producing, what will be the default partition assigned ?</p>