title: What is the parameter "max_q_size" used for in "model.fit_generator"?
body: <p>I built a simple generator that yields a <code>tuple(inputs, targets)</code> with only single items in the <code>inputs</code> and <code>targets</code> lists. Basically, it is crawling the data set, one sample item at a time.</p>
  
  <p>I pass this generator into: </p>
  
  <pre><code>  model.fit_generator(my_generator(),
                        nb_epoch=10,
                        samples_per_epoch=1,
                        max_q_size=1  # defaults to 10
                        )
  </code></pre>
  
  <p>I get that:</p>
  
  <ul>
  <li><code>nb_epoch</code> is the number of times the training batch will be run</li>
  <li><code>samples_per_epoch</code> is the number of samples trained with per epoch</li>
  </ul>
  
  <p>But what is <code>max_q_size</code> for and why would it default to 10?  I thought the purpose of using a generator was to batch data sets into reasonable chunks, so why the additional queue? </p>