title: What is the role of "chunksize" in pool.map?
body: <p>I am having trouble understanding the "chunksize" parameter in pool.map.  </p>
  
  <p>For the following codes, I get the same results whether I use '2' or nothing for the chunksize parameter.</p>
  
  <pre class="lang-py prettyprint-override"><code>import multiprocessing
  from multiprocessing import Pool
  lst_of_lst = [[1,2],[3,4],[5,6],[7,8]]
  def count(lst):
      return len(lst)
  if __name__ == '__main__':
      P = Pool(2)
      for results in P.map(count,lst_of_lst,2):
          print (results)
      P.close()
      P.join()
  </code></pre>
  
  <p>Result are always: <code>"2 2 2 2"</code></p>
  
  <p>With a chunksize of '2', I was expecting <code>[[1,2],[3,4]]</code> to be sent to one worker and <code>[[5,6],[7,8]]</code> to the second worker giving me "2 2" as an answer.</p>
  
  <p>What am I missing? What does the chunksize do?</p>