title: Iterator and Memory Usage
body: <p>I was reading the MapReduce paper (<a href="http://static.googleusercontent.com/media/research.google.com/en/us/archive/mapreduce-osdi04.pdf" rel="nofollow">MapReduce</a>) and came across the below statement:</p>
  
  <blockquote>
    <p>The intermediate values are supplied to the user's reduce function via
    an iterator. This allows us to handle lists of values that are too
    large to fit in memory.</p>
  </blockquote>
  
  <p>Does this mean there's a relation between using <em>Iterators</em> and the memory usage of large lists?</p>