title: mergeFactor usage in solr 4.0
body: <p>I thought mergeFactor could be think as max number of in segment, but when it set to 10, I got 16 segments after index, and merge happened when number of in segment exceed 15 and 20. I am really confused about the mean of mergeFactor.</p>
  
  <p>Here is my config </p>
  
  <pre><code>&lt;ramBufferSizeMB&gt;32&lt;/ramBufferSizeMB&gt;
  &lt;maxBufferedDocs&gt;100000&lt;/maxBufferedDocs&gt;
  &lt;mergeFactor&gt;10&lt;/mergeFactor&gt;
  </code></pre>