title: Command to reindex all mongodb collections
body: <p>References to reindexing MongoDB collections are usually per collection:</p>
  
  <pre><code>db.mycollection.reIndex();
  </code></pre>
  
  <p>I'd like to reindex a number of collections all at once. One-by-one can get a bit tiring.</p>
  
  <p>What's the appropriate command to issue <code>reIndex();</code> across all collections? </p>