title: mongodb sort order on _id
body: <p>I wonder how mongodb compare the "_id" field when doing query like the following:</p>
  
  <pre><code>db.data.find({"_id":{$gt:ObjectId("502aa46c0674d23e3cee6152")}}).sort({"_id":1}).limit(10);
  </code></pre>
  
  <p>Is it purely based on timestamp portion of the id?</p>