title: mongodb index strategy for range query with different fields
body: <p>Almost all my documents include 2 fields, <strong>start</strong> timestamp and <strong>final</strong> timestamp. And in each query, I need to retrieve elements which are in selected period of time. so <strong>start</strong> should be after selected value and <strong>final</strong> should be before selected timestamp.</p>
  <p>query looks like</p>
  <pre><code>db.collection.find({start:{$gt:DateTime(...)}, final:{$lt:DateTime(...)}})
  </code></pre>
  <p>So what is the best indexing strategy for that scenario?</p>
  <hr />
  <p>By the way, which is better for performance - to store date as datetimes or as unix timestamps, which is long value itself</p>