title: MongoDB fulltext search not using index
body: <p>We use mongoDB fulltext search to find products in our database.
  Unfortunately it is incredible slow.
  The collection contains 89.114.052 documents and I have the suspicion, that the full text index is not used.
  Performing a search with explain(), nscannedObjects returns 133212.
  Shouldn't this be 0 if an index is used?</p>
  
  <p>My index:</p>
  
  <pre><code>{
      "v" : 1,
      "key" : {
          "_fts" : "text",
          "_ftsx" : 1
      },
      "name" : "textIndex",
      "ns" : "search.products",
      "weights" : {
          "brand" : 1,
          "desc" : 1,
          "ean" : 1,
          "name" : 3,
          "shop_product_number" : 1
      },
      "default_language" : "german",
      "background" : false,
      "language_override" : "language",
      "textIndexVersion" : 2
  }
  </code></pre>
  
  <p>The complete test search:</p>
  
  <pre><code>&gt; db.products.find({ $text: { $search: "playstation" } }).limit(100).explain()
  {
      "cursor" : "TextCursor",
      "n" : 100,
      "nscannedObjects" : 133212,
      "nscanned" : 133212,
      "nscannedObjectsAllPlans" : 133212,
      "nscannedAllPlans" : 133212,
      "scanAndOrder" : false,
      "nYields" : 1041,
      "nChunkSkips" : 0,
      "millis" : 105,
      "server" : "search2:27017",
      "filterSet" : false
  }
  </code></pre>