code: func EnsureIndex(collectionName string, index mgo.Index) {
  	session := GetSession()
  	defer session.Close()
  
  	c := GetCollection(session, collectionName)
  
  	// Make sure idices are created.
  	if err := c.EnsureIndex(index); err == nil {
  		log.Debugf("Ensured \"%s\" collection indices", collectionName)
  	} else {
  		// Important: Mongo3 doesn't support DropDups!
  		log.Fatalf("Failed to create index on collection \"%s\": %s. Aborting", collectionName, err.Error())
  	}
  }
docs: //EnsureIndex make sure indices are created on certain collection.