code: func (ins *instance) getCollection() (*mgo.Collection, error) {
  	session, err := ins.getConnection()
  	if err != nil {
  		return nil, err
  	}
  	session.SetSafe(&mgo.Safe{})
  	session.SetMode(mgo.Strong, true)
  	c := session.DB(ins.database).C(CollectionName)
  	return c, nil
  }
docs: // TODO(mpl): I'm only calling getCollection at the beginning, and
  // keeping the collection around and reusing it everywhere, instead
  // of calling getCollection everytime, because that's the easiest.
  // But I can easily change that. Gustavo says it does not make
  // much difference either way.
  // Brad, what do you think?