code: func (db *DB) Has(key []byte) (yes bool, err error) {
  	yes, err = db.ldb.Has(key, nil)
  	if err != nil {
  		metrics.GetOrRegisterCounter("DB.hasFail", nil).Inc(1)
  		return false, err
  	}
  	metrics.GetOrRegisterCounter("DB.has", nil).Inc(1)
  	return yes, nil
  }
docs: // Has wraps LevelDB Has method to increment metrics counter.