code: func (db *nodeDB) fetchInt64(key []byte) int64 {
  	blob, err := db.lvl.Get(key, nil)
  	if err != nil {
  		return 0
  	}
  	val, read := binary.Varint(blob)
  	if read <= 0 {
  		return 0
  	}
  	return val
  }
docs: // fetchInt64 retrieves an integer instance associated with a particular
  // database key.