code: func (db *DB) fetchUint64(key []byte) uint64 {
  	blob, err := db.lvl.Get(key, nil)
  	if err != nil {
  		return 0
  	}
  	val, _ := binary.Uvarint(blob)
  	return val
  }
docs: // fetchUint64 retrieves an integer associated with a particular key.