code: func setManagerSessionTTL() error {
  	ttlStr := os.Getenv("tidb_manager_ttl")
  	if len(ttlStr) == 0 {
  		return nil
  	}
  	ttl, err := strconv.Atoi(ttlStr)
  	if err != nil {
  		return errors.Trace(err)
  	}
  	ManagerSessionTTL = ttl
  	return nil
  }
docs: // setManagerSessionTTL sets the ManagerSessionTTL value, it's used for testing.