code: func (l *WAL) WriteMulti(values map[string][]Value) (int, error) {
  	entry := &WriteWALEntry{
  		Values: values,
  	}
  
  	id, err := l.writeToLog(entry)
  	if err != nil {
  		l.tracker.IncWritesErr()
  		return -1, err
  	}
  	l.tracker.IncWritesOK()
  
  	return id, nil
  }
docs: // WriteMulti writes the given values to the WAL. It returns the WAL segment ID to
  // which the points were written. If an error is returned the segment ID should
  // be ignored.