code: func (i *Index) MeasurementSeriesIDIterator(name []byte) (tsdb.SeriesIDIterator, error) {
  	itr, err := i.measurementSeriesIDIterator(name)
  	if err != nil {
  		return nil, err
  	}
  
  	release := i.sfile.Retain()
  	defer release()
  	return tsdb.FilterUndeletedSeriesIDIterator(i.sfile, itr), nil
  }
docs: // MeasurementSeriesIDIterator returns an iterator over all non-tombstoned series
  // for the provided measurement.