code: func (i *Index) TagValueSeriesIDIterator(name, key, value []byte) (tsdb.SeriesIDIterator, error) {
  	release := i.sfile.Retain()
  	defer release()
  
  	itr, err := i.tagValueSeriesIDIterator(name, key, value)
  	if err != nil {
  		return nil, err
  	}
  	return tsdb.FilterUndeletedSeriesIDIterator(i.sfile, itr), nil
  }
docs: // TagValueSeriesIDIterator returns a series iterator for a single tag value.