class SortValues extends PTransform<
        PCollection<KV<PrimaryKeyT, Iterable<KV<SecondaryKeyT, ValueT>>>>,
        PCollection<KV<PrimaryKeyT, Iterable<KV<SecondaryKeyT, ValueT>>>>> {

  public static <PrimaryKeyT, SecondaryKeyT, ValueT>
      SortValues<PrimaryKeyT, SecondaryKeyT, ValueT> create(
          BufferedExternalSorter.Options sorterOptions) {
    return new SortValues<>(sorterOptions);
  }

  private  SortValues(BufferedExternalSorter.Options sorterOptions);

}