code: @Override
    protected Long boundaryForSegment(String segmentName) throws IOException {
      if (segmentRegistration.equals(SEGMENT_SORT_ASC)
          || segmentRegistration.equals(SEGMENT_SORT_DESC)) {
        Long thisLast = segmentValueTopListLast.get(segmentName);
        if (thisLast == null) {
          return null;
        } else if (segmentRegistration.equals(SEGMENT_SORT_ASC)) {
          return thisLast * segmentNumber;
        } else {
          return Math.floorDiv(thisLast, segmentNumber);
        }
      } else {
        throw new IOException("can't compute boundary for segmentRegistration "
            + segmentRegistration);
      }
    }
docs: /*
  (non-Javadoc)
  
  @see mtas.codec.util.DataCollector.MtasDataCollector#boundaryForSegment()