code: private void createAndSetTSUIDFilter(final Scanner scanner) {
      if (regex == null) {
        regex = QueryUtil.getRowKeyTSUIDRegex(tsuids);
      }
      scanner.setKeyRegexp(regex, CHARSET);
    }
docs: Sets the server-side regexp filter on the scanner.
  This will compile a list of the tagk/v pairs for the TSUIDs to prevent
  storage from returning irrelevant rows.
  @param scanner The scanner on which to add the filter.
  @since 2.0