public List<SortReader> getReaders(SortBufferManager sortBufferManager) throws IoTDBException {
    List<String> filePaths = getFilePaths();
    List<SortReader> sortReaders = new ArrayList<>();
    try {
      for (String filePath : filePaths) {
        sortReaders.add(new FileSpillerReader(filePath, sortBufferManager, serde));
      }
    } catch (IOException e) {
      throw new IoTDBException(
          "Can't get file for FileSpillerReader, check if the file exists: " + filePaths,
          e,
          TSStatusCode.INTERNAL_SERVER_ERROR.getStatusCode());
    }
    return sortReaders;
  }
todo: directly serialize the sorted line instead of copy into a new tsBlock.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/utils/sort/DiskSpiller.java