code: protected int writeTo(SparseBufferOperator<B> op, Splitter<SparseBufferOperator<B>> splitter, int start, int length) throws IOException
      {
          return splitter.split(op, start, length);
      }
docs: Write buffers content from start
  @param op
  @param splitter
  @param start
  @param length
  @return
  @throws IOException