code: @Override
    public void writeRaw(byte[] bytes, int offset, int length) throws IOException {
      doubleBuf.writeRaw(bytes, offset, length);
    }
docs: Write a transaction to the stream. The serialization format is:
  <ul>
  <li>the opcode (byte)</li>
  <li>the transaction id (long)</li>
  <li>the actual Writables for the transaction</li>
  </ul>