code: public void markRecord(BufferedRecord<D> record, int bytesWritten) {
      synchronized (this) {
        thunks.add(new Thunk<>(record, bytesWritten));
        byteSize += bytesWritten;
      }
    }
docs: Mark the record associated with this request
  
  @param record buffered record
  @param bytesWritten bytes of the record written into the request