private byte[] dataKey(long offset){
  return subspace.pack(Tuple2.from(DATA_KEY,String.format("%16d",offset)));
}

private byte [ ] dataKey ( long offset ) { return subspace . pack ( Tuple2 . from ( DATA_KEY , String . format ( "%16d" , offset ) ) ) ; }
the key to data " offset " chunks from the beginning of the blob .
