code: public void close( int cidx, Futures fs ) {
      int len = _len;
      if( this  instanceof NewChunk ) _chk2 = this;
      if( _chk2 == null ) return;          // No change?
      if( _chk2 instanceof NewChunk ) _chk2 = ((NewChunk)_chk2).new_close();
      assert _chk2._len == len:"incompatible length after compression, " +  len + " != " +  _chk2._len + ", " + ", chunk = " + _chk2.getClass().getSimpleName();
      DKV.put(_vec.chunkKey(cidx),_chk2,fs,true); // Write updated chunk back into K/V
      if( _vec._cache == this ) _vec._cache = null;
    }
docs: After writing we must call close() to register the bulk changes