code: public void truncate64(long len) throws SQLException {
      FastpathArg[] args = new FastpathArg[2];
      args[0] = new FastpathArg(fd);
      args[1] = new FastpathArg(len);
      fp.getInteger("lo_truncate64", args);
    }
docs: Truncates the large object to the given length in bytes. If the number of bytes is larger than
  the current large object length, the large object will be filled with zero bytes. This method
  does not modify the current file offset.
  
  @param len given length in bytes
  @throws SQLException if something goes wrong