docs: public synchronized ByteBuffer getRecordBuffer(int index) throws IOException {
      if (index < 0 || index >= numrecs) {
        throw new IOException("Access beyond end of file.");
      }
      // Adjust buffer view
      synchronized (map) {
        map.limit(recordsize * (index + 1));
        map.position(recordsize * index);
        return map.slice();
      }
    }