docs: public Deferred<Object> flush() throws HBaseException {
      final class HClientFlush implements Callback<Object, ArrayList<Object>> {
  	public Object call(final ArrayList<Object> args) {
          return client.flush();
        }
  	public String toString() {
          return "flush HBase client";
        }
      }
  
      return config.enable_compactions() && compactionq != null
        ? compactionq.flush().addCallback(new HClientFlush())
        : client.flush();
    }