lan(s) executed asynchronously.
       In such a case, if the asynchronous subplans are ones processed using
       <code class="filename">postgres_fdw</code>, tuples from the asynchronous
       subplans are not returned until after at least one synchronous subplan
       returns all tuples, as that subplan is executed while the asynchronous
       subplans are waiting for the results of asynchronous queries sent to
       foreign servers.
       This behavior might change in a future release.
      </p></