ction is used in the current local
      transaction but its foreign server or user mapping is changed or
      dropped (Note that server name of an invalid connection will be
      <code class="literal">NULL</code> if the server is dropped),
      and then such invalid connection will be closed at
      the end of that transaction. <code class="literal">true</code> is returned
      otherwise. If there are no open connections, no record is returned.
      Example usage of the function:
</p><pre class="scre