public function rollback($session, Google_Service_Spanner_RollbackRequest $postBody, $optParams = array())
  {
    $params = array('session' => $session, 'postBody' => $postBody);
    $params = array_merge($params, $optParams);
    return $this->call('rollback', array($params), "Google_Service_Spanner_SpannerEmpty");
  }