public function onPreSendHAHeaders(HttpClientPreSendRequestEvent $event)
    {
        if ($event->getRequest()->getQueryMode() == 'WRITE') {
            $event->getRequest()->setHeader($this->queryModeHeaderName, $this->queryModeWriteQueryHeaderValue);
        } elseif ($event->getRequest()->getQueryMode() == 'READ') {
            $event->getRequest()->setHeader($this->queryModeHeaderName, $this->queryModeReadQueryHeaderValue);
        }
    }