long polling ajax is not keeping realtime updates - php

Question

i was doing long polling , but it can see in my network chrome my long polling in status pending that means is waiting for new data and changes the database , but when I try to insert one item to my database then , but when I try to insert one value show keep that long polling in real time i cant see real time updatings .. how can I fix it?
pusher controller codeigiter
public function pusher() {
header('Content-Type: application/json');
$user_id = $this->session->log['id'];
set_time_limit(0);
while (true) {
$firstCall = false;
if (isset($_GET['timestamp'])) {
$last_ajax_call = $_GET['timestamp'];
} else {
$last_ajax_call = time();
$firstCall = true;
}
clearstatcache();
$notificationsCount = $this->notification->checkForNotifications($last_ajax_call, $user_id);
$newData = (int) $notificationsCount > 0 ? true : false;
$notifications = [];
if ($newData) {
$dataSet = $this->notification->getNotifications($user_id, $last_ajax_call);
foreach($dataSet as $data) {
$notifications[] = $data;
$finalNotificationTime = $data['timestamp'];
}
$result = array('notifications' => $notifications, 'timestamp' => $finalNotificationTime);
$json = json_encode($result);
echo $json;
break;
} else {
if ($firstCall) {
$dataSet = $this->notification->getUnreadNotifications($user_id);
foreach($dataSet as $data) {
$notifications[] = $data;
}
$result = array('notifications' => $notifications, 'timestamp' => $last_ajax_call);
$json = json_encode($result);
echo $json;
break;
}
sleep(1);
session_write_close();
continue;
}
}
exit();
}
ajax
function check_notifications(timestamp) {
var queryString = {
'timestamp': timestamp
};
$.ajax({
type: 'GET',
url: URL_GET_NOTIFICATION,
data: queryString,
success: function (data) {
// put result data into "obj"
for (var i in data.notifications) {
notify(data.notifications[i].message, data.notifications[i].type, data.notifications[i].timestamp);
}
check_notifications(data.timestamp);
}
});
}
check_notifications();