How To Send GCM Message More Then 1000 users in one time - google-cloud-messaging

Question

I am new to php and GCM. i am using following code to send gcm message using php and mysqldb as i am getting notification successfully however the android guidelines state that gcm message should be send in batch of 1000 each so i am looking for a solution so i can send notification in chunks so all user will receive the notification. i have seen some answers on some similar question but no one seems to be as much detailed for a beginner.
My question is that how i will be able to send GCM message more then 1000 user in one time as i have more then 20,000 users in my scenario. how i will be able to make 1000
Below Is The Code
<?php
include_once 'db_functions.php';
$db = new DB_Functions();
$appId= $_POST["appIdSelect"];
if($appId==0)
{
echo "App not selected, Please choose app first!!";
return;
}
$users = $db->getAllDevicesByAppId($appId);
$message = $_POST["message"];
$message = array("alert" => $message);
$i=0;
while ($row = mysql_fetch_array($users)) {
$regId = $row["device_id"];
//$regId."<br/>";
include_once './GCM.php';
$gcm = new GCM();
$registatoin_ids = array($regId);
$result = $gcm->send_notification($registatoin_ids, $message);
$result;
$i++;
}
echo "Notification send to APP ID= ".$appId." successfully. Total notification sends = ".$i;
?>

Answer 1

The 1000 limit is for when using the registration_ids parameter.
For your scenario, it is suggested to make use of Topic Messaging. Depending on which platform your users are, you simply have to have them subscribe to your topic, and as soon as you send a message to that topic, all subscribers will receive that message.
With all that said, is there a reason why you're not using the newer version of GCM which Firebase Cloud Messaging (FCM)?