Optimizing instant notifications

Question

Scenario

To deliver instant notifications to the client, I'm sending an AJAX request to a PHP page that checks if there are new notifications: if there are, it outputs them, otherwise it sleeps for 10 seconds before trying again, so it has a basic structure similar to the following one.

<?php
$max_attempts = 10000;
for($i=0;$i<=$max_attempts;$i++){
    check_new_notifications(); //checking notifications in an sql database
    if(new_notification){
      echo $notification;
      break;
    }
    else{
      sleep(10);
    }
}
?>

What is missing

While this is great for the client, as it doesn't have to send a request every 10 seconds, but just one, I can't find a better way for the server than to check every 10 seconds if there are new notifications.

My question

What solution could I adopt in order to avoid the server to constantly check for new notifications?

Answer 1

You can:

Use polling

However, think about sending a request every 10 seconds.
By using your suggested approach, you are keeping a long connection to the server, which is in turn keeping a busy process/thread. If this is used only by you, it's fine. If it's meant to be used by many users, it's a huge waste of resources, since the server will be busy doing nothing 99% of the time.

Use Websockets

This is the thing you need.
Websockets provide a direct and continous TCP communication between the browser and your server. Check out Ratchet, that's a great PHP library for websockets on the server side.

Use an external service

There are services like Pusher which also utilize websockets. However, you don't need a socket server yourself, but send them an event from your backend. Then their service pushes new data to your browser.