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Asked: 2026-05-29T16:22:45+00:00

Recently, I am going to make a instant-notification system for my website. I heard

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Recently, I am going to make a instant-notification system for my website. I heard COMET is an essential in such cases.

I have been searching about PHP & Comet for a while already, however, the guides & articles I have found seems like just ajax requests in a loop. For example, there is a basic javascript code which gets the value from PHP file every 2 seconds and outputs to HTML. As far as I know, it should be COMET pushing new values to HTML, hence, the loop should be on server side, not client. Half of the articles in my native language was using setInterval() and contact PHP file every X seconds.

So, I have some questions to ask you.

  1. Is there any guides or examples, which doesn’t use any external framework like XAJAX/NOLOH that is easy to understand?
  2. What is the performance difference between using COMET in server side, or requesting value from ajax.php every X seconds?
  3. The timed requests I mentioned above can be called as COMET? (ex. Long Polling using jQuery and PHP)
  4. Do I need any extensions to run COMET serverside? (My webhost is using Apache, I personally use Nginx)
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  1. Editorial Team

    You have to use a client-side script (AJAX), because the server has to be polled. The server cannot simply send messages to someone’s browser without an open connection.
    I’m not too familiar with HTML5 websockets, but I believe this allows you can have a persistent connection with the server, however HTML5 browsers aren’t used widely to use this as a solution on a ‘public’ website.

    How long polling works is that an asynchronous request is sent from the browser with a long time-out time (e.g. 30 seconds), when the request arrives at the server, it goes and checks for new messages, but when there are now messages to be displayed, instead of directly outputting the result, it goes into an infinite loop, polling the database e.g. every second (using sleep to postpone the queries), until a message has been found. When a message has been found it terminates the loop and outputs the result. If there have been no messages after 30 seconds, the script times out and sends back an empty request.

    So the request can be sent back between 0 and 30 seconds. As soon as the request arrives in the browser, it is handled and a new 30 second request is sent.

    As for your questions;

    1. You will need a client-side framework for doing the polling
    2. You cannot use Comet only on server-side. Using longpolling over normal polling (e.g. polling every second) is significant because you make much less server requests
    3. To my understanding; yes
    4. You can use any server-side language, as long as it can keep the connection open while querying for messages.

    Also take a look at http://nodejs.org/

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