Building a social network, I'm trying to fetch live notifications. Currently, the site sends an AJAX request every few seconds using setInterval. It looks something like this:

setInterval ( function(){
    url = base_dir+"/ajax/file.php";
    data = "data=someData";
    $.ajax({
        type: "POST",
        url: url,
        data: data,
        dataType: "json",
        beforeSend: function(x) {
            if(x && x.overrideMimeType) {
                x.overrideMimeType("application/json;charset=UTF-8");
            }
        },
        success: function(JSON){
            // retrieve data here   
        }
    });
}, 5000);

That works perfectly, but I'm very worried about that creating servers overload. I tried the et technique but for some reason it sends much more requests than the above code. Is there any other more useful technique for pushing this data live?

EDIT: For implementing long polling I used the following (used the example mentioned here: ):

(function poll(){
    url = base_dir+"/ajax/file.php";
    data = "data=someData";
    $.ajax({
        type: "POST",
        url: url,
        data: data,
        dataType: "json",
        beforeSend: function(x) {
            if(x && x.overrideMimeType) {
                x.overrideMimeType("application/json;charset=UTF-8");
            }
        },
        success: function(JSON){
            // retrieve data here   
        },
plete: poll,
timeout: 5000
    });
})();

There's a possibility that I might not get the et principle right.

PHP code:

// Checks for new notifications, and updates the title and notifications bar if there are any
 private static function NotificationsCounter (){
    //self::$it_user_id                                     = query that retrieves my id for further checks;                                                        
    //$friend_requests_count                                = query that retrieves the friend requests count;
    //$updates_count                                        = query that retrieves the updates count;               
    $total_notifications                                    = $friend_requests_count+$updates_count;

    if ($total_notifications > 0) $addToTitle = "(".$total_notifications.")";
    else $addToTitle = "";

    if ($updates_count > 0) $counterHTML = "<span class='notification_counter' id='updates_counter' style='float: right;'>".$updates_count."</span>";
    else $counterHTML = "";

    $data = array("counter"=>$total_notifications,"addToTitle"=>$addToTitle,"counterHTML"=>$counterHTML,);
    echo json_encode($data); // parse to json and print
}

Since Facebook uses PHP as well, how do they do it?

Building a social network, I'm trying to fetch live notifications. Currently, the site sends an AJAX request every few seconds using setInterval. It looks something like this:

setInterval ( function(){
    url = base_dir+"/ajax/file.php";
    data = "data=someData";
    $.ajax({
        type: "POST",
        url: url,
        data: data,
        dataType: "json",
        beforeSend: function(x) {
            if(x && x.overrideMimeType) {
                x.overrideMimeType("application/json;charset=UTF-8");
            }
        },
        success: function(JSON){
            // retrieve data here   
        }
    });
}, 5000);

That works perfectly, but I'm very worried about that creating servers overload. I tried the et technique but for some reason it sends much more requests than the above code. Is there any other more useful technique for pushing this data live?

EDIT: For implementing long polling I used the following (used the example mentioned here: http://techoctave./c7/posts/60-simple-long-polling-example-with-javascript-and-jquery):

(function poll(){
    url = base_dir+"/ajax/file.php";
    data = "data=someData";
    $.ajax({
        type: "POST",
        url: url,
        data: data,
        dataType: "json",
        beforeSend: function(x) {
            if(x && x.overrideMimeType) {
                x.overrideMimeType("application/json;charset=UTF-8");
            }
        },
        success: function(JSON){
            // retrieve data here   
        },
plete: poll,
timeout: 5000
    });
})();

There's a possibility that I might not get the et principle right.

PHP code:

// Checks for new notifications, and updates the title and notifications bar if there are any
 private static function NotificationsCounter (){
    //self::$it_user_id                                     = query that retrieves my id for further checks;                                                        
    //$friend_requests_count                                = query that retrieves the friend requests count;
    //$updates_count                                        = query that retrieves the updates count;               
    $total_notifications                                    = $friend_requests_count+$updates_count;

    if ($total_notifications > 0) $addToTitle = "(".$total_notifications.")";
    else $addToTitle = "";

    if ($updates_count > 0) $counterHTML = "<span class='notification_counter' id='updates_counter' style='float: right;'>".$updates_count."</span>";
    else $counterHTML = "";

    $data = array("counter"=>$total_notifications,"addToTitle"=>$addToTitle,"counterHTML"=>$counterHTML,);
    echo json_encode($data); // parse to json and print
}

Since Facebook uses PHP as well, how do they do it?

• javascript
• ajax
• et

• 9 You might want to look into using websockets. – user1726343 Commented Jan 1, 2013 at 17:42
• Can you please post the code you are using for the long polling technique? There isn't much else that can be done using HTTP. – user1726343 Commented Jan 1, 2013 at 17:46
• Have you configured the timeout settings server side? – user1726343 Commented Jan 1, 2013 at 18:03
• I'm not sure... How can I do that? – talhof9 Commented Jan 1, 2013 at 18:05
• You use set_time_limit to set the upper limit on script run time. See this answer for a simple demonstration of long polling in PHP. – user1726343 Commented Jan 1, 2013 at 18:12

2 Answers 2

You should use websockets. You can connect to the server and register onmessage handler. Whenever the server has anything to be send to client, your handler will get invoked. No timeout needed.

Check for websocket support in your browser. As of now, only Chrome, Opera and Safari support them.

if ('WebSocket' in window){
   /* WebSocket is supported. You can proceed with your code*/
} else {
   /*WebSockets are not supported. Try a fallback method like long-polling etc*/
}

Connecting

var connection = new WebSocket('ws://example:12345/myapp');

Handlers

connection.onopen = function(){
   console.log('Connection open!');
}

connection.onclose = function(){
   console.log('Connection closed');
}

connection.onmessage = function(e){
   var server_message = e.data;
   console.log(server_message);
}

Documentation: http://www.developerfusion./article/143158/an-introduction-to-websockets/

Websockets will be the way to go once they are more universally implemented across the major browsers - I would guess a minimum of 5 years.

The last I heard Facebook chat uses et and a whole bunch of servers. If you want something more lightweight I can think of two options.

1. Reduce the polling interval. This is strictly a UI issue - users may have a perfectly acceptable experience with intervals as long as a couple minutes. The only way to know for certain is through user testing, but polling every 5 seconds is probably overkill. No matter what you choose as the optimal interval, this does give you an quick way to scale if you are getting hammered - just crank up the interval until the servers stop melting.

2. Use HTTP validation caching. You can make the requests more lightweight if the server only returns a response body when the content has changed since the last request. You will have to build something custom using ETag or Last-Modified headers and a lightweight modification checking system on the server, but it might save you a few bytes.