Notification when the user first login, not so hard, just require a database scan, I can deal with that. However, when a friend send a request or comment on profile X, a notification is sent, and almost immediately receive on the other end even when the user X not making any request. Is it polling? Does not feel like it, since the page never refresh itself. It must be something else? Anyone have any idea? maybe Web Push?
+1
A:
I believe they use AJAX/Javascript for that. It would allow the page to get information from the server and display it without reloading the page. You should be able to do this with an AJAX library like JQuery or something similar. As for whether or not Facebook itself does push or poll, I have no idea, but you can get a similar behavior by polling with AJAX.
jonescb
2010-09-24 15:43:47
Firebug certainly shows a continuous stream of get requests being made to the server.
David Thomas
2010-09-24 15:44:49
I know polling reload your page, I dont want that behavior. Let me try component polling and see if I can avoid this effect.
Harry Pham
2010-09-24 15:51:56
+2
A:
Facebook uses long-polling.
While you're on their page, they have a script continually issue requests to a particular URL. Instead of immediately responding, the server handling that URL first waits for a message to come in to its queue, and then sends that message out to the user. If a certain timeout is reached, the server responds without sending a message, and the client-side script makes another request to that URL.
To see this in action, open up Firebug's Net tab while on a Facebook page and wait for a couple minutes. You should see requests that last for a minute and then are followed up with a new request.
Yuliy
2010-09-24 17:04:51