Best way to show notifications and messages LIVE on a webpage?

Question

I am interested in a really good way of doing instant messaging like meebo and facebook and myspace all have, also for notifications on a page. Example on my site now, when a user receives a new mail message, photo comment, profile comment, friend request, some other things, they will receive a notification message and link on the page they are on using jQuery and AJAX. I beleive on a large scale that this is not the best way to do it though as my jquery code will have to basicly run a PHP script to query the mysql table every 30 seconds or so for every user who has the page open with this script running. I would like to eventually add in some sort of instant messaging like facebook has in a chat bar at the bottom of the screen if I can find out an efficient way of doing it. I have heard the terms Comet and HTML5 WebSockets but I am not sure if these are the solutions I should be looking at for such a feature? I would like to keep bandwidth at a minimum and running a queary every few seconds does not seem very efficient on a high traffic site.

If you know some good solutions, please explain how they work a little bit please

Answer 1

Could you have a shared message queue that ajax can query? Maybe its a php script that stores a majority of the message in memcached (and possibly write to db in case of failure).

Not sure, but curious to hear other solutions ...

Answer 2

I think Facebook uses XMPP for their chat, so have a look at it.

XMPP is

an open technology for real-time communication, which powers a wide range of applications including instant messaging, presence, multi-party chat, voice and video calls, collaboration, lightweight middleware, content syndication, and generalized routing of XML data.

You'd install a separate server to handle messaging and in your app you'd implement a client with one of the available libraries.

Answer 3

You're looking for a "comet" server. Since you're talking PHP, your best solution would be a SaaS solution, such as WebSync On-Demand, since PHP has issues with scaling when it comes to large numbers of concurrent connections being held open. See also this question.

Answer 4

The basic problem is that you need to implement a Comet server (ie implement Server Push). The standard web hosts and apache don't readily allow you to do this easily. Another hosted solution (apart from Web Sync) is Goldfish Server. Currently free.