web based chat application

hii.. i am designing a chat application. i have tried using php + MySQL + JavaScri开发者_开发问答pt and developed the web based chat app. But the application is quite slow. What all i do is, just store the messages from the clients in a table, and each client retrieves the table at a lag of 2 seconds.... I manage this by ajax. But the app response becomes very bad when many user joins. Is their any other technique to build the chat app ??? or what else i can do to make my app better. help plzz .. thanks in advance :)

Don't know if you've touched upon it, but I'd recomend using an IRC server as backend.

If you have the ability to install nodejs(basicly server side javascript) on your server you should take a look at socket.io which is a plugin for nodejs. This gives you almost an instant response time, even for quite large masses of users.

There are almost no libraries/projects for real-time web applications in PHP. But if you really want to use it you can take a look at a technique called long-polling. This can still be quite heavy on your server though.

Maybe it is slow because each client retrieves full table of chat contents - try appending only the new messages.

I've done the same thing last year.

I suggest retrieving only so many chats when the user first logs in, e.g. the last 30, and displaying them. Then on each subsequent AJAX call only retrieve any new chat messages, rather than everything else again. You can do this by storing the latest chat id (a unique id) when you first retrieve all the chat msgs and then only retrieve anything with a chat id greater than that.

How often do you check for new msgs? You could also increase that time.