How to reduce a number of AJAX requests for a chat?

Question

I have a chat on my web site and it needs to send many AJAX requests to my server (at least 2 times per second) in order to check if there are new messages.
Is there a way to reduce the number of requests and reload messages only after they have been posted?
I know that there are no possibility to use sockets (because I can't use flash, java or features of HTML5), but maybe there is some trick dealing with keep alive option of HTTP 1.1?

Answer 1

Yes, there is an easy way to do this. Effectively, what you do is you increase the timeout for your ajax call to a long timeout (say, 5 minutes). Your server receives the request and then holds it, occasionally checking for new responses. Then, when a new response is warranted, it simply responds to the request, and your client receives the update.

If no response is had within 5 minutes, your client simply timeouts and starts a new ajax request. Your server, if it hasn't responded within 5 minutes, usually then just terminates the held request to get it out of the queue.

Effectively 'server-side' pushing.