Comet VS Ajax polling

Question

I need to create a chat like facebook chat.

With Comet I need more memory to keep the connection.

With Ajax polling there is a latency problem if I send request every 3-4 seconds.

So... If the latency ( 3-4 seconds ) doesn't matter, Is Ajax Polling better for my case ?

Answer 1

If latency isn't an issue then AJAX is probably better. Comet can encounter problems maintaining multiple connections between the same client/server pair if you're not very, very careful. (Ref)

Answer 2

Latency is not the only problem. COMET (long-polling) "saves" your traffic - when you use polling, you cannot know, if there were changes on the server, so some of the calls may be just a waste of traffic and resources (e.g., even if no one's chatting, you're making calls every 3-4 seconds). In case of COMET, you generally need one just call to get an update from the server (with 100% hit rate).