javascript - Client notification, should I use an AJAX Push or Poll?

Question

I am working on a simple notification service that will be used to deliver messages to the users surfing a website. The notifications do not have to be sent in real time but it might be a better user experience if they happened more frequently than say every 5 minutes. The data being sent to and from the client is not very large and it is a straight forward database query to retrieve the data.

In reading other conversations on the topic it would appear that an AJAX push can result in higher server loads. Since I can tolerate longer server delays is it worth while to have the server push notifications or to simply poll.

It is not much harder to implement the push scenario and so I thought I would see what the opinion was here.

Thanks for your help.

EDIT: I have looked into a simple AJAX Push and implemented a simple demo based on this article by Mike Purvis. The client load is fairly low at around 5k for the initial version and expected to stay that way for quite some time.

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Thank you everyone for your responses. I have decided to go with the polling solution but to wrap it all within a utility library so that if they want to change it later it is easier.

Answer 1

I'm surprised noone here has mentioned long-polling. Long polling means keeping an open connection for a longer period (say 30-60 seconds), and once it's closed, re-opening it again, and simply having the socket/connection listen for responses. This results in less connections (but longer ones), and means that responses are almost immediate (some may have to wait for a new polling connection). I'd like to add that in combination with technologies like NodeJS, this results in a very efficient, and resource-light solution, that is 100% browser compatible across all major browsers and versions, and does not require any additional tech like Comet or Flash.

I realize this is an old question, but thought it might still be useful to provide this information :)