online game best-practice

Question

I'm developing a django-based MMO, and I'm wondering what would be the best way for server-client communication. The solutions I found are:

• periodical AJAX calls
• keeping a connection alive and sending data through it

Later edit:

This would consist in "you have a message", "user x attacked you", "your transport to x has arrived" and stuff like this. They could grow in number (something like 1/second), but for a typical user they shouldn't reach 1/minute

Answer 1

There's also a third technique involving "hanging" queries:

• Client requests an updated page (or whatever)
• Server doesn't answer right away
• Sometime before the request times out, there's a state update in the server, and the server finally answers the client, which can then update.
• If there really is nothing new to tell the client within the update period, then the server responds before the timeout with a "no news" message, and the client starts up another "hanging" request.

Advantages:

• Client doesn't have to do Ajax. You could even make regular HTML pages "interactive" like this.
• Probably not quite as much senseless polling traffic.

Disadvantages:

• Server needs to keep more active connections open, and service them at least once per timeout period. Also,
• depending on how well the server code supports multi-threading (does PHP provide any help there?), it may be more difficult to code than AJAX response handling.

Answer 2

Not sure if it's applicable to what you're looking for, but there's a pretty good live example of lightweight server-client communication using node.js for a simple chat service:

http://chat.nodejs.org/