Flash Chat scaling problems
Just when I finally thought that I’d resolved the chat room it turns out that Flash Chat won’t scale. The standard Flash Chat relies on calling an XML method via HTTP every 3 seconds (you can change this value but 3 seconds seems a reasonable compromise between server load and responsiveness of the chatroom). This means that if you have 90 users chatting there will be 30 hits per second on your server. Unfortunately the query also seems to be fairly heavy and the consensus from the forums seems to be that Flash Chat will only run with a maximum of about 20 users.
There are two socket servers available - one written in Java and one in PHP. However, again the consensus seems to be that these sockets servers are very unreliable and that’s certainly been my experience.
I briefly considered writing my own socket server in Twisted but it looks like far too much work considering the relatively low cost of scalable products.
The new plan is to stick with Flash Chat for now as the chatroom isn’t very heavily used. As soon as I’m getting 15-20 users I’ll switch to 123 Flash Chat which starts at a reasonable $300 for 100 users.