Asynchronous chat [closed]

Question

I was following a PHP-MySQL shoutbox tutorial that covered just sending and storing messages in the database. After I finished it, temporarily I chose to refresh the list of messages every 5 seconds or every time you send a new one using AJAX. But this would be too inefficient and server consuming(practically a low-intensity DDOS) in real life applications. So how do I refresh the list of new messages just when necessary? More precisely, how do I get notified that a new message was sent exactly when this happens so that I can display it?

Answer 1

A solution to your problem is called long polling, you'll find more information in this SO question.

The idea is to load information with AJAX as you currently do, but the server will not return a response immediately if there's nothing to return. Instead it will just keep the connection open for a predefined number of seconds before returning an empty response, or return as soon as a message becomes available. The max response time should be long enough to make it worthwhile, but not too long to risk a timeout on the client side - something around 20s should be fine.

Although this solution allows you to reduce the number of HTTP calls to your server, it just shifts the problem: you PHP script, while waiting for a message to be available, still needs to poll your database. If you're expecting moderate traffic, you'll be fine. But if you want to be able to seriously scale, you'll have to look for another solution.

The best solution would be to use a proper message queue instead of a database, such as Amazon SQS or IronMQ.

These will scale without limit, and will offer features such as long polling (not sure about IronMQ, but SQS definitely does).