如何加快jquery / php / ajax聊天室的速度？

Question

I've created a small jquery and php chatroom with some .get and .post functions and php docs that read and write data to a sql server. It works fine, but the small problem is when someone posts something, it takes about half a second for it to appear (because of the lag). I fear there's something wrong with my coding. im using

setinterval (listen, 300)

as my continuous jquery function for reading new db entries, listen is a function with a .get inside. How does stackoverflow or facebook do it so that the user types something in and immediately it pops out?

Answer 1

Maybe try displaying the inputted chat message immediately to the user who posted it, prior to posting it to the database.

Like this:

• User enters message, submits
• Update users chat window so they see it immediately
• POST message to database
• GET from db and update all chat windows

Answer 2

This can be implemented using various techniques, which have many names: Long-polling, Server Sent Events, Comet, WebSockets, and others.

Basic idea is this:

Alice opens facebook. Her browser makes a request for updates ($.get, for example), but the server does not respond if there are no new updates and the request remains in 'waiting' state.

Bob opens facebook. He decides to comment on Alice's wall. His browser posts his comment to the server ($.post).

The server accepts this post, handles it properly (saves onto Alice's wall, etc) But ALSO server checks if there is a waiting update request from Alice. If there is, server renders info about this update into response stream and closes the connection. Alice's browser finally gets a response to this long hanging request and happily draws a red "1" in the notification area. It also immediately opens another update request (to not miss any).

Alice sees comment from Bob, which was delivered instantly.

The technique described is called "long polling" and it was first introduced by Google in Gmail.

Answer 3

You can use HTML5 sockets, however these are very much in their infancy and not widely supported (ie by IE).

Lots of systems use Flash as a middle-man as that can hold a connection open.

With either of these you can use your PHP code that stores the comment to the database to also push this out to every "listener". This will be the quickest way possible. If your system is super clever it'll incorporate all three - HTML5 sockets where it can, Flash where it can't, and your regular polling were there's no Flash either.

http://pusher.com/ might be a good starting point for further learning.

Answer 4

Most sites that have fast chat use a technique called comet. You can read more about it here: http://ajaxian.com/archives/comet-a-new-approach-to-ajax-applications

It essentially is a piece of modified server software that waits to return a response to the user until either a message is sent or it is about to timeout.