Advice for ajax message notifications?

I'm here to ask you if what I think is the right way to go around coding this.

I have a site that receives private messages and I wish a flag to show up the moment the person receives a message. Should I check for new messages every 3 seconds and show the flag if there is a new message or is there a better way?

If I did it in ajax, I was thinking check every 3-5 seconds for new messages, and once there's a flag, stop checking for more.

My only concern is, if it checks every 3-5 second, will it cause any lag or glitchyness for the person when they're typing? Lets say they're typing out a paragraph somewhere, I don't want their writing to glitch while开发者_StackOverflow社区 it checks those 3-5 second intervals.

One of my coder friends mentioned there is a method with Ping(?) or something like that. Where the person is always connected to the server and when there's a change it notifies the user. I'm totally unsure of how this works.

Anyone know how facebook does it? haha.

Thank you!

If you have done the AJAX well, it should not lag/glitch while typing. Something like 3-5s is good as its fast enough but won't slow down server/browser.

Did he mean "push"? In push the messages are pushed to client in realtime, client is not asking if there is new messages. This is most likely the method Facebook is using.

One of my coder friends mentioned there is a method with Ping(?) or something like that

To be honest I really don't like periodic refresh(polling at intervals), because tt has scaling problems(I got notice from hosting provider when using periodic refresh). You should use more efficient transports like for example:

• WebSocket
• Adobe® Flash® Socket
• AJAX long polling
• AJAX multipart streaming
• Forever Iframe
• JSONP Polling(cross domain)

To use this you could for example use:

• hosted solution pusher with API and generous free plan. This gives you max 20 concurrent and 100,000 messages per day, but no SSL, so do not transmit sensitive information over the wire. They also provide third-party PHP client available at github implementing REST API.
• socket.io (I like this a lot)
• tornado
• netty

Anyone know how facebook does it? haha.

For chat they use Erlang. They also have open-sourced tornado(see link above) which they required from friendfeed which they acquired in the past. Facebook is a PHP-shop, but they decided to not use PHP for this, because PHP can not yet do this efficiently. Anyway they are using one of the efficients transports above.