Model PHP/Ajax Notification System?

I'm making a website similar to Facebook - with things such as Notifications which make it similar. I don't really see how I can get notifications working. Well, I figured out how I coul开发者_高级运维d get them from the database, with a query.

The structure I think the site will follow would be multiple tables for different applications - ie: Photos would add in an ID for the picture, a filename, and a few user IDs if 'tagged' or something, and how to send that information to the user in real time.. is beyond me.

So I would have to run several queries every few seconds scanning the database tables for the $_SESSION['id'] of the user being found in all the applications tables with a status of unread?

Another possibility is that every user has their own table? That's .. a lot. lol.

Or just a notifications table with the most recent notification being pushed to the table with a unique id and a user id?

I really can't wrap my head around this, lol.

Also, displaying notifications in real time? I understand Facebook uses long-polling and gets the notifications in real time, but I don't think I could leave about 5-10 queries (for each app) running on a long poll for multiple clients, or that'd completely crash my server, right?

Any advice/code on how I could try and make a notification system for a social networking-ish site? If not, I think i'll go with static notifications rather than any sort of realtime.

Then again, that'd be too much load querying the server every few seconds for a new notification on every page load? Using ajax would mean long polling, so it's a lose-lose.

I would say Long polling is the answer. Gmail and Facebook both use this method for real-time notifications. Your only other alternative is Flex with a dataservice, but that is not PHP.

In terms of performance, the query is only going to pull from 0-5 notifications at a time, and if the tables are indexed properly, and the query is written well, then 5 of these queries will not be a significant impact on your server.

Furthermore, if Gmail and facebook are doing it, then it stands to reason you can also do this. Granted, they have a ton of servers to support all their users, but I am going to go out on a limb and say you don't have as many users as they do, so as a result the server technology will work for now. And when you get so many users your current servers can't handle the load, then you invest in newer more powerful ones.

Well here is my take on it.

You could create different tables for status, photos and videos. Everytime somebody comments on a video or something you can do the query to store the notification along with the information of the user who liked it, you should set a status field too, so you can query based on which has been seen and which has not been seen by the user. You can put the url of the page where the photo is or status is located so when the user is logged in you do a query every five minutes checking for unread notifications, if there are any you display them in a tiny toast message on left bottom side of the screen like facebook.

On click of the toast message you can do an ajax call to update that status of the notifcation to read so it does not show up again and in the success call back you can take the user to the page where the status update is.