How can I display currently online users, without a database? Or at least very efficiently. Preferably in PHP

Question

This issue has been quite the brain teaser for me for a little while. Apologies if I write quite a lot, I just want to be clear on what I've already tried etc.

I will explain the idea of my problem as simply as possible, as the complexities are pretty irrelevant. We may have up to 80-90 users on the site at any one time. They will likely all be accessing the same page, that I will call result.php. They will be accessing different results however via a get variable for the ID (result.php?ID=456). It is likely that less than 3 or 4 users will be on an individual record at any one time, and there are upwards of 10000 records.

I need to know, with less than a 20-25 second margin of error (this is very important), who is on that particular ID on that page, and update the page accordingly. Removing their name once they are no longer on the page, once again as soon as possible.

At the moment, I am using a jQuery script which calls a php file, reading from a database of "Currently Accessing" usernames who are accessing this particular ID, and only if the date at which they accessed it is within the last 25 seconds. The file will also remove all entries older than 5 minutes, to keep the table tidy.

This was alright with 20 or 30 users, but now that load has more than doubled, I am noticing this is a particularly slow method.

What other methods are available to me? Has anyone had any experience in a similar situation?

Everything we use at the moment is coded in PHP with a little jQuery. We are running on a server managed offsite by a hosting company, if that matters.

I have come across something called Comet or a Comet Server which sounds like it could potentially be of assistance, but it also sounds extremely complicated for my purposes and far beyond my understanding at the moment.

Answer 1

Look into websockets for a realtime socket connection. You could use websockets to push out updates in real time (instead of polling) to ensure changes in the 'currently online users' is sent within milliseconds.

Answer 2

What you want is an in-memory cache with a service layer that maintains the state of activity on the site. Using memcached might be a good starting point. Your pseudo-code would be something like:

• On page access, make a call to CurrentUserService
• CurrentUserService takes as a parameter the page you're accessing and who you are.
• Each time you call it, it removes whatever you were accessing before from the cache.
• Then it adds what you're currently accessing.
• Then it compiles a list of who else is accessing the same thing based on the current state in the cache.
• It returns this list, which your page processes and displays.

If you record when someone accesses a page, you can set a timeout for when the service stops 'counting' them as accessing the page.