Question

I need to know users login and logout, the problem is when the user session timeouts, how can i handle this to update application.

On session destroy, i want to update a db table for example ?

I prefer no to use a cron job, since it will load much on the server.

Thanks in advance.

Answer 1

In general there is no way to keep concurrent information on session state for all users without incurring a large performance hit. As you already said, this is a result of not being able to properly terminate a session when one times out.

At this point you have two options:

1. Run a cron job (deterministic)

You can set up a cron job to run as often as you require. This will ensure that the information you have is at most as old as the cron interval.

2. Set the session GC probability

Setting the session.gc_probability and session.gc_divisor PHP options allows you to specify a probability with which session cleanup will be initiated on every request. Typically this is a relatively low value (e.g. 1/100) because at very high server loads it can kill your performance very quickly.

The benefits of this approach is that it’s built-in and that it doesn’t cost you anything if your server isn’t actually being hit by users.

The main drawback is that the probability has to be always tweaked taking into account the number of requests/sec on your server, which is not a constant. Other drawbacks are the fact that it relies on requests to actually work (will never clean up sessions if noone visits your server) and that it’s a global setting (works server-wide, not application-wide).