Impact of Session variables on server's performance



Hello everyone!

From a long time of developing in the Microsoft world using mainly ASP as web programming code I learned that in programming with ASP it is not very wise to use many session variables, as their impact on the server's speed can be very demanding, resulting in a highly reduced performance.

Now that I am introduced to PHP, I would like to know if the event I described above also occurs with PHP.

Could someone please comment on this, perhaps backed by articles?
I don't have any articles to back this up, but here's what I've gathered: Since Sessions data is generally stored on the disk (though it is possible to change this), having lots of access to session data (e.g. on the order of several thousand accesses per hour) can indeed impact performance (since disk access is always slow). Keeping session data in memory can essentially nullify this impact, however.
In that case I guess I'll stick to programming keeping in mind that an absolute minimum of session variables is the most wise solution.