Shopping Cart / Temp. QTY storage?

[Lashiec]

I've got this shopping cart to build for some site, and I was wondering what a good way to do what I need to do.

 

It's for a large company, so it'll be hit a lot and when people add an item to their cart I need it to take away the qty of the item that the warehouse has. But, the question I had was if the shopping cart doesn't get canceled or submitted, how can I take that temporary storage and return the qty of items from the cart back into the database?

 

Is there some sort of thing that can run when a session variable times out (give I put qty and item in the session, that way when it times out the cart is destroyed and the inventory is returned to the database)? Or is there some better way to go about this?

 

The project is in the starting phase of planning, so I wanted to work some of these things out before I got to involved in it.

 

Thanks!