SQL is fairly easy to learn, the initial concepts take very little time. Making your own custom format will be harder, less efficient and far less reliable.

Your options are pretty much SQL, an existing text storage method (CSV, XML, ect) and a custom method made by you. SQL is the easiest.

Partially true. Sessions exist until the machine destroys them. This can be manually or automatically done (the same exact process is called). If Apache works like IIS (it should in this respect), there is a set time limit till the server deletes the session, the session will remain until that period of inactivity has passed unless a manual deletion is called. This is because the server can not really know if you have left the page, all it knows is when you access it.

Sessions are not designed to be shared or constantly modified. Every time the session gets modified the computer has to modify the text file it is being held in (the format is almost plain text). If you have a value that is being modified very often over a large period of time, don't use sessions.

__________________