DB sessions, performances worries...

[eluser]Référencement Google[/eluser]
Thank to both of you for your answers.

Your solution Alibi looks great for me, I didn't know about that kind of engine, I will try.
One question about it, as they said in the MySQL documentation, it is very fast, but will the MySQL server not too much overloaded while there will be 1000 visitors logged in at the same time on the website ?

Your solution Alpar looks also good, but seems very complex to script, then I will choose the MySql Heap table engine solution.