10's of thousands of simultaneous users? That would be totally huge!!
I once wrote a web-app that about 200 odd user had to log in with - using access as a back end database (it was just a fun app - for our office-group). Access wasn't able to scale and broke soon as the load got more than 40-50 user. I had to switch to oracle.
but for someone who has
I am just using JSP servlets and JDBC but declaring all variables local in JSP and Servlets too.
I'd say look out with those 100 users for sure! (By the way I'm not sure what local means here - I assumed 'instance-variables')