>>50 users all time connected to the database
Connected to the database, or connected to the application? There is a huge difference! The 50 users will always be connected to the application, but only when a request is in progress will a database connection be needed. As soon as the request is done, that connection is no longer needed. As an example, if your 50 users all go to lunch at the same time, then during the lunch hours there will be 50 idle connections - none will be in use.