title: How to keep track of users in given activity online?
body: <p>I need to add counter of online users (players) that are currently playing my game. This is similar to online users counter online on webpages. All users are anonymous. The question is, what is the proper way to do it? Should I adopt some PHP solutions found on the Internet?</p>
  
  <p>I have a PHP backend server for this and using Slim framework for usedata synchronisation.</p>
  
  <p>My idea was to keep track of one time generated UUID in the DB but i don't think that is the best aproach due to performance reasons.</p>