title: Algorithm for A/B testing
body: <p>I need to develop an A/B testing method for my users. Basically I need to split my users into a number of groups - for example 40% and 60%.<br>
  I have around 1,000,00 users and I need to know what would be my best approach. Random numbers are not an option because the users will get different results each time. My second option is to alter my database so each user will have a predefined number (randomly generated). The negative side is that if I get 50 for example, I will always have that number unless I create a new user. I don't mind but I'm not sure that altering the database is a good idea for that purpose. </p>
  
  <p>Are there any other solutions so I can avoid that?</p>