title: What is a more efficient way to keep a daily ranking log for each user with MySQL?
body: <p>I have a database called RankHistory that is populated daily with each user's username and rank for the day (rank as in 1,2,3,...).  I keep logs going back 90 days for every user, but my user base has grown to the point that the MySQL database holding these logs is now in excess of 20 million rows.</p>
  
  <p>This data is recorded solely for the use of generating a graph showing how a user's rank has changed for the past 90 days.  Is there a better way of doing this than having this massive database that will keep growing forever?</p>