Let take Twitter as an example. All the tweets are timestamped. I want to keep only a month's worth of tweets for each user. The number of tweets that fit within this one month window varies from user to user. What is the best way to accomplish this? There are millions of users. Do I need to loop through all of them and handle the delete one user at a time? Or is there a better way to do this? If a user has not post a new tweet in more than a month, I also want to remove the user itself. Do I also need to do looking through all the users one at a time?