Facebook has over 500 million active users, with half logging in every day. It processes over 4 trillion feed actions per day and caches over 2 trillion objects. Facebook has scaled to over 1 million active users per engineer, significantly more efficient than other large tech companies. To achieve this scale, Facebook relies on techniques like frequent small releases, dark launching of major changes, and shedding load during outages to maintain reliability as the site grows enormously.