The document discusses how Redis is used at Facebook to solve two problems: 1) Serving user configurations in real-time by using a hierarchical master-slave replication architecture with global and regional masters and slaves to distribute reads and allow writes at different levels. 2) Processing stats data in real-time by using a split data processing model where daily bulk processing is done separately from real-time processing by tailers that insert stats into a sharded Redis cluster using HINCRBY.