Jon Hyman and Kenny Gorman presented on how Appboy scaled their MongoDB platform 40x over a year and a half as data volume and user growth increased dramatically. They started with a single unsharded replica set on AWS that struggled with locking issues as data and users grew. They then scaled vertically, added sharding across multiple servers, implemented write buffering to Redis to address a bottleneck, split collections across databases, and finally isolated large enterprise customers onto their own databases for performance. These changes helped Appboy scale from handling 2.5 million events per day for 8 million users to over 4 billion events per month.