Parse powers over 250k mobile apps on MongoDB. Since we can have no prior knowledge of the schemas or usage patterns or scaling requirements for each app, we rely on advanced operational techniques and best practices for managing MongoDB and maintaining peak performance. In this talk we will talk about the unique challenges of this use case, such as dealing with cotenancy issues and how to automatically generate good indexes for each app. I will talk about some of the interesting operational techniques involved in managing hundreds of databases and millions of collections on MongoDB, as well as running large and growing database ecosystems on AWS. I will also talk about some of our favorite black belt tips for tuning and scaling MongoDB. And finally we will talk about how to recover from performance-impacting incidents gracefully, without making everything worse for yourself.