MongoDB Performance Optimization with MMS` is a story about how a startup, CMP.LY, used MongoDB Management Service to identify performance issues in their MongoDB deployment. The company's monitoring service, CommandPost, was experiencing slower API responses due to high lock contention caused by concurrent writes. By analyzing the Lock Percentage metric in MongoDB Management Service, they identified that the issue was related to the writers being "greedy" and holding locks exclusively, preventing reads from accessing data. To address this, CMP.LY implemented strategies such as schema changes, use of message queues, multiple databases, and eventually sharding to reduce lock contention and improve performance. These changes yielded significant results, reducing the Lock Percentage to around 50% on their primary client-serving database, resulting in improved application performance and faster access to data for their users.