Welcome to the third and final part of the series “The Cost of Not Knowing MongoDB.” Building upon the foundational optimizations explored in Part 1 and Part 2, this article delves into advanced MongoDB design patterns that can dramatically transform application performance. In Part 1, we improved application performance by concatenating fields, changing data types, and shortening field names. In Part 2, we implemented the Bucket Pattern and Computed Pattern and optimized the aggregation pipeline to achieve even better performance.