High Latency in Course Data Fetching: Optimizing Nested Loops and Cache Utilization Reduces Latency to 400ms

Introduction to the Problem Imagine a student eagerly clicking on a course, only to stare at a loading spinner for a full 4 seconds. That's the reality of the current edtech app's performance, where fetching course data feels like watching paint dry. The culprit? A tangled web of nested loops and a cache system that's more hindrance than help. Symptoms: A Slow Death by a Thousand Loops The app's data retrieval process resembles a Russian nesting doll, with courses containing lessons, lessons containing files, and files containing chapters. This hierarchical structure, while logical, becomes a performance nightmare when implemented with three nested loops. Each loop iterates through its respective entities, triggering a cache lookup (getSetAsync) in the innermost loop for each file's chapters. This lookup, with its granular key structure (file:chapters:{fileId}), forces the system to check the cache for every single file, leading to a cascade of N+1 database calls when cache misses occu