Designing High-Performance System Caches: A Practical Guide Using LRU & LFU (with TypeScript Implementations)

Explores two fundamental cache eviction policies: LRU (Least Recently Used) and LFU (Least Frequently Used). Explains when to use each policy, how they work internally using hash maps and doubly linked lists, and provides complete TypeScript implementations achieving O(1) operations. LRU suits workloads with temporal locality (recent items accessed again soon), while LFU works better when certain items remain consistently hot. Includes practical examples from databases, browsers, CDNs, and guidance on choosing between the two approaches.