Explore the principles behind Least Recently Used (LRU) caching, understand why it outperforms FIFO and LFU strategies, and follow a step‑by‑step C++ implementation using hash tables and doubly linked lists, complete with detailed code, testing, and performance optimization tips.
LinkedHashMap extends HashMap by maintaining a doubly linked list to preserve insertion or access order, allowing optional LRU cache behavior via the accessOrder flag, and its source code shows how entries are linked, reordered on get, and how to override removeEldestEntry for eviction.
Meituan’s DSP system boosted high‑QPS ad serving performance by layering an LRU cache in front of Redis, then adding time‑based eviction, sharding the cache into HashLruCache instances to cut lock contention, and employing a zero‑copy, reference‑counted design, ultimately cutting average latency to about 20 % of the original and similarly reducing 99.9th‑percentile delays.
