In Memory Database
An in-memory database keeps the working set in RAM for sub-millisecond reads/writes, typically adding durability via logs/snapshots and HA via replication/sharding.
LRU Cache
Design a data structure that follows Least Recently Used (LRU) eviction with O(1) get and put operations.
Redis
In-memory data structure store designed for high-performance caching, sessions, and real-time applications