Distributed Key-Value Stores

A distributed KV store spreads keys across many nodes and replicates each key for durability and availability. The storage engine is a core choice: in-memory (Redis) for microsecond reads, LSM-trees (RocksDB, Cassandra) for write-heavy workloads, B-trees for read-heavy. Replication plus quorum reads and writes (R + W > N) tunes the consistency-availability tradeoff, and hinted handoff keeps writes accepted while a replica is down. Applied-AI interviews probe it because feature stores, KV caches, vector metadata, and session state all live in these systems, and the quorum math is a favorite probe.