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 accepting writes while a replica is down. AI, ML, and GenAI engineer 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.