What is Redis?
An in-memory data store used as a cache, message broker, and low-latency database.
Definition
Redis keeps its dataset in memory and serves operations in microseconds, with optional durability via point-in-time snapshots (RDB) or an append-only command log (AOF). Beyond simple key-value storage it offers native data structures—lists, sets, sorted sets, hashes, streams, HyperLogLog—that make patterns like leaderboards, rate limiters, and job queues a few commands rather than an application-layer construction. Commands execute on a single thread, so operations are atomic without locking, and Redis Cluster shards keys across nodes for horizontal scale. It is the default answer for session storage, cache-aside layers in front of a slower database, and pub/sub fan-out. Its 2024 licensing change to RSALv2/SSPL prompted the Valkey fork under the Linux Foundation.