Redis

Redis is an in-memory key-value database used as a cache, session store, message broker, or low-latency data store: strings, hashes, lists, sets, sorted sets, streams, and more with optional persistence and clustering. It sits beside primary databases like Postgres rather than replacing them for durable relational workloads. Deeper topics live in dedicated notes: data types, caching, streams, clustering, and the rest of the Redis cluster belongs under Key-value database.