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Redis

Redis is an in-memory key-value store maintained by Redis Ltd, with its core kept open-source. It's the fifth most-used database in developer surveys, at roughly 28% usage share. Because it reads and writes straight from RAM, it delivers sub-millisecond response times, which is why it's the default choice for caching, session storage, leaderboards, rate limiting, and pub/sub messaging.

Quick facts
Type: In-memory key-value store / cache
Made by: Redis Ltd (open-source core)
License: Free / open-source, with newer licensing caveats on some modules, plus a paid managed cloud
Hosting: Self-hosted or cloud-managed (Redis Cloud, AWS ElastiCache, Azure Cache)
Primary use case: Caching, session stores, real-time leaderboards, rate limiting, pub/sub

Jump to: Example Getting started Best for

Example

Real commands run against the Redis CLI — simple key-value operations plus an atomic counter and an expiring key.

SET user:1001:name "Ava Chen"
GET user:1001:name
# => "Ava Chen"

EXPIRE user:1001:name 3600   # key auto-deletes after 1 hour

INCR page:home:views      # atomic counter, returns the new value

Getting started

Run Redis locally with Docker in seconds, then connect with the redis-cli client.

# Docker: run a local Redis instance
docker run --name redis -p 6379:6379 -d redis:7

# connect with redis-cli
redis-cli -h localhost -p 6379

Best for: Speeding up an existing app — sitting in front of a slower primary database as a cache, or holding short-lived data like sessions, rate-limit counters, and real-time leaderboards that don't need permanent disk storage.