Redis
An in-memory data store used for caching, session management, and real-time features — dramatically speeds up applications by reducing database load.
Redis is an in-memory key-value store that serves as the caching and message brokering layer for the majority of high-traffic web applications. It stores data in RAM for sub-millisecond reads, making it the standard solution for caching expensive database queries, storing user sessions, rate limiting API requests, and powering real-time features like leaderboards and pub/sub messaging. Redis appears in backend and infrastructure job requirements across nearly every modern technology stack.
Typical time to job-readiness: ~2 weeks.
Learning Redis
Beginner
Learn the core data types — strings, hashes, lists, sets, sorted sets — and basic commands (GET, SET, EXPIRE, LPUSH). Spin up Redis with Docker and connect from your language of choice.
Intermediate
Implement caching patterns (cache-aside, write-through), use sorted sets for leaderboards, and understand TTL management. Learn pub/sub for simple event messaging between services.
Advanced
Redis Cluster for horizontal scaling, Redis Streams for event sourcing, Lua scripting for atomic operations, and persistence options (RDB vs AOF). Senior backend interviews often include a system design question where Redis is the right answer for caching or rate limiting.
Key concepts
- In-memory: Redis stores data in RAM — microsecond reads vs milliseconds for disk-based databases
- Data structures: strings, hashes (objects), lists (queues), sets (unique collections), sorted sets (leaderboards)
- TTL (Time To Live): set an expiry on any key — critical for cache invalidation and session management
- Cache-aside pattern: check Redis first; on miss, query the database and write the result to Redis
- Pub/Sub: Redis can broadcast messages to multiple subscribers — simple event messaging between services
- Persistence: RDB (periodic snapshots) vs AOF (append-only log) — trade recovery time for durability
Common interview topics
- What is Redis and when would you use it instead of a relational database
- Explain the cache-aside pattern
- What Redis data structure would you use to implement a leaderboard
- How do you handle cache invalidation
- Design a rate limiter using Redis