An in-memory data store used for caching, session management, and real-time applications.
Redis is an in-memory database that stores data in RAM instead of on disk. This makes it extremely fast - retrieving data takes microseconds instead of milliseconds.
Think of Redis as a super-fast sticky note holder. You store small pieces of data that you need to access quickly.
In-Memory Storage: Data lives in RAM, not on disk. RAM is 100x faster than SSDs.
Simple Data Structures: Redis stores key-value pairs. No complex queries or joins to slow things down.
Caching: Store frequently accessed data (user profiles, product details) in Redis instead of hitting the database every time.
Session Storage: Store user login sessions. Fast reads keep your app responsive.
Real-Time Analytics: Count page views, track active users, leaderboards.
Message Queues: Temporary storage for background job queues.
Rate Limiting: Track API request counts per user.
Store data with a key, retrieve it later using the same key:
SET user:123 "John Doe"
GET user:123
// Returns: "John Doe"
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Strings: Simple text or numbers
Lists: Ordered collections
Sets: Unique values
Hashes: Key-value pairs within a key
Sorted Sets: Sets with scores for ranking
Twitter: Caches user timelines in Redis. Millions of reads per second.
GitHub: Stores background job queues in Redis.
Stack Overflow: Caches frequently viewed questions.
Redis: Super fast, data in memory, simple queries, limited storage (RAM is expensive).
PostgreSQL/MySQL: Slower, data on disk, complex queries, unlimited storage (disk is cheap).
Use Redis for speed. Use traditional databases for permanent storage.
In-Memory Only: Data lost on restart. Fine for caches.
Snapshots: Save to disk periodically. Some data loss possible.
Append-Only File: Every write saved to disk. No data loss but slower.
Use Redis: Caching, sessions, real-time features, temporary data.
Do Not Use Redis: Primary database for critical data. Redis is fast but not designed for complex queries or large datasets.
Most cloud providers offer managed Redis (AWS ElastiCache, Azure Cache, Redis Cloud). No server management needed.
For local development, Redis installs in minutes and runs easily.
Redis makes applications faster by storing frequently accessed data in memory. Nearly every major website uses Redis for caching or sessions.
Understanding Redis helps you build faster, more responsive applications.