Redis
What it is: In-memory data structure store. Key-value database, cache, message broker. Sub-millisecond latency, simple and fast.
What It Does Best
Speed. All data in RAM. Sub-millisecond reads and writes. Nothing faster for caching and session storage.
Data structures. Not just strings—lists, sets, sorted sets, hashes, bitmaps, streams. Rich operations on each type.
Simplicity. Simple key-value interface. Easy to learn, easy to use. Get productive in minutes.
Key Features
Rich data types: Strings, lists, sets, sorted sets, hashes, streams, bitmaps
Persistence options: Snapshots (RDB) and append-only file (AOF)
Pub/Sub: Built-in publish-subscribe messaging
Replication: Master-slave replication for high availability
Lua scripting: Atomic server-side scripting
Pricing
Open Source: Free, BSD license (self-hosted)
Redis Enterprise: From $0.046/hour per GB (managed)
AWS ElastiCache: From $0.017/hour for smallest node
Azure Cache: Similar pricing, managed service
When to Use It
✅ Caching database queries and API responses
✅ Session storage for web applications
✅ Real-time leaderboards and counters
✅ Rate limiting and throttling
✅ Pub/sub messaging for simple use cases
When NOT to Use It
❌ Primary database (volatile, data fits in RAM)
❌ Complex queries and analytics
❌ Large datasets (expensive to keep in memory)
❌ Durable persistence critical (use database)
❌ Complex transactions across multiple keys
Common Use Cases
Database caching: Cache frequently accessed database queries
Session store: User sessions for web applications
Leaderboards: Sorted sets for real-time rankings
Rate limiting: Track API request counts with TTL
Message queue: Lightweight pub/sub and job queues
Redis vs Alternatives
vs Memcached: Redis more features (data structures, persistence), Memcached simpler
vs DynamoDB: Redis faster for cache, DynamoDB better for persistence
vs In-memory SQL: Redis simpler and faster, SQL better for complex queries
Unique Strengths
Simplicity: Easiest in-memory store to use
Rich data structures: Beyond key-value, with atomic operations
Performance: Millions of operations per second per instance
Versatility: Cache, database, message broker in one
Bottom line: The Swiss Army knife of in-memory data stores. Fast, simple, versatile. Essential for caching and session management. Not a replacement for databases, but perfect complement. Every high-performance app uses Redis somewhere.