Redis — In-Memory Data Structure Store
Redis stores data in RAM, making it 100-1000× faster than disk databases. It's the Swiss Army knife of backend infrastructure — used as a cache, message queue, session store, rate limiter, leaderboard, and pub/sub system.
What Redis Is Used For
| Use Case | Redis Feature | Example |
|---|
|---|---|---|
| **Caching** | String/Hash | Cache API responses, user sessions |
|---|
| Session Store | String + TTL | Web session storage |
| Rate Limiting | Incr + TTL | 100 requests/minute per user |
| Leaderboards | Sorted Set | Game rankings by score |
| Message Queue | List (BRPOP) | Job queues, task workers |
| Pub/Sub | Pub/Sub | Real-time notifications |
| Distributed Lock | SET NX PX | Prevent duplicate processing |
| Counting | Incr | Page views, analytics counters |
Quick Start
bash
# Start Redis
docker run -d --name redis -p 6379:6379 redis:7-alpine
# Connect
redis-cli
redis-cli -h host -p 6379 -a password
# Basic operations
SET name "Alice"
GET name # "Alice"
DEL name
EXISTS name # 0 or 1
TTL name # -2=gone, -1=no expiry, N=seconds left
EXPIRE name 3600 # Set expiry
PERSIST name # Remove expiry
KEYS user:* # Pattern match (careful in production!)
SCAN 0 MATCH user:* COUNT 100 # Safe alternative to KEYS
Data Structures
bash
# Strings — simplest, most versatile
SET counter 0
INCR counter # Atomic increment → 1
INCRBY counter 5 # → 6
MSET k1 v1 k2 v2 # Multiple set
MGET k1 k2 # Multiple get
# Hashes — object storage
HSET user:1 name "Alice" email "alice@example.com" age 30
HGET user:1 name
HGETALL user:1
HINCRBY user:1 age 1 # Atomic increment on hash field
# Lists — queues and stacks
LPUSH queue task1 task2 # Push to left
RPUSH queue task3 # Push to right
LPOP queue # Pop from left (FIFO with RPUSH+LPOP)
BRPOP queue 0 # Blocking pop — wait until item available
LRANGE queue 0 -1 # Get all items
# Sets — unique collections
SADD tags python devops k8s
SMEMBERS tags
SISMEMBER tags python # Check membership O(1)
SUNION tags1 tags2 # Union
SINTER tags1 tags2 # Intersection
# Sorted Sets — scored ranking
ZADD leaderboard 1500 alice 1200 bob 1800 charlie
ZRANGE leaderboard 0 -1 WITHSCORES REV # Top to bottom
ZRANK leaderboard alice # 0-based rank
ZINCRBY leaderboard 100 alice # Add to score
