eliferjunior Redis
Build fast, scalable applications with Redis as a cache, message broker, session store, or real-time data engine.
Setup
Docker (quickstart)
# Redis 7 with persistence
docker run -d --name redis -p 6379:6379 \
-v redis-data:/data \
redis:7-alpine redis-server --appendonly yes --requirepass "your-password"
Connection
"""redis_client.py — Redis connection with connection pooling."""
import redis
# Single connection
r = redis.Redis(host="localhost", port=6379, password="your-password", db=0,
decode_responses=True) # Auto-decode bytes to strings
# Connection pool (recommended for production)
pool = redis.ConnectionPool(
host="localhost", port=6379, password="your-password",
max_connections=20, # Match your app's concurrency
decode_responses=True,
)
r = redis.Redis(connection_pool=pool)
# Verify connection
r.ping() # Returns True
// redis-client.js — Node.js connection with ioredis
import Redis from 'ioredis';
const redis = new Redis({
host: 'localhost', port: 6379, password: 'your-password',
maxRetriesPerRequest: 3,
retryStrategy: (times) => Math.min(times * 50, 2000),
});
Caching Patterns
Cache-Aside (most common)
"""cache_aside.py — Cache-aside pattern with automatic expiration."""
import json
def get_user(user_id: int) -> dict:
"""Fetch user from cache, falling back to database.
Args:
user_id: The user's ID.
Returns:
User dict from cache or database.
"""
cache_key = f"user:{user_id}"
cached = r.get(cache_key)
if cached:
return json.loads(cached)
# Cache miss — fetch from database
user = db.query("SELECT * FROM users WHERE id = %s", user_id)
r.setex(cache_key, 3600, json.dumps(user)) # Cache for 1 hour
return user
def update_user(user_id: int, data: dict):
"""Update user in database and invalidate cache.
Args:
user_id: The user's ID.
data: Fields to update.
"""
db.execute("UPDATE users SET ... WHERE id = %s", user_id)
r.delete(f"user:{user_id}") # Invalidate — next read repopulates
Write-Through Cache
"""write_through.py — Write-through: update cache and DB together."""
def save_product(product_id: str, data: dict):
"""Save product to both database and cache atomically.
Args:
product_id: Product identifier.
data: Product data dict.
"""
# Write to DB first (source of truth)
db.execute("INSERT INTO products ... ON CONFLICT UPDATE ...", data)
# Then update cache
r.setex(f"product:{product_id}", 7200, json.dumps(data)) # 2h TTL
Session Storage
"""session_store.py — HTTP session storage in Redis."""
import secrets, json
SESSION_TTL = 86400 # 24 hours
def create_session(user_id: int, metadata: dict = None) -> str:
"""Create a new session and return the session token.
Args:
user_id: Authenticated user's ID.
metadata: Optional session metadata (IP, user-agent, etc.).
"""
token = secrets.token_urlsafe(32)
session_data = {"user_id": user_id, "created_at": time.time(), **(metadata or {})}
r.setex(f"session:{token}", SESSION_TTL, json.dumps(session_data))
# Track active sessions per user for "log out everywhere"
r.sadd(f"user_sessions:{user_id}", token)
return token
def get_session(token: str) -> dict | None:
"""Validate and return session data, extending TTL on access.
Args:
token: Session token from cookie/header.
"""
data = r.get(f"session:{token}")
if not data:
return None
r.expire(f"session:{token}", SESSION_TTL) # Sliding expiration
return json.loads(data)
def destroy_all_sessions(user_id: int):
"""Invalidate all sessions for a user (password change, security breach).
Args:
user_id: The user whose sessions to destroy.
"""
tokens = r.smembers(f"user_sessions:{user_id}")
if tokens:
r.delete(*[f"session:{t}" for t in tokens])
r.delete(f"user_sessions:{user_id}")
Rate Limiting
Sliding Window
"""rate_limiter.py — Sliding window rate limiter using sorted sets."""
import time
def is_rate_limited(key: str, limit: int, window_seconds: int) -> bool:
"""Check if a key has exceeded its rate limit.
Args:
key: Identifier (e.g., IP address, API key, user ID).
limit: Maximum requests allowed in the window.
window_seconds: Window size in seconds.
Returns:
True if rate limited, False if request is allowed.
"""
now = time.time()
window_start = now - window_seconds
pipe = r.pipeline()
rk = f"ratelimit:{key}"
pipe.zremrangebyscore(rk, 0, window_start) # Remove expired entries
pipe.zadd(rk, {f"{now}": now}) # Add current request
pipe.zcard(rk) # Count requests in window
pipe.expire(rk, window_seconds) # Auto-cleanup
results = pipe.execute()
count = results[2]
return count > limit
For smoother rate limiting, consider a token bucket implementation using a Lua script that tracks tokens and refill timestamps in a Redis hash.
Pub/Sub
"""pubsub.py — Real-time messaging with Redis pub/sub."""
import threading
def publish_event(channel: str, event: dict):
"""Publish an event to a channel.
Args:
channel: Channel name (e.g., "notifications:user:123").
event: Event data dict — serialized to JSON.
"""
r.publish(channel, json.dumps(event))
def subscribe_to_events(pattern: str, callback):
"""Subscribe to channels matching a pattern.
Args:
pattern: Glob pattern (e.g., "notifications:*").
callback: Function called with (channel, data) for each message.
"""
ps = r.pubsub()
ps.psubscribe(pattern)
def listener():
for msg in ps.listen():
if msg["type"] == "pmessage":
callback(msg["channel"], json.loads(msg["data"]))
thread = threading.Thread(target=listener, daemon=True)
thread.start()
return ps # Return for cleanup: ps.punsubscribe()
Streams (persistent messaging)
Unlike pub/sub, streams persist messages and support consumer groups. Use XADD to add events, XGROUP CREATE to create consumer groups, and XREADGROUP/XACK to consume and acknowledge messages. Set maxlen on XADD to cap stream memory.
Distributed Locking
"""distributed_lock.py — Distributed lock using Redis (Redlock pattern)."""
def acquire_lock(name: str, timeout: int = 10) -> str | None:
"""Acquire a distributed lock.
Args:
name: Lock name (e.g., "process:invoice:12345").
timeout: Lock expiration in seconds (prevents deadlocks).
Returns:
Lock token if acquired, None if already held.
"""
token = secrets.token_urlsafe(16)
acquired = r.set(f"lock:{name}", token, nx=True, ex=timeout)
return token if acquired else None
# Lua script ensures atomic check-and-delete (only owner can release)
RELEASE_SCRIPT = """
if redis.call('GET', KEYS[1]) == ARGV[1] then
return redis.call('DEL', KEYS[1])
end
return 0
"""
def release_lock(name: str, token: str) -> bool:
"""Release a lock (only if we own it).
Args:
name: Lock name.
token: Token returned by acquire_lock.
"""
return r.eval(RELEASE_SCRIPT, 1, f"lock:{name}", token) == 1
Leaderboards
Use sorted sets (ZADD, ZREVRANGE, ZREVRANK) for real-time leaderboards. ZADD sets scores, ZREVRANGE returns top N entries, and ZREVRANK gets a member's rank.
Production Configuration
Key settings: maxmemory 2gb, maxmemory-policy allkeys-lru, appendonly yes, appendfsync everysec. Always set a maxmemory limit to prevent out-of-memory crashes.
Guidelines
- Use
SETEX/SET ... EXwith TTLs for all cache keys -- keys without expiration leak memory - Pipeline multiple commands when doing batch operations -- reduces round trips
- Use Lua scripts for atomic multi-step operations (check-and-set, compare-and-delete)
- Prefer Streams over pub/sub when message persistence matters -- pub/sub drops messages if no subscriber is listening
- Key naming convention: use colons as separators (
user:123:profile,cache:product:456) - Monitor memory usage with
INFO memory-- Redis is in-memory, running out kills the process - Use
SCANinstead ofKEYS *in production --KEYSblocks the server on large datasets - Connection pooling is essential -- creating a new connection per request adds 1-2ms latency
- Redis is single-threaded for commands -- one slow Lua script blocks everything