redis-patterns

Redis Patterns

Quick reference for Redis best practices across common backend use cases.

How It Works

Redis is an in-memory data structure store that supports strings, hashes, lists, sets, sorted sets, streams, and more. Individual Redis commands are atomic on a single instance; multi-step workflows require Lua scripts, MULTI/EXEC transactions, or explicit synchronization to stay atomic. Data is optionally persisted via RDB snapshots or AOF logs. Clients communicate over TCP using the RESP protocol; connection pools are essential to avoid per-request handshake overhead.

When to Activate

• Adding caching to an application
• Implementing rate limiting or throttling
• Building distributed locks or coordination
• Setting up session or token storage
• Using Pub/Sub or Redis Streams for messaging
• Configuring Redis in production (pooling, eviction, clustering)

Data Structure Cheat Sheet

Use Case	Structure	Example Key
Simple cache	String	product:123
User session	Hash	session:abc
Leaderboard	Sorted Set	scores:weekly
Unique visitors	Set	visitors:2024-01-01
Activity feed	List	feed:user:456
Event stream	Stream	events:orders
Counters / rate limits	String (INCR)	ratelimit:user:123
Bloom filter / HLL	HyperLogLog	hll:pageviews

Core Patterns

Cache-Aside (Lazy Loading)

import redis
import json

r = redis.Redis(host='localhost', port=6379, decode_responses=True)

def get_product(product_id: int):
    cache_key = f"product:{product_id}"
    cached = r.get(cache_key)

    if cached:
        return json.loads(cached)

    product = db.query("SELECT * FROM products WHERE id = %s", product_id)
    r.setex(cache_key, 3600, json.dumps(product))  # TTL: 1 hour
    return product

Write-Through Cache

def update_product(product_id: int, data: dict):
    # Write to DB first
    db.execute("UPDATE products SET ... WHERE id = %s", product_id)

    # Immediately update cache
    cache_key = f"product:{product_id}"
    r.setex(cache_key, 3600, json.dumps(data))

Cache Invalidation

# Tag-based invalidation — group related keys under a set
def cache_product(product_id: int, category_id: int, data: dict):
    key = f"product:{product_id}"
    tag = f"tag:category:{category_id}"
    pipe = r.pipeline(transaction=True)
    pipe.setex(key, 3600, json.dumps(data))
    pipe.sadd(tag, key)
    pipe.expire(tag, 3600)
    pipe.execute()

def invalidate_category(category_id: int):
    tag = f"tag:category:{category_id}"
    keys = r.smembers(tag)
    if keys:
        r.delete(*keys)
    r.delete(tag)

Session Storage

import time
import uuid

def create_session(user_id: int, ttl: int = 86400) -> str:
    session_id = str(uuid.uuid4())
    key = f"session:{session_id}"
    pipe = r.pipeline(transaction=True)
    pipe.hset(key, mapping={
        "user_id": user_id,
        "created_at": int(time.time()),
    })
    pipe.expire(key, ttl)
    pipe.execute()
    return session_id

def get_session(session_id: str) -> dict | None:
    data = r.hgetall(f"session:{session_id}")
    return data if data else None

def delete_session(session_id: str):
    r.delete(f"session:{session_id}")

Rate Limiting

Fixed Window (Simple)

def is_rate_limited(user_id: int, limit: int = 100, window: int = 60) -> bool:
    key = f"ratelimit:{user_id}:{int(time.time()) // window}"
    pipe = r.pipeline(transaction=True)
    pipe.incr(key)
    pipe.expire(key, window)
    count, _ = pipe.execute()
    return count > limit

Sliding Window (Lua — Atomic)

-- sliding_window.lua
local key = KEYS[1]
local now = tonumber(ARGV[1])
local window = tonumber(ARGV[2])
local limit = tonumber(ARGV[3])

redis.call('ZREMRANGEBYSCORE', key, 0, now - window)
local count = redis.call('ZCARD', key)

if count < limit then
    -- Use unique member (now + sequence) to avoid collisions within the same millisecond
    local seq_key = key .. ':seq'
    local seq = redis.call('INCR', seq_key)
    redis.call('EXPIRE', seq_key, math.ceil(window / 1000))
    redis.call('ZADD', key, now, now .. '-' .. seq)
    redis.call('EXPIRE', key, math.ceil(window / 1000))
    return 1
end
return 0

sliding_window = r.register_script(open('sliding_window.lua').read())

def allow_request(user_id: int) -> bool:
    key = f"ratelimit:sliding:{user_id}"
    now = int(time.time() * 1000)
    return bool(sliding_window(keys=[key], args=[now, 60000, 100]))

Distributed Locks

Distributed Lock (Single Node — SET NX PX)

import uuid

def acquire_lock(resource: str, ttl_ms: int = 5000) -> str | None:
    lock_key = f"lock:{resource}"
    token = str(uuid.uuid4())
    acquired = r.set(lock_key, token, px=ttl_ms, nx=True)
    return token if acquired else None

def release_lock(resource: str, token: str) -> bool:
    release_script = """
    if redis.call('get', KEYS[1]) == ARGV[1] then
        return redis.call('del', KEYS[1])
    else
        return 0
    end
    """
    result = r.eval(release_script, 1, f"lock:{resource}", token)
    return bool(result)

# Usage
token = acquire_lock("order:payment:123")
if token:
    try:
        process_payment()
    finally:
        release_lock("order:payment:123", token)

For multi-node setups use the redlock-py library which implements the full Redlock algorithm.

Pub/Sub & Streams

Pub/Sub (Fire-and-Forget)

# Publisher
def publish_event(channel: str, payload: dict):
    r.publish(channel, json.dumps(payload))

# Subscriber (blocking — run in separate thread/process)
def subscribe_events(channel: str):
    pubsub = r.pubsub()
    pubsub.subscribe(channel)
    for message in pubsub.listen():
        if message['type'] == 'message':
            handle(json.loads(message['data']))

Redis Streams (Durable Queue)

# Producer
def emit(stream: str, event: dict):
    r.xadd(stream, event, maxlen=10000)  # Cap stream length

# Consumer group — guarantees at-least-once delivery
try:
    r.xgroup_create('events:orders', 'processor', id='0', mkstream=True)
except Exception:
    pass  # Group already exists

def consume(stream: str, group: str, consumer: str):
    while True:
        messages = r.xreadgroup(group, consumer, {stream: '>'}, count=10, block=2000)
        for _, entries in (messages or []):
            for msg_id, data in entries:
                process(data)
                r.xack(stream, group, msg_id)

Prefer Streams over Pub/Sub when you need delivery guarantees, consumer groups, or replay.

Key Design

Naming Conventions

# Pattern: resource:id:field
user:123:profile
order:456:status
cache:product:789

# Pattern: namespace:resource:id
myapp:session:abc123
myapp:ratelimit:user:123

# Pattern: resource:date (time-bound keys)
stats:pageviews:2024-01-01

TTL Strategy

Data Type	Suggested TTL
User session	24h (86400)
API response cache	5–15 min
Rate limit window	Match window size
Short-lived tokens	5–10 min
Leaderboard	1h–24h
Static/reference data	1h–1 week

Always set a TTL. Keys without TTL accumulate indefinitely and cause memory pressure.

Connection Management

Connection Pooling

from redis import ConnectionPool, Redis

pool = ConnectionPool(
    host='localhost',
    port=6379,
    db=0,
    max_connections=20,
    decode_responses=True,
    socket_connect_timeout=2,
    socket_timeout=2,
)

r = Redis(connection_pool=pool)

Cluster Mode

from redis.cluster import RedisCluster

r = RedisCluster(
    startup_nodes=[{"host": "redis-1", "port": 6379}],
    decode_responses=True,
    skip_full_coverage_check=True,
)

Sentinel (High Availability)

from redis.sentinel import Sentinel

sentinel = Sentinel(
    [('sentinel-1', 26379), ('sentinel-2', 26379)],
    socket_timeout=0.5,
)
master = sentinel.master_for('mymaster', decode_responses=True)
replica = sentinel.slave_for('mymaster', decode_responses=True)

Eviction Policies

Policy	Behavior	Best For
noeviction	Error on write when full	Queues / critical data
allkeys-lru	Evict least recently used	General cache
volatile-lru	LRU only among keys with TTL	Mixed data store
allkeys-lfu	Evict least frequently used	Skewed access patterns
volatile-ttl	Evict soonest-to-expire	Prioritize long-lived data

Set via redis.conf: maxmemory-policy allkeys-lru

Anti-Patterns

Anti-Pattern	Problem	Fix
Keys with no TTL	Memory grows unbounded	Always set TTL
KEYS * in production	Blocks the server (O(N))	Use SCAN cursor
Storing large blobs (>100KB)	Slow serialization, memory pressure	Store reference + fetch from object store
Single Redis for everything	No isolation between cache & queue	Use separate DBs or instances
Ignoring connection pool limits	Connection exhaustion under load	Size pool to workload
Not handling cache miss stampede	Thundering herd on cold start	Use locks or probabilistic early expiry
FLUSHALL without thought	Wipes entire instance	Scope deletes by key pattern

Cache Miss Stampede Prevention

import threading

_locks: dict[str, threading.Lock] = {}
_locks_mutex = threading.Lock()

def get_with_lock(key: str, fetch_fn, ttl: int = 300):
    cached = r.get(key)
    if cached:
        return json.loads(cached)

    with _locks_mutex:
        if key not in _locks:
            _locks[key] = threading.Lock()
        lock = _locks[key]
    with lock:
        cached = r.get(key)  # Re-check after acquiring lock
        if cached:
            return json.loads(cached)
        value = fetch_fn()
        r.setex(key, ttl, json.dumps(value))
        return value

Note: for multi-process deployments, replace the in-process lock with acquire_lock/release_lock from the Distributed Locks section above.

Examples

Add caching to a Django/Flask API endpoint: Use cache-aside with setex and a 5-minute TTL on the response. Key on the request parameters.

Rate-limit an API by user: Use fixed-window with pipeline(transaction=True) for low-traffic endpoints; use sliding-window Lua for accurate per-user throttling.

Coordinate a background job across workers: Use acquire_lock with a TTL that exceeds the expected job duration. Always release in a finally block.

Fan-out notifications to multiple subscribers: Use Pub/Sub for fire-and-forget. Switch to Streams if you need guaranteed delivery or replay for late consumers.

Quick Reference

Pattern	When to Use
Cache-aside	Read-heavy, tolerate slight staleness
Write-through	Strong consistency required
Distributed lock	Prevent concurrent access to a resource
Sliding window rate limit	Accurate per-user throttling
Redis Streams	Durable event queue with consumer groups
Pub/Sub	Broadcast with no delivery guarantees needed
Sorted Set leaderboard	Ranked scoring, pagination
HyperLogLog	Approximate unique count at low memory

Related

• Skill: postgres-patterns — relational data patterns
• Skill: backend-patterns — API and service layer patterns
• Skill: database-migrations — schema versioning
• Skill: django-patterns — Django cache framework integration
• Agent: database-reviewer — full database review workflow