redis-patterns

Redis Patterns

Production patterns for Redis covering caching, session management, rate limiting, distributed systems, and performance optimization.

Cache-Aside Pattern

BAD: No TTL, cache stampede vulnerability

// ioredis
import Redis from 'ioredis';
const redis = new Redis();

async function getUser(id: string) {
  const cached = await redis.get(`user:${id}`);
  if (cached) return JSON.parse(cached);

  const user = await db.query('SELECT * FROM users WHERE id = $1', [id]);
  await redis.set(`user:${id}`, JSON.stringify(user)); // No TTL!
  return user;
}

GOOD: TTL + stampede protection with locking

async function getUser(id: string) {
  const key = `user:${id}`;
  const cached = await redis.get(key);
  if (cached) return JSON.parse(cached);

  // Acquire lock to prevent stampede
  const lockKey = `lock:${key}`;
  const acquired = await redis.set(lockKey, '1', 'NX', 'EX', 10);

  if (!acquired) {
    // Wait and retry if another process is loading
    await new Promise(resolve => setTimeout(resolve, 100));
    return getUser(id);
  }

  try {
    const user = await db.query('SELECT * FROM users WHERE id = $1', [id]);
    await redis.setex(key, 3600, JSON.stringify(user)); // 1 hour TTL
    return user;
  } finally {
    await redis.del(lockKey);
  }
}

Write-Through Cache

BAD: Cache and DB out of sync

// go-redis
import "github.com/redis/go-redis/v9"

func updateUser(ctx context.Context, rdb *redis.Client, user User) error {
    data, _ := json.Marshal(user)
    rdb.Set(ctx, fmt.Sprintf("user:%s", user.ID), data, 0)
    return db.Exec("UPDATE users SET name = $1 WHERE id = $2", user.Name, user.ID)
    // If DB fails, cache is dirty!
}

GOOD: Write DB first, then invalidate cache

func updateUser(ctx context.Context, rdb *redis.Client, user User) error {
    // Write to DB first
    if err := db.Exec("UPDATE users SET name = $1 WHERE id = $2", user.Name, user.ID); err != nil {
        return err
    }

    // Invalidate cache, don't care if this fails
    key := fmt.Sprintf("user:%s", user.ID)
    rdb.Del(ctx, key)
    return nil
}