caching-strategies

Development

Implement multi-layer caching with Redis, in-memory, and HTTP caching. Covers cache invalidation, stampede prevention, and cache-aside patterns.

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Caching Strategies

Speed up your app with smart caching at every layer.

When to Use This Skill

Slow database queries
Expensive computations
External API responses
Session data
Frequently accessed data

Cache Layers

┌─────────────────────────────────────────────────────┐
│                    Request                           │
└─────────────────────────────────────────────────────┘
         │
         ▼
┌─────────────────────────────────────────────────────┐
│  Layer 1: HTTP Cache (CDN/Browser)                  │
│  - Static assets, public API responses              │
│  - Cache-Control headers                            │
└─────────────────────────────────────────────────────┘
         │ miss
         ▼
┌─────────────────────────────────────────────────────┐
│  Layer 2: In-Memory Cache (Node/Process)            │
│  - Hot data, computed values                        │
│  - LRU eviction                                     │
└─────────────────────────────────────────────────────┘
         │ miss
         ▼
┌─────────────────────────────────────────────────────┐
│  Layer 3: Distributed Cache (Redis)                 │
│  - Shared across instances                          │
│  - Session data, rate limits                        │
└─────────────────────────────────────────────────────┘
         │ miss
         ▼
┌─────────────────────────────────────────────────────┐
│  Layer 4: Database                                  │
└─────────────────────────────────────────────────────┘

TypeScript Implementation

Multi-Layer Cache

// cache.ts
import { Redis } from 'ioredis';
import { LRUCache } from 'lru-cache';

interface CacheOptions {
  ttl?: number;           // Time to live in seconds
  staleWhileRevalidate?: number;
  tags?: string[];        // For invalidation
}

class MultiLayerCache {
  private memory: LRUCache<string, { value: unknown; expires: number }>;
  private redis: Redis;

  constructor(redis: Redis) {
    this.redis = redis;
    this.memory = new LRUCache({
      max: 1000,
      ttl: 60 * 1000, // 1 minute default
    });
  }

  async get<T>(key: string): Promise<T | null> {
    // Layer 1: Memory
    const memoryHit = this.memory.get(key);
    if (memoryHit && memoryHit.expires > Date.now()) {
      return memoryHit.value as T;
    }

    // Layer 2: Redis
    const redisValue = await this.redis.get(key);
    if (redisValue) {
      const parsed = JSON.parse(redisValue) as T;
      // Populate memory cache
      this.memory.set(key, { value: parsed, expires: Date.now() + 60000 });
      return parsed;
    }

    return null;
  }

  async set<T>(key: string, value: T, options: CacheOptions = {}): Promise<void> {
    const ttl = options.ttl || 3600; // 1 hour default

    // Set in Redis
    await this.redis.setex(key, ttl, JSON.stringify(value));

    // Set in memory (shorter TTL)
    this.memory.set(key, {
      value,
      expires: Date.now() + Math.min(ttl * 1000, 60000),
    });

    // Track tags for invalidation
    if (options.tags) {
      for (const tag of options.tags) {
        await this.redis.sadd(`cache:tag:${tag}`, key);
      }
    }
  }

  async getOrSet<T>(
    key: string,
    fetcher: () => Promise<T>,
    options: CacheOptions = {}
  ): Promise<T> {
    const cached = await this.get<T>(key);
    if (cached !== null) {
      return cached;
    }

    // Prevent cache stampede with lock
    const lockKey = `lock:${key}`;
    const acquired = await this.redis.set(lockKey, '1', 'EX', 10, 'NX');

    if (!acquired) {
      // Another process is fetching, wait and retry
      await new Promise(resolve => setTimeout(resolve, 100));
      return this.getOrSet(key, fetcher, options);
    }

    try {
      const value = await fetcher();
      await this.set(key, value, options);
      return value;
    } finally {
      await this.redis.del(lockKey);
    }
  }

  async invalidate(key: string): Promise<void> {
    this.memory.delete(key);
    await this.redis.del(key);
  }

  async invalidateByTag(tag: string): Promise<void> {
    const keys = await this.redis.smembers(`cache:tag:${tag}`);
    if (keys.length > 0) {
      await this.redis.del(...keys);
      for (const key of keys) {
        this.memory.delete(key);
      }
    }
    await this.redis.del(`cache:tag:${tag}`);
  }
}

export { MultiLayerCache, CacheOptions };

Cache-Aside Pattern

// user-service.ts
class UserService {
  constructor(private cache: MultiLayerCache) {}

  async getUser(id: string): Promise<User> {
    return this.cache.getOrSet(
      `user:${id}`,
      async () => {
        return db.users.findUnique({ where: { id } });
      },
      { ttl: 3600, tags: ['users', `user:${id}`] }
    );
  }

  async updateUser(id: string, data: Partial<User>): Promise<User> {
    const user = await db.users.update({
      where: { id },
      data,
    });

    // Invalidate cache
    await this.cache.invalidate(`user:${id}`);

    return user;
  }

  async deleteUser(id: string): Promise<void> {
    await db.users.delete({ where: { id } });
    await this.cache.invalidateByTag(`user:${id}`);
  }
}

HTTP Caching Middleware

// http-cache-middleware.ts
import { Request, Response, NextFunction } from 'express';

interface HttpCacheOptions {
  maxAge?: number;
  sMaxAge?: number;
  staleWhileRevalidate?: number;
  private?: boolean;
  vary?: string[];
}

function httpCache(options: HttpCacheOptions = {}) {
  return (req: Request, res: Response, next: NextFunction) => {
    const directives: string[] = [];

    if (options.private) {
      directives.push('private');
    } else {
      directives.push('public');
    }

    if (options.maxAge !== undefined) {
      directives.push(`max-age=${options.maxAge}`);
    }

    if (options.sMaxAge !== undefined) {
      directives.push(`s-maxage=${options.sMaxAge}`);
    }

    if (options.staleWhileRevalidate !== undefined) {
      directives.push(`stale-while-revalidate=${options.staleWhileRevalidate}`);
    }

    res.setHeader('Cache-Control', directives.join(', '));

    if (options.vary) {
      res.setHeader('Vary', options.vary.join(', '));
    }

    next();
  };
}

// Usage
app.get('/api/products',
  httpCache({ maxAge: 60, sMaxAge: 300, staleWhileRevalidate: 86400 }),
  async (req, res) => {
    const products = await getProducts();
    res.json(products);
  }
);

Python Implementation

# cache.py
import json
import time
from typing import TypeVar, Callable, Optional
from functools import lru_cache
import redis

T = TypeVar('T')

class MultiLayerCache:
    def __init__(self, redis_client: redis.Redis):
        self.redis = redis_client
        self._memory: dict[str, tuple[any, float]] = {}

    def get(self, key: str) -> Optional[any]:
        # Layer 1: Memory
        if key in self._memory:
            value, expires = self._memory[key]
            if expires > time.time():
                return value
            del self._memory[key]

        # Layer 2: Redis
        redis_value = self.redis.get(key)
        if redis_value:
            parsed = json.loads(redis_value)
            self._memory[key] = (parsed, time.time() + 60)
            return parsed

        return None

    def set(self, key: str, value: any, ttl: int = 3600, tags: list[str] = None):
        self.redis.setex(key, ttl, json.dumps(value))
        self._memory[key] = (value, time.time() + min(ttl, 60))

        if tags:
            for tag in tags:
                self.redis.sadd(f"cache:tag:{tag}", key)

    async def get_or_set(
        self,
        key: str,
        fetcher: Callable[[], T],
        ttl: int = 3600,
    ) -> T:
        cached = self.get(key)
        if cached is not None:
            return cached

        # Simple lock for stampede prevention
        lock_key = f"lock:{key}"
        if not self.redis.set(lock_key, "1", ex=10, nx=True):
            await asyncio.sleep(0.1)
            return await self.get_or_set(key, fetcher, ttl)

        try:
            value = await fetcher()
            self.set(key, value, ttl)
            return value
        finally:
            self.redis.delete(lock_key)

    def invalidate_by_tag(self, tag: str):
        keys = self.redis.smembers(f"cache:tag:{tag}")
        if keys:
            self.redis.delete(*keys)
            for key in keys:
                self._memory.pop(key.decode(), None)
        self.redis.delete(f"cache:tag:{tag}")

Decorator Pattern

# cache_decorator.py
from functools import wraps

def cached(key_template: str, ttl: int = 3600, tags: list[str] = None):
    def decorator(func):
        @wraps(func)
        async def wrapper(*args, **kwargs):
            # Build cache key from template
            key = key_template.format(*args, **kwargs)
            
            cached_value = cache.get(key)
            if cached_value is not None:
                return cached_value

            result = await func(*args, **kwargs)
            cache.set(key, result, ttl=ttl, tags=tags)
            return result
        return wrapper
    return decorator

# Usage
@cached("user:{user_id}", ttl=3600, tags=["users"])
async def get_user(user_id: str) -> User:
    return await db.users.find_unique(where={"id": user_id})

Cache Invalidation Strategies

1. Time-Based (TTL)

await cache.set('key', value, { ttl: 3600 }); // Expires in 1 hour

2. Event-Based

// On data change
eventBus.on('user.updated', async (userId) => {
  await cache.invalidate(`user:${userId}`);
});

3. Tag-Based

// Set with tags
await cache.set(`product:${id}`, product, { tags: ['products', `category:${categoryId}`] });

// Invalidate all products in category
await cache.invalidateByTag(`category:${categoryId}`);

4. Write-Through

async function updateUser(id: string, data: Partial<User>) {
  const user = await db.users.update({ where: { id }, data });
  await cache.set(`user:${id}`, user); // Update cache immediately
  return user;
}

Best Practices

Cache at the right layer - Don't cache everything in Redis
Use appropriate TTLs - Balance freshness vs performance
Prevent stampedes - Use locks or stale-while-revalidate
Monitor hit rates - Track cache effectiveness
Plan for invalidation - Use tags for related data

Common Mistakes

Caching user-specific data without proper keys
No cache invalidation strategy
TTLs too long (stale data) or too short (no benefit)
Caching errors or null values
Not handling cache failures gracefully

Other versions