Caching Strategies
Cache-Aside (Lazy Loading) — Most Common
async function getUser(id: string): Promise<User> {
const cached = await redis.get(`user:${id}`);
if (cached) return JSON.parse(cached);
const user = await db.user.findUnique({ where: { id } });
if (user) {
await redis.set(`user:${id}`, JSON.stringify(user), 'EX', 3600); // 1h TTL
}
return user;
}
// Invalidate on update
async function updateUser(id: string, data: UpdateUserDto): Promise<User> {
const user = await db.user.update({ where: { id }, data });
await redis.del(`user:${id}`);
return user;
}
Write-Through
async function updateProduct(id: string, data: UpdateDto): Promise<Product> {
const product = await db.product.update({ where: { id }, data });
await redis.set(`product:${id}`, JSON.stringify(product), 'EX', 3600);
return product;
}
HTTP Caching
// Express middleware
app.get('/api/products', (req, res) => {
res.set({
'Cache-Control': 'public, max-age=60, stale-while-revalidate=300',
'ETag': generateETag(products),
});
res.json(products);
});
// Conditional requests
app.get('/api/products/:id', (req, res) => {
const product = getProduct(req.params.id);
const etag = generateETag(product);
if (req.headers['if-none-match'] === etag) {
return res.status(304).end();
}
res.set({ ETag: etag, 'Cache-Control': 'private, max-age=0, must-revalidate' });
res.json(product);
});
Cache-Control Cheat Sheet
| Directive | Use Case |
|---|
public, max-age=3600 | Static assets, CDN-cacheable |
private, max-age=60 | User-specific data |
no-cache | Always revalidate (ETag/Last-Modified) |
no-store | Sensitive data (banking, health) |
stale-while-revalidate=300 | Serve stale, refresh in background |
Redis Caching Patterns
// Hash for structured data
await redis.hset(`user:${id}`, { name, email, plan });
const user = await redis.hgetall(`user:${id}`);
// Sorted set for leaderboards
await redis.zadd('leaderboard', score, `user:${id}`);
const top10 = await redis.zrevrange('leaderboard', 0, 9, 'WITHSCORES');
// Cache with refresh-ahead
async function getWithRefresh<T>(key: string, ttl: number, fetcher: () => Promise<T>): Promise<T> {
const cached = await redis.get(key);
if (cached) {
const { data, expiresAt } = JSON.parse(cached);
// Refresh in background if nearing expiry
if (Date.now() > expiresAt - ttl * 200) {
fetcher().then((fresh) =>
redis.set(key, JSON.stringify({ data: fresh, expiresAt: Date.now() + ttl * 1000 }), 'EX', ttl)
);
}
return data;
}
const data = await fetcher();
await redis.set(key, JSON.stringify({ data, expiresAt: Date.now() + ttl * 1000 }), 'EX', ttl);
return data;
}
Invalidation Strategies
| Strategy | Description |
|---|
| TTL-based | Set expiration, tolerate staleness |
| Event-driven | Invalidate on write events |
| Tag-based | Group keys by tag, purge by tag |
| Versioned keys | user:v2:${id} — change version to invalidate all |
Anti-Patterns
| Anti-Pattern | Fix |
|---|
| No TTL on cache entries | Always set TTL to prevent stale data |
| Cache stampede (many misses at once) | Use locking or stale-while-revalidate |
| Caching mutable data without invalidation | Invalidate on writes or use short TTL |
| Caching everything | Cache hot data only; measure hit rates |
| Serializing large objects | Cache only needed fields |
Production Checklist
- TTL set on all cache entries
- Cache invalidation on data mutations
- Hit rate monitoring (aim for >90%)
- Memory limits configured on Redis
- Cache key naming convention documented
- Graceful fallback when cache unavailable
