cache-strategy

Cache Strategy

Overview

This skill helps you design and implement multi-layer caching strategies for high-traffic APIs. It covers choosing the right caching pattern for your data access profile, configuring TTLs, preventing cache stampedes, and setting up cache invalidation that actually works in production.

Instructions

1. Analyze the caching opportunity

Before adding caching, identify what to cache by examining query patterns:

// Instrument your API routes to log response times and call frequency
// Look for: high frequency + low change rate = best cache candidates
// Example analysis output:
// GET /api/products      → 12,000 req/min, changes every 30min → CACHE (TTL: 5min)
// GET /api/products/:id  → 8,000 req/min, changes on update   → CACHE (invalidate on write)
// POST /api/orders       → 200 req/min, always unique          → DO NOT CACHE
// GET /api/user/profile  → 3,000 req/min, changes rarely       → CACHE (TTL: 15min)

2. Implement cache-aside pattern (most common)

The application checks cache first, falls back to database, then populates cache:

import Redis from "ioredis";

const redis = new Redis({ host: "localhost", port: 6379, maxRetriesPerRequest: 3 });

async function getCached<T>(
  key: string,
  fetcher: () => Promise<T>,
  ttlSeconds: number = 300
): Promise<T> {
  const cached = await redis.get(key);
  if (cached) return JSON.parse(cached);

  const data = await fetcher();
  await redis.set(key, JSON.stringify(data), "EX", ttlSeconds);
  return data;
}

// Usage in route handler
app.get("/api/products/:id", async (req, res) => {
  const product = await getCached(
    `product:${req.params.id}`,
    () => db.products.findById(req.params.id),
    600 // 10 minutes
  );
  res.json(product);
});

3. Prevent cache stampedes

When a popular key expires, hundreds of requests hit the database simultaneously:

async function getCachedWithLock<T>(
  key: string,
  fetcher: () => Promise<T>,
  ttlSeconds: number = 300
): Promise<T> {
  const cached = await redis.get(key);
  if (cached) return JSON.parse(cached);

  const lockKey = `lock:${key}`;
  const acquired = await redis.set(lockKey, "1", "EX", 10, "NX");

  if (acquired) {
    try {
      const data = await fetcher();
      await redis.set(key, JSON.stringify(data), "EX", ttlSeconds);
      return data;
    } finally {
      await redis.del(lockKey);
    }
  }

  // Another process is refreshing — wait and retry
  await new Promise((r) => setTimeout(r, 100));
  return getCachedWithLock(key, fetcher, ttlSeconds);
}