Caching in Modern Applications

Caching means storing frequently used data in a faster temporary layer so the system does not repeat expensive work for every request.

Cache Aside

async function getProduct(id: string) {
  const key = `product:${id}`;

  const cached = await redis.get(key);

  if (cached) {
    return JSON.parse(cached);
  }

  const product = await database.product.findUnique({
    where: { id }
  });

  await redis.set(key, JSON.stringify(product), { EX: 300 });

  return product;
}

TTL

A TTL defines how long a cached value should exist.

product:123
TTL = 300 seconds

Cache Invalidation

Update database
       ↓
Delete cache key
       ↓
Next read fetches fresh data
       ↓
Cache is populated again

Cache Stampede

When a very popular key expires, thousands of requests can miss at the same time and hit the database.

Possible protections include:

• request coalescing,
• distributed locks,
• TTL jitter,
• background refresh,
• stale-while-revalidate.

Redis is useful, but Redis is not automatically required for every application.