Why Caching Without TTL is a Silent Killer

Caching without an expiration time creates bugs that never go away. Learn how TTL works in Redis, real-world consequences, and best practices to keep your cache fresh.

Why Caching Without TTL is a Silent Killer

You add Redis caching.

Everything becomes fast.

API responses drop from 800ms to 20ms. Database load decreases. Pages feel instant.

Everyone is happy.

But you forgot one thing:

TTL.

Now stale data lives forever.

Users start seeing:

- outdated profiles
- wrong prices
- deleted records
- old analytics
- stale dashboards

And the most dangerous part?

The system still appears to work correctly.

This is the silent killer of caching.

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The Mistake That Hides in Production

A lot of developers implement caching like this:

const cached = await redis.get(product:${id});
if (cached) {
  return JSON.parse(cached);
}
const product = await db.products.findById(id);
await redis.set(product:${id}, JSON.stringify(product));
return product;