Distributed
← Caching

Lesson 04.2

TTLs, invalidation & stale reads

A TTL limits how long a cached value may live, while invalidation removes it after a change; both must account for in-flight reads that can refill an older version.

🍪 The fast copy can be wrong

Ava and Ben are workers using the computer to manage cookie price. Removing an old copy is not enough if a slow worker is still carrying that old copy back.

In this lesson you'll

  1. 1Watch the fast copy answer a request
  2. 2Guess where the unsafe gap appears
  3. 3Change the rule and protect the source of truth