3.4 Versioned Keys and Invalidation Events

Expiry alone cannot tell the cache that a product has changed. The previous lesson made TTLs safe for the catalog cached under keys such as product:42: every entry carries a TTL as a fallback, jitter spreads expirations over a window, and probabilistic early refresh or a rebuild lock stops one popular key from starting many rebuilds. Those techniques control when entries expire, but a changed product still stays stale until its timer fires.

This lesson covers the two techniques that remove an entry when its data changes