Cache stampede
Also called: Thundering herd, Dog-pile effect
Many requests missing the same cache entry at once and all rebuilding it from the database at the same time.
Definition
When a popular key expires or the cache is flushed, every concurrent request misses and queries the database, often overloading it exactly when traffic is highest. Defenses are letting only one request rebuild each key (single flight or a lock), refreshing hot keys before they expire, and adding random jitter to TTLs so keys don't expire together.
In practice
A home page cached for 60 seconds expires at 12:00:00 and 5,000 requests query the database in the same second.
Learn it in context
Lessons that use this term.