What is a cache stampede, and how do you soften it?
PICTURE THIS: DATABASE INDEX
Simple meaning
When a hot key expires, thousands of requests miss together and stampede the database.
WHY — Redis instead of guessing?
Why interviewers care about Redis:
who only read docs from people who shipped.
and tied to Backend work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1When a hot key
expires, thousands of requests miss together and stampede the database.
- 2Mitigations include a short
lock or mutex around rebuild, probabilistic early expiry, and serving slightly stale data while one thread refreshes.
- 3Also keep TTL jitter
so keys do not expire in the same millisecond.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
When a hot key expires, thousands of requests miss together and stampede the database. Mitigations include a short lock or mutex around rebuild, probabilistic early expiry, and serving slightly stale data while one thread refreshes.