How do you prevent a cache stampede or thundering herd?
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of Redis conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
A stampede happens when a popular key expires and many clients simultaneously hit the database to rebuild it. Several mitigations exist.
- Locking or mutex: only the first request rebuilds while others wait briefly or serve stale data, using SET NX with a short TTL as a rebuild lock.
- Probabilistic early expiration: refresh before expiry with random jitter so rebuilds spread out.
- Stale-while-revalidate: serve the expired value while one worker refreshes in the background.
- TTL jitter: add a random offset so many keys do not expire at once.
- Request coalescing: deduplicate concurrent misses for the same key in-process.
- Never expire hot keys, refreshing them with a scheduled job.
Combine TTL jitter with a rebuild lock for most read-heavy systems, and monitor hit rate and database load during incidents.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.