Redis / Cache Stampede Interview Questions 2026

Explain Redis pub/sub vs Redis Streams. When would you use each?

Your Redis sorted set is used for a leaderboard with 10 million players. ZRANGEBYSCORE queries are slow. How do you optimize?

What is Redis pipelining and how does it differ from transactions? When should you use each?

Redis is using 80% of available memory. Your application isn't caching more data than before. What could cause Redis memory growth?

You store user sessions in Redis with 2-hour TTL. Users complain they're logged out after 30 minutes of browsing. What's likely wrong?

Implement a distributed lock using Redis. What can go wrong with a naive SETNX approach?

Your application uses Redis KEYS * command in production to list all cache keys. The application hangs for several seconds periodically. Why?

Explain Redis persistence options: RDB vs AOF. Your service can tolerate losing at most 1 second of data. Which do you configure?

You're using Redis as a session store. A Redis failover takes 30 seconds. During this time, all users are logged out. How do you make sessions resilient to Redis failures?

Your Redis cache stores 100,000 keys. At midnight, all keys expire simultaneously (same TTL set when deployed). This causes a thundering herd that crashes your database. How do you prevent this?

What is Redis Pub/Sub and how does it differ from using Redis as a message queue with Lists?

How does Redis handle persistence? What are the trade-offs between RDB and AOF?

Your Redis cluster goes down. How do you design your application so it degrades gracefully?

Explain Redis data structures and give a use case for each: String, Hash, List, Set, Sorted Set.

You need to track the top 10 most active drivers by trip count, updated in real time. Which Redis data structure fits this, and why not just a plain hash with manual sorting?

You use Redis to cache OTPs with a 5-minute TTL. How does Redis actually expire keys internally — does it scan the whole keyspace on a timer?

How does Redis's GEO command family (GEOADD, GEORADIUS) let you find nearby drivers efficiently, and what data structure underlies it?