Cache invalidation strategies in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Cache Expiration

Which cache invalidation strategy automatically removes cached data after a set time period?

A Cache-aside pattern

B Write-through caching

C Manual cache clearing

D Time-to-live (TTL) expiration

💡 Hint

Think about a timer that deletes cache entries after some seconds.

TTL expiration sets a timer on cached data so it is removed automatically after that time.

❓ query_result

intermediate

Result of Cache Miss in Cache-Aside Pattern

In the cache-aside pattern, what happens when a requested key is not found in Redis cache?

A The application fetches data from the database and updates the cache

B Redis returns an error immediately

C Redis automatically loads data from the database

D The cache is cleared entirely

💡 Hint

Consider who is responsible for loading data when cache misses occur.

In cache-aside, the application loads data from the database on a cache miss and then updates the cache.

📝 Syntax

advanced

Correct Redis Command for Cache Invalidation

Which Redis command correctly deletes a cached key named 'user:123' to invalidate it?

A DEL user:123

B REMOVE user:123

C DELETE user:123

D CLEAR user:123

💡 Hint

Check Redis documentation for the command that deletes keys.

The DEL command deletes one or more keys from Redis.

❓ optimization

advanced

Optimizing Cache Invalidation for High Write Traffic

Which strategy best reduces cache stampede when many clients try to update the same cache key simultaneously?

A Disable caching for that key

B Set a very short TTL to expire cache quickly

C Use distributed locks to allow only one client to update cache

D Use write-through caching without locks

💡 Hint

Think about controlling who updates the cache to avoid overload.

Distributed locks ensure only one client updates the cache, preventing many simultaneous updates (cache stampede).

🔧 Debug

expert

Identifying the Cause of Stale Cache Data

A Redis cache is returning outdated data even after the database has been updated. Which is the most likely cause?

A The database update failed silently

B The cache key was never invalidated or updated after database change

C Redis server is down and serving old data

D The cache TTL is set to zero

💡 Hint

Consider what happens if cache is not refreshed after data changes.

If the cache key is not invalidated or updated after the database changes, the cache will serve stale data.