Cache-aside (lazy loading) deep dive in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Cache miss handling in cache-aside pattern

In a cache-aside pattern using Redis, when a cache miss occurs, what is the correct sequence of actions to retrieve and cache the data?

A Return null immediately without fetching from database

B Fetch data from database, store it in cache, then return data

C Fetch data from cache again, then return null if not found

D Store null in cache first, then fetch data from database

💡 Hint

Think about how lazy loading works to reduce database hits.

In cache-aside, on a cache miss, the application fetches data from the database, stores it in the cache, then returns it. This avoids repeated database hits for the same data.

🧠 Conceptual

intermediate

Why avoid caching null values in cache-aside?

In cache-aside pattern, why is it generally discouraged to cache null or empty results directly?

A Because caching null can cause stale data if the database later has valid data

B Because Redis does not support storing null values

C Because caching null values increases memory usage unnecessarily

D Because null values cause Redis to crash

💡 Hint

Consider what happens if the database updates after caching null.

Caching null means the cache will serve empty results even if the database later has valid data, causing stale cache issues.

📝 Syntax

advanced

Correct Redis command sequence for cache-aside get

Which Redis command sequence correctly implements a cache-aside get operation for key 'user:123' assuming a database fetch function fetchUserFromDB()?

Redis

Pseudocode:
1. Try to get value from Redis
2. If not found, fetch from DB
3. Store in Redis
4. Return value

A

GET user:123
IF null THEN fetchUserFromDB()
SET user:123 value
RETURN value

B

SET user:123 value
GET user:123
RETURN value

C

GET user:123
RETURN value

D

DEL user:123
GET user:123
fetchUserFromDB()
RETURN value

💡 Hint

Remember to fetch from DB only if cache miss occurs.

The correct flow is to GET from Redis, if null then fetch from DB, SET in Redis, then return.

❓ optimization

advanced

Reducing cache stampede in cache-aside pattern

What is an effective technique to reduce cache stampede (many requests causing DB overload) in cache-aside pattern with Redis?

A Disable caching and always fetch from DB

B Increase Redis cache TTL to infinite

C Use distributed locks or mutexes to allow only one DB fetch on cache miss

D Use Redis DEL command frequently to clear cache

💡 Hint

Think about controlling concurrent access to DB on cache miss.

Using distributed locks ensures only one request fetches from DB and others wait, preventing overload.

🔧 Debug

expert

Diagnosing stale data in cache-aside pattern

You notice your Redis cache returns outdated user profile data even after the database was updated. Which of the following is the most likely cause?

A Redis automatically updates cache when database changes

B The cache TTL is set to zero causing immediate expiration

C The database update failed silently

D The application updates the database but does not invalidate or update the cache

💡 Hint

Think about cache consistency with database updates.

Cache-aside requires explicit cache invalidation or update after DB changes; otherwise stale data remains.