Cache-aside pattern in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Cache Miss Handling in Cache-Aside Pattern

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

A The cache automatically fetches data from the database and updates itself without application intervention.

B The application returns an error immediately without querying the database.

C The application fetches data from the database, stores it in the cache, then returns it.

D The cache deletes the missing key and waits for the database to push data.

💡 Hint

Think about who is responsible for loading data into the cache when it is missing.

In the cache-aside pattern, the application checks the cache first. If data is missing, it loads data from the database, stores it in the cache, then returns it.

❓ query_result

intermediate

Result of Cache-Aside Data Retrieval Sequence

Given the following sequence in a cache-aside pattern using Redis:
1. Application checks Redis key 'user:123'.
2. Key is missing.
3. Application queries database and gets user data: {"id":123, "name":"Alice"}.
4. Application stores this data in Redis under 'user:123'.
5. Application reads 'user:123' from Redis.
What is the output of the final Redis read?

A {"id":123, "name":"Alice"}

B null

C "user:123"

D An error because Redis cannot store JSON

💡 Hint

Consider what data was stored in Redis and what is returned when reading that key.

After storing the user data as a JSON string in Redis, reading the key returns the stored JSON string representing the user.

📝 Syntax

advanced

Identify the Correct Redis Command to Store Data in Cache-Aside Pattern

Which Redis command correctly stores the user data JSON string '{"id":123, "name":"Alice"}' under the key 'user:123'?

A SET user:123 '{"id":123, "name":"Alice"}'

B GET user:123 '{"id":123, "name":"Alice"}'

C PUT user:123 '{"id":123, "name":"Alice"}'

D STORE user:123 '{"id":123, "name":"Alice"}'

💡 Hint

Remember the Redis command to set a key's value.

The Redis command to store a value under a key is SET. GET retrieves a value. STORE and PUT are not valid Redis commands.

❓ optimization

advanced

Optimizing Cache Expiration in Cache-Aside Pattern

To prevent stale data in a cache-aside pattern, which approach optimizes cache expiration for user data in Redis?

A Never expire cached keys to ensure data is always available.

B Set a TTL (time-to-live) on cached keys to automatically expire after a fixed time.

C Manually delete keys only when the database is updated, without TTL.

D Use Redis transactions to lock keys indefinitely.

💡 Hint

Think about automatic ways to keep cache fresh without manual intervention.

Setting a TTL on cached keys ensures data expires automatically, reducing stale data risk and manual cache management.

🔧 Debug

expert

Diagnosing Cache Inconsistency in Cache-Aside Pattern

An application uses the cache-aside pattern with Redis. After updating user data in the database, the cache is not updated, causing stale data to be served. What is the most likely cause?

A The cache key expired too soon, causing stale data.

B Redis automatically updates cached data when the database changes.

C The database update failed silently, so cache was correct.

D The application did not invalidate or update the Redis cache after the database update.

💡 Hint

Consider the responsibilities of the application in cache-aside pattern after database writes.

In cache-aside, the application must explicitly update or invalidate cache after database changes. Redis does not sync automatically.