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

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does the cache-aside pattern handle cache misses?

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

A The system duplicates the request to multiple caches to find the data.

B The system fetches data from the database, stores it in the cache, then returns it to the requester.

C The system waits for the cache to update automatically before responding.

D The system immediately returns an error to the requester without fetching data.

💡 Hint

Think about what happens when the cache does not have the data and how the system ensures data availability.

In the cache-aside pattern, when data is missing in the cache, the system loads it from the database, updates the cache, and then returns the data. This ensures the cache stays updated and data is available.

❓ Architecture

intermediate

Identify the correct sequence in cache-aside pattern request flow

Which sequence correctly describes the steps when a client requests data using the cache-aside pattern?

A 1,2,3,4

B 1,4,3,2

C 1,3,2,4

D 1,3,4,2

💡 Hint

Remember the cache check happens first, then data fetch if missing, then cache update, then return.

The correct flow is: check cache, if miss fetch from database, store in cache, then return data.

❓ scaling

advanced

Scaling challenges with cache-aside pattern in high traffic systems

What is a common scaling challenge when using the cache-aside pattern under heavy load?

A Cache stampede where many requests simultaneously miss cache and hit the database.

B Cache automatically updates too frequently causing stale data.

C Database rejects all requests due to cache saturation.

D Cache never expires data leading to outdated responses.

💡 Hint

Consider what happens when many users request the same uncached data at once.

Cache stampede happens when many requests miss the cache simultaneously, causing a flood of database queries that can overwhelm the system.

❓ tradeoff

advanced

Tradeoff of cache consistency in cache-aside pattern

What is a key tradeoff of using the cache-aside pattern regarding data consistency?

A Data in cache may be stale because updates to the database do not automatically update the cache.

B Cache always has the latest data because it updates before the database.

C Cache and database are always perfectly synchronized with no delay.

D Cache automatically deletes data when the database changes.

💡 Hint

Think about how cache updates happen in cache-aside pattern after database changes.

Cache-aside pattern does not automatically update cache on database writes, so cache can serve stale data until updated.

❓ estimation

expert

Estimating cache hit ratio impact on database load in cache-aside pattern

Assume a system using cache-aside pattern has 1 million requests per hour. The cache hit ratio is 80%. How many requests per hour hit the database?

A 1,000,000 requests per hour

B 800,000 requests per hour

C 200,000 requests per hour

D 100,000 requests per hour

💡 Hint

Calculate the percentage of requests that miss the cache and must query the database.

With 80% cache hits, 20% miss and hit the database. 20% of 1,000,000 is 200,000.