Rating and review system in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

Design components for a scalable rating and review system

Which of the following component sets best supports a scalable rating and review system that handles millions of users submitting reviews and ratings concurrently?

A Single web server, relational database, no caching, direct database writes

B Load balancer, API servers, relational database, caching layer, message queue, search engine

C Load balancer, API servers, flat file storage, no caching, no message queue

D Single web server, NoSQL database, no caching, no message queue

💡 Hint

Think about components that help with high traffic, fast reads, and asynchronous processing.

Option B includes load balancing for traffic distribution, caching for fast reads, message queue for asynchronous processing, and a search engine for efficient review search. This combination supports scalability and performance.

❓ scaling

intermediate

Handling sudden spikes in review submissions

During a product launch, the system experiences a sudden spike in review submissions. Which approach best helps maintain system stability?

A Reject all new review submissions until the spike ends

B Directly write all reviews synchronously to the database without any queueing

C Use a message queue to buffer incoming reviews and process them asynchronously

D Store reviews only in cache without persisting to the database

💡 Hint

Think about how to handle bursts without overwhelming the database.

Using a message queue buffers incoming requests and allows the system to process reviews at a manageable rate, preventing database overload and improving stability.

❓ tradeoff

advanced

Choosing database type for storing reviews and ratings

Which database choice best balances consistency, scalability, and query flexibility for a rating and review system?

A Relational database with strong consistency and support for complex queries

B NoSQL document store with eventual consistency and flexible schema

C In-memory key-value store without persistence

D Flat file storage on a single server

💡 Hint

Consider the need for accurate ratings and complex queries like filtering and sorting reviews.

Relational databases provide strong consistency and support complex queries needed for filtering, sorting, and aggregating reviews and ratings, which is critical for accuracy and user experience.

🧠 Conceptual

advanced

Ensuring data integrity in concurrent review submissions

What mechanism best prevents race conditions when multiple users submit or update reviews for the same product simultaneously?

A Use optimistic concurrency control with version numbers or timestamps

B Lock the entire database during every review submission

C Allow all writes without any concurrency control and overwrite data

D Store reviews only in cache without synchronization

💡 Hint

Think about a method that detects conflicts without blocking all users.

Optimistic concurrency control allows multiple users to work concurrently and detects conflicts by checking version numbers or timestamps before committing changes, preventing lost updates.

❓ estimation

expert

Estimating storage needs for a rating and review system

Estimate the approximate storage needed per year if the system expects 10 million new reviews annually, each review averaging 1 KB, and ratings stored separately averaging 100 bytes each. Assume each review has one rating.

A Approximately 100 MB per year

B Approximately 1.1 TB per year

C Approximately 110 GB per year

D Approximately 11 GB per year

💡 Hint

Calculate total size by adding review and rating sizes multiplied by number of reviews.

Each review is 1 KB and each rating is 0.1 KB (100 bytes). Total per review+rating = 1.1 KB. For 10 million reviews: 10,000,000 * 1.1 KB = 11,000,000 KB = ~11 GB.