CQRS (Command Query Responsibility Segregation) in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the core principle of CQRS

Which statement best describes the main idea behind CQRS?

A Combining command and query operations into one service to reduce latency.

B Using a single database for both reading and writing to simplify data management.

C Separating the system into two parts: one for handling commands (writes) and another for handling queries (reads).

D Storing all data in a cache to speed up both reads and writes.

💡 Hint

Think about how CQRS splits responsibilities to improve scalability and clarity.

CQRS divides the system into separate parts for commands and queries to optimize each independently.

❓ Architecture

intermediate

Identifying components in a CQRS architecture

In a typical CQRS system, which component is responsible for updating the data store after receiving a command?

A Command Handler

B Event Publisher

C Read Repository

D Query Model

💡 Hint

Consider which part processes write requests and changes the data.

The Command Handler processes commands and updates the write data store accordingly.

❓ scaling

advanced

Scaling reads and writes in CQRS

Which approach best explains how CQRS helps scale read and write workloads independently?

A By using separate databases for reads and writes, allowing each to be optimized and scaled based on its workload.

B By merging read and write operations into a single database to reduce complexity.

C By caching all writes and delaying reads to reduce load on the database.

D By replicating the write database multiple times without separating reads.

💡 Hint

Think about how separating responsibilities affects scaling.

CQRS uses separate data stores for commands and queries, so each can be scaled independently to handle different loads.

❓ tradeoff

advanced

Tradeoffs of using CQRS

What is a common tradeoff when implementing CQRS in a system?

A Elimination of the need for event-driven communication.

B Reduced performance because reads and writes are combined into one model.

C Simplified data management by using a single database for all operations.

D Increased complexity due to managing separate models and eventual consistency challenges.

💡 Hint

Consider what extra work CQRS introduces beyond simple CRUD.

CQRS adds complexity by requiring separate models and handling synchronization between them, often leading to eventual consistency.

❓ estimation

expert

Estimating capacity for a CQRS system

A CQRS system handles 10,000 write commands per second and 100,000 read queries per second. If the write database can handle 15,000 writes per second and the read database can handle 120,000 reads per second, what is the maximum sustainable throughput for the system?

A 15,000 writes and 120,000 reads per second

B 10,000 writes and 100,000 reads per second

C 10,000 writes and 120,000 reads per second

D 15,000 writes and 100,000 reads per second

💡 Hint

The system throughput is limited by the component with the lowest capacity for each operation.

The maximum sustainable throughput is limited by the actual workload: 10,000 writes and 100,000 reads per second.