CQRS (Command Query Responsibility Segregation)

Separate read and write responsibilities to improve performance, scalability, and maintainability of your applications.

Why CQRS Matters

Traditional systems mix reads and writes in the same model. CQRS separates them, allowing each to scale, evolve, and be optimized independently.

“CQRS clarifies intent: writes handle commands, reads answer questions — complexity becomes manageable.”
— Viswa

Key Principles

Command: An action that changes state (write).
Query: A request to read data (read).
Separate Models: Use different models for reading and writing to optimize performance.
Event Sourcing (optional): Store state changes as a series of events for full history and auditability.

Advantages

Read operations can be scaled independently of writes.
Improves maintainability — changes to reads don’t break writes.
Supports complex domain logic and event-driven systems.
Enables eventual consistency without slowing down user-facing queries.

Challenges

Increased complexity — two models to maintain.
Eventual consistency can confuse users if updates lag.
Requires careful handling of events and errors.
Not necessary for very small, simple apps.

Use Cases

High-scale applications where read traffic far exceeds write traffic.
Financial, trading, or order-processing systems requiring auditability.
Event-driven microservices architectures.
Applications needing separate optimization for reporting vs transaction handling.