CQRS Architecture
CQRS (Command Query Responsibility Segregation) is an architectural pattern that separates read and write operations into distinct models. This separation allows for greater scalability, flexibility, and optimisation in complex systems, particularly those requiring high performance, event sourcing, or domain-driven design.
Core Concepts of CQRS
1. Command Model (Write Side)
- Handles all changes to the system state.
- Ensures business rules are enforced before persisting data.
- Often works alongside event sourcing, storing events instead of just the final state.
2. Query Model (Read Side)
- Optimised for retrieving data efficiently.
- Can use different storage solutions (e.g., NoSQL for fast reads, SQL for complex queries).
- May be asynchronously updated via event-driven mechanisms.
Key Benefits
- Performance & Scalability: Independent scaling of read and write operations, allowing optimisations specific to each use case.
- Flexibility in Data Models: Read models can be tailored for query efficiency, while write models focus on consistency and business logic.
- Event Sourcing Synergy: By capturing all state changes as events, historical analysis and auditing become significantly easier.
- Improved Security & Fault Isolation: Reduces the risk of unintentional read/write conflicts by enforcing explicit separation.
Trade-offs & Considerations
- Increased Complexity: Requires additional infrastructure, such as event buses or messaging queues.
- Eventual Consistency: Read models may lag behind writes in distributed systems.
- Development Overhead: Requires careful design to manage synchronisation and event handling.
When to Use CQRS
- High-read, high-write workloads needing independent scaling.
- Complex domains where business rules must be strictly enforced before data is written.
- Systems requiring an immutable audit log (e.g., financial transactions, healthcare records).
- Microservices architectures that benefit from loosely coupled components.
While CQRS is not necessary for all applications, it can provide significant advantages in scenarios where scalability, performance, and consistency must be balanced carefully.