Module 5 - Architecture Patterns

CQRS Pattern

Separate read and write operations for scalability and optimization.

1The Library Analogy

Simple Analogy
A library has one desk for returning books (writes) and another for checking out (reads). Each desk is optimized for its specific task. You wouldn't return a book at the checkout counter-that's CQRS.

CQRS (Command Query Responsibility Segregation) separates read and write operations into different models. Commands modify state. Queries read state.

2Traditional vs CQRS

Traditional (CRUD)

  • • Same model for reads and writes
  • • Same database for both
  • • Simple but limited optimization

CQRS

  • • Separate read and write models
  • • Can use different databases
  • • Optimize each independently

3Benefits

Independent Scaling

Scale read and write sides separately based on load.

Optimized Models

Read model can be denormalized. Write model stays normalized.

Different Tech Stacks

SQL for writes, Elasticsearch for reads.

Security

Different auth rules for commands vs queries.

4When to Use

Good Fit

  • ✓Read-heavy applications
  • ✓Complex domain logic
  • ✓Different read/write patterns
  • ✓High scalability needs

Avoid When

  • ✗Simple CRUD apps
  • ✗Small team
  • ✗No clear read/write imbalance
  • ✗Tight consistency required

5Key Takeaways

1CQRS separates read (Query) and write (Command) operations
2Each side can have different models, databases, scaling
3Read side often denormalized for fast queries
4Adds complexity-eventual consistency between sides
5Often paired with Event Sourcing

?Quiz

1. E-commerce with 95% reads, 5% writes. CQRS benefit?

2. CQRS adds what challenge?