CQRS (Command Query Responsibility Segregation)

Most services use the same model for reads and writes. That works until the two need different optimizations.

Writes need correctness, constraints, and transactional safety. Reads need speed, denormalized views, search indexes, and caches.

CQRS separates them: commands change state through a write model, while queries read from a model optimized for access patterns.

This chapter covers simple and advanced CQRS, separate read and write stores, syncing the read side, handling lag, and when CQRS is worth the added complexity.