The traditional CRUD (Create, Read, Update, Delete) pattern has been a mainstay in system architectures for many years. In CRUD, reading and writing operations are usually handled by the same data model and often by the same database schema. While this approach is straightforward and intuitive, it becomes less effective as systems scale and as requirements become more complex.
For instance, consider a large-scale e-commerce application with millions of users. This system may face conflicting demands: it needs to quickly read product details, reviews, and user profiles, but it also has to handle thousands of transactions, inventory updates, and order placements efficiently. As both reading and writing operations grow, using a single model for both can lead to bottlenecks, impacting performance and user experience.
CQRS was introduced to address these scaling challenges. The essence of the pattern lies in its name — Command Query Responsibility Segregation. Here, Commands are responsible for any change in the system’s state (like placing an order or updating a user profile), while Queries handle data retrieval without any side effects.