Why apps split 'changing data' and 'reading data' into two completely separate lanes

Sat, 29 Aug 2026 00:14:56 +0900

🤔 What Is It?

CQRS(Command Query Responsibility Segregation)

CQRS is a rule for building apps that says: the part of the app that changes data (like posting a comment) must be completely separate from the part that reads data (like scrolling through comments). Keeping them apart means each side can be made super-fast at its one job.

🧩 Like a school library with two separate desks

Imagine your school library has two completely different desks on opposite sides of the room. At the REQUEST DESK you hand the librarian a slip saying ‘I’d like to borrow Harry Potter’ — the librarian fetches the book, stamps it, and updates the big official record book. That desk’s only job is to change things. On the other side is the SEARCH COMPUTER — you type in any title and it instantly shows you what’s available, who wrote it, how many pages it has. The search computer never stamps anything or moves a single book; its only job is to read and display. The search computer even has its own simplified copy of the information it needs, so it never has to wait around while the librarian is busy stamping books. These two desks are completely independent — and that’s exactly what CQRS does inside an app.

Backend on Explain It

Why apps split 'changing data' and 'reading data' into two completely separate lanes

🤔 What Is It?

🧩 Like a school library with two separate desks