CQRS — Command Query Responsibility Segregation

Sources: Greg Young (2010); Martin Fowler — bliki/CQRS; Vaughn Vernon — Implementing DDD (2013)

Pain Signals — You Are in This Branch When:

• Read queries are slow because the domain model's shape is optimised for writes, not reads
• Complex reporting requires loading and traversing large object graphs just to flatten them for display
• Read and write load profiles are very different and need to scale independently
• The domain model is rich and correct for writes but awkward to query from
• Event sourcing is in use and projections are needed for efficient reads

Before applying CQRS, confirm the pain exists. Fowler's warning: "CQRS is a significant mental leap for all concerned, so shouldn't be tackled unless the benefit is worth that leap."

Core Principle