Solving the Fan-Out Query Problem in Microservices Architecture using CQRS

A fan-out query occurs when a query lacks a partition key and must hit every physical partition. Solve this via CQRS and Materialized Views.

When a microservice needs to query data across multiple dimensions (e.g., searching by Email, then by Phone, then by AccountNum), using a single container partitioned by 'Id' causes 'Fan-out' queries. These are highly inefficient as they consume RUs from every partition. The solution is CQRS (Command Query Responsibility Segregation). The 'Write' model stays in the primary container. The Change Feed projects data into 'Read' containers, each partitioned by the secondary search keys (Email, Phone, etc.).