Implementing CQRS and Resilient Persistence

Analyze the Command Query Responsibility Segregation (CQRS) pattern, explaining when its complexity is justified.

Design separate write (command) and read (query) models for the financial scenario modeled in the previous module.

Implement a projection that consumes an event stream to build and maintain a denormalized read model.

Address eventual consistency between write and read models, including strategies for communicating data staleness to clients.

Define the API contract for a generic event store service, including methods for appending events and retrieving event streams.

Implement optimistic concurrency control in an event store service by using aggregate version numbers to detect write conflicts.

Compare the trade-offs between different persistence technologies for implementing an event store (e.g., relational DB, document DB, specialized event store).