Intermediate LevelSystem Design & Architecture
What is Event Sourcing and how does it pair with CQRS?
❓ Interview Prompt: Explain Event Sourcing, append-only event logs, CQRS (Command Query Responsibility Segregation), projections, and temporal state replay.
Event Sourcing and CQRS are architectural patterns that decouple write and read data operations:
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Event Sourcing: Stores state mutations as an append-only sequence of immutable events ('OrderCreated', 'PaymentReceived', 'OrderShipped'). Current state is derived by replaying events.
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CQRS: Separates the write model (Commands) from read models (Queries). Event projections update optimized read stores (Elasticsearch/Redis) asynchronously.
Code Implementation Example
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CQRS + Event Sourcing Architecture:
[Write Command] ──> [Command Service] ──> (Event Store: Append Event)
│
(Async Event Projection)
│
▼
[Read Query] <── [Query Service] <── [Read DB (Redis / Elastic)]💡CQRS and Event Sourcing architecture pipeline.
🎯 Interview Key Takeaway
Pair Event Sourcing with CQRS to maintain complete auditability and optimize read and write models independently.
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