Pattern 05 / DATA

Event Sourcing

Use this when needing a perfect audit trail and the ability to reconstruct old states.

Pressure: Needing a perfect audit trail and the ability to reconstruct old states
Mechanism: Store facts as immutable events and derive current state by replaying or snapshotting those events
Toll: Schema evolution, replay cost, and unbounded event growth require discipline

Diagram for Event Sourcing — Architecture plate05

Executive brief

Event Sourcing fits when needing a perfect audit trail and the ability to reconstruct old states. Mechanism: store facts as immutable events and derive current state by replaying or snapshotting those events. Use it for finance, compliance, order lifecycle, healthcare audit, and state reconstruction. The toll: schema evolution, replay cost, and unbounded event growth require discipline.

Use when

Finance, compliance, order lifecycle, healthcare audit, and state reconstruction.

Example

Ordercreated → itemadded → paymentcaptured → shipped.

Review framing

Describe the pressure first, then the mechanism, then the cost. That keeps the design grounded.

Same pressure family

Data Storage Patterns

01Primary-Replica (Leader-Follower)02Sharding (Horizontal Partitioning)03Consistent Hashing 04Write-Ahead Log (WAL)06CQRS (Command Query Responsibility Segregation)