EventSourcingArchitekturen

Event sourcing is a software architectural pattern in which all changes to an application’s state are stored as a sequence of domain events. Instead of persisting the final state, an event store records each event in an append-only log. Events are immutable facts about what happened, such as OrderPlaced or ItemShipped. The current state is reconstructed by replaying the stored events from an initial state, optionally applying snapshots to optimize performance.

Key concepts include aggregates that enforce business invariants, domain events that capture state changes, and projects or read models that provide queryable views. Commands represent intent to change state and are validated against the current state before emitting one or more events. The architecture often uses a separate read model that is updated by event handlers or projections to support queries, which is related to the CQRS pattern.

Benefits include full auditability and traceability, the ability to reconstruct past states, time-based queries, and improved scalability for write workloads by decoupling write and read paths. It also supports complex domain logic and temporal analyses.

Drawbacks include added complexity, eventual consistency between event stores and read models, and the need for careful schema evolution and migration of historical events. It is most beneficial in domains with rich business history, regulated auditing, or where the ability to replay events is important; otherwise, simpler persistence models may be preferred.