Event sourcing overview
Orleans Event Sourcing uses JournaledGrain<T, U> from the supported Microsoft.Orleans.EventSourcing package. A journaled grain represents changes as events and derives its state by applying those events in order.
JournaledGrain<T, U> separates:
- State, the aggregate view used to answer requests.
- Events, the immutable changes submitted by the grain.
- Log consistency, the protocol that orders, confirms, persists, and refreshes events.
- Storage, selected by the configured log-consistency provider.
The built-in providers support snapshot storage, a complete event sequence stored as one record, and application-defined storage. Their scalability and retrieval capabilities differ, so select a provider based on the provider comparison.
Consistency model
Section titled “Consistency model”The confirmed Version is the number of confirmed events. A confirmed state at a given version is derived from one ordered event sequence. Locally raised events can also contribute to TentativeState before confirmation.
Log-consistency providers use optimistic concurrency and protocol notifications to coordinate instances that can exist in advanced deployment topologies. This isn’t automatic geographic replication: Orleans doesn’t provision replicated storage, deploy multiple clusters, route users between regions, or define disaster-recovery policy. Any multi-cluster design must separately provide shared/reachable storage and Orleans multi-cluster connectivity, and must be validated for the selected provider.
Articles
Section titled “Articles”- JournaledGrain basics
- Replicated instances and conflicts
- Immediate and delayed confirmation
- Notifications
- Event sourcing configuration
- Log-consistency providers
- JournaledGrain diagnostics
Event Sourcing and experimental Journaling
Section titled “Event Sourcing and experimental Journaling”Microsoft.Orleans.EventSourcing and Microsoft.Orleans.Journaling are separate packages and programming models.
- Event Sourcing uses
JournaledGrain<TState, TEvent>and log-consistency providers. - Journaling uses DurableGrain, journaled state, and durable collections.
Microsoft.Orleans.Journaling is an alpha package whose APIs are marked experimental with diagnostic ORLEANSEXP005. It isn’t a replacement for Event Sourcing. Evaluate it as an experimental feature and expect API or storage-format changes.