Table of Contents

Events

What it shows

Orleans.Lattice publishes metadata-only event notifications on a per-tree Orleans stream, so caches, projections, audit pipelines, and dashboards can react to mutations without polling. This sample enables publication, subscribes to a tree's event stream, performs four writes (three sets and a delete), and prints each LatticeTreeEvent as it arrives. Events carry only metadata - the operation kind, tree id, key, originating shard (when shard-scoped), saga operation id (for an atomic write) and publish timestamp - never the value bytes, so a subscriber that needs the new value issues its own GetAsync.

Run it

dotnet run --project samples/Events

Expected output

Silo starting... ready.

Subscribed to stream 'orleans.lattice.events' for tree 'catalog'.

Performing writes:
  set    sku-1
  set    sku-2
  set    sku-1 (update)
  delete sku-2

Received 4 event(s):
  Set      tree=catalog key=sku-1 shard=-
  Set      tree=catalog key=sku-2 shard=-
  Set      tree=catalog key=sku-1 shard=-
  Delete   tree=catalog key=sku-2 shard=-

When to use

  • Out-of-process, fire-and-forget reactions to tree mutations: cache invalidation, UI refreshes, dashboards, or feeding an audit projection.
  • You only need to know what changed (key + kind), not the new bytes.

When not to use

  • When you need the full value on the write path synchronously - use an IMutationObserver instead (in-process, value-carrying, but it adds latency to every write).
  • As a durable change log: events are best-effort and not persisted. A silo crash between the write and the publish loses the event; the write survives. Use a durable stream provider (EventHubs, AzureQueue) for stronger delivery.

Notes

  • Lattice never registers a stream provider for you. This sample adds AddMemoryStreams("Default") plus its PubSubStore and names the provider in EventStreamProviderName. Memory streams are at-most-once per activation; for at-least-once delivery use a durable provider.

Feature doc