PHP Event Sourcing Snapshoting

In general having streams in need for snapshots may indicate that our model needs revisiting. We may cut the stream on some specific event and begin new one, like at the end of month from all the transactions we generate invoice and we start new stream for next month. However if cutting the stream off is not an option for any reason, we snapshot aggregate state at given point of time, so we can skip previous events. This process continues on predefined threshold, like every 1000 events.

Setting up

EventSourcingConfiguration provides the following interface to set up snapshots.

use Ecotone\Messaging\Store\Document\DocumentStore;

class EventSourcingConfiguration

    public function withSnapshotsFor(
        string $aggregateClassToSnapshot, // 1.
        int $thresholdTrigger = self::DEFAULT_SNAPSHOT_TRIGGER_THRESHOLD, // 2.
        string $documentStore = DocumentStore::class // 3.
    ): static
  1. $aggregateClassToSnapshot - class name of an aggregate you want Ecotone to save snapshots of

  2. $thresholdTrigger - amount of events for interval of taking a snapshot

  3. $documentStore - reference to document store which will be used for saving/retrieving snapshots

To set up snapshots we will define ServiceContext configuration.

public function aggregateSnapshots()
    return EventSourcingConfiguration::createWithDefaults()
            ->withSnapshotsFor(Ticket::class, 1000)
            ->withSnapshotsFor(Basket::class, 500, MyDocumentStore::class)

Ecotone make use of Document Store to store snapshots, by default it's enabled with event-sourcing package. If you want to clean the snapshots, you can do it manually. Snapshots are stored in aggregate_snapshots collection.

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