Package org.apache.pekko.persistence

Interface AtLeastOnceDelivery

All Superinterfaces:
Actor, AtLeastOnceDeliveryLike, Eventsourced, PersistenceIdentity, PersistenceRecovery, PersistenceStash, PersistentActor, RequiresMessageQueue<DequeBasedMessageQueueSemantics>, Snapshotter, Stash, StashFactory, StashSupport, UnrestrictedStash
public interface AtLeastOnceDelivery extends PersistentActor, AtLeastOnceDeliveryLike
Scala API: Mix-in this trait with your PersistentActor to send messages with at-least-once delivery semantics to destinations. It takes care of re-sending messages when they have not been confirmed within a configurable timeout. Use the AtLeastOnceDeliveryLike#deliver method to send a message to a destination. Call the AtLeastOnceDeliveryLike.confirmDelivery(long) method when the destination has replied with a confirmation message.

At-least-once delivery implies that original message send order is not always retained and the destination may receive duplicate messages due to possible resends.

The interval between redelivery attempts can be defined by AtLeastOnceDeliveryLike.redeliverInterval(). After a number of delivery attempts a AtLeastOnceDelivery.UnconfirmedWarning message will be sent to self. The re-sending will still continue, but you can choose to call AtLeastOnceDeliveryLike.confirmDelivery(long) to cancel the re-sending.

The AtLeastOnceDelivery trait has a state consisting of unconfirmed messages and a sequence number. It does not store this state itself. You must persist events corresponding to the deliver and confirmDelivery invocations from your PersistentActor so that the state can be restored by calling the same methods during the recovery phase of the PersistentActor. Sometimes these events can be derived from other business level events, and sometimes you must create separate events. During recovery calls to deliver will not send out the message, but it will be sent later if no matching confirmDelivery was performed.

Support for snapshots is provided by AtLeastOnceDeliveryLike.getDeliverySnapshot() and AtLeastOnceDeliveryLike.setDeliverySnapshot(org.apache.pekko.persistence.AtLeastOnceDelivery.AtLeastOnceDeliverySnapshot). The AtLeastOnceDeliverySnapshot contains the full delivery state, including unconfirmed messages. If you need a custom snapshot for other parts of the actor state you must also include the AtLeastOnceDeliverySnapshot. It is serialized using protobuf with the ordinary Akka serialization mechanism. It is easiest to include the bytes of the AtLeastOnceDeliverySnapshot as a blob in your custom snapshot.

See Also:

  • Method Details

    • deliver

      void deliver(ActorPath destination, scala.Function1<Object,Object> deliveryIdToMessage)
      Scala API: Send the message created by the deliveryIdToMessage function to the destination actor. It will retry sending the message until the delivery is confirmed with AtLeastOnceDeliveryLike.confirmDelivery(long). Correlation between deliver and confirmDelivery is performed with the deliveryId that is provided as parameter to the deliveryIdToMessage function. The deliveryId is typically passed in the message to the destination, which replies with a message containing the same deliveryId.

      The deliveryId is a strictly monotonically increasing sequence number without gaps. The same sequence is used for all destinations of the actor, i.e. when sending to multiple destinations the destinations will see gaps in the sequence if no translation is performed.

      During recovery this method will not send out the message, but it will be sent later if no matching confirmDelivery was performed.

      This method will throw AtLeastOnceDelivery.MaxUnconfirmedMessagesExceededException if AtLeastOnceDeliveryLike.numberOfUnconfirmed() is greater than or equal to AtLeastOnceDeliveryLike.maxUnconfirmedMessages().

    • deliver

      void deliver(ActorSelection destination, scala.Function1<Object,Object> deliveryIdToMessage)
      Scala API: Send the message created by the deliveryIdToMessage function to the destination actor. It will retry sending the message until the delivery is confirmed with AtLeastOnceDeliveryLike.confirmDelivery(long). Correlation between deliver and confirmDelivery is performed with the deliveryId that is provided as parameter to the deliveryIdToMessage function. The deliveryId is typically passed in the message to the destination, which replies with a message containing the same deliveryId.

      The deliveryId is a strictly monotonically increasing sequence number without gaps. The same sequence is used for all destinations of the actor, i.e. when sending to multiple destinations the destinations will see gaps in the sequence if no translation is performed.

      During recovery this method will not send out the message, but it will be sent later if no matching confirmDelivery was performed.

      This method will throw AtLeastOnceDelivery.MaxUnconfirmedMessagesExceededException if AtLeastOnceDeliveryLike.numberOfUnconfirmed() is greater than or equal to AtLeastOnceDeliveryLike.maxUnconfirmedMessages().