AsyncWriteJournal

Plugin API: asynchronously deletes all persistent messages up to toSequenceNr (inclusive).

This call is protected with a circuit-breaker. Message deletion doesn't affect the highest sequence number of messages, journal must maintain the highest sequence number and never decrease it.

Plugin API: asynchronously reads the highest stored sequence number for the given persistenceId. The persistent actor will use the highest sequence number after recovery as the starting point when persisting new events. This sequence number is also used as toSequenceNr in subsequent call to #asyncReplayMessages unless the user has specified a lower toSequenceNr. Journal must maintain the highest sequence number and never decrease it.

This call is protected with a circuit-breaker.

Please also note that requests for the highest sequence number may be made concurrently to writes executing for the same persistenceId, in particular it is possible that a restarting actor tries to recover before its outstanding writes have completed.

Plugin API: asynchronously replays persistent messages. Implementations replay a message by calling replayCallback. The returned future must be completed when all messages (matching the sequence number bounds) have been replayed. The future must be completed with a failure if any of the persistent messages could not be replayed.

The replayCallback must also be called with messages that have been marked as deleted. In this case a replayed message's deleted method must return true.

The toSequenceNr is the lowest of what was returned by #asyncReadHighestSequenceNr and what the user specified as recovery akka.persistence.Recovery parameter. This does imply that this call is always preceded by reading the highest sequence number for the given persistenceId.

This call is NOT protected with a circuit-breaker because it may take long time to replay all events. The plugin implementation itself must protect against an unresponsive backend store and make sure that the returned Future is completed with success or failure within reasonable time. It is not allowed to ignore completing the future.

Plugin API: asynchronously writes a batch (Seq) of persistent messages to the journal.

The batch is only for performance reasons, i.e. all messages don't have to be written atomically. Higher throughput can typically be achieved by using batch inserts of many records compared to inserting records one-by-one, but this aspect depends on the underlying data store and a journal implementation can implement it as efficient as possible. Journals should aim to persist events in-order for a given persistenceId as otherwise in case of a failure, the persistent state may be end up being inconsistent.

Each AtomicWrite message contains the single PersistentRepr that corresponds to the event that was passed to the persist method of the PersistentActor, or it contains several PersistentRepr that corresponds to the events that were passed to the persistAll method of the PersistentActor. All PersistentRepr of the AtomicWrite must be written to the data store atomically, i.e. all or none must be stored. If the journal (data store) cannot support atomic writes of multiple events it should reject such writes with a Try Failure with an UnsupportedOperationException describing the issue. This limitation should also be documented by the journal plugin.

If there are failures when storing any of the messages in the batch the returned Future must be completed with failure. The Future must only be completed with success when all messages in the batch have been confirmed to be stored successfully, i.e. they will be readable, and visible, in a subsequent replay. If there is uncertainty about if the messages were stored or not the Future must be completed with failure.

Data store connection problems must be signaled by completing the Future with failure.

The journal can also signal that it rejects individual messages (AtomicWrite) by the returned immutable.Seq[Try[Unit]]. It is possible but not mandatory to reduce number of allocations by returning Future.successful(Nil) for the happy path, i.e. when no messages are rejected. Otherwise the returned Seq must have as many elements as the input messages Seq. Each Try element signals if the corresponding AtomicWrite is rejected or not, with an exception describing the problem. Rejecting a message means it was not stored, i.e. it must not be included in a later replay. Rejecting a message is typically done before attempting to store it, e.g. because of serialization error.

Data store connection problems must not be signaled as rejections.

It is possible but not mandatory to reduce number of allocations by returning Future.successful(Nil) for the happy path, i.e. when no messages are rejected.

Calls to this method are serialized by the enclosing journal actor. If you spawn work in asynchronous tasks it is alright that they complete the futures in any order, but the actual writes for a specific persistenceId should be serialized to avoid issues such as events of a later write are visible to consumers (query side, or replay) before the events of an earlier write are visible. A PersistentActor will not send a new WriteMessages request before the previous one has been completed.

Please note that the sender field of the contained PersistentRepr objects has been nulled out (i.e. set to ActorRef.noSender) in order to not use space in the journal for a sender reference that will likely be obsolete during replay.

Please also note that requests for the highest sequence number may be made concurrently to this call executing for the same persistenceId, in particular it is possible that a restarting actor tries to recover before its outstanding writes have completed. In the latter case it is highly desirable to defer reading the highest sequence number until all outstanding writes have completed, otherwise the PersistentActor may reuse sequence numbers.

This call is protected with a circuit-breaker.

Plugin API

Allows plugin implementers to use f pipeTo self and handle additional messages for implementing advanced features