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WriteMessagesAsync ( IEnumerable messages ) : Task> |
Plugin API: asynchronously writes a batch 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 Persistent that corresponds to the event that was passed to the PersistentActor.Persist{TEvent}(TEvent,Action{TEvent}) method of the PersistentActor, or it contains several Persistent that correspond to the events that were passed to the PersistentActor.PersistAll{TEvent}(IEnumerable{TEvent},Action{TEvent}) method of the PersistentActor. All Persistent 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 NotSupportedException 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 Task must be completed with failure. The Task 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 Task must be completed with failure. Data store connection problems must be signaled by completing the Task with failure. The journal can also signal that it rejects individual messages (AtomicWrite) by the returned Task. It is possible but not mandatory to reduce number of allocations by returning null for the happy path, i.e. when no messages are rejected. Otherwise the returned list must have as many elements as the input messages. Each result 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 null 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 asyncronous 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 not that the IPersistentRepresentation.Sender of the contained Persistent objects has been nulled out (i.e. set to ActorRefs.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. |
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