Saga warranties - assynchonous

Imported from Google Groups
#1

Consider the following use case:

My system must upload files. The uploading is started by an event on the eventbus (i.e. NewFileEvent), and should be performed assynchronously.
So i have a Saga has a #SagaEventHandler and @StartSaga on handle(NewFileEvent event).
Suppose my SagaManager is configured with a thread pool with 2 workers, and a JdbcSagaRepository.
While those two workers are busy (so there are 2 active Sagas), a third “NewFileEvent” is fired.
At this point, the application is stopped (before the 2 original workers were fininished uploading). Will the third saga be persisted by axon? Under which condition?

#2

Hi,

if you process asynchronously, it all depends on the queue implementation that you use. If the queue is in-memory, you will lose data when you abruptly shutdown the application. When doing a clean shutdown, new events are blocked from being accepted, but Axon will attempt to finish processing of whatever is left in the queue.

If you’re on Axon 3, consider using a TrackingEventProcessor for asynchronous processing instead. It has better mechanisms to track progress and can guarantee it continues processing where it left off.

Cheers,

Allard

#3

Hi,
I’am on Axon 2. I was using the AsyncSagaManager with its threadpool as a queue for queing Saga’s, but the ThreadPool is (of course) not persistent, so I must implement a simple ‘databased’ queue to ensure persistence.

#4

Or dispatch your events on a message broker, such as RabbitMQ. That will also give you the persistence you need.