Out of Box - Idempotent Event Handling

Imported from Google Groups
1

Hello,

I wanted to know if Axon provides idempotent event handling (out of box), or this is up to the user to customize based on application requirement.

2

If you have a tracking processor, and the token store and event handler both work within the scope of the same transaction, yes, Axon will provide “idempotency”. Otherwise, it is something that involves both event handler and event design, and is something only the application is able to take care of.

Cheers,

Allard

3

Hello Allard,

That is a good news, I have used tracking processors before while using Axon 3.X and they work really great for event replay.

  1. Are tracking processors supported in Axon 2.4.X, If yes, then can the implementation handle idempontency and out of order events.
  2. Can you elaborate more on what you mean by “the token store and event handler both work within the scope of the same transaction” Does this need some customization. I thought it is by default the same transaction.
4

Hi,

no, Axon 2 does not support tracking processors. They were introduced in Axon 3.

By “the token store and event handler both work within the scope of the same transaction”, I basically mean that they should be stored in the same database, so that a single commit would commit both the changes to the token, as well as any changes made in the projections.

Cheers,

Allard