Improvements to avoid out-of-order events / lost events in sos-restful about sos

[mszarlinski]

I think events ordering and clock synchronisation in distributed systems is far harder topic than just generating timestamp on database node. For example, database can be replicated or sharded onto multiple nodes as well. There are already available solutions like vector clocks, but isn't it out of a scope of Spring Data?

[stefanocke]

I am aware that I don't achieve something like 'global ordering' by the proposed improvements. But when using the sequence number instead of timestamp and by getting the sequence number after the insert statement for the aggregate (enforced by flush), I think it is at least guaranteed that the events for one aggregate are in the right order.

[stefanocke]

By the way, we seem to agree that sos-restful has some flaws regarding event timestamps. So what is the solution you propose to make it work for 'real life'?

[stefanocke]

I changed the description and title to make clear it is not my intention to get reliable timestamps.

[mszarlinski]

We should discuss what kind of consistency guarantees you need in the first place. Spring Data is an abstraction over diverse types of storage, including NoSQL databases as well. We should decide on application characteristic first, then come up with a solution.

[stefanocke]

IMHO, sos-restful is an approach that is based on the transactional guarantees of a relational database. To be more specific: It relies on persisting the aggregate and the domain event within the same transaction. If the database does not support this, the sos-restful approach cannot be used.
For more details on this approach see also "Implementing Domain-Driven Design" by Vaughn Vernon. And there especially chapter 8, "Messaging Infrastructure Consistency".

To make clear: I am not talking about Spring Data at all (as you seem to assume in your comments). All I wrote is specific to the sos-restful example where JPA and a relational DB are used.