Can Axon 2 and Axon 3 run side by side using the same event sourcing database? We would like to start building new axon 3 components and migrate existing axon 2 components over time.
Regards,
Joe
Hi Joey,
Should be pretty easy to check whether axon 3 ES is backwards compatible with Axon 2.
For the SQL based ES in Axon 3: There is a new globalIndex column in table DomainEventEntry but I think it is defined as IDENTITY.
Don't know about the other implementations though.
Benoit
Hi Joey,
the only change is the new “globalIndex” column, which is an autoincrement primary key. If you don’t use the same aggregate identifiers for different aggregates, then you should be able to use both versions simultaneously. Note that things haven’t been designed to do that, nor has it been tested. So your mileage may vary 
Cheers,
Allard
Hi Allard,
What is the purpose of that globalIndex?
Regards,
Benoît
We have been advised that numeric primary keys perform better than combined textual ones. It makes the indices considerably smaller, making more of it fit in memory.
Secondly, the TrackingEventProcessor uses the globalIndex to track its progress in the event store.
Cheers,
Allard