Forbid/discourage connecting to a database through Hibernate using both blocking and reactive in the same transaction scope

[yrodiere]

Description

Panache 2 (#46096) will make it (much) easier to switch from different paradigms to connect to databases through Hibernate: Session vs. StatelessSession, JDBC vs. reactive, ...

That's great, and is perfectly fine if you pick a single one of these options in each transaction, but can be dodgy if you use more than one of these options in a single transaction.

Here's the current situation as far as I know:

1. When in a (JTA) transaction and using Hibernate ORM, using both a Session and StatelessSession in the same transaction is fine (I told you the opposite @FroMage: I was wrong): the JDBC connection is shared at the Agroal level, and all connection requests during a single JTA transaction yield the same connection, so the Session and StatelessSession will just share their connection, and thus the same DB transaction.
2. When using Hibernate Reactive, using both a Session and StatelessSession in the same transaction is probably not fine at all: I suspect each will leverage an independent transaction. Conflicting updates will yield transaction rollbacks, and worse: rollback in one of the transactions will not trigger a rollback in the other one, leading to inconsistency in the DB. => It's fine now, see Hibernate Reactive: allow mixing Session and StatelessSession in the same transaction #52828
3. When using both Hibernate ORM and Hibernate Reactive in the same endpoint, ORM will enroll in a JTA transaction but Reactive will not: it will use non-JTA transactions. Conflicting updates will yield transaction rollbacks, and worse: rollback in one of the transactions will not trigger a rollback in the other one, leading to inconsistency in the DB.

I think we need to address this: at the very least document limitations, and perhaps even forbid using Hibernate Reactive and Hibernate ORM in the same endpoint, or forbid having a blocking (JTA) and reactive transaction scope active at the same time.

Implementation ideas

No response

[quarkus-bot]

/cc @DavideD (hibernate-reactive), @gavinking (hibernate-reactive)

[FroMage]

I didn't know about 1. Nice.

I agree we should detect and throw when opening more than one of the following:

• ORM Session + StatelessSession
• HR Session
• HR StatelessSession

[FroMage]

Note that at the moment, we don't support HR StatelessSession in Quarkus. This is a new feature in my Panache 2 branch.