Concurrent Reactive Transactions

[Ealrann]

Hello,
I'd like to be sure how to properly use the sessions/transactions of Quarkus Reactive.

I mainly do this type of process, in a Uni<> when a user call an endpoint:

1. Read the DB => 2. Check/Do something => 3. Write on DB the new status

More precisely, as an example:

1. Check a server status on DB => 2. Verify if need to change its status and operate => 3. Write the new status on DB
   During step 2, I suppose the status of the server cannot change (since there's only one I/O thread).

But as stated by the Quarkus documentation, if I do some blocking operation during a reactive transaction (like reading some files, fetching data on another endpoint...), my Uni could be paused (run in worker thread), and another process could run in the I/O thread.
This situation is dangerous for my usecase because 2 different transactions could operate on the same server with a false assumption on its status.

Do I understand properly?
How should I properly manage this use case?
Thanks