Pessimistic Deadlocks with Optimistic Locking in Hibernate

This is a small example project to show that deadlock from pessimistic locks occur, when using optimistic locking (@Version) with Hibernate in parallel sessions.

Reproduce

• make sure you have git, Java 17 and Maven installed and execute

git clone https://github.com/ccschneidr/hibernate-deadlock-example.git
cd hibernate-deadlock-example
mvn test

The test will print an error about a deadlock in 99% of the cases:

Deadlock detected. The current transaction was rolled back. Details: "APPLICATION_USER"; SQL statement:
...

Please note, the test will still run successfully, because there is no check about successfully writing to the database.