A very simple Spring Boot application with a couple of tests to show the Lost Update anomaly and the possibilities to handle it with Optimistic Locking in JPA and Hibernate.
The application was written as a showcase for the following article: https://blog.arnoldgalovics.com/optimistic-locking-in-jpa-hibernate/
The test shows the lost update anomaly. Two concurrent transactions are updating the very same entity and the update made earlier is overwritten by the latter one.
The test contains 4 different use-cases
- Optimistic locking with versioning
- Optimistic locking with versioning when non-overlapping changes were made to the entity
- Versionless optimistic locking
- Versionless optimistic locking when non-overlapping changes were made to the entity
The test shows how an exclusive lock can be acquired with H2 and also demonstrates that H2 doesn't support shared locks thus Hibernate is falling back to requesting an exclusive lock even in case of an exclusive request.
The test shows off the following use-cases with an embedded PostgreSQL database
- Shared locks are supported via the
FOR SHAREclause - Multiple readers can acquire shared lock to the same row
- One shared lock is already applied and then an exclusive lock tries to be acquired to the same row
- Locking a row after fetching the entity
- Locking the result of a query