Under what conditions can the use of the @Transactional annotation be ineffective or not work properly?

The @Transactional annotation in Java (for example, in the Spring Framework) can be ineffective or not work properly in the following cases:

1. Calling a method with @Transactional within the same class — if the annotated method is called directly from another method of the same class, Spring's proxy does not intercept the call, and the transaction does not start.

2. Using @Transactional on private methods — proxies cannot wrap private methods, so the annotation will not work.

3. Lack of proxy support — if Spring configuration is not set up to create proxies (for example, aspect support is disabled), the annotation will not work.

4. Exceptions that do not lead to rollback — by default, transactions rollback only on unchecked exceptions (RuntimeException and Error). If a checked exception is thrown, rollback will not occur unless explicitly specified.

5. Using @Transactional on methods not called from the Spring context — for example, if an object is created manually via new rather than through Spring, the annotation will not work.

To avoid problems, you should:

• Call transactional methods through Spring beans
• Use public methods
• Configure rollback for exceptions if necessary

Example of incorrect usage:

@Service
public class MyService {
    @Transactional
    public void transactionalMethod() {
        // ...
    }

    public void caller() {
        transactionalMethod(); // Transaction will not start if called within the same class
    }
}