EclipseLink Performance Problem on Update to Vaadin 24 / Springboot 3

Question

I am working on an Web-Application which is in productive use for about 17 years. Currently it's using Vaadin 23 and EclipseLink 2.7.8. After the end of the support for Vaadin 23 it is necessary to update to Vaadin 24, which needs SpringBoot 3. This seems to cause a need to change the Java Persistence API from 2.1 (javax.persistence) to 3.x. (jakarta.persistence) as well.

The problem: The JUnit-Tests take about 10 Minutes to run with EclipseLink 2.7.8. Changing nothing but Eclipselink to 2.7.9 increases the runtime up to 20 Minutes. Changing to 2.7.14 increases to 30 Minutes. And with 3.0.4 the tests take 40 Minutes at least. The Application slows down accordingly.

It seems, that simple selects ("select o from YXZ o") are causing the rising of the runtime. All list dependencies (@OneToMany) are annotated as "fetch = FetchType.LAZY" explicitly, although this should be default.

As a workaround I tried to keep Eclipselink 2.7.8 with SpringBoot 3. Compilation and starting Test-Cases worked at last. The properties could been read from persistence.xml but the @Entity Classes are not recognized by the EntityManager.

Has anyone an idea how to fix this or is there a way for making the workaround to keep Eclipselink 2.7.8 working?

I made an special JUnit-Testcase to demonstrate the problem. A simple "select all" on 5 Entities / Tables:

EntityManager em =  Persistence.createEntityManagerFactory(Constants.PERSISTENCE_UNIT).createEntityManager();
String format = "%-20s: %6d %8d \n";
System.out.printf("%-20s: %6s %8s \n", "Entity", "Count", "Duration");
long start = System.currentTimeMillis();
String[] entities = {"Enity1", "Enity2", "Enity3", "Enity4", "Enity5"};
for (String entity: entities) {
   String query = String.format("select o from %s o", entity);;
   long sStart = System.currentTimeMillis();
   int size =  em.createQuery(query).getResultList().size();
   System.out.printf(format, entity, em.createQuery(query).getResultList().size(), System.currentTimeMillis() - sStart);
}
System.out.println("Duration summary:" + (System.currentTimeMillis() - start));

Results:

EclipseLink 2.7.8:

Entity	Count	Duration
Entity1	3448	328
Entity2	1224	560
Entity3	1427	533
Entity4	9407	3172
Entity5	23548	8970

Duration summary:13565

EclipseLink 2.7.9:

Entity	Count	Duration
Entity1	3448	465
Entity2	1224	5187
Entity3	1427	5834
Entity4	9407	40513
Entity5	23548	114871

Duration summary:166872

Althogh there must be more issues causing the runtime increase over the versions (write access), the main problem is the dramatic runtime increase to access the table contents from version 2.7.8 to version 2.7.9.