Hibernate batch delete with quarkus.hibernate-orm.jdbc.statement-batch-size not working?

Question

According to the Quarkus docs, including the line below in the application.properties should result in delete statements to be batched.

quarkus.hibernate-orm.jdbc.statement-batch-size=1000

However, I can't get this to work. Regardless of this property all delete statements are sent to the database individually instead of in batches.

Is there anything else I need to do?

To reproduce, use a simple entity like this:

@Entity
@Table(name = "book")
public class Book {
  @GeneratedValue(strategy = IDENTITY)
  @Id
  private Long id;
  private String title;

  public Book() {
  }

  public Long getId() {
    return id;
  }
}

insert records into the database like this (on PostgreSQL):

INSERT INTO book (id, title)
VALUES(generate_series(1, 200), 'a title');

and a simple integration test like this:

@QuarkusTest
class BookDeleteIT {
  @Inject EntityManager em;

  @Test
  void deletes_records_in_batches() {
    List<Book> books = getBooks();
    deleteBooks(books);
  }

  @Transactional
  List<Book> getBooks() {
    return em.createQuery("SELECT b FROM Book b").getResultList();
  }

  @Transactional
  void deleteBooks(List<Book> books) {
    books.forEach(book -> delete(book));
  }

  private int delete(Book book) {
    return em.createQuery("DELETE FROM Book b WHERE b.id = :id")
        .setParameter("id", book.getId())
        .executeUpdate();
  }
}

When I run this test, the deletes are sent to the database individually instead of in batches.

Answer 1

I suppose the error is the way you're deleting a book: use em.remove(book) instead of the query and Hibernate will accumulate deletions.
There are possibilities that deleting a managed entity using a query instead of EntityManager prevents your JPA provider (Hibernate) to manage entity lifecycle and do some optimizations (like batch deletion).