Transactional in both service and dao layers

Question

I have a question regarding @Transactional annotation. Nothing special defined, so as I understand is PROPAGATION_REQUIRED Let’s say I have a transactional annotation which on both service and dao layer.

Service

@Transactional
public long createStudentInDB(Student student) {
    final long id = addStudentToDB (student);
    addStudentToCourses (id, student.getCourseIds());
    return id;
}

private long addStudentToDB (Student student) {
    StudentEntity entity = new StudentEntity ();
    convertToEntity(student, entity);
    try {
        final id = dao.create(entity);
     } catch (Exception e){
        //   
      }
    return id;
}

private void addStudentToCourses (long studentId, List<String> coursesIds){
    //add user to group
    if(coursesIds!= null){
        List<StudentCourseEntity> studentCourses = new ArrayList<>();
        for(String coursesId: coursesIds){
            StudentCourseEntity entity = new StudentCourseEntity ();
            entity.setCourseId(coursesId);
            entity.setStudentId(userId);
            studentCourses.add(studentId);
        }
        anotherDao.saveAll(studentCourses);
    }
}

DAO

@Transactional
public UUID create(StudentEntity entity) {

   if ( entity == null ) { throw new Exception(//…); }

   getCurrentSession().save(entity);
   return entity.getId();
}

ANOTHER DAO:

@Transactional
public void saveAll(Collection< StudentCourseEntity > studentCourses) {
    List< StudentCourseEntity > result = new ArrayList<>();
    if(studentCourses!= null) {
        for (StudentCourseEntity studentCourse : studentCourses) {
            if (studentCourse!= null) {
                save(studentCourse);
            }
        }
    }

}

Despite the fact that’s not optimal, it seems it causing deadlocks. Let’s say I have max 2 connections to the database. And I am using 3 different threads to run the same code. Thread-1 and thread-2 receive a connection, thread-3 is not getting any connection. More than that, it seems that thread-1 become stuck when trying to get a connection in dao level, same for thread-2. Causing a deadlock.

I was sure that by using propagation_required this would not happen. Am I missing something? What’s the recommendation for something like that? Is there a way I can have @transactional on both layers? If not which is preferred? Thanks Fabrizio

If you are running out of connections you either don't have transactions setup correctly or are messing around with connections yourself instead of letting Spring manage things. Only adding method signatures without an implementation will not help in solving your issue. First check your setup (make sure you have tx setup correctly) and check your implementations as well. — M. Deinum

Maciej Kowalski Maciej Kowalski · Accepted Answer · 2017-01-22T16:12:19

As the dao.doSomeStuff is expected to be invoked from within other transactions I would suggest you to configure this method as:

@Transaction(propagation=REQUIRES_NEW)

Thanks to that the transaction which is invoking this method will halted until the one with REQUIRES_NEW will be finished.

Not sure if this is the fix for your particular deadlock case but your example fits this particular set-up.

Transactional in both service and dao layers

3 Answers