Hibernate Pessimistic Locking mode

Question

I am trying to understand pessimistic locking mechanism in Hibernate (Over MySQL DB).

I tried running the following example:

    public static void main(String[] args) {
    SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
            Session session = sessionFactory.openSession();
    Student student = null;
    Student studentTwo = null;
            try {
                session.beginTransaction();     
                student = (Student) session.get(Student.class, 1, LockMode.PESSIMISTIC_WRITE);
//I was hoping this line would thrown an error
                studentTwo = (Student) session.get(Student.class, 1, LockMode.PESSIMISTIC_WRITE);            
                System.out.println(student.getName());
                System.out.println(studentTwo.getName());
                student.setName("John Doe"); 
                session.getTransaction().commit();

                session.close();
            }catch(HibernateException ex){

            }
    }

But instead of giving me an error it just executes fine. Is there some sort of concept that I have misunderstood. Is this behavior normal?

I was able to test Optimistic locking perfectly fine so for pessimistic locking is there some misunderstanding of the concept or there is something that my code is missing.

Vlad Mihalcea · Accepted Answer · 2018-01-06T09:29:19.543

1

You are using a single session and a single transaction too. The database locks are re-entrant, as otherwise you would end up deadlocking by yourself.

Change your example to start two sessions, each one with its own transaction. Then you'll see the second transaction waiting for the first one to release the acquired locks.

edited Jan 06 '18 at 09:29

answered Jan 16 '15 at 05:46

Vlad Mihalcea

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Yes, trying to access using two session did the trick. Thanks a lot for the explanation. – Nick Div Jan 16 '15 at 06:19

score 0 · Answer 2 · answered Mar 02 '15 at 18:29

To clarify the concept generate two scheduled jobs in quartz running every second to persist in your DB.

The bellow link contains the code.

https://github.com/bozorgvar/JTA-Locking/tree/master/src/transaction

check the following files:

schedule.java
HelloJob.java
HelloJob2.java

Hibernate Pessimistic Locking mode

2 Answers2