Hibernate's Pessimistic Locking

mimi_tan1985 · **Posted:** Fri Dec 07, 2007 1:33 am

Hi All,

I'm having a serious concurrency problem with hibernate.
I'm writing a program which need to update a row of customer's balance everytime the customer made a transaction.

When 2 transactions come together, this will happened:
1. Transaction 1 retrieve the last state of customer balance (say it A)
2. Transaction 1 updated the balance to B
3. Transaction 2 retrieve the last state of customer balance (it's B)
4. Transaction 2 updated the balance to C

While in my code, what happened exactly is like this:
1. Transaction 1 retrieve the last state of customer balance (say it A)
2. Transaction 1 updated the balance to B = (A + difference1)
3. Transaction 2 retrieve the last state of customer balance (it should be B, but in reality it retrieved A)
4. Transaction 2 updated the balance to C = (A+ difference2)

The final result should be C = A + difference1 + difference2
But in my code, it's C = A + difference2

{code}
session.refresh(customer.getBalance(), LockMode.UPGRADE);
customer.setCashBalance(customer.getBalance() + difference);
session.update(customer.getBalance());
{code}

Thanks in Advance for any suggestion, sharing, or solution.

pramodkp · **Joined:** Mon Mar 26, 2007 12:38 am **Posts:** 119

Hi,
it's a classical problem. Lost Updates.
If it's okay to change schema,
<version>
element can be used on the table that has concurrent modifications.

For more information, please refer to hibernate documentation.
Let me know if it helps.
Correct me if I am wrong.

-------------------------------------------
Rate the reply if you find it helpful

enjoy · **Joined:** Thu Feb 01, 2007 12:57 pm **Posts:** 18

The use of <version> is not pessimistic locking but optimistic according to what i've read...

I have a pb too with pessimistic locking,
I thought it was very simple and all i needed to do is something like

Code:

getHibernateTemplate().lock(object, LockMode.UPGRADE);

But it doesn't seem to lock anything to me...
If anybody can help..

pramodkp · **Joined:** Mon Mar 26, 2007 12:38 am **Posts:** 119

Hi,
>> The use of <version> is not pessimistic locking but optimistic according to what i've read...

Yes. It is.
All we need is a solution to Lost Updates.
Pessimistic Locking / Optimistic Locking are just means.
Correct me If I am wrong.

>>But it doesn't seem to lock anything to me...
It does.
It's like Select For Update.
This is how I have seen it behave on Oracle.
It locks the row at the database level and any other concurrent transaction ( not necessarily from inside Hibernate, even from sqlplus ) that tries to update the same row gets blocked until our transaction releases the lock either through commit or rollback.

khangharoth · **Joined:** Fri Aug 31, 2007 11:58 am **Posts:** 19

Code:

The use of <version> is not pessimistic locking but optimistic according to what i've read...

I have a pb too with pessimistic locking,
I thought it was very simple and all i needed to do is something like

getHibernateTemplate().lock(object, LockMode.UPGRADE);

But it doesn't seem to lock anything to me...
If anybody can help..

What you may need is LockModeType.WRITE .

enjoy · **Joined:** Thu Feb 01, 2007 12:57 pm **Posts:** 18

Well, i don't manage to LOCK using

Code:

getHibernateTemplate().lock(object, LockMode.UPGRADE);

However I have an Hibernate request in the Log console

Code:

Hibernate: select APPLICATION_ID from seeapp.application where APPLICATION_ID =? for update

which seems to mean that the lock is done but...
When i try this request directly in my Database, it works...It's really strange...
I read that AUTOCOMMIT must be disabled...I already check that point i think.

and about LockMode.WRITE it doesnt work with lock() function...

If anyone can help.

mimi_tan1985 · **Posted:** Fri Dec 07, 2007 11:46 am

Well,before I added some Sets as the properties of the object, the locking did worked. I read on the documentation that hibernate's lock won't work if there is dirty collection. Is the Sets I added have something to do with it?

mimi_tan1985 · **Posted:** Fri Dec 07, 2007 11:48 am

Well,before I added some Sets as the properties of the object, the locking did worked. I read on the documentation that hibernate's lock won't work if there is dirty collection. Is the Sets I added have something to do with it?

enjoy · **Joined:** Thu Feb 01, 2007 12:57 pm **Posts:** 18

Well, personnally I perform the LOCK before opening the modification PopUP, so the object is not dirty...

mimi_tan1985 · **Posted:** Mon Dec 10, 2007 6:00 am

I solved this problem by changing the save and update action like this:

before:

Code:

session.save(transaction);
... some codes
sessionsession.refresh(transaction.getCustomer(), LockMode.UPGRADE); 
customer.setCashBalance(customer.getBalance() + difference);
session.update(transaction.getCustomer());
...some codes
session.update(transaction);

after:

Code:

sessionsession.refresh(transaction.getCustomer(), LockMode.UPGRADE); 
...some codes
customer.setCashBalance(customer.getBalance() + difference);
session.update(transaction.getCustomer());
...some codes
session.save(transaction);

Thansk for all your posts.
Seems that the lock wasn't performed because of the dirty object (transaction.customer)