JPA Pessimistic Lock Not Working

问题

I'm using Spring Boot, JPA, Oracle 12C and a Typed Query below to select 'NEW' items to process. Once I've selected a 'NEW' item, I update its status so it's no longer eligible for selection but I'm seeing a concurrency issue with the same items getting picked up.

I read here that i needed to set a 'LockModeType.PESSIMISTIC_WRITE' on the query to prevent other Threads from selecting the same row but it doesn't appear to be working.

Have I missed something below or do i need another configuration to prevent concurrent threads from retrieving the same rows from my Table? Is the issue to do with the lock level or the Entity Manager not getting updated/refreshed?

My @Transactional Service:

@Override
@Transactional(isolation = Isolation.READ_COMMITTED, rollbackFor=RuntimeException.class)
public MyObject retrieveItemByStatus(StatusEnum status) {
    return myRepository.retrieveItemByStatus(status);
}

The Query in my repository layer:

@Override
public MyObject retrieveItemByStatus(StatusEnum status) {

    String sql = "SELECT t FROM myTable t WHERE status = :status ORDER BY id ASC";      
    try {
        TypedQuery<MyObject> query = em.createQuery(sql, MyObject.class).setParameter("status", status);
        query.setLockMode(LockModeType.PESSIMISTIC_WRITE);
        query.setFirstResult(0);
        query.setMaxResults(1);
        MyObject myObject = (MyObject) query.getSingleResult();
        if (myObject != null) {
            myObject.setStatus(StatusEnum.IN_PROGRESS);
            MyObject myUpdatedObject = em.merge(myObject);                              
            return myUpdatedObject;
        }
    } catch (IllegalArgumentException iae) {
        //some logging
    } catch(NoResultException nrf) {            
        //some logging
    } catch(Exception ex) {
        //some logging
    }       
    return null;
}

回答1:

I can confirm this observation. I have several Lock-Modes tested with a H2-Database, and all worked as expected. Neither of the pessimistic Lock-Modes worked correctly in combination with an Oracle database. Therefore, the question: what is wrong with this code?

With Oracle two of these concurrent code executions yield the same data although the first should block the second one:

// Every Thread gets its own Hibernate session:
final Session session = HibernateSessionHolder.get();

session.getTransaction().begin();
final List<EventDeliveryDataDB> eddList = 
        session.createCriteria(EventDeliveryDataDB.class)
            .setLockMode(LockMode.PESSIMISTIC_WRITE) // with READ the same
            .add(eq("progress", NEW))
            .list();
eddList.stream().forEach(eddElem -> eddElem.setProgress(IN_PROGRESS));
session.getTransaction().commit();

Hibernate Log:

Hibernate: select this_.DD_ID as DD_ID1_2_0_, this_.CHANNEL_NAME as CHANNEL_NAME2_2_0_, this_.created as created3_2_0_, this_.DELIVERY_TIME as DELIVERY_TIME4_2_0_, this_.ERROR_CODE as ERROR_CODE5_2_0_, this_.ERROR_MESSAGE as ERROR_MESSAGE6_2_0_, this_.EVENT_ID as EVENT_ID7_2_0_, this_.MAX_RETRIES as MAX_RETRIES8_2_0_, this_.PROGRESS as PROGRESS9_2_0_, this_.PROGRESS_ID as PROGRESS_ID10_2_0_, this_.RECIPIENT_CRID as RECIPIENT_CRID11_2_0_, this_.RETRY_COUNTER as RETRY_COUNTER12_2_0_, this_.RETRY_TIME as RETRY_TIME13_2_0_, this_.updated as updated14_2_0_ from HR.NOS_DELIVERY_DATA this_ where this_.PROGRESS=?
Hibernate: select this_.DD_ID as DD_ID1_2_0_, this_.CHANNEL_NAME as CHANNEL_NAME2_2_0_, this_.created as created3_2_0_, this_.DELIVERY_TIME as DELIVERY_TIME4_2_0_, this_.ERROR_CODE as ERROR_CODE5_2_0_, this_.ERROR_MESSAGE as ERROR_MESSAGE6_2_0_, this_.EVENT_ID as EVENT_ID7_2_0_, this_.MAX_RETRIES as MAX_RETRIES8_2_0_, this_.PROGRESS as PROGRESS9_2_0_, this_.PROGRESS_ID as PROGRESS_ID10_2_0_, this_.RECIPIENT_CRID as RECIPIENT_CRID11_2_0_, this_.RETRY_COUNTER as RETRY_COUNTER12_2_0_, this_.RETRY_TIME as RETRY_TIME13_2_0_, this_.updated as updated14_2_0_ from HR.NOS_DELIVERY_DATA this_ where this_.PROGRESS=?
Hibernate: select DD_ID from HR.NOS_DELIVERY_DATA where DD_ID =? for update
Hibernate: select DD_ID from HR.NOS_DELIVERY_DATA where DD_ID =? for update
Hibernate: update HR.NOS_DELIVERY_DATA set CHANNEL_NAME=?, created=?, DELIVERY_TIME=?, ERROR_CODE=?, ERROR_MESSAGE=?, EVENT_ID=?, MAX_RETRIES=?, PROGRESS=?, PROGRESS_ID=?, RECIPIENT_CRID=?, RETRY_COUNTER=?, RETRY_TIME=?, updated=? where DD_ID=?
Hibernate: update HR.NOS_DELIVERY_DATA set CHANNEL_NAME=?, created=?, DELIVERY_TIME=?, ERROR_CODE=?, ERROR_MESSAGE=?, EVENT_ID=?, MAX_RETRIES=?, PROGRESS=?, PROGRESS_ID=?, RECIPIENT_CRID=?, RETRY_COUNTER=?, RETRY_TIME=?, updated=? where DD_ID=?

回答2:

AFAIK you can't block "reading" in oracle... pessimistic lock corresponds select for update which doesn't block other select statements ... It only forces it to read the old version of the data (before the select for update ran) ... It will block only other select for update statements (thus other queries having pessimistic lock)

来源：https://stackoverflow.com/questions/48885249/jpa-pessimistic-lock-not-working