Transactions and Concurrency

• Hibernate provides comprehensive transaction management and concurrency control mechanisms.

• It supports both optimistic and pessimistic locking strategies to handle concurrent data access.

stateDiagram-v2
    state concurrency <>
    
    [*] --> OptimisticLocking
    [*] --> PessimisticLocking
    
    OptimisticLocking --> Versioning : @Version
    Versioning --> CheckOnUpdate : version comparison
    CheckOnUpdate --> concurrency
    
    concurrency --> Success : versions match
    concurrency --> Failure : versions differ
    
    Success --> [*]
    Failure --> StaleStateException
    
    PessimisticLocking --> DatabaseLock : SELECT FOR UPDATE
    DatabaseLock --> BlockOtherTransactions
    BlockOtherTransactions --> [*]

Isolation Levels

<property name="hibernate.connection.isolation">2</property>
<!-- 1: READ_UNCOMMITTED, 2: READ_COMMITTED, 4: REPEATABLE_READ, 8: SERIALIZABLE -->

Optimistic Locking

@Entity
public class Account {
    @Id
    @GeneratedValue
    private Long id;

    private BigDecimal balance;

    @Version
    private Long version; // Optimistic lock version
}

Pessimistic Locking

// Lock during transaction
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
User user = session.get(User.class, 1L, LockMode.PESSIMISTIC_WRITE);
// Modify user
tx.commit();
session.close();

// Lock with query
Query<User> query = session.createQuery("FROM User WHERE id = :id", User.class);
query.setParameter("id", 1L);
query.setLockMode("user", LockMode.PESSIMISTIC_WRITE);
User user = query.uniqueResult();