It looks like Hibernate is optimistic by default because optimistic-lock attribute of the <class> element has a default value of version

It looks like Hibernate is pessimistic by default because the docs say that every Hibernate connection to a database will use the database’s default isolation level. However, I can change this by setting hibernate.connection.isolation = 4

Is Hibernate optimistic or pessimistic or both?

you can choose for each entity type if you want to enable optimistic locking by adding a version attribute.

If this version attribute is not used, and you use the lock() API you get a pessimistic lock; if you don't use any, then no locks are used.

Connection isolation doesn't affect optimistic locking, please read http://en.wikipedia.org/wiki/Isolation_ ... systems%29

So when you use the version attribute you won't get pessimistic locking even if you use the lock() API?

Thanks.