Hibernate version:
2.16
Code between sessionFactory.openSession() and session.close():

AttributeType type = new AttributeType();
type.setType(AttributeType.STRING);
session.save(type);
session.flush();

Name and version of the database you are using:
mysql 4.0.21

The generated SQL (show_sql=true):
insert into AttributeType (Type) values (?)

MySQL log
SET autocommit=1
Query SET autocommit=0
Query SHOW VARIABLES LIKE 'tx_isolation'
Query insert into AttributeType (Type) values ('String')

And that's it. it does not commit though it sets autocommit=0.

Transaction is not set at all, but hibernate seems to set "autocommit=0" itself.

Thanks in advance.

you're right,
you have to manage beginTrans et commit, it has been said 50 000 times, it's better, even in jdbc, not to use autocommit.