I could understand the following behavior of the session when i wrote some code to experiment with session's transactions. I listed my scenarios #2 is the actual question.

1)First i got session using sessionfactory.opensession() and with out beginning a transaction i saved a entity and then flushed and closed the session , obviously the data is not persisted and cannot be seen outside this code (transaction). Code looked like this

session = sessionFactory.openSession()
session.save(myObject);
session.flush();
session.close();

2) Then i did this.
session1 = sessionFactory.openSession()
session1.save(myObject);
session1.flush();
session1.close();

session2 = sessionFactory.openSession();
session2.beginTransaction();
session2.save(myObject2);
session2.getTransaction().commit();

Then both myObject and myObject2 got persisted. why did session1 got committed even tho it was closed before the transaction began on session2. Strangely they both use same connection object. I am using hsqldb as the database

Thanks in advance.

Thanks!
I figured that its because hibernate has its own connection pooling and was returning the same connection for which autocommit was disabled earlier and there are pending transactions on it.
They got committed with next commit command on the connection object.