If I fetch a connection from a session, am I asking the session for his connection or will he give me one from the connection pool?

Case in point:

1.) I ask the session for a db connection.
2.) Do some db procedure junk.
3.) Update an object in the session.
4.) Commit my transaction.
5.) Give the connection back.

Will the update of the object use the same connection I asked the session for?

As per the JavaDoc on net.sf.hibernate.Session:

public Connection connection()
throws HibernateException

Get the JDBC connection. Applications are responsible for calling commit/rollback upon the connection before closing the Session.

Returns:
the JDBC connection in use by the Session
Throws:
HibernateException - if the Session is disconnected

The Session.connection() method returns the Session's connection. It originates from the connection pool, but it is the connection currently in use by the session.

The answer is yes, any updates occuring during Session.flush will use that same connection.