Cannot open connection Error on large hibernate updates/inserts

Recently I was getting "Cannot open connection/Transaction Inactive" Error when doing
large number (20000) updates with hibernate.

The solution was using batch update with hibernate.

A naive approach to inserting 20,000 rows in the database using Hibernate might look like this:

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
for ( int i=0; i<100000; i++ ) {
Customer customer = new Customer(.....);
session.save(customer);
}
tx.commit();
session.close();
We can also do this kind of work in a process where interaction with
the second-level cache is completely disabled:    
hibernate.cache.use_second_level_cache false

Solution is as below:
When making new objects persistent flush() and then clear() the session regularly
in order to control the size of the first-level cache.
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();

for ( int i=0; i<100000; i++ ) {
Customer customer = new Customer(.....);
session.save(customer);
if ( i % 20 == 0 ) { //20, same as the JDBC batch size
//flush a batch of inserts and release memory:
session.flush();
session.clear();
}
}

tx.commit();
session.close();