Hi,
We are using Hibernate-3.x in our application. We have a code where we create large number of hibernate objects(mapped to tables) as part of a single transaction. We create the Session during this process. Here's a pseudo code:


In the above code, the myMethod is called as part of a transaction on a SessionBean. The loop in the code will be iterated around 60K to 80K times. As can be seen in the code, the hibernate objects are created and saved in this loop. Since this is part of the transaction, the actual save to database never happens until the transaction is committed. The objects to be saved are maintained in memory by the Hibernate Session.
So to avoid OutOfMemory issues, we introduced the logic of flushing and clearing the session for every 50 objects.

As per the documentation of the flush API:


Does this mean that the save/update queries will be issued by Hibernate when we invoke the flush method? Or is it the other way around, is Hibernate going to repopulate the contents of the Session using the information from the database? The reason i ask this is because if its the latter then we are going to lose the objects that we had maintained in the Session for being saved later.

Any help in understanding this, is appreciated.

Thank you.

AFAIK the flush() will just "commit" any pending changes in hibernate session to the underlying persistent store. Not the other way around. Hibernate does not populate its session with data, unless you ask it to do so (session.get(), session.load(), ...).

But in my application I never explicitly call the flush() method. And I guess it is better to let hibernate handle it when needed. For example I use the "FLUSH_ON_COMMIT" policy, and use a transaction.commit() whenever I want it.

Your pseudo code will then became:


A this way you could also call "tx.rollback()" when needed (to handle error recovery for instance)

--
Hugo

The code that i mentioned is in a SessionBean and it is part of Container Manager Transaction(CMT), so we are not allowed to invoke the tx.commit() or tx.rollback().



Makes sense. Thanks, Hugo.