I have an operation that will generated a collection of
objects needs to be deleted from the database,
about 1 million of them.

The way I used now, is to delete the entry one by one in
one transaction.
iter = list.iterator();
tran.begin();
while(iter.hasNext())
sesssion.delete(iter.next());
tran.commit();

However, this has been really really slow.
And one thing I don't understand is why hibernate will first do
a select then do a delete.

How can I improve the performance in this situation?

your best bet probably is to turn this into a hql, specially one that deletes a range of objects. This will eliminate the selects and improves performance of deletes. However, if you can't do this you might want to look at L2 cache to improve the performance with the selects, if the objects have been fetched on the same machine at some point. As for why selects happen, I would say its because those object are not managed and HB will have to go to database to make them managed.



Farzad-