Are objects kept in memory when saveOrUpdate() from Session is called or is that using a weak reference to the objects? I couldn't find any pointer (pun intended) in the documentation.

I have a small application uploading test data and I create lists of objects and call saveOrUpdate() on each object.

If I cycle through a list and then create a new list within the same transaction, only the elements from the second list are inserted in the database.

If I size the list large enough to contain all the elements then all objects are inserted.

List l;

l = readDataSet1
for each item in the list
session.saveOrUpdate(obj)

l = readDataSet2
for each item in the list
session.saveOrUpdate(obj)

doesn't work but:

l = readDataSet1 + readDataSet2
for each item in the list
session.saveOrUpdate(obj)

works.

H puts inserted instances in 2nd level cache, not sure about updated instances. You can stop this by setting hibernate.cache.use_second_level_cache = false , but that has of course has consequences.