Hibernate session.flush（）导致ORA-00001：唯一约束

Question

I have this method that inserts thousands of records to the database using hibernate.

According to this article , flushing and clearing helps to release some precious memory, and the code below does this every 100 records. But the problem:

ORA-00001: unique constraint (OWNER.FOO_TABLE_PK) violated

always occurs when the code session.flush() is invoked, which is after the 100th save (the PK of FOO_TABLE is a simple long id). I have tried removing the session.flush() and session.clear() entirely and added session.evict(obj) after the session.save() and that fixed the problem. I am not sure if it is a good practice though.

Would you guys have any idea why session.flush() causes a unique constraint error? Flushing and clearing at regular intervals are heavily suggested, but I am not sure if I am using them properly. Any inputs will be appreciated. Thanks!

    @Override
    @Transactional
    public void bulkSave(List<Foo> objList) {
        Session session = sessionFactory.getCurrentSession();

        if (objList != null) {
            if (!objList.isEmpty()) {
                int counter = 0;

                for (Foo obj : objList) {
                    session.save(objList);
                    counter++;


                    if ((counter % 100) == 0) {
                        session.flush();
                        session.clear();
                    }

                }

            }
        }

    }

Answer 1

Well flushing causes the state to be flushed through to the database. If there's a primary key violation, there's something wrong with how you're assigning the primary key for your object.

Answer 2

After a more in-depth investigation, I have determined that this is not the fault of Hibernate. Hibernate uses the number provided by the ID Sequence Generator as primary keys. Someone manually uploaded a test data which used IDs not accounted for by the Sequence Generator. Eventually when hibernate caught-up, it cannot use the ID provided by the generator because the ID already exists in the Database, hence the Unique Constraint violation after the session.flush().