How can I keep the persistence context small in a Spring JPA environment?
Why: I know that by keeping the persistence context small, there will be a significant performance boost!
The main problem area is:
@Transactional
void MethodA() {
WHILE retrieving next object of 51M (via a stateless session connection) DO
get some further (readonly) data
IF condition holds THEN
assessment = retrieve assession object (= record from database)
change assessment data
save the assessment to the database
}
Via experiments in this problem domain I know that when cleaning the persistence context every 250 iterations, then the performance will be a lot better.
When I add these lines to the code, so every 250 iterations:
@PersistenceContext
private EntityManager em;
WHILE ...
...
IF counter++ % 250 == 0 THEN
em.flush()
em.clear()
}
Then I get errors like "cannot reliably perform the flush operation".
I tried to make the main Transactional read-only and the asssessment-save part 'Transaction-requires-new', then I get errors like 'operating on a detached entity'. Very strange, because I never revisit an open entity.
So, how can I keep the persistence context small? Have tried 10s of ways. Help is really appreciated.