Performance problem StatelessSession and StatefulPersistenceContext.clear ------------------------------------------------------------------------- Key: HHH-1157 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-1157 Project: Hibernate Core Issue Type: Bug Components: core Affects Versions: 3.1 rc2 Environment: win2k, db2 Reporter: Barthel Steckemetz The StatelessSession in h3.1 is using the StatefulPersistenceContext, which has a lot of maps and sets to keep track of instances loaded etc. This is quite useful in the stateful Session, but yields to the following problems. When first loading a lot of instances like: Query queryA = session.createQuery("from A"); List listA = queryA.list(); The instances maps in StatefulPersistenceContext are cleared, i.e. HashMap.clear is used like: public void clear() { modCount++; Entry tab[] = table; for (int i = 0; i < tab.length; i++) tab[i] = null; size = 0; } Thus no references to the loaded instances are kept by the session. But the HashMap.table array has still the same (possibly large) size. Every subsequent load operation will call StatefulPersistenceContext.clear too. So that the loop in HashMap.clear is run again. This is especially costly when using ScrollableResults where this happens for every call of next. The solution may be to create a new instance of StatefulPersistenceContext instead of calling clear. This may have side effect if references to its members are kept elsewhere. We could fix our performance problems this way. A better solution could be to write an own StatelessPersistenceContext class.