We are using JTASessionContext, CMTTransaction and WebSphereExtendedJTATransactionLookup. We have experienced some memmory leak problems and after closer inspection we have found that Hibernate sessions are not removed from currentSessionMap inside JTASessionContext.
Method JTASessionContext.CleanupSynch.afterCompletion() is called as expected but code "context.currentSessionMap.remove( txn );" does not remove session from Map because of key's hashcode has changed. This is due to fact that com.ibm.websphere.jtaextensions.ExtendedJTATransaction.hashCode is actually ID of underlaying transaction. But if it comes to the afterCompletion method in CleanupSynch the underlaying transaction is already closed. Closed transaction has ID 0 (default value) and it is different from ID under which the Hibernate session was previously inserted into Map.
Possible patch is in attachements.
IBM WebSphere 126.96.36.199, Hibernate CVS snapshot from 2006-02-24