[eclipselink-users] The ScrollableCursor's issues

[dmitryerkin <dmitryerkin@xxxxxxxxxxxxx>]

Hi
I am trying to use the ScrollableCursor for retrieving about 10.000 records.
I have to get them divided into small portions which include 100 records
each.
All works well except two issues.

Firstly I see that the size of memory which is used by JVM is being
increased while the sequence of invocations of the cursor's next(100) method
is happening although I want memory which was allocated for previous
portions to be released.
The total amount of used memory is about 1Gb for 10.000 records.

Secondly the transaction which is started to scroll through the cursor
switches to rollback state after 5 minutes although a lot of invocations of
the cursor's next(100) method are happening.

My questions are:
1. How can I decrease the size of memory which is used by Eclipselink to
walk through the cursor?
2. Can I set the period of transaction's timeout?


Here is my code:

The servlet:

oebs.findOebsByTime(time);

int from = 10000;
int quantity = 100;
Vector<RootType> rootList = null;
while((rootList = oebs.getOebsByTime(from, quantity)) != null){
	
	int i = 0;
	HeaderBaseType header;
	System.out.println("rootList.size is " + rootList.size());
	
	while(i < rootList.size()){
		header = rootList.elementAt(i).getHeader();
                      ...
		i++;
	}
		
	from = from - quantity;
}
			
oebs.releaseOebsByTime();



The session bean:

@Stateful
@TransactionManagement(TransactionManagementType.BEAN)
public class OebsInterfaceImpl implements OebsInterface {
	
	@PersistenceContext(name="oebsEJB")
	EntityManager em;

	@Resource javax.transaction.UserTransaction ut;
...

	protected JpaEntityManager jpaEM = null;
	protected UnitOfWork uow = null;
	protected ScrollableCursor cursorByTime = null;
	

	public void findOebsByTime(XMLGregorianCalendar time) throws
NotSupportedException, SystemException{
		
		ExpressionBuilder oebs = new ExpressionBuilder();
	           Vector arguments = new Vector();
	           arguments.addElement("/o:root/o:header[o:timeOfCreation=\"" +
time.toString() + "000+00:00\"]");
	           arguments.addElement("xmlns:o=\"http://www.rosbank.ru/oebs\"";);
		Expression where =
oebs.getField("OBJECT_VALUE").getFunction(Oracle10Platform_Customizer.ExistsNodeWithNamespaces,
arguments).greaterThan(0);
		
		ReadAllQuery queryByTime = new ReadAllQuery(OebsView.class, where);
		queryByTime.useScrollableCursor();
		
		ut.begin();
		
		jpaEM = org.eclipse.persistence.jpa.JpaHelper.getEntityManager(em);
		uow = jpaEM.getActiveSession().getActiveUnitOfWork();
		if(uow == null){
    		       uow = jpaEM.getActiveSession().acquireUnitOfWork();
		}
		cursorByTime = (ScrollableCursor) uow.executeQuery(queryByTime);		
	}


	public Vector<RootType> getOebsByTime(int from, int quantity) throws
JAXBException{
		
		Vector<RootType> rootList = null;

		if(from <= cursorByTime.size()){

			rootList = new Vector<RootType>();

			cursorByTime.absolute(from);
			
			int q;
			if((cursorByTime.size() - from) + 1 >= quantity){
				q = quantity;
			}
			else{
				q = cursorByTime.size() - from + 1;
			}
			
			Vector<ejb3.OebsView> oebsList = new Vector<ejb3.OebsView>();
			oebsList = cursorByTime.next(q);
			System.out.println("oebsList.size is " + oebsList.size());    		
			
			JAXBContext jaxbContext =
JAXBContext.newInstance("ru.rosbank.oebs:ru.rosbank.oebs.header:ru.rosbank.oebs.content.assignment:ru.rosbank.oebs.content.organization:ru.rosbank.oebs.content.qualifications:com.ibm.xmlns.prod.websphere.j2ca.jdbc.appsxx_assignment_v:com.ibm.xmlns.prod.websphere.j2ca.jdbc.appsxx_organization_v:com.ibm.xmlns.prod.websphere.j2ca.jdbc.appsxx_qualifications_v");
	    		Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
		    	JAXBElement<RootType> jaxbElement;
		    	RootType root;
	    	
		    	int i = 0;
			while(i < oebsList.size()){
				jaxbElement = (JAXBElement<RootType>) unmarshaller.unmarshal(new
InputSource(new StringReader(oebsList.elementAt(i).getObjectValue())));
				root = (RootType) jaxbElement.getValue();
				rootList.add(root);
				i++;
			}
		}
		
		return rootList;
	}

public void releaseOebsByTime() throws SecurityException,
IllegalStateException, RollbackException, HeuristicMixedException,
HeuristicRollbackException, SystemException{
		uow.release();
		
		ut.commit();
	} 

This code workes in the Websphere container.

Regards
Dmitry
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