Hibernate: Walk millions of rows and don't leak memory
- by Autocracy
The below code functions, but Hibernate never lets go of its grip of any object. Calling session.clear() causes exceptions regarding fetching a joined class, and calling session.evict(currentObject) before retrieving the next object also fails to free the memory. Eventually I exhaust my heap space.
Checking my heap dumps, StatefulPersistenceContext is the garbage collector's root for all references pointing to my objects.
public class CriteriaReportSource implements JRDataSource {
private ScrollableResults sr;
private Object currentObject;
private Criteria c;
private static final int scrollSize = 10;
private int offset = 1;
public CriteriaReportSource(Criteria c) {
this.c = c;
advanceScroll();
}
private void advanceScroll() {
// ((Session) Main.em.getDelegate()).clear();
this.sr = c.setFirstResult(offset)
.setMaxResults(scrollSize)
.scroll(ScrollMode.FORWARD_ONLY);
offset += scrollSize;
}
public boolean next() {
if (sr.next()) {
currentObject = sr.get(0);
if (sr.isLast()) {
advanceScroll();
}
return true;
}
return false;
}
public Object getFieldValue(JRField jrf) throws JRException {
Object retVal = null;
if(currentObject == null) { return null; }
try {
retVal = PropertyUtils.getProperty(currentObject, jrf.getName());
} catch (Exception ex) {
Logger.getLogger(CriteriaReportSource.class.getName()).log(Level.SEVERE, null, ex);
}
return retVal;
}
}
