I have a large table which contains millions of records. I code the following method to randomly get certain record:

public Item getNthItem(Session session, int nth) throws HibernateException {
Query q = session.createQuery("from hibernate.Item");
List list = q.list();
return (Item) list.get(nth);
}

Will q.list() fetch all the objects that matched into memory ? Or fetch them one by one when list.get(nth) is executed ? What I want is the latter situation. Who could tell me if it is okay or not?

Thanks!

If you want the latter, you must use iterate() or scroll(), together with Session.evict() or Session.clear().

Is there some config to limit number of cached objects ? I mean not running into OutOfMemoryException without calling evict () manually.

If I am not mistaken the lazy paramater of a collection mapping will produce the desired behavior when set to true. For example, when you use the following mapping the collection returned by the getLocalizedStrings method will load objects from the database only as needed.

<set name="localizedStrings" cascade="all" inverse="true" lazy="true">
<key column="stringCollection"/>
<one-to-many class="com.atwoodsoft.data.LocalizedString"/>
</set>

No, the lazy setting on a collection only makes Hibernate be lazy about loading the entire collection. That is, it will only load the (entire) collection when you first try to do an operation on it, as opposed to when the entity containing the collection is loaded...

I spent my whole life trying not to be careless. Women and children can be careless. But not men.