code: protected Set<Integer> __getCategories() {
  
          // TODO this should be replaced with the buffered category iterator, as it might produce an HeapSpace Overflow, if there are too many categories.
          Session session = this.__getHibernateSession();
          session.beginTransaction();
          List<Integer> idList = session.createQuery(
                  "select cat.pageId from Category as cat", Integer.class).list();
          Set<Integer> categorySet = new HashSet<Integer>(idList);
          session.getTransaction().commit();
  
          return categorySet;
      }
docs: Protected method that is much faster than the public version, but exposes too much implementation details.
  Get a set with all category pageIDs. Returning all category objects is much too expensive.
  @return A set with all category pageIDs