code: public ArrayList<User> lookupUsersWhere (final String where)
          throws PersistenceException
      {
          ArrayList<User> users = loadAll(_utable, where);
          for (User user : users) {
              // configure the user record with its field mask
              user.setDirtyMask(_utable.getFieldMask());
          }
          return users;
      }
docs: Looks up a list of users that match an arbitrary query. Care should be taken in constructing
  these queries as the user table is likely to be large and a query that does not make use of
  indices could be very slow.
  
  @return the users matching the specified query or an empty list if there are no matches.