# lock the jobs using ownerId
        try:
            cu = self.db.transaction()             # <- dies here
            cu.execute("""UPDATE Jobs SET owner=?
                              WHERE owner IS NULL AND status=?""",
                       ownerId, jobstatus.WAITING)
            self.db.commit()
        except sqlerrors.DatabaseLocked: 
            # do nothing if we fail to lock any rows; we'll be back...
            self.db.rollback()
            return 0
        except:
            # unhandled exception; pass it up
            self.db.rollback()
            raise