func (s *MemoryStore) On() (changed bool, err error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	if s.on {
		return
	}
	s.on = true
	changed = true
	return
}
func (s *MemoryStore) On() (changed bool, err error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	if s.on {
		return
	}
	s.on = true
	changed = true
	return
}
// On enables maintenance.