public function gc($ttl) {
    $store  = $this->psl['store'];

    $Ids = $store->listIds('session');
    foreach($Ids as $Id) {
      $data = $store->meta('session', $Id);
      if($data->time + $ttl < time()) {
        $store->delete('session', $Id);
      }
    }
    return true;
  }