protected function gc(&$manifest)
    {
        if (count($manifest) > $this->module->historySize + 10) {
            $n = count($manifest) - $this->module->historySize;
            foreach (array_keys($manifest) as $tag) {
                $file = $this->module->dataPath . "/$tag.data";
                @unlink($file);
                if (isset($manifest[$tag]['mailFiles'])) {
                    foreach ($manifest[$tag]['mailFiles'] as $mailFile) {
                        @unlink(Yii::getAlias($this->module->panels['mail']->mailPath) . "/$mailFile");
                    }
                }
                unset($manifest[$tag]);
                if (--$n <= 0) {
                    break;
                }
            }
        }
    }