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($file);
unset($manifest[$tag]);
if (--$n <= 0) {
break;
}
}
}
}