protected function performRollBack($toLevel)
    {
        if ($toLevel === 0) {
            $this->getPdo()->rollBack();
        } elseif ($this->queryGrammar->supportsSavepoints()) {
            $this->getPdo()->exec(
                $this->queryGrammar->compileSavepointRollBack('trans' . ($toLevel + 1))
            );
        }
    }