public function retryLater($delay) {
        $this->runUpdate("
            UPDATE " . self::$jobsTable . "
            SET run_at = DATE_ADD(NOW(), INTERVAL ? SECOND),
                attempts = attempts + 1
            WHERE id = ?",
            array(
              $delay,
              $this->job_id
            )
        );
        $this->releaseLock();
    }