public function purge( $days_older_than = 60, \wpdb $wpdb ) {

		$days_older_than = absint( $days_older_than );

		$tn = $this->table->get_table_name( $wpdb );

		$sql = "DELETE FROM {$tn} WHERE time < DATE_SUB(NOW(), INTERVAL $days_older_than DAY)";

		$wpdb->query( $sql );
	}