Laravel 是怎麼 open mysql connection 的？又是在哪邊關閉的？

$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');

mysql_close($link);

類似以上的兩行

Laravel 在哪邊出現了？

Illuminate\Database\Connectors\Connector

    protected function createPdoConnection($dsn, $username, $password, $options)
    {
        if (class_exists(PDOConnection::class) && ! $this->isPersistentConnection($options)) {
            return new PDOConnection($dsn, $username, $password, $options);
        }

        return new PDO($dsn, $username, $password, $options);
    }