Constructor.
string $dsn A data source name:
string $username The username for the database:
string $password The password for the database:
integer $lifetime The lifetime to use for the purge:
public function __construct($dsn, $username = '', $password = '', $lifetime = 86400) {
$this->dsn = $dsn;
$this->username = $username;
$this->password = $password;
$this->lifetime = (int) $lifetime;
}