I read about session and I have a lot of doubt about it.
Silverstripe set session in main.php with Session::start().
When Silverstrupe write or update session? Is possible save data in session in every part of my site? For exampe in Page.php or not (this question is connect with time to long for writing ad reading data in session)?
If I set a session varaible for example $_SESSION['test']=$xml->saveXML(); can I repeat this action more then one time in my Page.php function? Or si there an exact point in witch is better to execute and only one time?