The biggest mistake in your code is that you are tring to access global variables the wrong way.. all the global variables are with capitalized letters, like: $_GET, $_POST, $_SESSION, $_COOKIES, $_SERVER, etc..
Note: $arv isn't the same as $_SESSION['arv']
And at:
PHP Code:
$_SESSION["arv"][$k]= $page_views;
You haven't set the $page_views so you assign empty value for $_SESSION["arv"][$k]
Hopefully you understand me