About PHP using unset to destroy variables but not destroy memory records

foreach ($tags as $value) {
    if (Isset ($alls [$value [' username ']]) {
$m =memory_get_usage ()
        Unset ($alls [$value [' username ']];
        Unset ($value);
    }else{
        $alls [$value [' username ']] = $value;
    }
}

Look at the code:  
             Variable address     =====================     memory address
         The print memory address has exceeded  255  

When destroying the data, the  specified  memory address is  not released if it is simply destroying the variable  

So when you release the memory, you release the memory address that it points to. To succeed.

About PHP using unset to destroy variables but not destroy memory records