Using Sessions for High Traffic with AJAX

I was reading the CodeIgniter 3 documentation on using sessions and high traffic with AJAX, and it recommends using session_write_close().
My application has functions that write and read directly from $_SESSION, as an example below.

PHP Code:

function setSession($index, $value) {
    $_SESSION[$index] = $value;
}
function getSession($index) {
    if (isset($_SESSION[$index]) {
        return $_SESSION[$index];
    } else {
        return FALSE;
    }
} 


From what I understand from the documentation these two functions should always have session_start() at the beginning and session_write_close() at the end, correct?

Another issue that I found strange, CodeIgniter already has by default a session_start() function that is automatically triggered at the beginning of execution, without intervention from my code.
What would this session_start() look like if my functions are going to call it every time something is fetched from the session?

I load the sessions in my BaseController like this.

PHP Code:

// Ensure that the session is started and running
if (session_status() == PHP_SESSION_NONE)
{
     // $this->session = \Config\Services::session();
     
     // Below - add to top - use \Config\Services;
     $this->session = Services::session();
} 


What did you Try? What did you Get? What did you Expect?

Joined CodeIgniter Community 2009.  ( Skype: insitfx )

I still use CodeIgniter version 3.

I'm basing myself on this sentence from the session documentation (Session Library — CodeIgniter 3.1.13 documentation):
Long story short - call session_write_close() once you no longer need anything to do with session variables. 

The problem is that sometimes I use session at the beginning of the code, then halfway through the code.

In this case from what I understand the best thing would be for my code to be like this, correct?

PHP Code:

function setSession($index, $value) {

    if (session_status() === PHP_SESSION_NONE) {
        session_start();
    }

    $_SESSION[$index] = $value;

    session_write_close();
}

function getSession($index) {

    if (session_status() === PHP_SESSION_NONE) {
        session_start();
    }

    $value = FALSE;

    if (isset($_SESSION[$index]) {
        $value = $_SESSION[$index];
    }

    session_write_close();
} 


That should work fine for you.

What did you Try? What did you Get? What did you Expect?

Joined CodeIgniter Community 2009.  ( Skype: insitfx )