I am creating a system where the objective is that only one person per user can access the system, for this I have in my DB two tables called: users and accesses What I am doing is that when person 1 logs in, it is saved in my DB the id of the session in the two tables, if person 2 with the same user tries to access then the first person to log in takes it out of the system. I do this with help with AJAX, comparing if the last user who started has the same session id then he can navigate without problem, if he does not close session.

The problem is that I make this ajax request every 10s, but I would have problems if 10,000 people or more log in, then the request will be sent to the server every 10 seconds and this could saturate the server.

Try an active field if the session is equal to 1 and if the session is equal to 0, then discard this since if the user closes the browser then I never close session and the person will not be able to access, I also tried using a ajax method to detect if you close the browser but it is not very reliable. Has anyone had the same problem? I would thank you a lot.

I leave my php and js code to display as I do:

Code JS:

 $(function() { 
    cron(); // Lanzo cron la primera vez
    function cron() {
         $.ajax({
          method: "POST",
          url: "closeuser.php", 
          data: { action: 1 }
          })
        .done(function(msg) {
            var trimmedString = msg.trim();
            console.log(trimmedString)
          if( trimmedString == 'success' ) {  // Valida si el server devolvió 'success'
                 location.href='logoutuser.php';
          }
        });
    }
    setInterval(function() {
        cron();
    }, 10000); // cada 10 segundos
});

Code PHP:

<?php

    require_once 'Connections/sesionunica.php';
    $connection_s = new sesionunica();
    
     if(!isset($_SESSION["id_user"])){ 
            echo"<script>location.href='index.php';</script>";  
        } 
    
    if(isset($_POST["action"])) { // Se pasa una acción
        switch(sprintf("%d", $_POST["action"])) { // ¿Qué acción?
            case 1:
                cerrar();
                break;
            default:
            echo "default";
        }
    }
    function cerrar(){
        $ses = session_id();
        $connection_s = new sesionunica();
        $userById = $connection_s->getUsers($_SESSION["id_user"]);
        if ($userById["id_sesion"] <> $ses) {
        echo "success"; 
        }
    }
    
    ?>

In the same way, I cannot use websockets since there are accessibility problems with the server.