session timeout

Hi,

I have set up my php application to store session data in a datbase by redefining, session_set_save_handler functions. The system seems to work fine, and I can see the sessions being stored in the database and being destroyed, however they do not seem to want to expire in the same way they used to when I wasn't storing them in the database. After 25 mins or so, the deafault expiration would kick in and when going to a page on the site the session would have expired. This is not happening now.I am using a shared host. Below is the code that I am calling on every page.

<?php
require_once("[database connection data]");
require_once('[session_set_save_handler functions]');
session_start();

/**
 * this redirects a non-logged in user to login.php
 * if logged in, nothing happens...
 */ 
function require_authentication($role = '') {
  $_SESSION['name'] = "MYSESSIONNAME";
  $ok=true;
  if (!isset($_SESSION['agent']) OR ($_SESSION['agent'] != md5($_SERVER['HTTP_USER_AGENT'])) ) {
  $ok=false;
  }
  if ($ok)
  {
    if(isset($_SESSION['user_id'])) 
    {
    // the session is valid and user is logged in.
    return;
    }
  }
  else
  {
  header("Location: login.php");
  }
	exit(); // Quit the script.
}

Code (markup):

I have tried adding the following lines and variations thereof, but to no avail:
ini_set('session.gc_maxlifetime',5);
ini_set('session.gc_probability',100);
ini_set('session.gc_divisor',100)

The following code is what I am using for sesssion_set_save_handler:

<?php
session_set_save_handler('_open',
                         '_close',
                         '_read',
                         '_write',
                         '_destroy',
                         '_clean');
               
$_sess_db=false;   
                 
function _open()
{
    global $_sess_db;
    global $address, $username, $password, $database;    
    $_sess_db = mysql_connect($address,$username,$password);
    if($_sess_db) {
        if(mysql_select_db($database, $_sess_db)) {
        }
        else {
           echo mysql_error($_sess_db);
        }
        
        return true;
    }
    else {
        echo mysql_error($_sess_db);
    }
    return false;
}
 
function _close()
{
    global $_sess_db;
 
    return mysql_close($_sess_db);
}
 
function _read($id)
{
    global $_sess_db;
    $id = mysql_real_escape_string($id, $_sess_db);
 
    $sql = "SELECT data FROM   sessions WHERE  id = '$id'";
    if ($result = mysql_query($sql, $_sess_db)) {
        if (mysql_num_rows($result)) {
            $record = mysql_fetch_assoc($result);
            return $record['data'];   
        }
    }
    return '';
}

function _write($id, $data)
{
    global $_sess_db;
 
    $access = time();
 
    $id = mysql_real_escape_string($id,$_sess_db);
    $access = mysql_real_escape_string($access,$_sess_db);
    $data = mysql_real_escape_string($data,$_sess_db);
 
    $sql = "REPLACE INTO sessions VALUES  ('$id', '$access', '$data')";
 
    return mysql_query($sql, $_sess_db);
}

function _destroy($id)
{
    global $_sess_db;
 
    $id = mysql_real_escape_string($id,$_sess_db);
 
    $sql = "DELETE FROM  sessions WHERE  id = '$id'";
    return mysql_query($sql, $_sess_db);
}

function _clean($max)
{
    global $_sess_db;
    $old = time() - $max;
    $old = mysql_real_escape_string($old,$_sess_db);
 
    $sql = "DELETE FROM   sessions WHERE  access < '$old'";
 
    return mysql_query($sql, $_sess_db);
}

Code (markup):

I'd be quite happy if the original timeout period of 25 mins or so were working again. But the session only seems to timeout when the window is closed.

I think I need to delete the specific cookie/session data from the database. and clear it from session history but I am not sure how to do this or where to do it in the code.

Thanks for any help in advance.