problème session

bonjour à tous
j'ai un probléme avec les session
j'ai stocker les les session dans une base de donnée mais les erreurs qui s'affichent "Undefined index: expsubs in c:\program files\easyphp1-8\www...... "
voila mon code:
<?php
//fonctions des sessions

function _open()
{
    global $_sess_db;
 
    if ($_sess_db = mysql_connect('localhost', 'root', '')) {
        return mysql_select_db('celibaliaudit', $_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);
 
    $sql = "SELECT data
            FROM  tblsessions
            WHERE  id = '$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);
    $access = mysql_real_escape_string($access);
    $data = mysql_real_escape_string($data);
 
    $sql = "REPLACE
            INTO   tblsessions
            VALUES  ('$id', '$access', '$data')";
 
    return mysql_query($sql, $_sess_db);
}

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

function _clean($max)
{
    global $_sess_db;
 
    $old = time() - $max;
    $old = mysql_real_escape_string($old);
 
    $sql = "DELETE
            FROM tblsessions
            WHERE  access < '$old'";
 
    return mysql_query($sql, $_sess_db);
}
//fin fonctions des sessions
session_save_path("tmp");
ini_set("session.gc_maxlifetime","360000");

session_set_save_handler('_open', '_close', '_read', '_write', '_destroy', '_clean');

session_start(); 
  
// local path of web root
 if (!defined("_PATH_USER"))
  define("_PATH_USER", $_SERVER['DOCUMENT_ROOT']);        

 // local path of web folder
 if (!defined("_LIB_PATH_USER"))
  define("_LIB_PATH_USER", _PATH_USER ."/");

 // URL of web root
 if (!defined("_WWWROOT_USER"))
  define("_WWWROOT_USER", "http://" . $_SERVER['SERVER_NAME']."/" ); 

 ?>
merci d'avance