Who's Online Performance Issue

[kanine]

I've isolated the problem area to the following code, can anyone give me pointers as to why the response from this section appears to be causing a timeout?

<?php
  $heading = array();
  $contents = array();
  if ($info) {
    $heading[] = array('text' => '<b>' . TABLE_HEADING_SHOPPING_CART . '</b>');

    if (STORE_SESSIONS == 'db') {
      $session_data = $db->Execute("select value from " . TABLE_SESSIONS . "
                                    WHERE sesskey = '" . $info . "'");

      $session_data = trim($session_data->fields['value']);
    } else {
      if ( (file_exists(zen_session_save_path() . '/sess_' . $info)) && (filesize(zen_session_save_path() . '/sess_' . $info) > 0) ) {
        $session_data = file(zen_session_save_path() . '/sess_' . $info);
        $session_data = trim(implode('', $session_data));
      }
    }

    if ($length = strlen($session_data)) {
      if (PHP_VERSION < 4) {
        $start_id = strpos($session_data, 'customer_id[==]s');
        $start_cart = strpos($session_data, 'cart[==]o');
        $start_currency = strpos($session_data, 'currency[==]s');
        $start_country = strpos($session_data, 'customer_country_id[==]s');
        $start_zone = strpos($session_data, 'customer_zone_id[==]s');
      } else {
        $start_id = strpos($session_data, 'customer_id|s');
        $start_cart = strpos($session_data, 'cart|O');
        $start_currency = strpos($session_data, 'currency|s');
        $start_country = strpos($session_data, 'customer_country_id|s');
        $start_zone = strpos($session_data, 'customer_zone_id|s');
      }

      for ($i=$start_cart; $i<$length; $i++) {
        if ($session_data[$i] == '{') {
          if (isset($tag)) {
            $tag++;
          } else {
            $tag = 1;
          }
        } elseif ($session_data[$i] == '}') {
          $tag--;
        } elseif ( (isset($tag)) && ($tag < 1) ) {
          break;
        }
      }

      $session_data_id = substr($session_data, $start_id, (strpos($session_data, ';', $start_id) - $start_id + 1));
// fix nnobo bug
      $session_data_cart = substr($session_data, $start_cart, $i - $start_cart);
      $session_data_currency = substr($session_data, $start_currency, (strpos($session_data, ';', $start_currency) - $start_currency + 1));
      $session_data_country = substr($session_data, $start_country, (strpos($session_data, ';', $start_country) - $start_country + 1));
      $session_data_zone = substr($session_data, $start_zone, (strpos($session_data, ';', $start_zone) - $start_zone + 1));

      session_decode($session_data_id);
      session_decode($session_data_currency);
      session_decode($session_data_country);
      session_decode($session_data_zone);
      session_decode($session_data_cart);

      if (PHP_VERSION < 4) {
        $broken_cart = $cart;
        $cart = new shoppingCart;
        $cart->unserialize($broken_cart);
      }

      if (is_object($_SESSION['cart'])) {
        $contents[] = array('text' => $full_name . ' - ' . $ip_address . '<br />' . $info);
        $products = $_SESSION['cart']->get_products();
        for ($i = 0, $n = sizeof($products); $i < $n; $i++) {
          $contents[] = array('text' => $products[$i]['quantity'] . ' x ' . '<a href="' . zen_href_link(FILENAME_CATEGORIES, 'cPath=' . zen_get_product_path($products[$i]['id']) . '&pID=' . $products[$i]['id']) . '">' . $products[$i]['name'] . '</a>');
// cPath=23&pID=74
        }

        if (sizeof($products) > 0) {
          $contents[] = array('text' => zen_draw_separator('pixel_black.gif', '100%', '1'));
          $contents[] = array('align' => 'right', 'text'  => TEXT_SHOPPING_CART_SUBTOTAL . ' ' . $currencies->format($_SESSION['cart']->show_total(), true, $_SESSION['currency']));
        } else {
          $contents[] = array('text' => TEXT_EMPTY_CART);
        }
      }
    }
  }

  if ( (zen_not_null($heading)) && (zen_not_null($contents)) ) {
    echo '            <td width="25%" valign="top">' . "\n";

    $box = new box;
    echo $box->infoBox($heading, $contents);

    echo '            </td>' . "\n";
  }
?>

If I remove this section of code the who's online responds instantly with a list of users and their cart status. But I would like to be able to see what is in their carts as it provides useful info.