Hi If you need to cache users on Drupal commerce I recommend using
Commerce Auth Cache
Authcache provides a way to cache pages for authenticated users, updating parts of the page via AJAX requests for dynamic content. In case of Drupal Commerce, many parts of some pages are unique to the current user. For example, the cart block is unique per user, and thus cannot be cached with the page it's displayed on. With Commerce Authcache, the cart block gets loaded via an AJAX request after the page is first loaded. This means the page loads very fast, and the cart is still relevant to the current user.
And of course
The Authcache module offers page caching for both anonymous users and logged-in authenticated users. This allows Drupal/PHP to only spend 1-2 milliseconds serving pages, greatly reducing server resources.
Please note that enabling authenticated user caching will require modifying how your user-customized content displays on your pages. You should be an experienced Drupal developer if you choose to implement the full functionality of this module.
But if you need to more :
then I suggest Varnish + Memcached