I am trying to understand what the role of Memcache is. A few of my friends who have been working with Drupal for more than a year tell me that Memcache would only work for logged in users, and I would have to look to Varnish or Boost for caching the content shown to anonymous users.
While I understand that varnish acts as a reverse proxy, and caches a copy of the page, I wanted to know if anonymous users make a request, and if varnish does not have a cached copy of it, would the webserver route the request to Memcache, or would the request directly go to the database?
Architecture example: Varnish/Boost, web server, Memcache, database.