xhprof

For all of the sites we consult on, and manage, we use the excellent memcache module, which replaces the core's database caching. Database caching works for low traffic simple sites, but cannot scale for heavy traffic or complex site.

Recently we were asked to consult on the slow performance of a site with an all authenticated audience. The site is indeed complex, with over 235 enabled modules, 130 enabled rules, and 110 views.