Cache: what to clear and when

Some pages are assembled in advance and kept ready. That speeds the site up noticeably, and does just as much harm if the right key is not cleared: the edit is in the database while the visitor still sees the old version.

home_pages           pages on the home screen
menu.header          menu items
template_NAME_...    a block of materials

The rule: when you add a cache, list EVERY model whose change makes it wrong. A menu item is built from a page, so deleting a page has to clear the menu cache as well — otherwise the deleted page hangs in the menu for another hour.