On the Tillate Blog today there's a new post from Leo looking at how you can give clients back the control on when your cache refreshes.

We worked hard on the right caching strategy over months now. But there are still caches that do not get invalidated right or are cached too long and we still get complaints from our users. So we decided to integrate a feature that allows certain users to invalidate the cache on the server side. The first idea was to add a link to every page that will append a GET-parameter to the site and then avoid the cache.

He used the apache_request_header function to get the current request's headers and noticed that they included a cache-control header. By changing up this on the client-side, it allows the site visitor to "force" an update to the information if your application pays attention to it.