Managing a cache is a complex task, at first you start placing random stuff on it, when you need to squeeze a few more hits per second you keep adding stuff to the cache. At the end of the day, if you've not planned it carefully, you might end up with a nightmare of stale data in your pages or even a completely broken site.
One easy way to apply some logic to the cached data and help in the invalidation of cached stuff is the use of tags. Cache tags are a simple way to group cached items so it gets easy to remove/invalidate them if needed.Read more