Drupal: cache tags for all, regardless your backend
Phil Karlton is quoted as having said, “There are only two hard things in Computer Science: cache invalidation and naming things.” As someone who suffers horribly from the latter, I’m glad Drupal’s caching APIs make the former a breeze. The long short of it is that caching of data improves performance by not having to perform the same operations multiple times after it has been done the first time until you need to re-run that operation again. It involves some storage (static variable in memory, memory backend storage, or the database.) Generally, you store the data with a given identifier for later retrieval, the actual data to be cached for later reuse, and possibly an expiration time for automatic invalidation.
And that’s where cache invalidation is hard. What if you need a cache object to be invalidated before its automatic invalidation? Or what if the cache is set to be permanent? First, you need to know when and how to invalidate something. This may get even more complicated if your when means you need to invalidate multiple cache objects. That’s where cache tags are helpful and allow invalidating a group of cache objects without knowing their identifiers.
Drupal’s 8.0.0 release introduced cache tags to the Cache API. Previously Drupal supported using wild card cache identifiers for bulk cache invalidation. Thanks to sdboyer, catch, and everyone else who made this possible!
