Cache subsets

[danibishop]

It might be interesting to model a way to invalidate sub-sets of the cache instead of having to clear all o nothing.

Pablo Caro has this model as of today (28.1.2019) in Merlin but it is not used.

Example

For the RamCache it could work using the root dictionary as "set container", where sets have keys like 0, 1, 2... and are assigned somehow when querying. (Maybe we could use path urls as keys?) Then, a .flush(key) could be sent to delete only that subset.

[josemazo]

It's an interesting feature, but even @pcaro is using it. We could mark it as a "possible future".