I'm currently working on dApps for a private blockchain based on ethereum. While it works fine and the dApps really show the power of the blockchain it lacks the speed and versatility of a SQL database. (I know i know blockchain != database).
Example where it lacks is getting specific data. Because you don't have SQL like queries you need to loop through a lot of data. Or if have a array of a struct you want that back, this also poses an issue.
So I was thinking about an caching mechanism to cache data that is verified by the network in a local database for fast querying.
Google failed when searching for this so my question does something like this really not exist? If it doesn't exists what do I need to keep in mind if I want to design a system like this myself.