how do I cache multiple databases (dynamic query)

Suggestion: don't use caching if you don't fully understand how it works.

CI's cache system works by creating a folder for the controller+method and is a very strange implementation imo. Especially if you have multiple models used across different controllers. This isn't so much of an issue if your data doesn't change that often - but if it does change through CRUD functions you'll have to make some house keeping functions to delete the cache files associated with all the controller+methods that query a specific table to which the CRUD operations were performed on; or delete all the cache files (inefficient).

Why the cache system doesn't work by making folders per database table is beyond me.

Just thought I'd bring your attention to these factors.