Is @jb55's nostrdb work useful in any way for android?
Sure, you just need to port filters to the content resolver calls (which look like SQLs if you ever used SQLs in Java). I just don't know if the LMDb idea of mapping file pages to memory works is optimized for android's filesystem.
Its a virtual memory thing more than a filesystem thing. Just need to make sure android supports allocating large virtual memory maps.
Android is linux, right? I don't see why it wouldn't allow big maps
Android exposes the filesystem through it's own interfaces that might get in the way. So, when it comes to file system access, I usually don't assume anything.