Using sqlite keeps a persistent open database connection, so you only have to send requests for content that sqlite has probably cached. When reading static files, you open, read, and close a file with every request, meaning more context switches, even though the filesystem layer will have cached the file content. If you want to speed this up, the appropriate solution is to add a caching front-end, not to turn everything into a database. It will be faster than using sqlite and easier to maintain and troubleshoot.
Well you can store metadata in SQLite. You can update metadata and files in a transaction. It already has a caching layer built in (I think 8mb by default, that might need some tuning for this use case). It is thread safe (I mean it is a giant rw mutex but whatever) Does not sound that bad to just use it instead of building a caching layer that might be marginally faster than sqlite. And if you restart your caching frontend thing, it will need to rebuild the cache using tons of syscalls. SQLite cache will fill up easier as it has less context switches.
One major downside I see would be backing up the database. You can do granular backups on a filesytem. Even rsync would work fine. You’d need to basically snapshot the entire thing here.
