[anamax]

> I can't find easy information about how search engines save their data (into a database or just locally to the filesystem) and we kind of feel at this end that it is fundamental at this point to decide on the correct path.

There are other possibilities, including both local and remote datastores that aren't really databases.

However, their approach doesn't matter because your problem is significantly (>1000x) smaller and different (for one, you're not running continuously).