I'm using magnetico (https://github.com/boramalper/magnetico), a selfhosted bittorrent DHT scraper. After a few months of running I now have a little bit under 1M magnets in a ~3G database. SQLite is useful not just because I can query it with the full power of a relational database, but because I'm using its FTS capability for searching.

If I had to install a typical database or some search engine I would never have used it. It is more than enough for what I'm using it for.