If you have spare CPU capacity, you might want to just re-run and diff the query results. You are already paying for the idle CPU anyway. I think the issue is

If you have spare CPU capacity, you might want to just re-run and diff the query results. You are already paying for the idle CPU anyway. I think the issue is that most SQL engines are not designed for streams, just a single request/response. Once the query is complicated enough I think it would be difficult to do efficiently and correctly. I would go with SQLite in WAL mode (concurrent reads), many cores, and many threads/green threads in a compiled language.