DuckDB v2.0 treats recursive CTEs as one long-lived query, netting a 42.6× speedup
DuckDB's old recursive CTE engine restarted its pipeline machinery on every iteration, paying setup and teardown costs even when the frontier barely changed. In v2.0, the optimizer owns the operator tree and pool of executors for the whole fixed-point computation, retaining state where it stays valid and reusing schedules across epochs. A one-million-edge reachability query drops from 4.05s to 0.095s with identical SQL. There's also a semantic shift: USING KEY ... UNION now surfaces changed-key payloads to the next iteration.