ALTER TABLE tasks ADD COLUMN port_base INTEGER NOT NULL DEFAULT 0;
UPDATE tasks SET port_base = (
	SELECT 41000 + 10 * (count(*) - 1) FROM tasks AS earlier
	WHERE earlier.status = 'active' AND (earlier.created_at < tasks.created_at OR (earlier.created_at = tasks.created_at AND earlier.id <= tasks.id))
) WHERE status = 'active' AND port_base = 0;