Given a SQL table `Employee` with columns `id`, `name`, `manager_id`, and `salary`, write a recursive Common Table Expression (CTE) query to calculate the total salary cost for every subtree in the organizational hierarchy. The output should list each manager and the sum of salaries of all employees reporting directly or indirectly to them, including themselves. Additionally, optimize the query for execution plans, specifically discussing how to handle indexing on the `manager_id` column to improve recursive traversal performance. Explain the potential pitfalls of infinite recursion in this context and how to guard against them.