To ensure Oracle uses a specific index, you can employ SQL hints. The INDEX hint directs the optimizer to use a particular index. Here's how you can implement it:

1. Use the INDEX Hint: Modify your SQL query to include the INDEX hint. For example:

   SELECT /*+ INDEX(e, HireDate_idx) */ * FROM Employees e WHERE e.HireDate > '2020-01-01';

   Replace e with your table alias and HireDate_idx with the index name.

2. Check Execution Plan: Use EXPLAIN PLAN or the execution plan feature to verify if the index is used:

   EXPLAIN PLAN FORSELECT /*+ INDEX(e, HireDate_idx) */ * FROM Employees e WHERE e.HireDate > '2020-01-01';

   Review the plan to confirm the index is utilized.

3. Consider Hints Sparingly: Only use hints when necessary, as the optimizer typically selects the optimal path. Forced indexes might not always improve performance.

4. Analyze Query and Data: Ensure the index is appropriate for the query. High-cardinality columns benefit more from indexing.

5. Test Performance: Measure query performance before and after applying the hint to assess impact.

By following these steps, you can effectively guide Oracle to use a specific index, optimizing your database performance.