The impact of Quest SQL Optimizer for Oracle on a database machine is relatively light as all it does is to gather the table information from the data dictionary and then retrieve execution plan for all. All other processing by SQL Optimization is done on the client PC.
However, during a test run, SQL will be sent to the database server for execution. This will have a big impact on database performance.
The best way to do SQL Optimization is to set up a testing environment similar to the production environment. Perform SQL Optimization against the testing database. Test run alternatives in the testing database to find the best results. Then confirm the performance of that best SQL in the production database before actually changing the source code.
