I am going to tune a system which is using "RULE" mode for optimizer_mode; according to people here this application was developed to work properly in "RULE" mode. I am going to start to look for those huge queries which are consuming a lot of BUFFER_GETS. My question here is how can I tune these kinds of queries if this system is not using statistics? I think I can only use HINTS and move "driving tables" to guess if an optimizer plan is better. Can stored outlines be used if code can't be touched? We are using 126.96.36.199. Thanks in advance.
Yes, you can use stored outlines; note that Oracle always uses the cost-based optimizer (CBO) when outlines are activated.
Even though the application was built to use rule-based optimization, it would be worth testing with the CBO. You may find that the results are acceptable.