We have a third party application that had been running on for a few years without any performance issues. The third party vendor has now certified the software to run on 11GR2. We upgraded the database to 11GR2 in test environment and noticed significant degradation in the performance. I turned on tracing a found many SQL statements that were causing the problems. These SQL would execute in seconds on 10G, and the same SQL took a few minutes to execute in 11GR2. I set the optimizer_features_enable= and restarted the database and everything went back to normal. Unfortunately, we cannot optimize the SQL code since this is vendor software.

Question: If I keep the optimizer_features_enable= permanantly, does this mean that all the SQL will use the 10G optimizer in the 11G instance and not the 11G optimizer ? .