To perform upgrade of a production database from 11gR1 to 11gR2 or to perform any patch set upgrade (for example, from 11.2.0.1 to 11.2.0.3), we need downtime. When upgrading a production database that includes movement of the database to new binaries, database upgrade, and post upgrade tasks, we may need a few hours or more downtime depending on the database size, runtime errors, and so on. However, with the feature of Rolling Upgrade Using Transient Logical Standby, we may only need a few minutes of downtime. We can also run load tests to check the performance on the upgraded logical standby database when keeping the primary database with the old version without any upgrade. If the performance test results in a good response, we can go ahead to perform the further steps.