Oracle rolling upgrade

Oracle rolling upgrade allows the Oracle RAC configuration to apply patch or upgrade one node at one time, so the RAC cluster is still online during the patch or upgrade. Currently, most new releases of CPU patches and upgrades support rolling upgrade. Rolling upgrade works very well for software upgrade but many patches and upgrades need to run database script in exclusive mode. Because RAC has only one database image so DBAs have to use logical standby database to do the rolling upgrade, which is complicated and costly in term of Oracle license and hardware. Until one day, Oracle can extend Edition-based Redefinition new feature in 11g R2 to sys tables and data dictionary, rolling upgrade will become more common practice.