For planned outages, you can achieve almost no interruption to users (zero brownout) in Oracle Database 21c. A phased shutdown of an instance allows the surviving instances to take ownership of locks and other resources so that after the instance is stopped, the amount of work required during reconfiguration is reduced. When the DBA issues a shutdown command for an instance, the instance is transitioned from an active instance to a passive instance.
A passive instance is in an ideal state to be stopped, which means as many resources and locks as possible are transitioned to the active instances. On a Oracle RAC cluster only one passive instance can exist at any time. When this process is initiated, the following actions take place:
- The services running on the passive instance are stopped and relocated to another instance. This includes moving the connections from the passive instance to the active instance with a targeted drain timeout. The drain timeout indicates how long you want to wait for everything to complete, including the shutting down of the passive instance.
- After the services have been drained from the passive instance, all pluggable databases (PDBs) are closed. All lock masters are transferred from the passive instance to active instances.
- The instance is shutdown normally.