Which two are true about the usage of DBMS_ROLLING?

A.
The leading group contains the original primary database.

B.
The trailing group contains the original primary database.

C.
The background process DMON must be enabled on all database instances that take part in the rolling
release upgrade process.

D.
At least one logical standby database must be part of the initial Data Guard configuration.

E.
The trailing group can contain standby databases that will protect the original primary database during the
rolling release upgrade process.

Explanation:
E: The trailing group contains the original primary database and standby databases that will protect the original
primary during the rolling upgrade process.
D: Databases in the leading group are upgraded first; hence the name leading group. The leading groupcontains the designated future primary database, and the physical standbys that you can configure to protect
the designated future primary. The future primary is first converted into a logical standby database and then the
new database software is installed on it and the upgrade process is run. Other standby databases in the
leading group also must have their software upgraded at this point.
Note: To upgrade the database software in an Oracle Data Guard configuration in a rolling fashion, you first
designate a physical standby as the future primary database.
Conceptually, the rolling upgrade process splits the Oracle Data Guard configuration into two groups: the
leading group (LG) and the trailing group (TG).
Incorrect Answers:
A: The leading group contains the designated future primary database, and the physical standbys that you can
configure to protect the designated future primary.
https://docs.oracle.com/database/121/SBYDB/dbms_rolling_upgrades.htm#SBYDB5431

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Chunn

Correct Ans: A, E

To upgrade the database in an Oracle Data Guard configuration in a rolling fashion, you first designate a **physical standby as the future primary database.

Conceptually, the rolling upgrade process splits the Oracle Data Guard configuration into two groups: the leading group (LG) and the trailing group (TG).

Databases in the leading group are upgraded first; hence the name leading group. The leading group contains the designated future primary database, and the physical standbys that you can configure to protect the designated future primary. The future primary is first converted into a logical standby database and then the new database software is installed on it and the upgrade process is run. Other standby databases in the leading group also must have their software upgraded at this point.

The trailing group contains the original primary database and standby databases that protect the original primary during the rolling upgrade process. While the databases in the leading group are going through the upgrade process, user applications can still be connected to the original primary and making changes. The trailing group databases continue running the old database software until all the databases in the leading group are upgraded and the future primary has caught up with the original primary by applying the changes that were generated at the original primary database during the upgrade window. At this point a switchover is done to transfer the primary role to the designated future primary database, and the user applications are switched over to the new primary database. New software is then installed on the databases that are part of the trailing group, and they are reinstated into the configuration as standbys to the new primary database.

The standbys in the respective groups are called the Leading Group Standbys (LGS) and Trailing Group Standbys (TGS). Other than the designated future primary, all other standbys in the leading group can only be physical standbys. The trailing group can contain both physical and logical standbys.

https://docs.oracle.com/database/121/SBYDB/dbms_rolling_upgrades.htm#SBYDB5214