You must configure flashback database for your Oracle 19c databases that will be part of a Data Guard Broker configuration. The databases are all in ARCHIVELOG mode. You will execute the SQL statement: ALTER DATABASE FLASHBACK ON; Which three are true concerning this command?

The ALTER DATABASE FLASHBACK ON command can only be executed when the database is in a MOUNT state, but not OPEN. This is a prerequisite for enabling Flashback Database because Oracle must start the Recovery Writer (RVWR) background process and perform other setup operations that cannot be done while the database is actively in use. This requirement applies to primary, physical standby, and logical standby databases.

A. This is incorrect. Executing ALTER DATABASE FLASHBACK ON while the database is open will result in an error (e.g., ORA-01153).
C. This is incorrect. Real Time Query requires the physical standby database to be open in read-only mode. The database must be in the MOUNT state to enable Flashback.
D. This is incorrect. Enabling Flashback Database is a physical change to the database control files and does not generate logical redo. It must be enabled separately on a logical standby.
E. This is incorrect. A logical standby with active SQL Apply is in an OPEN state. The database must be shut down and restarted in the MOUNT state to enable Flashback.
F. This is incorrect. The Flashback Database setting is not automatically propagated from the primary to its physical standbys. Official documentation explicitly states it must be enabled on each standby database individually. Note on the Question: The question asks for three true statements. Based on official Oracle documentation, only one of the provided options (B) is correct. ---

1. Oracle Database SQL Language Reference, 19c, "ALTER DATABASE". In the Semantics section for the FLASHBACK DATABASE clause, under FLASHBACK ON, the usage notes state: "The database must be mounted but not open."

2. Oracle Data Guard Concepts and Administration, 19c, Chapter 12, "Using Oracle Flashback Database and Restore Points in a Data Guard Configuration", Section 12.1.1, "Enabling Oracle Flashback Database". The documentation states: "You must explicitly enable Oracle Flashback Database on each standby database on which you want to use it. To enable Oracle Flashback Database on a physical or logical standby database, connect to the standby database and issue the same ALTER DATABASE FLASHBACK ON; statement that you use to enable it on a primary database. Oracle Flashback Database must be enabled while the standby database is mounted." This directly refutes options D and F.

3. Oracle Database Backup and Recovery User's Guide, 19c, Chapter 17, "Using Flashback Database and Restore Points", Section 17.2.1, "Enabling Flashback Database". This section outlines the procedure: "Ensure that the database is mounted, but not open... Run the ALTER DATABASE FLASHBACK ON; statement." This confirms option B and refutes options A, C, and E.