Logical standby databases are a key feature of Oracle Data Guard and offer several distinct advantages, especially in terms of flexibility for reporting, upgrades, and disaster recovery:
Disaster-recovery solution with switchover and failover options (A): Logical standby databases provide a robust disaster-recovery solution, ensuring that any data updated on the primary database can be recovered. They support both switchover and failover operations, allowing for smooth role transitions between the primary and standby databases.
Used for reporting workloads requiring additional indexes or materialized views (B): Logical standby databases can be opened for read-write operations and can have additional indexes or materialized views that are not present in the primary database. This makes them ideal for offloading reporting and querying workloads from the primary database.
Database rolling release upgrades (D): Logical standby databases can be used to perform rolling upgrades of the Oracle Database software. This allows the database to be upgraded with minimal downtime, as the standby database is upgraded first, followed by a switchover to make it the new primary.
Reference:
Oracle Data Guard Concepts and Administration Guide
Oracle Database High Availability Overview