To increase the number of applier processes on a logical standby database, the following changes can be made:
* C: Increasing the value for the MAX_SERVERS SQL apply parameter would allow for more applier processes to be initiated, assuming that system resources permit.
* D: Increasing the PARALLEL_MAX_SERVERS initialization parameter would allow for more parallel execution processes, which can be used by SQL apply to increase the number of applier processes.
Option A is incorrect as decreasing the number of archiver processes will not necessarily increase the number of applier processes; these are unrelated components.
Option B is incorrect because the 'FREPARER' processes do not exist, it seems to be a typographical error, and the 'REPARER' is not a valid Oracle process or parameter.
Option E is incorrect because the RECOVERY_PARALLELISM parameter controls the number of processes used for instance recovery and media recovery, not for SQL apply.
References: Oracle Data Guard Concepts and Administration guide details the configuration and tuning of SQL apply-related parameters in logical standby databases.

Enterprise Manager Cloud Control provides a graphical interface to manage multiple standby databases, simplify switchovers and failovers, and automate failover processes to a specified target standby database. It offers a comprehensive view and control over the Data Guard configuration, making complex operations more manageable.
DGMGRL is a command-line tool specifically designed for managing Data Guard configurations. It allows the administration of multiple standby databases, simplifies the execution of switchovers and failovers, reinstatements, and conversions to and from snapshot standby databases, and supports the automation of failover processes to a specified standby database.
Other options like RMAN, SQL*Plus, CRSCTL, SRVCTL, and GDCCTL do not provide the same level of integrated management functionality for Data Guard environments as Enterprise Manager Cloud Control and DGMGRL.

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.References:
* Oracle Data Guard Concepts and Administration Guide
* Oracle Database High Availability Overview