In Oracle, a sequence created with the GLOBAL keyword is available and can produce values across all sessions and instances. However, a sequence created with the SESSION keyword is only specific to the session it was created in. When the NEXTVAL is called for a sequence, it will increment according to the sequence's properties set during its creation.
Given the sequence creation statements and the actions performed:
The a sequence is global, which means it is available across the entire database, including the standby database with Real-Time Query enabled. So, when session 2 calls a.nextval, it will get the next value in the sequence, which is 21 since session 1 already retrieved 1.
The b sequence is session-specific, so when session 2 calls b.nextval, it will get the value 1 because for this new session on the standby, this is the first time the sequence is being accessed.
Therefore, the output for session 2 will be a output as 21 and b output as 1, which corresponds to Option C.

The SQL apply lag on a logical standby database can be caused by several factors:
* A: An undersized undo tablespace can lead to delays in SQL apply operations as it may not be able to handle the volume of undo records generated by the SQL apply process.
* B: SQL apply operations that do full table scans can consume significant system resources, potentially leading to higher apply lag.
* C: An increased number of bulk updates on the primary database may generate a large volume of redo data, which can cause apply lag if the logical standby cannot apply the changes quickly enough.
* F: An undersized shared pool may affect the parsing and execution of SQL statements by SQL apply, which can contribute to the apply lag.
Option D is less likely to be a direct cause of SQL apply lag compared to bulk updates, as inserts generate new data rather than modifying existing data, which SQL apply can typically handle more efficiently.
Option E is incorrect because the size of the standby redo log files on the primary database impacts redo transport lag, not SQL apply lag.
References: Oracle Database High Availability Overview and Oracle Data Guard Concepts and Administration guide provide insights into the factors affecting SQL apply performance on logical standby databases.

The rate of SQL apply on a logical standby database can be influenced by:
* A: The number of PREPARER processes (which seems to be a typographical error and should read as PREPARER or similar) which prepare the redo data for the applier processes.
* B: The number of coordinator processes on the standby database instance which coordinate the SQL apply activities.
* C: The number of full table scans performed by SQL apply since full table scans can be resource-intensive and slow down the apply rate.
* E: The number of applier processes which apply the redo data to the logical standby database.
Option D is incorrect as the size of the undo tablespace on the logical standby database is more likely to affect the SQL apply lag rather than the rate of SQL apply.
Option F is incorrect because the size of the shared pool would typically not influence the rate of SQL apply.
The shared pool is more related to the caching of shared SQL and PL/SQL code and control structures.
References: Oracle's documentation on SQL Apply in Data Guard configurations discusses the factors affecting the performance of SQL Apply operations on logical standby databases.

Based on the Oracle Database 19c documentation, the correct answers about SQL Apply filters for a logical standby database are:A. They can be used to skip execution of DML triggers on a table while allowing the DML to execute.B. They can be used to skip CREATE TABLE commands.C. They can be used to skip ALTER SYSTEM and ALTER DATABASE commands.G. They can be used to skip ALTER TABLE commands on specific tables.
Comprehensive Detailed Explanation:SQL Apply filters in a logical standby database can be set to control which SQL operations are applied to the standby. These filters allow for certain commands to be skipped, ensuring that they do not impact the standby database. For example, filters can be used to skip the execution of DML triggers to prevent them from firing during SQL Apply, while still allowing the underlying DML to be executed on the logical standby database. This is particularly useful when certain triggers are not desired to run in a standby environment. CREATE TABLE, ALTER SYSTEM, ALTER DATABASE, and specific ALTER TABLE commands can also be skipped using SQL Apply filters to prevent unwanted structural changes or administrative operations from affecting the logical standby database. These capabilities provide a level of control to ensure that the logical standby database reflects only the desired state of the primary database.
References:Oracle Database SQL Language Reference and Oracle Data Guard Concepts and Administration guide offer comprehensive details on the use of SQL Apply filters, including the range of SQL statements that can be influenced by these filters in a logical standby database environment.

When issuing a "switchover to sheep;" command in a Data Guard configuration, the primary database (Dogs) transitions to a standby role, and the target standby database (Sheep) becomes the new primary database.
Fast-Start Failover (FSFO) remains enabled, but its target changes according to the new roles of the databases.
Since Cats is also a physical standby database, it does not become the failover target by default unless it is specified in the broker configuration. After the switchover, the original primary (Dogs) becomes the new standby database and thus the new failover target for FSFO.References:Oracle Data Guard Broker documentation provides detailed procedures and explanations of switchover operations, including how FSFO targets are affected post-switchover. This behavior is consistent across different Oracle Database versions that support Data Guard and FSFO.