A: Below we see a case where we set the row archival visibility parameter to "all"
thereby allowing us to see all of the rows that have been logically deleted:
alter session set row archival visibility = all;
We can then turn-on row invisibility back on by changing row archival visibility = "active":
alter session set row archival visibility = all;
B: To use ora_archive_state as an alternative to deleting rows, you need the following settings and parameters:
1.Create the table with the row archival clause
create table mytab (col1 number, col2 char(200)) row archival;
2.Now that the table is marked as row archival, you have two methods for removing rows, a permanent solution with the standard delete DML, plus the new syntax where you set ora_archive_state to a non-zero value:
3.To make "invisible rows" visible again, you simply set the rows ora_archive_state to zero:
update mytab set ora_archive_state=2 where col2='FRED';
update mytab set ora_archive_state=0 where col2='FRED';
Note:
* Starting in Oracle 12c, Oracle provides a new feature that allow you to "logically delete" a row in a table without physically removing the row. This effectively makes deleted rows "invisible" to all SQL and DML, but they can be revealed at any time, providing a sort of "instant" rollback method.
To use ora_archive_state as an alternative to deleting rows.

*A fundamental aspect of the workload repository is that it collects and persists database performance data in a manner that enables historical performance analysis. The mechanism for this is the AWR snapshot. On a periodic basis, AWR takes a "snapshot" of the current statistic values stored in the database instance's memory and persists them to its tables residing in the SYSAUX tablespace.
*AWR is primarily designed to provide input to higherlevel components such as automatic tuning algorithms and advisors, but can also provide a wealth of information for the manual tuning process.

A: In certain situations, you may want to exclude selected columns or tables from scanning or conversion steps of the migration process.
D: Exceed column limit
The cell data will not fit into a column after conversion.
E: Need conversion
The cell data needs to be converted, because its binary representation in the
target character set is different than the representation in the current character
set, but neither length limit issues nor invalid representation issues have been
found.
* Oracle Database Migration Assistant for Unicode (DMU) is a unique next-generation migration
tool providing an end-to-end solution for migrating your databases from legacy encodings to
Unicode.
Incorrect:
Not C: The release of Oracle Database must be 10.2.0.4, 10.2.0.5, 11.1.0.7, 11.2.0.1, or later.

*The choice of threading model is dictated by the THREADED_EXECUTION initialization parameter.
THREADED_EXECUTION=FALSE : The default value causes Oracle to run using the
multiprocess model.
THREADED_EXECUTION=TRUE : Oracle runs with the multithreaded model.
*OS Authentication is not supported with the multithreaded model.
*THREADED_EXECUTION When this initialization parameter is set to TRUE, which enables the multithreaded Oracle model, operating system authentication is not supported. Attempts to connect to the database using operating system authentication (for example, CONNECT / AS SYSDBA or CONNECT / ) when this initialization parameter is set to TRUE receive an ORA-01031"insufficient privileges" error.
F: The new SET CONTAINER statement within a call back function:
The advantage of SET CONTAINER is that the pool does not have to create a new connection to a PDB, if there is an exisitng connection to a different PDB. The pool can use the existing connection, and through SET CONTAINER, can connect to the desired PDB. This can be done using:
ALTER SESSION SET CONTAINER=<PDB Name>
This avoids the need to create a new connection from scratch.

C:Setting the CONTROL_MANAGEMENT_PACK_ACCESS initialization parameter to DIAGNOSTIC+TUNING (default) enables monitoring of database operations. Real-Time SQL Monitoring is a feature of the Oracle Database Tuning Pack.
Note:
*The DBMS_SQL_MONITOR package provides information about Real-time SQL Monitoring and Real-time Database Operation Monitoring.
*(not B)BEGIN_OPERATION Function
starts a composite database operation in the current session.
/(E)FORCE_TRACKING - forces the composite database operation to be tracked when the operation starts. You can also use the string variable 'Y'.
/ (not A)NO_FORCE_TRACKING - the operation will be tracked only when it has consumed at least 5 seconds of CPU or I/O time. You can also use the string variable 'N'.