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:
update mytab set ora_archive_state=2 where col2='FRED';
3. To make "invisible rows" visible again, you simply set the rows ora_archive_state to zero:
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.

Explanation/Reference:
Explanation:

Explanation/Reference:
Explanation:
CREATE DISKGROUP NORMAL REDUNDANCY
* For Oracle ASM to mirror files, specify the redundancy level as NORMAL REDUNDANCY (2-way mirroring by default for most file types) or HIGH REDUNDANCY (3-way mirroring for all files).