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Explanation:
Note:
* DBMS_REDACT.FULL completely redacts the column data.
* DBMS_REDACT.NONE applies no redaction on the column data. Use this function for development testing purposes. LOB columns are not supported.
* The DBMS_REDACT package provides an interface to Oracle Data Redaction, which enables you to mask (redact) data that is returned from queries issued by low-privileged users or an application.
* If you create a view chain (that is, a view based on another view), then the Data Redaction policy also applies throughout this view chain. The policies remain in effect all of the way up through this view chain, but if another policy is created for one of these views, then for the columns affected in the subsequent views, this new policy takes precedence.

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Explanation:
Step 1 (2). Seed column usage
Oracle must observe a representative workload, in order to determine the appropriate column groups.
Using the new procedure DBMS_STATS.SEED_COL_USAGE, you tell Oracle how long it should observe the workload.
Step 2: (3) You don't need to execute all of the queries in your work during this window. You can simply run explain plan for some of your longer running queries to ensure column group information is recorded for these queries.
Step 3. (1) Create the column groups
At this point you can get Oracle to automatically create the column groups for each of the tables based on the usage information captured during the monitoring window. You simply have to call the DBMS_STATS.CREATE_EXTENDED_STATS function for each table.This function requires just two arguments, the schema name and the table name. From then on, statistics will be maintained for each column group whenever statistics are gathered on the table.
Note:
* DBMS_STATS.REPORT_COL_USAGE reports column usage information and records all the SQL operations the database has processed for a given object.
* The Oracle SQL optimizer has always been ignorant of the implied relationships between data columns within the same table. While the optimizer has traditionally analyzed the distribution of values within a column, he does not collect value-based relationships between columns.
* Creating extended statisticsHere are the steps to create extended statistics for related table columns withdbms_stats.created_extended_stats:
1 - The first step is to create column histograms for the related columns.2 - Next, we run dbms_stats.create_extended_stats to relate the columns together.
Unlike a traditional procedure that is invoked via an execute ("exec") statement, Oracle extended statistics are created via a select statement.

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Explanation:
To perform operations on a single PDB, you can connect as target either to the root or directly to the PDB.
* (A) If you connect to the root, you must use the PLUGGABLE DATABASE syntax in your RMAN commands. For example, to back up a PDB, you use the BACKUP PLUGGABLE DATABASE command.
* (C)If instead you connect directly to a PDB, you can use the same commands that you would use when connecting to a non-CDB. For example, to back up a PDB, you would use the BACKUP DATABASE command.

A: Variable size extents enable support for larger ASM datafiles, reduce SGA memory requirements for very large databases (A), and improve performance for file create and open operations.
C: You don't have to worry about the sizes; the ASM instance automatically allocates the appropriate extent size.
Note:
*The contents of ASM files are stored in a disk group as a set, or collection, of data extents that are stored on individual disks within disk groups. Each extent resides on an individual disk. Extents consist of one or more allocation units (AU). To accommodate increasingly larger files, ASM uses variable size extents.
*The size of the extent map that defines a file can be smaller by a factor of 8 and 64 depending on the file size. The initial extent size is equal to the allocation unit size and it increases by a factor of 8 and 64 at predefined thresholds. This feature is automatic for newly created and resized datafiles when the disk group compatibility attributes are set to Oracle Release 11 or higher.