AB: You can make individual table columns invisible. Any generic access of a table does not show the invisible columns in the table. For example, the following operations do not display invisible columns in the output:
*SELECT * FROM statements in SQL
*DESCRIBE commands in SQL*Plus
*%ROWTYPE attribute declarations in PL/SQL
*Describes in Oracle Call Interface (OCI)
Incorrect:
Not D: You can make invisible columns visible.
You can make a column invisible during table creation or when you add a column to a table, and you can later alter the table to make the same column visible.

* Smart Flash Cache concept is not new in Oracle 12C - DB Smart Flash Cache in Oracle 11g.
In this release Oracle has made changes related to both initialization parameters used by DB Smart Flash cache. Now you can define many files|devices and its sizes for "Database Smart Flash Cache" area. In previous releases only one file|device could be defined.
DB_FLASH_CACHE_FILE = /dev/sda, /dev/sdb, /dev/sdc
DB_FLASH_CACHE_SIZE = 32G, 32G, 64G
So above settings defines 3 devices which will be in use by "DB Smart Flash Cache"
/dev/sda ?size 32G
/dev/sdb ?size 32G
/dev/sdc ?size 64G
New view V$FLASHFILESTAT ?it's used to determine the cumulative latency and read counts of each file|device and compute the average latency

HCC requires the use of Oracle Storage - Exadata (A), Pillar Axiom (G) or Sun ZFS Storage Appliance (ZFSSA).
Note:
* Hybrid Columnar Compression, initially only available on Exadata, has been extended to support Pillar Axiom and Sun ZFS Storage Appliance (ZFSSA) storage when used with Oracle Database Enterprise Edition 11.2.0.3 and above
* Oracle offers the ability to manage NFS using a feature called Oracle Direct NFS (dNFS). Oracle Direct NFS implements NFS V3 protocol within the Oracle database kernel itself. Oracle Direct NFS client overcomes many of the challenges associated with using NFS with the Oracle Database with simple configuration, better performance than traditional NFS clients, and offers consistent configuration across platforms.

Multipartition maintenance enables adding, dropping, truncate, merge, split operations on multiple partitions.
A:Merge Multiple Partitions:
The new "ALTER TABLE ... MERGE PARTITIONS " help merge multiple partitions or subpartitions with a single statement. When merging multiple partitions, local and global index operations and semantics for inheritance of unspecified physical attributes are the same for merging two partitions.
B:Drop Multiple Partitions:
The new "ALTER TABLE ... DROP PARTITIONS " help drop multiple partitions or subpartitions with a single statement.
Example:
view plaincopy to clipboardprint?
SQL> ALTER TABLE Tab_tst1 DROP PARTITIONS
Tab_tst1_PART5, Tab_tst1_PART6, Tab_tst1_PART7;
Table altered
SQL>
Restrictions :
-You can't drop all partitions of the table.
-If the table has a single partition, you will get the error: ORA-14083: cannot drop the only partition of a partitioned.

RMAN> ALTER TABLESPACE sysaux OFFLINE IMMEDIATE;
RMAN> RESTORE TABLESPACE sysaux;
RMAN> RECOVER TABLESPACE sysaux;
RMAN> ALTER TABLESPACE sysaux ONLINE;
*Example:
While evaluating the 12c beta3 I was not able to do the recover while testing "all pdb files lost".
Cannot close the pdb as the system datafile was missing...
So only option to recover was:
Shutdown cdb (10)
startup mount; (1)
restore pluggable database
recover pluggable database
alter database open;
alter pluggable database name open;
Oracle support says: You should be able to close the pdb and restore/recover the system
tablespace of PDB.
*Inconsistent backups are usually created by taking online database backups. You can also make
an inconsistent backup by backing up data files while a database is closed, either:
/ Immediately after the crash of an Oracle instance (or, in an Oracle RAC configuration, all instances) / After shutting down the database using SHUTDOWN ABORT Inconsistent backups are only useful if the database is in ARCHIVELOG mode and all archived redo logs created since the backup are available.
* Open the database with the RESETLOGS option after finishing recovery: SQL> ALTER DATABASE OPEN RESETLOGS;