New Features of Oracle 12c Summarized
Oracle is doing every thing to jump into the cloud bandwagon. With
12C, Oracle is trying to address the problem of Multitenancy through
this feature. There is a radical change and a major change in the core
database architecture through the introduction of Container Databases
also called CBD and Pluggable Databases (PDB). The memory and process is
owned by the Container Database. The container holds the metadata where
the PDBs hold the user data. You can create upto 253 PDBs including the
seed PDB.
In a large setup, it is common to see 20 or 30 different instances
running in production environment. With these many instances, it is a
maintenance nightmare as all these instances have to be separately
•Upgraded
•Patched
•Monitored
•Tuned
•RAC Enabled
•Adjusted
•Backed up and
•Data Guarded.
With Pluggable Databases feature, you just have to do all this for
ONE single instance. Without this feature, prior to 12C, you would have
to create separate schemas and there is always a thread of security how
much ever the isolation we build into it. There are problems with
namespace conflicts, there is always going to be one public synonym that
you can create. With PDBs you can have a separate HR or Scott schema
for each PDB, separate Emp, Dept Tables and separate public synonyms.
Additionally, 2 PDBs can talk to each other through the regular DB Link
feature. There is no high startup cost of creating a database any more.
Instead of one instance per day, the shift is into one instance per many
databases. For the developer community, you can be oblivious of all
this and still continue to use the PDBs as if it were a traditional
database, but for the DBAs the world would look like it has changed a
lot.
Another cool feature is, you can allocate a CPU percentage for each PDB.
Another initiative being, it has announced a strategic tieup with salesforce.com during the first week of July 2013.
This is one of the top features in Oracle 12C. Data Redaction in
simple terms means, masking of data. You can setup a Data Redaction
policy, for example SSN field in a Employee table can be masked. This is
called redaction. From Sql Develop you can do this by going to the
table: Employee->Right click on Security Policy->click on
New->click on Redaction Policy->Enter SSN.
When you do a select * from employee, it will show that the SSN is masked.
The new data masking will use a package called DBMS_REDACT. It is the extension to the FGAC and VPD present in earlier versions.
By doing this, whoever needs to view the data will be able to see it where as the other users will not be able to view it.
With the release of Oracle Database 12c, Oracle has introduced this
new SQL syntax to simplify fetching the first few rows. The new sql
syntax "Fetch First X Rows only" can be used.
With this feature, it helps the optimizer to make runtime adjustments
to execution plan which leads to better stats. For statements like CTAS
(Create Table As Select) and IAS (Insert As Select), the stats is
gathered online so that it is available immediately.
Earlier if you had to restore a particular table, you had to do all
sorts of things like restoring a tablespace and or do Export and Import.
The new restore command in RMAN simplifies this task.
The previous limit on these data types was 4K. In 12C, it has been
increased to 32,767 bytes. Upto 4K, the data is stored inline. I am sure
everyone will be happy with this small and cute enhancement.
The in line feature is extended in Oracle 12C. In addition to Views,
we can now have PL/SQL Procedures and Functions as in line constructs.
The query can be written as if it is calling a real stored procedure,
but however the functions do not actually exist in the database. You
will not be able to find them in ALL_OBJECTS. I think this will be a
very good feature for the developers to explore as there is no code that
needs to be compiled.
You can now create a col with 'generated as identity' clause. Thats
it. Doing this is equivalent to creating a separate sequence and doing a
sequence.nextval for each row. This is another handy and a neat feature
which will help developer community. This is also called No Sequence
Auto Increment Primary Key.
Prior to 12C, a column cant be in more than one index. In 12C, you
can include a column in B-tree index as well as a Bit Map index. But,
please note that only one index is usable at a given time.
You can very easily migrate a partition or sub partition from one
tablespace to another. Similar to how the online migration was achieved
for a non-partitioned table in prior releases, a table partition or sub
partition can be moved to another tablespace online or offline. When an
ONLINE clause is specified, all DML operations can be performed without
any interruption on the partition|sub-partition which is involved in the
procedure. In contrast, no DML operations are allowed if the
partition|sub-partition is moved offline.
Prior to 12C, undo records generated by TEMP Tablespace is stored in
the undo tablespace. With Temp undo feature in 12C, temp undo records
can be stored in temporary table instead of UNDO TS. The benefit is -
reduced undo tablespace and reduced redo log space used.
SQL> ALTER SYSTEM SET PGA_AGGREGATE_LIMIT=2G;
SQL> ALTER SYSTEM SET PGA_AGGREGATE_LIMIT=0; --disables the hard limit
This feature enables archiving rows within a table by marking them as
inactive. These inactive rows are in the database and can be optimized
using compression but are not visible to the application. These records
are skipped during FTS (Full Table Scan).
Advanced Replication and Streams are Dead. It is being replaced with Oracle Golden Gate.
Invisible Columns. You can now have a invisible column in a table.
When a column is defined as invisible, the column won’t appear in
generic queries
PGA Aggregate Limit setting:
In 12c, you can set a hard limit on PGA by enabling the automatic PGA
management, which requires PGA_AGGREGATE_LIMIT parameter settings.
Therefore, you can now set the hard limit on PGA by setting the new
parameter to avoid excessive PGA usage.
DDL Logging:
The DDL statements will automatically get recorded in xml/log file if
ENABLE_DDL_LOGGING is set to True. ALTER SYSTEM|SESSION SET
ENABLE_DDL_LOGGING=TRUE
