Oracle Database 12c

(12.1.0.1)

New Features

Who AM I?

Navneet Upneja (Oracle DBA)

7 Years of Experience in Oracle Databases and

Middleware Applications Oracle Certified Professional

Hand on experience on OLTP, Datawarehouse,

Oracle BI, APEX…

Member of North India Chapter.

Overview

• Optimizer Statistics

• DDL Logging

• Invisible Columns

• Multiple Indexes

• Nologging – Data Pump

• Limit on PGA

• Moving Datafile Online

• Global Temporary Undo

• Duplicate Database Enhancement

• Table Level Recovery using RMAN

• Q&A

Optimizer Statistics

Online Statistics Gathering Prior to 12c, only Index creation use to gather statistics during creation.

With 12c, Statistics are being gathered for objects created using Direct

Path operations like CTAS and Insert as select operations.

This will save extra Full Data scan required to gather statistics

immediately after creating a new object.

Will be useful in ETL Jobs.

Histograms are not generated by the online statistics gathering Job

since it require additional data scans and can impact the overall time

require to create the object or perform batch Insert operation.

Contd.

Statistics for GTT’s

GTT shares its definition with system wide users

Content in GTT is private to particular session.

Pre 12c, statistics gathered on GTT’s were published system wide. In 12c, statistics on GTT’s can be kept private to the session collecting

the stats.

Useful in cases, where volume of data varies greatly across sessions.

Controlled with GLOBAL_TEMP_TABLE_STATS preference of DBMS_STATS

By default, preference is set to Session {SHARED}

DBMS_STATS.SET_TABLE_PREFS('NUPNEJA','TEMP_GT','GLOBAL_TEMP_TABLE_STATS','SHARED');

SELECT dbms_stats.get_prefs('GLOBAL_TEMP_TABLE_STATS','NUPNEJA','TEMP_GT')

FROM DUAL;

Invisible Column

• Starting from 12c, one can add column to a table and make It as invisible.

• Can be used as low level security for a column.

• Different from system generated hidden columns

• Would not be shown up in result of select if not explicitly defined in Select

list of columns.

• Describe command will not show invisible column as part of table definition.

• Cannot create invisible column in

– External Tables

– Cluster Tables

– Temporary Tables

Contd.

Multiple Indexes on same column

• Now, you can multiple Indexes on same column or same set of columns as long as some characteristics of Index/Indexes are

different. • Unique and non Unique

• B*Tree and Bitmap

• Partitioning Strategies like Local and Global.

• One of the Index needs to be Invisible.

Can be used if

optimizer_use_invisible_indexes

set to True. Need to change the Index Type in

production on a big table.

Doing Troubleshooting for performance.

Need to change the Primary

key/Unique Key Index..

Do we need

this?

Contd.

DDL Logging

• In 12c, we can log the DDL statements running in a session or at system

level.

• Controlled by parameter “ENABLE_DDL_LOGGING” • Can be set at Session level as well.

• DDL log is stored in the log/ddl subdirectory of the ADR home.

• DDL log contains one log record for each DDL statement issued by the database/session.

• Two types of log files: XML and Text File.

• Can be useful to diagnose all the DDL’s running in a big package/program. • Can be useful in troubleshooting any application program.

Contd.

Contd.

Temporary Undo

• By default, undo records for temporary tables are stored in the undo

tablespace and are logged in the redo.

• 12c introduces new concept of Temporary Undo: Undo generated by

transactions on temporary tables managed inside temporary undo

segments.

• Reduces amount of undo stored in undo tablespace.

• Inturn, reduces amount of redo generated.

• Managed using TEMP_UNDO_ENABLED parameter.

• Can be set at session level or system level.

• Default value is “FALSE”. • Temp Undo statistics can be monitored through “V$TEMPUNDOSTAT”.

Limit on PGA

• The Program Global Area (PGA) is a private memory region that contains

the data and control information for a server process.

• PGA_AGGREGATE_TARGET: Target aggregate PGA memory available to

all server processes attached to the instance.

Is it a hard limit?

Shocked????

PGA_AGGREGATE_LIMIT

• PGA_AGGREGATE_TARGET setting acts as a target, and not a

limit.

• PGA_AGGREGATE_LIMIT initialization parameter enables you to specify a hard limit on PGA memory.

• Oracle Database aborts or terminates the sessions or processes that are consuming the most untunable PGA memory

– Calls for sessions that are consuming the most untunable PGA memory are

aborted.

– If PGA memory usage is still over the PGA_AGGREGATE_LIMIT, then the

sessions and processes that are consuming the most untunable PGA memory

are terminated.

Contd.

Recover Table using RMAN

TSPITR DBPITR

Pre Oracle 12 Way

Recylebin Flashback

Oracle 12c way

• RMAN enables you to recover one or more tables or table partitions to a

specified point in time without affecting the remaining database objects.

• Is a mix bag of already available techniques for recovery but with

automation added to it.

• Need to have backup available which contains the missing table/tables.

• Make use of Duplicate database concept and created an auxiliary instance

to recover the table.

• Make use of Data pump to export the table from auxiliary instance and

import into target database.

• Auxiliary Instance is removed after the table is recovered.

Contd.

Contd.

Additional Clauses

• DUMP FILE and DATAPUMP DESTINATION

• NOTABLEIMPORT

• REMAP TABLE

• REMAP TABLESPACE

Duplicate Enhancements

• With Introduction of Multitenant database architecture in Oracle 12c, there

has been more options added to duplicate database command as well.

• Duplicate CDB’s

• Duplicate PDB’s

• Duplicate with Noopen.

Moving Datafile Online

• Starting with Oracle 12c, we can move the datafile while it is online.

• ALTER DATABASE MOVE DATAFILE SQL statement to rename or relocate online data files.

• Enables you to rename or relocate a data file while the database is open

and users are accessing the data file.

• If a file with the same name already exists in the destination location, the

existing file is not overwritten, and the statement returns an error.

• Keep option to retain the original file as well.

• Datafile must be online to perform this.

• You cannot move datafile of a pluggable database from container database.

Contd.