Article: Mastering Data History using Oracle's Flashback Data Archive Feature

The Historical data is key for business decisions and having reliable data is very important for organizations. There are frequent implications for both financial and legal data for organizations and having a secure and accurate history of change of data is crucial for business.

Oracle Flashback technology offers significant benefits for database management and recovery. 

Please see the below article how it will help to meet the organizational needs.

Mastering Data History : A Guide using Oracle's Flashback Data Archive Feature
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Flashback Data Archive enhancements in Oracle 12c

Flashback feature uses Automatic Undo Management for historical and metadata transactions. Flashback Data archive (FDA) feature introduced in Oracle 11g for undo-based flashback operations, and it is configured using retention time. Flashback data archive supported for multitenant (12.1.0.2 and above versions) as well using local or shared undo configuration.

Oracle 12c (12.1.0.1) has below enhancements in FDA

• Data Hardening
• User context tracking

Data Hardening – This feature helps to associate set of tables for a specific application, so that you can enable Flashback Data archive for all those tables in a single command. Use DMBS_FLASHBACK_ARCHIVE.REGISTER_APPLICATION to register an application

You can create new application using REGISTER_APPLICATION

SQL> Begin
DBMS_FLASHBACK_ARCHIVE.register_application(
application_name => 'ORACLERACEXPERT',
flashback_archive_name => 'FDA1');
end;
/

You can add tables to the application using ADD_TABLE_TO_APPLICATION procedure

SQL> Begin
DBMS_FLASHBACK_ARCHIVE.ADD_TABLE_TO_APPLICATION (

application_name=> 'ORACLERACEXPERT', 

table_name=> 'EMP' , 

schema_name -> 'USER1');
end;
/

SQL> Begin
DBMS_FLASHBACK_ARCHIVE.ADD_TABLE_TO_APPLICATION (

application_name=> 'ORACLERACEXPERT', 

table_name=> 'DEPT' , 

schema_name -> 'USER1');
end;
/

You can remove the tables using REMOVE_TABLE_FROM_APPLICATION procedure from

The application will not enable automatically, use ENABLE_APPLICATION procedure to enable Flashback Data Archive for all tables in the specified application.

SQL> Begin
DBMS_FLASHBACK_ARCHIVE.enable_application(

application_name => 'ORACLERACEXPERT');
end;
/

To disable the application use disable_application procedure

SQL> Begin
DBMS_FLASHBACK_ARCHIVE.disable_application(
application_name => 'ORACLERACEXPERT');
end;
/

User context tracking - By enabling this feature it is easy to track which user made what changes to the table.

Use DMBS_FLASHBACK_ARCHIVE.SET_CONTEXT_LEVEL procedure to Set the user content level and procedure DMBS_FLASHBACK_ARCHIVE.GET_SYS_CONTEXT procedure To Access the context

There are 3 options depending upon how much user context needs to save
ALL – The entire SYS_CONTEXT is stored
TYPICAL – The user context is stored
NONE- Nothing

For ex: - To set context level to ALL
SQL> DBMS_FLASHBACK_ARCHIVE.SET_CONTEXT_LEVEL ( level=>‘ALL’);

You can get the XID from the archive table

SQL> select XID from SYS_FBA_HIST_93222;
XID
----------------
05000A0B7040000

Now with XID you can get the context information using dbms_flashback_archive.get_sys_context procedure


SQL> begin
dbms_output.put_line(dbms_flashback_archive.get_sys_context ('05000A0B7040000', 'USERENV', 'SESSION_USER'));
dbms_output.put_line(dbms_flashback_archive.get_sys_context ('05000A0B7040000', 'USERENV', 'HOST'));
dbms_output.put_line(dbms_flashback_archive.get_sys_context ('05000A0B7040000', 'USERENV', 'MODULE'));
end;
/
USER1
SRVHOST
SQL*Plus

You can get all Transactions ID using below query

SQL> select empno, empname, VERSIONS_XID
from EMP order by empno;

EMPNO EMPNAME VERSIONS_XID
----------- --------------- ---------------------
1              ORARAC    05000A0B7040000

You can use SYS_FBA_CONTEXT_AUD to get context information for each transaction.

There are many Flashback data archive view available and to get the list of all views run below query

SQL> SET PAGESIZE 1000
SQL> SET LINESIZE 600
SQL> COLUMN owner FORMAT A10
SQL> COLUMN table_name FORMAT A25

SQL> SELECT owner, table_name FROM dba_tables WHERE table_name LIKE '%FBA%';

 
OWNER       TABLE_NAME
--------------  -------------------------
SYS              SYS_FBA_FA
SYS              SYS_FBA_TSFA
SYS              SYS_FBA_TRACKEDTABLES
SYS              SYS_FBA_PARTITIONS
SYS              SYS_FBA_USERS
SYS              SYS_FBA_BARRIERSCN
SYS              SYS_FBA_DL
SYS              SYS_FBA_CONTEXT
SYS              SYS_FBA_CONTEXT_AUD
SYS              SYS_FBA_CONTEXT_LIST
SYS              SYS_FBA_APP
SYS              SYS_FBA_APP_TABLES
SYS              SYS_FBA_COLS
SYS              SYS_FBA_PERIOD
SYS              SYS_MFBA_STAGE_RID
SYS              SYS_MFBA_TRACKED_TXN
SYS              SYS_MFBA_NROW
SYS              SYS_MFBA_NCHANGE
SYS              SYS_MFBA_NTCRV

You can refer below Oracle Doc for best practices

FDA - Flashback Data Archive Usage and Best Practices (Doc ID 2370465.1)

Flashback Data Archive provides many benefits for maintaining historic data against tracked tables. The FDA helps to perform undo-based flashback operations for an extended period and take advantage of this feature.

Oracle Flashback Technology and features

Oracle Flashback Technology is a group of Database features that that will help you to view past states of database objects or to return database objects to a previous state without using point-in-time media recovery.

With flashback features, you can do the following:
· Queries that return past data
· Recover rows or tables to a previous point in time
· Track and archive transactional data changes
· Roll back a transaction and its dependent transactions while the db online

Oracle flashback uses automatic undo management (AUM) for all flashback transactions.

Here are few Oracle flashback features.
· Flashback Database
· Flashback Table
· Flashback drop
· Flashback query
· Flashback Version/Transaction Query
· Flashback Data Archive (From Oracle 11g)
· Flashback Recovery Area:-

Flashback Database:- The FLASHBACK DATABASE is a fast alternative to performing an incomplete recovery. The database must be running in ARCHIVELOG mode, because archived logs are used in the Flashback Database operation. You must have a flash recovery area enabled, because flashback logs can only be stored in the flash recovery area.

To enable logging for Flashback Database, set the DB_FLASHBACK_RETENTION_TARGET initialization parameter and issue the ALTER DATABASE FLASHBACK ON statement.

DB_FLASHBACK_RETENTION_TARGET- length of the desired flashback window in minutes (1440 min)

SQL> ALTER SYSTEM SET DB_FLASHBACK_RETENTION_TARGET=4320; # 3 days

For ex-
FLASHBACK DATABASE TO TIMESTAMP my_date;
FLASHBACK DATABASE TO SCN my_scn;

Limitations:
· It cannot be used to repair media failures, or to recover from accidental deletion of data files.
· You cannot use Flashback Database to undo a shrink data file operation.
· If the database control file is restored from backup or re-created, all accumulated flashback log information is discarded
· Flashback database cannot be used against block corruptions.

Flashback Table The FLASHBACK TABLE used to restore an earlier state of a table in the event of human or application error. The time in the past to which the table can be flashed back is dependent on the amount of undo data in the system and cannot restore a table to an earlier state across any DDL operation.

SQL> FLASHBACK TABLE test TO TIMESTAMP (SYSTIMESTAMP - INTERVAL '1' minute);

Flashback Drop:

The Oracle 10g provides the ability to reinstating an accidentally dropped table from recyclebin.
SQL> FLASHBACK TABLE test TO BEFORE DROP;

Flashback Query The feature allows the DBA to see the value of a column as of a specific time, as long as the before-image copy of the block is available in the undo segment.

For ex:-
SQL> SELECT comments FROM employee AS OF TIMESTAMP TO_TIMESTAMP ('2004-03-29 13:34:12', 'YYYY-MM-DD HH24:MI:SS');

SQL> SELECT comments FROM employee AS OF SCN 722452;

Flashback Version/Transaction Query Flashback Query only provides a fixed snapshot of the data as of a time. Use Flashback Version Query feature to see the changed data between two time points.

Ex: - The following query shows the changes made to the table:

SQL> select versions_starttime, versions_endtime, versions_xid, versions_operation, rate from rates versions between timestamp minvalue and maxvalue order by VERSIONS_STARTTIME

Flashback transaction query can be used to get extra information about the transactions listed by flashback version queries using FLASHBACK_TRANSACTION_QUERY view. The UNDO_SQL column in the table shows the actual SQL Statement.

For Ex:-
SQL> SELECT xid, operation, start_scn, commit_scn, logon_user, undo_sql FROM flashback_transaction_query

Oracle 11g has more enhancements in Flashback Transaction and LogMiner. The LogMiner Viewer has been incorporated into Enterprise Manager and integrated with the new Flashback Transaction feature, making it simple to recover transactions. Flashback Transaction allows the changes made by a transaction to be undone.

Flashback Data Archive (From Oracle 11g) : Flashback data archive allows long-term retention (for ex years) of changed data to a table or set of tables for a user-defined period of time. Flashback Data Archive (which can logically span one or more table spaces) specifies a space quota and retention period for the archive, and then creates the required tables in the archive.

User needs the FLASHBACK ARCHIVE ADMINISTER, FLASHBACK ARCHIVE privileges

SQL> CREATE FLASHBACK ARCHIVE flash_back_archive

TABLESPACE flash_back_archive QUOTA 10G RETENTION 5 YEARS;

Flashback Recovery Area:-
Flash recovery area is a disk location in which the database can store and manage files related to Backup and Recovery. To setup a flash recovery area, you must choose a directory location or Automatic Storage Management disk group to hold the files.

Flash recovery area simplifies the administration of your database by automatically naming recovery-related files, retaining the files as long as they are needed for restore and recovery activities, and deleting the files when they are no longer needed to restore your database and space is needed for some other backup and recovery-related purpose.

To Setup Flash Recovery Area (FRA), you just need to specify below two parameters.
1. DB_RECOVERY_FILE_DEST_SIZE (Specifies max space to use for FRA)

2. DB_RECOVERY_FILE_DEST (Location of FRA)

Performance Guidelines for Oracle Flashback Technology
· For Oracle Flashback Version Query, use index structures.

· Not to scan entire tables and use indexes to query small set of past data. If you need to scan a full table then use parallel hint to the query

· Keep the statistics current as cost-based optimized relies on statistics and use the DBMS_STATS package to generate statistics for tables involved in a Oracle Flashback Query.

· In a Oracle Flashback Transaction Query, the xid column is of the type RAW(8). Use the HEXTORAW conversion function: HEXTORAW(xid)to take advantage of inbuilt function

· The I/O performance cost is mainly paging in the data and undo blocks I the buffer cache. The CPU performance cost is to apply undo.

· A Oracle Flashback Query against a materialized view does not take advantage of query rewrite optimization.

Regards

Satishbabu Gunukula, Oracle ACE

http://www.oracleracexpert.com