閃回資料歸檔-- Flashback Data Archive

閃回資料歸檔是oracle 11g的特性之一，如果對某個物件（表）使用該功能，那麼從功能啟用開始，針對該物件的所有事務修改都會保留一段時間，

透過 select  as of timestamp 查詢 到特定時期的歷史資料。

Purpose

Scope

This feature can be used by DBA's and Support Analysts to understand and
configure Flashback Data Archive

Details

A new database object, a flashback data archive is a logical container for storing historical information. It is stored in one or more tablespaces and tracks the history for one or more tables.
You specify retention duration for each flashback data archive (could be # of years).
SQL> create flashback archive fla1 tablespace tbs1 retention 2 year;

With the "Oracle Total Recall" option, Oracle database 11g has been specifically enhanced to track history with minimal performance impact and to store historical data in compressed form to minimize storage requirements, completely transparent to applications, easy to setup . This efficiency cannot be duplicated by your own triggers, which also cost time and effort to set up and maintain.

To satisfy long-retention requirements that exceed the undo retention, create a flashback data archive.

To satisfy long-retention requirements, use flashback data archives. Begin with the following steps:

# For your archive administrator:
1:?? Create one or more tablespaces for data archives and grant QUOTA on the tablespaces.
2:?? Grant the FLASHBACK ARCHIVE ADMINISTER system privilege to create and maintain flashback archives.

# For archive users:
Grant the FLASHBACK ARCHIVE object privilege (to enable history tracking for specific tables in the given flashback archives).

>SCOTT (Archive user)

SQL> alter table emp flashback archive fla1;
alter table emp flashback archive fla1
*
ERROR at line 1:
ORA-55620: No privilege to use Flashback Archive

As SYS use or Archive Administrator (who granted FLASHBACK ARCHIVE ADMINISTER system privilege)

SQL> grant flashback archive on fla1 to scott;

Grant succeeded



Note:
Grant the FLASHBACK ARCHIVE ADMINISTER system privilege to your archive administrator,to allow execution of the following statements:
- CREATE FLASHBACK ARCHIVE
- ALTER FLASHBACK ARCHIVE
- DROP FLASHBACK ARCHIVE

The Flashback Data Archive background process, FBDA, starts with the database.
1. FBDA operates first on the undo in the buffer cache.
2. In case the undo has already left the buffer cache, FBDA could also read the required values from the undo segments.
3. FBDA consolidates the modified rows of flashback archive???enabled tables and writes them into the appropriate history tables, which make up the flashback data
archive.

You can find the internally assigned names of the history tables by querying the *_FLASHBACK_ARCHIVE_TABLES view. History tables are compressed and internally partitioned. The database automatically purges all historical information on the day after the retention period expires. (It deletes the data, but does not destroy the flashback data archive.) For example, if the retention period is 10 days, then every day after the tenth day, the oldest information is deleted; thus
leaving only 10 days of information in the archive. This is a way to implement digital shredding.

1. Create the flashback data archive:

The archive administrator creates a flashback data archive named fla1, which uses up to unlimited of the tbs1 tablespace and whose data will be retained for two years. If you want to set up your database so that information in the fla1 is automatically deleted, the day after 2 years is complete.

SQL> create flashback archive fla1 tablespace tbs1 retention 2 year;  << data will be retained for 2 years.!

Flashback archive created.

2- Grant Flashback Archive objects privilege on Flashback data archive (fla1) to Archive User (SCOTT).

SQL> grant flashback archive on fla1 to Scott;

Grant succeeded

3- Enable history tracking for a table in the FLA1 archive:
????As Flashback Archive User (SCOTT)

SQL> alter table EMP flashback archive fla1;
Table altered.

4- View the historical data:
SQL> select to_timestamp(sysdate) from dual;

TO_TIMESTAMP(SYSDATE)
---------------------------------------------------------------------------
02-DEC-07 12.00.00 AM


SQL> alter table EMP flashback archive fla1;

Table altered.

SQL> update emp set sal=sal+100 where empno=7788;

1 row updated.

SQL> select sal from emp as of timestamp to_timestamp('2007-12-02 00:00:00','yyyy-mm-dd hh24:mi:ss') 3 where empno=7788;

SAL
----------
3100

SQL> select sal from emp where empno=7788;

SAL
----------
3200

Note:

To use the flashback_archive_clause to enable/disable historical tracking for the table, you must have the FLASHBACK ARCHIVE ADMINISTER system privilege or you must be logged in as SYSDBA.

Flashback archiving is handled by fbda background process, and it checks for tablespace quota every 1 hour. If you run out of flashback archival space and must extend the tablespace you may also need to reset the quota for the tablespace.