Configure flashback database [ID 249319.1]-TOMSYAN-ChinaUnix博客

Configure flashback database [ID 249319.1]

修改时间25-MAY-2011 类型 BULLETIN 状态 ARCHIVED

Applies to:
Enterprise Manager for RDBMS
Oracle Server - Enterprise Edition
Oracle Server - Personal Edition
Oracle Server - Standard Edition
Information in this document applies to any platform.
***Checked for relevance on 25-May-2011***
Purpose
- What is Flashback Database?

- How to Configure a Flashback Database?
Scope and Application
This feature can be used by DBA's and Support Analysts to understand and
configure Flashback database.
Configure flashback database
Flashback database
-----------------------------
- This a new feature introduced in 10g.
- Flashbacking a database means going back to a previous database state.
- The Flashback Database feature provides a way to quickly revert entire
   Oracle database to the state it was in at a past point in time.
- This is different from traditional point in time recovery.
- A new background process RVWR introduced which is responsible for writing
flashback logs which stores pre-image(s) of data blocks
- One can use Flashback Database to back out changes that:
- Have resulted in logical data corruptions.
    - Are a result of user error.
- This feature is not applicable for recovering the database in case of media
failure.
- The time required for flashbacking a database to a specific time in past is
DIRECTLY PROPORTIONAL to the number of changes made and not on the size
   of the database.

How to Configure Flashback database
------------------------------------
Prerequisites
--------------
a) Database must be in archivelog mode.
b) Last clean shutdown.
c) Enterprise and Personal Edition required

Configuration: -
---------------
Initialization Parameters required: -
a) DB_RECOVERY_FILE_DEST (dynamically modifiable) --> Physical location where RVWR background process
    writes flashback logs.
b) DB_RECOVERY_FILE_DEST_SIZE (dynamically modifiable) --> Maximum size flashback logs can occupy in
   DB_RECOVERY_FILE_DEST.
c) DB_FLASHBACK_RETENTION_TARGET (dynamically modifiable) --> upper limit in minutes on how far back
    one can flashback the database.

After setting these parameters in parameter file(init.ora) or spfile.

Note:- Clean shutdown is mandatory.

SQL> Startup mount;

SQL> Alter database flashback on;

SQL> Alter database open;

SQL> select flashback_on from v$database;
FLASHBACK_ON
------------
YES

To see the background process :-
$ ps -eaf | grep rvwr
oracle 10302 1 0 10:58:09 ? 0:00 ora_rvwr_db10g
oracle 22353 12428 1 13:31:16 pts/tL 0:00 grep rvwr

The above two output confirms that the datbase has its flashback feature ON.

How to Flashback the database to the previous state on basis of :
----------------------------------------------------------------
a) SCN
b) Timestamp
c) Log Sequence Number

Timestamp=12-09-2003:10:00:00 Timestamp=12-09-2003:12:00:00

Log Sequence Number= 50 Log Sequence Number= 55

Using SCN :-
----------
SQL> shutdown immediate
SQL> startup mount
SQL> flashback database to SCN 100;

Flashback complete.

SQL> alter database open resetlogs;

Database altered.

Note:- This feature can be used with RMAN or Enterprise Manager also.

Using Timestamp :-
---------------
SQL> shutdown immediate
SQL> startup mount
SQL> flashback database to TIMESTAMP(sysdate - 2/24);

Flashback complete.

SQL> alter database open resetlogs;

Database altered.

Using Log sequence Number and RMAN
----------------------------------
RMAN> flashback database to sequence=50 thread=1;

RMAN> alter database open resetlogs;

RELATED DOCUMENTS
-----------------
Oracle Database 10g: Maximize Availability