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  Disabling Flashback Database

Oracle Tips by Burleson

Flashback Standby Database

If you have multiple standby sites, you may utilize the DELAY option in Data Guard to prevent physical/logical corruption or user errors in your primary database. 

For example, the first scenario in the diagram below has only one standby database. Here, a logical or physical corruption in the primary database will cause an immediate corruption in the standby database. 

To avoid such a pitfall, you can implement a second standby database with the ‘Delay’ option (introducing a delay of minutes or hours on the second standby database for applying archive log changes). This will prevent the corruptions on the second standby database and allow recovery from a possible physical/logical corruption or user errors in the primary database.

You can issue the following command to accomplish this:

SQL> alter database recover managed standby database delay 60 disconnect;

Figure 12.3 Using Flashback Database in a Standby Database Configuration

However, in Oracle 10g, you can configure the standby database with Flashback Database to achieve the same benefit as the DELAY option. Therefore, there is no need to implement a second standby database with the DELAY option.

 

Oracle 10g Disabling Flashback Database

Issue the following command to disable Flashback Database:

SQL> ALTER DATABASE FLASHBACK OFF;

You can also perform the same task in Enterprise Manager:

Figure 12.2 Disabling Flashback Database in Enterprise Manager

Monitoring Flashback Database

The following displays a selection of the Flashback Database logs:

SQL> select begin_time, flashback_data,
   2        db_data, redo_data, ESTIMATED_FLASHBACK_SIZE
   3 from   v$flashback_database_stat;
 

BEGIN_TIME           FLASHBACK_DATA    DB_DATA  REDO_DATA ESTIMATED_FLASHBACK_SIZE
-------------------- -------------- ---------- ---------- ------------------------
Oct 08 2003 14:17:34         753664    5324800     970752                        0
Oct 08 2003 13:17:32        1720320    4751360    3124224                 21749760
Oct 08 2003 12:17:31        1802240    4833280    3168256                 21774336
Oct 08 2003 11
Oct 07 2003 16:46:24        1851392    4603904    3120128                 21577728
Oct 07 2003 15:46:21        1720320    4816896    3154944                 21577728
Oct 07 2003 14:46:18        1736704    4587520    3196928                 21577728
Oct 07 2003 13:46:16        1736704    4685824    3194880                 21602304

25 rows selected.

You can use the v$flashback_database_log to monitor the Flashback Database retention target.

 SQL> select *
    2 from   v$flashback_database_log;

 

OLDEST_FLASHBACK_SCN OLDEST_FLASHBACK_TIME RETENTION_TARGET FLASHBACK_SIZE ESTIMATED_FLASHBACK_SIZE
-------------------- --------------------- ---------------- -------------- ------------------------
             2.2029E+12 Oct 06 2003 09:44:42             1440       48316416                 21774336

Note: The default flashback retention time is 1400 minutes.  See Chapter 8 for more details on how to set up this value.

You can also use the v$flashback_database_log view to assist in adjusting the recovery area disk quota:

SQL> select estimated_flashback_size
       2 from   v$flashback_database_log;

ESTIMATED_FLASHBACK_SIZE
------------------------
                21823488

Example 1: Flashback a Database using RMAN

RMAN> FLASHBACK DATABASE
   2> TO TIME = TO_DATE
   3> (‘06/25/03 12:00:00’,’MM/DD/YY HH:MI:SS’);

Example 2: Flashback a database using SQL command

The database must be in mount state to issue these commands:

SQL> FLASHBACK DATABASE TO TIMESTAMP (SYSDATE – 5/24);
SQL> FLASHBACK DATABASE TO SCN 76239;

You must issue the following command afterwards:

SQL> ALTER DATABASE RESETLOGS;

 

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