5 copyright © 2006, oracle. all rights reserved. database recovery

5Copyright © 2006, Oracle. All rights reserved.

Database Recovery

5-2 Copyright © 2006, Oracle. All rights reserved.

Objectives

After completing this lesson, you should be able to:

• Perform complete or incomplete user-managed recovery

• Identify situations where incomplete recovery is necessary

• Perform complete or incomplete recovery by using RMAN

• Perform incomplete recovery based on time, SCN, log sequence, restore points, or the cancel method

• Recover an automatically backed up control file

• Use Enterprise Manage to perform recovery

• Recover read-only tablespaces

User man.RMAN CLIEMCompleteIncompleteControl fileRO TBS


Recovery Methods

There are two methods for performing recovery:

• User-managed recovery– Files must be maintained and moved into place

manually.– Use SQL*Plus commands.

• RMAN recovery– Files are managed automatically.– Use RMAN functionality including all repository

maintenance and reporting capabilities.– This can be done by using Enterprise Manager.– Oracle Corporation recommends using this method.


User-Managed Recovery:RECOVER Command

• Restore all database files from a backup and then recover the database:

• Restore the damaged data files from a backup and then recover the data files:

Or:

SQL> RECOVER DATABASE

SQL> RECOVER TABLESPACE index_tbs

SQL> RECOVER DATAFILE 2> '/oradata/indx01.dbf'


RMAN Recovery: RESTOREand RECOVER Commands

run{

sql "ALTER TABLESPACE inv_tbs OFFLINE IMMEDIATE";

RESTORE TABLESPACE inv_tbs;

RECOVER TABLESPACE inv_tbs DELETE ARCHIVELOG;

sql "ALTER TABLESPACE inv_tbs ONLINE";

}

User man.> RMAN CLI

EMCompleteIncompleteControl fileRO TBS


Recovery UsingEnterprise Manager

With the Enterprise Manager Recovery Wizard, you can create and run an RMAN script to perform the recovery.

RMAN> RECOVER DATABASE …

User man.RMAN CLI

> EMCompleteIncompleteControl fileRO TBS


Complete Versus Incomplete Recovery

There are two types of recovery:

• Complete recovery brings the database up to the present, including all data changes made to the point in time when the recovery was requested.

• Incomplete recovery brings the database up to a specified point in time in the past, before the recovery operation was requested.

Recoverytask startedat this time

Completerecovery

Incompleterecovery

Missing transactionsafter incomplete recovery

Restore fromthis backup


Complete Recovery

Restoreddata files

Data files containingcommitted anduncommittedtransactions

Recovereddata files

Changes applied

Undo applied

6

5

3

2

1

Archivedlog Archived

log OnlineRedo log

User man.RMAN CLIEM

> CompleteIncompleteControl fileRO TBS

4

Databaseopened


Incomplete Recovery

Data files containingcommitted anduncommitted

Transactions up to PIT

PIT-recovereddata files

Undo applied

6

5

3

2

1

Archivedlog Archived

log OnlineRedo log

4

Databaseopened

XX

Changes applied to point in time (PIT)

Restored datafiles from as far

back as necessary

User man.RMAN CLIEMComplete

> IncompleteControl fileRO TBS


Situations Requiring Incomplete Recovery

• Complete recovery fails because of a missing archived log file.

• One or more unarchived redo log files and a data file are lost.

• A backup of the control file is used to open or recover the database.


Types of Incomplete Recovery

There are four types of incomplete recovery:

• Time-based recovery

• Cancel-based recovery

• Change-based recovery

• Log sequence recovery


Performing User-ManagedIncomplete Recovery

• Recover a database until time:

• Recover a database until cancel:

• Recover using the backup control file:

SQL> RECOVER DATABASE UNTIL CANCEL;

SQL> RECOVER DATABASE UNTIL

2 TIME '2005-12-14:12:10:03';

SQL> RECOVER DATABASE 2 UNTIL TIME '2005-12-14:12:10:03' 3 USING BACKUP CONTROLFILE;


Performing User-Managed Incomplete Recovery

To perform user-managed incomplete recovery, follow these steps:

1. Shut down the database.

2. Restore data files.

3. Mount the database.

4. Recover the database.

5. Open the database with the RESETLOGS option.


User-Managed Time-Based Recovery: Example

SQL> SHUTDOWN IMMEDIATE$ cp /BACKUP/* /u01/db01/ORADATASQL> STARTUP MOUNTSQL> RECOVER DATABASE UNTIL TIME '2005-11-28:11:44:00';SQL> ALTER DATABASE OPEN RESETLOGS;

This is the scenario:

• A job ran in error, and its effects have to be undone.

• This happened 15 minutes ago, and there has been little database activity since then.

• You decide to perform incomplete recovery to restore the database back to its state as of 15 minutes ago.


User-Managed Cancel-Based Recovery: Example

The scenario is the same as the one for the time-based example, except for these findings:

• Redo logs are not multiplexed.

• One of the online redo logs is missing.

• The missing redo log is not archived.

• The redo log contained information from 11:34 a.m.

• Twenty-six minutes of data are lost.

• Users can reenter their data manually.


User-Managed Cancel-Based Recovery: Example

Recover the database as follows:

1. Shut down the database.

2. Restore all data files from the most recent backup.

3. You already have a valid backup, so mount the database.

4. Execute RECOVER DATABASE UNTIL CANCEL.

5. Execute ALTER DATABASE OPEN RESETLOGS to open the database.


Performing Incomplete Recoveryby Using RMAN

1. Mount the database.

2. Allocate multiple channels for parallelization.

3. Restore all data files.

4. Recover the database by using UNTIL TIME, UNTIL SEQUENCE, or UNTIL SCN.

5. Open the database by using RESETLOGS.


Time-Based RecoveryUsing RMAN: Example

RMAN> RUN {

2> SET UNTIL TIME = '2005-11-28:11:44:00';

3> RESTORE DATABASE;

4> RECOVER DATABASE;

5> ALTER DATABASE OPEN RESETLOGS; }


Log Sequence RecoveryUsing RMAN: Example

RMAN> RUN { 2> SET UNTIL SEQUENCE 120 THREAD 1; 3> ALTER DATABASE MOUNT; 4> RESTORE DATABASE; 5> RECOVER DATABASE; # recovers through log 119 6> ALTER DATABASE OPEN RESETLOGS; 7> }


Incomplete Recovery UsingEnterprise Manager


Incomplete Recovery and the Alert Log

The following are some best practices regarding the alert log in incomplete recovery scenarios:

• Check the alert log before and after recovery.

• Look for error information, hints, and SCNs.

• Confirm that steps in the recovery process were successful.


Restore Points

A restore point:

• Serves as an alias for anSCN or a specific point in time

• Is stored in the control file

• Can be used with:– RECOVER DATABASE– FLASHBACK DATABASE– FLASHBACK TABLE

SQL> CREATE RESTORE POINT before_load;

before_load

RMAN> RECOVER DATABASE UNTIL RESTORE POINT before_load;2

1


Incomplete Recovery: Best Practices

• Plan for and practice scenarios ahead of time.

• Investigate and verify that incomplete recovery is necessary.

• Follow all steps carefully.

• Take whole database backups before and after recovery.

• Always verify that the recovery was successful.

• Take advantage of restore points.


Recovering a Control FileAutobackup

RecoveryManager(RMAN) Flash recovery

area

Database

Controlfile

RECOVER DATABASE;

ALTER DATABASE OPEN RESETLOGS;

ALTER TABLESPACE temp ADD TEMPFILE...;

RMAN> RESTORE CONTROLFILE TO 2> '/oradata/ctlfile.bak' FROM AUTOBACKUP;

User man.RMAN CLIEMCompleteIncomplete

> Control fileRO TBS


Creating a New Control File

SQL> ALTER DATABASE BACKUP CONTROLFILE TO TRACE;

Passwordfile

Parameter file

SYSTEM

SYSAUX

UNDO TEMP

USERS

INDEX

Redo logfile 1B

Redo logfile 1A

Redo logfile 2B

Redo logfile 2A

Controlfiles


Creating a New Control File


Recovering Read-OnlyTablespaces

ChangeTablespace

State

Crashand perform

recovery

Case 1

Case 2

Case 3

Backup

Read-only

Read/write

Read-only

Read-only

Read/write

*

*

*

* Control filebackup to be

used for recoveryif current one lost

User man.RMAN CLIEMCompleteIncompleteControl file

> RO TBS


Read-Only Tablespace Recovery Issues

Special considerations must be taken for read-onlytablespaces when:

• Re-creating a control file

• Renaming data files

• Using a backup control file


Summary

In this lesson, you should have learned how to:

• Perform complete or incomplete user-managed recovery

• Perform complete or incomplete recovery by using RMAN

• Identify situations where incomplete recovery is necessary

• Perform incomplete recovery based on time, SCN, log sequence, restore points, or the cancel method

• Recover a control file autobackup

• Use Enterprise Manage to perform recovery

• Recover read-only tablespaces


Practice Overview: Performing Incomplete Recovery

This practice covers the following topics:

• Point-in-time recovery using RMAN

• Recovery from the loss of control files

5 copyright © 2006, oracle. all rights reserved. database recovery

Documents

recovery recover

rman recovery files

incomplete recovery

database recovery slide

recovery methods

types of recovery

recovery task

recovery operation