Database Recovery Copyright © 2006, Oracle. All rights reserved. Objectives User man. RMAN CLI EM Complete Incomplete Control file RO TBS 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 5-2 Copyright © 2006, Oracle. All rights reserved. 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. 5-3 Copyright © 2006, Oracle. All rights reserved. User-Managed Recovery: RECOVER Command • Restore all database files from a backup and then recover the database: SQL> RECOVER DATABASE • Restore the damaged data files from a backup and then recover the data files: SQL> RECOVER TABLESPACE index_tbs Or: SQL> RECOVER DATAFILE 2> '/oradata/indx01.dbf' 5-4 Copyright © 2006, Oracle. All rights reserved. RMAN Recovery: RESTORE and RECOVER Commands User man. > RMAN CLI EM Complete Incomplete Control file RO TBS run{ sql "ALTER TABLESPACE inv_tbs OFFLINE IMMEDIATE"; RESTORE TABLESPACE inv_tbs; RECOVER TABLESPACE inv_tbs DELETE ARCHIVELOG; sql "ALTER TABLESPACE inv_tbs ONLINE"; } 5-5 Copyright © 2006, Oracle. All rights reserved. Recovery Using Enterprise Manager User man. RMAN CLI > EM Complete Incomplete Control file RO TBS With the Enterprise Manager Recovery Wizard, you can create and run an RMAN script to perform the recovery. RMAN> RECOVER DATABASE … 5-6 Copyright © 2006, Oracle. All rights reserved. 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. Complete recovery Incomplete recovery Restore from this backup • 5-7 Missing transactions after incomplete recovery Recovery task started at this time Incomplete recovery brings the database up to a specified point in time in the past, before the recovery operation was requested. Copyright © 2006, Oracle. All rights reserved. User man. RMAN CLI EM > Complete Incomplete Control file RO TBS Complete Recovery Archived log Archived log Online Redo log Changes applied 2 1 Restored data files 5-8 Database opened Undo applied 4 5 3 Data files containing committed and uncommitted transactions Copyright © 2006, Oracle. All rights reserved. 6 Recovered data files User man. RMAN CLI EM Complete > Incomplete Control file RO TBS Incomplete Recovery Archived log Archived log Online Redo log X X Changes applied to point in time (PIT) 2 Database opened 4 1 Restored data files from as far back as necessary 5-9 3 Data files containing committed and uncommitted Transactions up to PIT Copyright © 2006, Oracle. All rights reserved. Undo applied 5 6 PIT-recovered data files Situations Requiring Incomplete Recovery • • • 5-11 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. Copyright © 2006, Oracle. All rights reserved. Types of Incomplete Recovery There are four types of incomplete recovery: • Time-based recovery • Cancel-based recovery • Change-based recovery • Log sequence recovery 5-12 Copyright © 2006, Oracle. All rights reserved. Performing User-Managed Incomplete Recovery • Recover a database until time: SQL> RECOVER DATABASE UNTIL 2 TIME '2005-12-14:12:10:03'; • Recover a database until cancel: SQL> RECOVER DATABASE UNTIL CANCEL; • Recover using the backup control file: SQL> RECOVER DATABASE 2 UNTIL TIME '2005-12-14:12:10:03' 3 USING BACKUP CONTROLFILE; 5-14 Copyright © 2006, Oracle. All rights reserved. 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. 5-15 Copyright © 2006, Oracle. All rights reserved. User-Managed Time-Based Recovery: Example 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. SQL> $ cp SQL> SQL> SQL> 5-16 SHUTDOWN IMMEDIATE /BACKUP/* /u01/db01/ORADATA STARTUP MOUNT RECOVER DATABASE UNTIL TIME '2005-11-28:11:44:00'; ALTER DATABASE OPEN RESETLOGS; Copyright © 2006, Oracle. All rights reserved. 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. 5-18 Copyright © 2006, Oracle. All rights reserved. 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. 5-19 Copyright © 2006, Oracle. All rights reserved. Performing Incomplete Recovery by Using RMAN 1. 2. 3. 4. Mount the database. Allocate multiple channels for parallelization. Restore all data files. Recover the database by using UNTIL TIME, UNTIL SEQUENCE, or UNTIL SCN. 5. Open the database by using RESETLOGS. 5-20 Copyright © 2006, Oracle. All rights reserved. Time-Based Recovery Using RMAN: Example RMAN> 2> 3> 4> 5> 5-21 RUN { SET UNTIL TIME = '2005-11-28:11:44:00'; RESTORE DATABASE; RECOVER DATABASE; ALTER DATABASE OPEN RESETLOGS; } Copyright © 2006, Oracle. All rights reserved. Log Sequence Recovery Using RMAN: Example RMAN> 2> 3> 4> 5> 6> 7> 5-23 RUN { SET UNTIL SEQUENCE 120 THREAD 1; ALTER DATABASE MOUNT; RESTORE DATABASE; RECOVER DATABASE; # recovers through log 119 ALTER DATABASE OPEN RESETLOGS; } Copyright © 2006, Oracle. All rights reserved. Incomplete Recovery Using Enterprise Manager 5-24 Copyright © 2006, Oracle. All rights reserved. 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. 5-25 Copyright © 2006, Oracle. All rights reserved. Restore Points A restore point: • Serves as an alias for an SCN or a specific point in time • Is stored in the control file • Can be used with: before_load – RECOVER DATABASE – FLASHBACK DATABASE – FLASHBACK TABLE 1 2 5-26 SQL> CREATE RESTORE POINT before_load; RMAN> RECOVER DATABASE UNTIL RESTORE POINT before_load; Copyright © 2006, Oracle. All rights reserved. Incomplete Recovery: Best Practices • • • • • • 5-27 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. Copyright © 2006, Oracle. All rights reserved. Recovering a Control File Autobackup RMAN> RESTORE CONTROLFILE TO 2> '/oradata/ctlfile.bak' FROM AUTOBACKUP; Recovery Manager (RMAN) User man. RMAN CLI EM Complete Incomplete > Control file RO TBS Flash recovery area RECOVER DATABASE; ALTER DATABASE OPEN RESETLOGS; Control file Database 5-29 ALTER TABLESPACE temp ADD TEMPFILE...; Copyright © 2006, Oracle. All rights reserved. Creating a New Control File SYSTEM USERS Redo log file 1A SYSAUX INDEX Redo log Redo log file 2A file 2B UNDO TEMP Control files Parameter file Password file Redo log file 1B SQL> ALTER DATABASE BACKUP CONTROLFILE TO TRACE; 5-31 Copyright © 2006, Oracle. All rights reserved. Creating a New Control File 5-32 Copyright © 2006, Oracle. All rights reserved. * Case 1 Recovering Read-Only Tablespaces User man. RMAN CLI EM Complete Incomplete Control file > RO TBS Read-only * Case 2 Read/write Read-only * Read/write Case 3 Read-only Control file * backup to be Backup 5-33 Change Tablespace State Crash and perform recovery Copyright © 2006, Oracle. All rights reserved. used for recovery if current one lost Read-Only Tablespace Recovery Issues Special considerations must be taken for read-only tablespaces when: • Re-creating a control file • Renaming data files • Using a backup control file 5-35 Copyright © 2006, Oracle. All rights reserved. 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 5-37 Copyright © 2006, Oracle. All rights reserved. Practice Overview: Performing Incomplete Recovery This practice covers the following topics: • Point-in-time recovery using RMAN • Recovery from the loss of control files 5-38 Copyright © 2006, Oracle. All rights reserved.