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Chapter 19

Chapter 19. RMAN Restore and Recovery. Introduction to RMAN Restore and Recovery. Prior two chapters prepares you to be able to perform perhaps the most critical DBA tasks: restore and recovery of a damaged mission critical database.

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Chapter 19

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  1. Chapter 19 RMAN Restore and Recovery

  2. Introduction to RMAN Restore and Recovery • Prior two chapters prepares you to be able to perform perhaps the most critical DBA tasks: restore and recovery of a damaged mission critical database. • Good news is that RMAN automates much of the restore and recovery process.

  3. Determining Media Recovery Required • Media recovery error is thrown when Oracle can’t read or write to a critical database file: ORA-01157: cannot identify/lock data file 1 - see DBWR trace file ORA-01110: data file 1: '/u02/oracle/oradata/E64208/system01.dbf'

  4. Performing Media Recovery • Determine what files need to be restored. • Depending on the damage, set your database mode to nomount, mount, or open. • Use the RESTORE command to retrieve files from RMAN backups. • Use the RECOVER command for datafiles requiring recovery. • Open your database.

  5. Using Data Recovery Advisor • Listing failures: RMAN> list failure; • Suggesting corrective action: RMAN> advise failure 665; • Running commands to repair failures: RMAN> repair failure;

  6. Using RMAN to Shutdown/Startup • You can use RMAN to shutdown and startup your database. • Many times during a restore and recovery scenario, it’s easier to use RMAN top stop/start your database. RMAN> shutdown immediate; RMAN> ..... RMAN> startup;

  7. Previewing Backups Used for Recovery • Use the RESTORE...PREVIEW command to list the backups and archive redo log files that RMAN will use to restore and recover database datafiles. • The RESTORE...PREVIEW does not actually restore any files. RMAN> restore database preview; RMAN> restore database preview summary;

  8. Validating Backup Files Before Restoring • Instruct RMAN to verify that the files exist and check the file headers, the use the RESTORE...VALIDATE HEADER command like so: RMAN> restore database validate header; • Further instruct RMAN to verify the integrity of blocks within backup files required to restore the database datafiles via the RESTORE...VALIDATE command: RMAN> restore database validate;

  9. Testing Media Recovery • Instruct RMAN to verify the recovery process via the RECOVER...TEST command: RMAN> connect target / RMAN> startup mount; RMAN> restore tablespace users; RMAN> recover tablespace users test;

  10. Restoring Entire Database Using Current Control File • This example assumes that you haven’t lost the control files as part of the media failure: RMAN> connect target / RMAN> startup mount; RMAN> restore database; RMAN> recover database; RMAN> alter database open;

  11. Restoring Entire Database Using Backup Control File • This example assumes that you have lost the current control files as part of the media failure: RMAN> connect target / RMAN> startup nomount; RMAN> restore controlfile from autobackup; RMAN> alter database mount; RMAN> restore database; RMAN> recover database; RMAN> alter database open resetlogs;

  12. Restoring Tablespace While Database is Open • Do this is you have an isolated tablespace that needs its datafiles to be restored and recovered: RMAN> connect target / RMAN> sql 'alter tablespace users offline immediate'; RMAN> restore tablespace users; RMAN> recover tablespace users; RMAN> sql 'alter tablespace users online';

  13. Restoring Tablespace While Database in Mount Mode • You can also restore tablespace datafiles while the database is in mount mode: RMAN> connect target / RMAN> shutdown immediate; RMAN> startup mount; RMAN> restore tablespace system; RMAN> recover tablespace system; RMAN> alter database open;

  14. Restoring Read-Only Tablespaces • RMAN will restore read-only tablespaces along with the rest of the database when you issue a RESTORE DATABASE command: RMAN> restore database; • This is different in versions prior to 11g where you had to specify that read-only tablespaces were restored.

  15. Restoring Temporary Tablespaces • RMAN doesn’t backup temporary tablespaces. • Starting with Oracle Database 10g, you don’t have to restore or re-create missing locally managed temporary tablespace tempfiles. • When you open your database for use, Oracle automatically detects and re-creates locally managed temporary tablespace tempfiles.

  16. Restoring Datafile While Database Is Open • Use the RESTORE DATAFILE and RECOVER DATAFILE commands to restore and recover at the datafile level. • When your database is open, you’re required to take offline any datafiles you’re attempting to restore and recover. RMAN> sql 'alter database datafile 32, 33 offline'; RMAN> restore datafile 32, 33; RMAN> recover datafile 32, 33; RMAN> sql 'alter database datafile 32, 33 online';

  17. Restoring Datafile While Database Is Not Open • You can only restore the system datafile while the database is not open: RMAN> connect target / RMAN> shutdown abort; RMAN> startup mount; RMAN> restore datafile 1; RMAN> recover datafile 1; RMAN> alter database open;

  18. Restoring Datafiles to Non-Default Locations • Sometimes a failure will occur that renders the disks associated with a mount point inoperable. • In situations like this, you will need to restore and recover the datafiles to a different location from where they originally resided. RMAN> connect target / RMAN> startup mount; RMAN> run{ 2> set newname for datafile 32 to '/ora02/dbfile/O11R2/mvdata01.dbf'; 3> set newname for datafile 33 to '/ora02/dbfile/O11R2/mvindex01.dbf'; 4> restore datafile 32, 33; 5> switch datafile all; # Updates repository with new datafile location. 6> recover datafile 32, 33; 7> alter database open; 8> }

  19. Performing Block Level Recovery • Block-level corruption is rare and is usually caused by some sort of I/O error. • However, if you do have an isolated corrupt block within a large datafile, it’s nice to have the option of performing a block-level recovery. • Block-level recovery is useful when a small number of blocks are corrupt within a datafile. • Block recovery is not appropriate if the entire datafile needs media recovery. RMAN> recover datafile 5 block 20;

  20. Restoring Archive Redo Logs to the Default Location • RMAN will automatically restore any archived redo log files that it needs during a recovery process. • You normally don't need to manually restore archived redo log files. • However, if you need to, you can restore all via: RMAN> restore archivelog all;

  21. Restoring Archive Redo Logs to the Non-Default Location • Sometimes the default location may not be available (due to media failure) or it may not have enough room. • Use SET ARCHIVELOG DESTINATION RMAN> run{ 2> set archivelog destination to '/ora01/archtemp'; 3> restore archivelog from sequence 68 force; 4> }

  22. Restoring the Spfile • RMAN allows you to restore the spfile • You may have one of the following scenarios: • You accidentally set a value in the spfile that keeps your instance from starting. • You accidentally deleted the spfile. • You are required to see what it looked like at some time in the past. • If you are using a recovery catalog, it’s a fairly simple procedure to restore the spfile: RMAN> connect target / RMAN> connect catalog rmancat/foo@rcat RMAN> startup nomount; RMAN> restore spfile;

  23. Restoring a Control File Using a Recovery Catalog • If you lose all of your control files, then you’ll need to restore one from a backup: RMAN> connect target / RMAN> connect catalog rcat/rcat@recov RMAN> startup nomount; RMAN> list backup of controlfile;

  24. Restoring a Control File Using an Autobackup Restore • If you’re using the autobackup of the control file feature, it’s fairly simple to restore a control file: RMAN> connect target / RMAN> startup nomount; RMAN> restore controlfile from autobackup;

  25. Performing Time-Based Recovery Incomplete Recovery • Time based is appropriate when you have a specific time in the past you’d like to reset the database to: RMAN> connect target / RMAN> startup mount; RMAN> restore database until time 2> "to_date('04-sep-2010 14:00:00', 'dd-mon-rrrr hh24:mi:ss')"; RMAN> recover database until time 2> "to_date('04-sep-2010 14:00:00', 'dd-mon-rrrr hh24:mi:ss')"; RMAN> alter database open resetlogs;

  26. Performing Log Sequenced-Based Recovery Incomplete Recovery • Use this type of incomplete recovery when you’re missing an archive log or required online redo log: RMAN> connect target / RMAN> startup mount; RMAN> restore database until sequence 45; RMAN> recover database until sequence 45; RMAN> alter database open resetlogs;

  27. Performing Change/SCN-Based Incomplete Recovery • If you know the SCN number to which you’d like to restore to in the past, then use SCN-based incomplete recovery: RMAN> connect target / RMAN> startup mount; RMAN> restore database until scn 95019865425; RMAN> recover database until scn 95019865425; RMAN> alter database open resetlogs;

  28. Restoring to a Restore Point • RMAN also allows you to restore back to a restore point: RMAN> connect target / RMAN> startup mount; RMAN> restore database until restore point MY_RP; RMAN> recover database until restore point MY_RP; RMAN> alter database open resetlogs;

  29. Table Level Restore • New in Oracle Database 12c, table level restore • Allows you to use RMAN to restore a table based on SCN, time, or log sequence number • Consider using flashback table to restore a table instead of RMAN table level restore

  30. Flashing Back a Table • Flashback to before drop (uses recyclebin) • Flashback to prior point in time (uses undo)

  31. Flashback Database • Another form of incomplete recovery • Often used as a mechanism to set a database back to a prior state • Prior to an application upgrade, create a restore point, if the application upgrade goes bad, flashback database to the restore point

  32. Restoring and Recovering to Different Server • Create an RMAN backup on the originating database. • Copy RMAN backup to the destination server. All steps after this step are performed on the destination database server. • Ensure that Oracle is installed. • Source the required OS variables. • Create an init.ora file for the database to be restored. • Create any required directories for datafiles, control files, and dump/trace files. • Startup the database in NOMOUNT mode. • Restore a control file from the RMAN backup. • Startup the database in MOUNT mode. • Make the control file aware of the location of the RMAN backups. • Rename and restore the datafiles to reflect new directory locations. • Recover the database. • Set the new location for the online redo logs. • Open the database. • Add tempfile. • Rename the database.

  33. Summary • RMAN automates most of the restore and recovery tasks. • Very flexible in ways to perform complete and incomplete recovery. • Arguably restore and recovery are the most critical skills a DBA can posses.

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