Oracle Backup And Recovery 2c64p

Oracle Backup and Recovery Created By: Saurabh Kulkarni

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Index  Backup and Need of it  Different types of backup  Hot vs cold  Full vs incremental  Physical vs logical

 Managed backup  RMAN  Database recovery  managed  RMAN based

 Flashback Recovery www.yogijicreations.com

Backup  What do we mean by database backup ? 

The process of periodically taking a copy of the database and log file (and possibly programs) onto offline storage media.

A backup is a copy of data.

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Need of taking backup  Instance Failures  

instance shuts down without synchronizing all the database files to the same system change number (SCN) A few causes for instance failure:    

A power outage A server hardware failure Failure of an Oracle background process Emergency shutdown procedures (intentional power outage or SHUTDOWN ABORT)

 Solution :STARTUP Database and let Oracle automatically perform instance recovery using the online redo logs and undo data in the undo tablespace. www.yogijicreations.com

Need of taking backup  Error Failures  Inadvertently delete or modify data in tables or drop an index.  the DROP TABLE command worked fine, but you really didn’t want to drop that table!

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 Media Failures  The loss of one or more database files (Datafiles, Control files, redo log files)  The database file can be lost or corrupted for a number of reasons:  Failure of a disk drive  Failure of a disk controller  Inadvertent deletion or corruption of a database file www.yogijicreations.com

Different types of backup techniques  Hot or On-line Backups  backup of one or more database files while the database is open  Inconsistent !!!  Mismatch in SCN SCN ( System change Number): A stamp that defines a committed version of a database at a point in time.

Oracle assigns every committed transaction a unique SCN.

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Different types of backup techniques  In 24 X 7 environment  Database should be in ARCHIVELOG mode

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Different types of backup techniques  Cold /offline Backup  Backing up the database when it is closed (shutdown state).  Consistent  No need of recovery because the data is already consistent.

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Different types of backup techniques  Whole database backups  Tablespace Backups  Datafile Backups

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Different types of backup techniques  Full Backup  Incremental Backup  Differential Incremental Backup  Cumulative Incremental Backup

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Differential Incremental Backup 

Backup all the blocks that have changed between level 0 and level 1

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Cumulative Incremental Backup 

Backup all the blocks till the level 1.

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-Managed Backups 

The basic -managed backup strategy is to make periodic backups of datafiles and archived logs with operating system commands.



Logical or physical.  Physical: Backup of physical file structure (datafiles, control files..)  Logical: backups of logical objects such as tables, views…  Export / Import utility is used to take logical backup and restore it back.

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Basic Backup Methodology 

Identify the datafiles, control files, and archived redo logs to be backed up by querying dynamic performance views or data dictionary tables

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Use an operating system command such as the UNIX command to back up datafiles and archived redo logs

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Use a SQL statement to back up the control file

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Use an operating system command such as the UNIX command to back up configuration files

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Basic Backup Methodology

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The RMAN  Oracle provided utility for backing-up, restoring and recovering Oracle Databases  Doesn't require a separate installation.  Off-line and on-line database backups.  Can not write directly to tape. 

3rd-party tools (like Veritas, Omiback) can integrate with RMAN to handle tape library management.

 Only compatible with Oracle release 8.0 or higher www.yogijicreations.com

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RMAN features  Compress backups of datafiles so that only those data blocks that have been written to are included in a backup  Store frequently executed backup and recovery operations in scripts.  Perform incremental backups  Create a duplicate production database for testing purpose  printable message log of all backup and recovery operations.  Recovery catalog automates both restore and recovery operations  Perform crosschecks www.yogijicreations.com

RMAN Backup Concepts  Server-managed backup  Can back up entire database, all datafiles in a tablespace, selected datafiles, control files, archived redo log files

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RMAN: Backup techniques  Image File Datafile 3 Control file Archived Log file

Datafile 3

Copy of datafile 3

Control file

Copy of control file

Archived Log file Copy of archived log

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RMAN: Backup techniques  Backup Set

Datafile 1

Datafile 4

Datafile 1

Datafile 3

Datafile 2

Control file

Datafile 2

Datafile 4

Backup set 1

Backup set 2

Datafile 3

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Control file

Backup set 3

Backup Set     

Usually contain more than one file. Can be written to a disk or tape. Required to extract files for restoration Can be incremental or full. Do not include never-used blocks.

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Backup Piece  A backup piece is a file in a backup set.  A backup piece can contain blocks from more than one datafile. Backup set 1 (Logical) Piece 1 (file) Piece 2 (file) Datafile 1

Datafile 4

Datafile 5

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RMAN commands  BACKUP Back up database files, archive logs, backups, or copies.  CATALOG Add information about files to the repository. (10g+)  CHANGE Update the status of a backup in the RMAN repository.  CONFIGURE Persistent RMAN settings.  CONNECT Connect to a recovery catalog or auxiliary database  CROSSCHECK Check whether backup items still exist.  DELETE Delete backups from disk or tape EXIT Exit the RMAN console  LIST List backups and copies www.yogijicreations.com

RMAN Commands          

RECOVER Apply redo logs or incremental backups to a restored backup set (or copy) in order to update it to a specified time. REPORT Report backup status: database, files, backups RESTORE Restore files from an RMAN backup (or copy) RUN Some RMAN commands are only valid inside a RUN block. SET Settings for the current RMAN session. SHOW Display the current configuration SHUTDOWN Shutdown the database SQL Execute a PL/SQL procedure or SQL statement(not SELECT) STARTUP Startup the database ADVISE FAILURE Display repair options (11g Data Recovery Advisor) REPAIR FAILURE Repair database failures (11g Data Recovery Advisor)

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Backing up database using RMAN  Command: Backup  During an RMAN backup, the Oracle database server reads the datafiles, not an operating system utility.  The server reads each block and determines whether the block is inconsistent.  If the block is inconsistent, then Oracle rereads the block until it gets a consistent picture of the data. www.yogijicreations.com

Backing up database using RMAN Logical name assigned to a backup set or image copy

month_full_backup

week_full_backup Wednesday_1_backup

Datafiles 1,3

Datafile 3

Datafiles 2,4

Datafile 4

Backup set

Backup set

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Datafile 1

Backup set

RMAN Control File Autobackups  CONFIGURE CONTROLFILE AUTOBACKUP  When enabled, RMAN automatically performs a control file autobackup after BACKUP or COPY commands

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Archived Redo Log Backups  Archived redo logs are essential for recovering an inconsistent backup.  BACKUP ARCHIVELOG

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RMAN Dynamic Views       

V$ARCHIVED_LOG V$BACKUP_CORRUPTION V$COPY_CORRUPTION V$BACKUP_DATAFILE V$BACKUP_REDOLOG V$BACKUP_SET V$BACKUP_PIECE www.yogijicreations.com

Database Recovery  Difference between restoring and recovering?  Restoring: copying backup files from secondary storage (backup media) to disk.  Recovering: process of applying redo logs to the database to roll it forward.

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Preparing to recover ( managed recovery)  Remain calm and do not panic  Restore database files to their respective locations  Recover the database to the point of failure using Online redo log files. (Roll forward)  Roll back to the last consistent state.

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Restoring Backups of the Damaged or Missing Files  Determine which datafiles to recover  SELECT * FROM V$RECOVER_FILE;

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Restoring Backups of the Damaged or Missing Files   

Query V$DATAFILE and V$TABLESPACE to obtain filenames and tablespace names for datafiles requiring recovery. Incase of media failure, indicate the new locations of datafiles files to the control file. If the database is open, then take the tablespaces containing the inaccessible datafiles offline. 

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Copy backups of the damaged datafiles to their default location 

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% /disk2/backup/tbs_24.bak /disk1/oracle/dbs/tbs_24.f

Recover the affected tablespace. 

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ALTER TABLESPACE s OFFLINE IMMEDIATE;

RECOVER TABLESPACE s

Bring the recovered tablespace online 

ALTER TABLESPACE s ONLINE www.yogijicreations.com

Re-Creating Datafiles When Backups Are Unavailable 

All archived log files written after the creation of the original datafile must be available

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The control file contains the name of the damaged file

 Create a new, empty datafile to replace a damaged datafile that has no corresponding backup. 

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ALTER DATABASE CREATE DATAFILE '/disk1/s1.f' AS '/disk2/s1.f';

Perform media recovery on the empty datafile. 

ALTER DATABASE CREATE DATAFILE '/disk1/s1.f' AS '/disk2/s1.f';

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Recovery of Database when Control files are lost  Find the location of the datafiles and log files.  Create a new control file based on above information 

CREATE CONTROLFILE REUSE DATABASE "ORCL10G" RESETLOGS LOGFILE GROUP 1 'K:\ORCL10G\LOG\REDO01.LOG' SIZE 50M, GROUP 2 'K:\ORCL10G\LOG\REDO02.LOG' SIZE 50M, DATAFILE 'K:\ORCL10G\DATA\SYSTEM01.DBF', 'K:\ORCL10G\DATA\UNDOTBS01.DBF', 'K:\ORCL10G\DATA\SYSAUX01.DBF‘;

 Open the database with resetlogs option.  alter database open resetlogs; www.yogijicreations.com

RMAN Recovery Techniques  Enhanced RMAN Features Automated File Creation During Recovery Simplified Recovery Through Resetlogs Change-Aware Incremental Backups Automated Disk-Based Backup and Recovery  RMAN Database Dropping and Deregistration    

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Automated File Creation During Recovery

 This feature enhances RMAN recovery by automatically creating and recovering datafiles that have never been backed up.  Archive log files are still required

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Automated File Creation During Recovery

data file #1

data file #2

Missing data file #3

RMAN

Control fle

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Archive log files

Importance of Redo log files 

The online redo logs are a set of two or more files that record

all changes made to Oracle datafiles and control files.



Whenever a change is made to the database, the Oracle database server writes the data and generates a redo record in the redo buffer

.

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Recovery using Flashback Functions  Flashback is an Oracle database facility to quickly move an entire database or a table back to a prior state for recovery purposes.  Flashback was first introduced with Oracle 9i with Oracle's Flashback Query feature.

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FRA ( Flashback Recovery area)  storage area (directory on disk or ASM diskgroup) that enables database Flash Backup and Recovery operations.  first introduced with Oracle 10g.  Related parameters:  db_recovery_file_dest  db_recovery_file_dest_size  db_flashback_retention_target www.yogijicreations.com

Flashback Query ( 9i Feature)  Allows s to see a consistent view of the database as it was at a point in the past. 

In Oracle 10g, we can now retrieve all versions of the rows that exist or ever existed between the time the query was issued and a point back in time.

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Flashback Database  Faster than traditional point-in-time recovery.  Traditional recovery method: Backups and Redo logs  Flashback Database is implemented using a new type of log file called the Flashback Database log.  Oracle database server periodically logs before images of data blocks in the Flashback Database logs.  The data block images are used to quickly back out changes to the database during Flashback Database.  RVWR: similar to the LGWR (log writer) process.  writes Flashback Database data to the Flashback Database logs.

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Enabling Flashback Database  Make sure the database is in archive mode.  Configure the recovery area by setting the two parameters:  DB_RECOVERY_FILE_DEST  DB_RECOVERY_FILE_DEST_SIZE  Open the database in MOUNT EXCLUSIVE mode and turn on the flashback feature: SQL> STARTUP MOUNT EXCLUSIVE; SQL> ALTER DATABASE FLASHBACK ON;  Set the Flashback Database retention target:  DB_FLASHBACK_RETENTION_TARGET

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Flashback Drop  DROP command permanently removed objects from the database…  In Oracle 10g, a DROP command places the object in the recycle bin.  You can restore the object from the recycle bin at any time.  Flashback table emp to before drop;  drop table emp PURGE; www.yogijicreations.com

Recycle Bin  A recycle bin contains all the dropped database objects until,  Permanently drop them with the PURGE command.  Recover the dropped objects with the FLASHBACK TABLE command.  There is no room in the tablespace for new rows or updates to existing rows.  The tablespace needs to be extended. www.yogijicreations.com

Flashback Table  Flashback Table allows you to recover a table or tables to a specific point in time without restoring a backup.  When you use the Flashback Table feature to restore a table to a specific point in time, all associated objects, such as, indexes, constraints, and triggers will be restored.  FLASHBACK TABLE emp TO SCN 76230;

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Flashback Transaction Query  It provides a way for you to view changes made to the database at the transaction level.  It allows you to diagnose problems in your database and perform analysis and audit transactions

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Questions ? For queries: [email protected] www.yogijicreations.com