oracle backup and recovery
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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
User Managed backup RMAN Database recovery
User managed RMAN based
Flashback Recovery
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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.
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Need of taking backup
User 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
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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 SCNSCN ( System change Number):A stamp that defines a committed version of a database at a pointin 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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User-Managed Backups
The basic user-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 Use an operating system command such as the
UNIX cp command to back up datafiles and archived redo logs Use a SQL statement to back up the control file Use an operating system command such as the
UNIX cp 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
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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
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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
ArchivedLog file
Datafile 3
Copy of datafile 3
Copy of archived log
Datafile 3
ArchivedLog file
Control file
Control file
Copy of control file
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RMAN: Backup techniques
Backup Set
Backup set 1
Backup set 2
Backup set 3
Datafile 1
Datafile 2
Datafile 3
Datafile 4
Controlfile
Datafile 4
Controlfile
Datafile 1
Datafile 2
Datafile 3
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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 2 (file)Piece 1 (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
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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 re-reads the block until it gets a consistent picture of the data.
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Backing up database using RMAN
Logical name assigned to a backup set or image copy
month_full_backup week_full_backup Wednesday_1_backup
Datafile 3
Datafile 4
Backup set
Datafiles 1,3
Datafiles 2,4
Backup set
Datafile 1
Backup set
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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$BACKUP_PIECE
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Database Recovery
Difference between restoring and recovering?
Restoring: copying backup files from secondary storage (backup media) to disk.
Recovering: process of applying redo logs to the database to roll it forward.
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Preparing to recover (user managed recovery)
Remain calm and do not panic Restore database files to their
respective locations Recover the database to the point of
failure using Online redo log files. (Roll forward)
Roll back to the last consistent state.
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Restoring Backups of the Damaged or Missing Files
Determine which datafiles to recover SELECT * FROM V$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. ALTER TABLESPACE users OFFLINE IMMEDIATE;
Copy backups of the damaged datafiles to their default location % cp /disk2/backup/tbs_24.bak /disk1/oracle/dbs/tbs_24.f
Recover the affected tablespace.
RECOVER TABLESPACE users Bring the recovered tablespace online
ALTER TABLESPACE users ONLINE
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Re-Creating Datafiles When Backups Are Unavailable All archived log files written after the creation of the original
datafile must be available
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. ALTER DATABASE CREATE DATAFILE '/disk1/users1.f' AS
'/disk2/users1.f';
Perform media recovery on the empty datafile. ALTER DATABASE CREATE DATAFILE '/disk1/users1.f' AS
'/disk2/users1.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;
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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
Missingdata file
#3
Control fle
RMAN
Archive log files
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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
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Flashback Query ( 9i Feature)
Allows users 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;
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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.
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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 ?Questions ?
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