Oracle backup and recovery

Oracle Backup and Recovery
Created By: Saurabh Kulkarni
www.yogijicreations.com

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

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.

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.

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!

 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

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.

techniques
 In 24 X 7 environment
 Database should be in ARCHIVELOG
mode

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.

techniques
 Whole database backups
 Tablespace Backups
 Datafile Backups

techniques
 Full Backup
 Incremental Backup
 Differential Incremental Backup
 Cumulative Incremental Backup

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

Cumulative Incremental Backup
 Backup all the blocks till the level 1.

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.

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

Basic Backup Methodology

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

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

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

RMAN: Backup techniques
 Image File
Archived
Log file
Datafile
3
Copy of datafile 3
Copy of archived log
Datafile
3
Archived
Log file
Control
file
Control
file
Copy of control file

RMAN: Backup techniques
 Backup Set
Backup
set 1
Backup
set 2
Backup
set 3
Datafile
1
Datafile
2
Datafile
3
Datafile
4
Control
file
Datafile
4
Control
file
Datafile
1
Datafile
2
Datafile
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.

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

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

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)

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.

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

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

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

RMAN Dynamic Views
 V$ARCHIVED_LOG
 V$BACKUP_CORRUPTION
 V$COPY_CORRUPTION
 V$BACKUP_DATAFILE
 V$BACKUP_REDOLOG
 V$BACKUP_SET
 V$BACKUP_PIECE

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.

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.

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

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

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';

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:ORCL10GLOGREDO01.LOG' SIZE 50M,
GROUP 2 'K:ORCL10GLOGREDO02.LOG' SIZE 50M,
DATAFILE
'K:ORCL10GDATASYSTEM01.DBF',
'K:ORCL10GDATAUNDOTBS01.DBF',
'K:ORCL10GDATASYSAUX01.DBF‘;
 Open the database with resetlogs option.
 alter database open resetlogs;

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

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

Automated File Creation During
Recovery
data file
#1
data file
#2
Missing
data file
#3
Control fle
RMAN
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.

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.

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

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.

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.

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

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;

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.

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;

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

Questions ?
For queries: info@yogijicreations.com

Oracle backup and recovery

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