Backup & Recovery Concepts for Oracle Database

CIS 764

Mustafa MohammedNovember 25, 2008

Contents Basics of Backup & Recovery. Different types of failure that can occur. What Information should be backed up? Logical backup-Exports & Imports. Why do we use Logical backup? Advantages & Disadvantages of Logical

Backup.

Basics of Backup and Recovery

Def:- A backup is a representative copy of data. It includes important parts of database such as

the control file, redo logs and data-files. Purpose:- It protects data from application error

and safeguards against unexpected data loss, by providing a way to restore original data.

Backups are divided into two types:

- Physical Backup

- Logical Backup

Physical backups are copies of physical database files.

To restore a Physical backup is to reconstruct it and make it available to the Oracle server.

To recover a restored backup, data is updated using redo records from the transaction log.

Logical backups contain data that is exported using SQL commands and stored in a binary file.

These are used as to supplement physical backups.

Different types of failure that can occur

Instance failure: Usually connected with an Oracle process failure

Media failure: Disk failure, storage array controller failure etc

Block Corruption: Usually caused by bugs in Oracle software

Human error: In most cases accidentally deleted/updated data Database user or DB

Statement failure: a statement which is not of a valid SQL construction.

Disaster: Fire, flood, earthquake, plane crash etc.

What Information should we backup? When developing a backup strategy , a DBA must decide the type of

information to be backed up.

The basic backup types include:

- Online Database Backup

- Offline Database Backup

- Whole Database Backup

- Tablespace Backup

- Data-file Backup

- Control File Backup

Logical Backup- Exports & Imports

These are utilities that allow us to make exports and imports of data objects( such as tables).

Exp/Imp allows transferring data across DB’s that reside on different hardware platforms or on different Oracle versions.

Exp/Imp can be used in four modes: - Full Export: The EXP_FULL_DATABASE and

IMP_FULL_DATABASE are used to perform full export. - Tablespace: use the tablespaces export parameter for a

tablespace export. - User: This mode can be used to export and import all objects

that being to a user. - Table: Specific tables can be exported/imported with table

export mode.

Sample Syntax for Full DB Exp/Imp

$ exp file=full.dmp log=fulldb.log full=Y

$ imp file=full.dmp log=fulldb.log

Why do we use Logical Backup?

It makes transferring DB easy when migrating from one OS to another; say from NT to Solaris as it is platform independent. We achieve this by exporting from NT and importing into Solaris.

Simplifies the task of upgrading Oracle versions.

Ex: upgrading from 9i to 10g , we first perform Oracle “Exp” on 9i DB and then upgrade the Server to 10g including DB upgrade.

To take objects from one DB to another DB or from one user to another.

For large database’s LB provides an incremental export which is performed on weekdays and a complete export on weekends.

Advantages & Disadvantages of Logical Backup

ADV:- Enables to copy objects from 1 schema to another within a database. Enables to copy objects across the DB’s running either in the same

server or in the different servers.

DISADV:- LB is very slow when compared with PB as it is done by file level at OS

level whereas in LB, we need to make selections from each table. Import is much slower(8-10 times) since it is DDL+DML which

eventually involves more I/O operations.

QUESTIONS?

References Backup and Recovery in Oracle—“Oracle site” November 25 2008

http://download-uk.oracle.com/docs/cd/B19306_01/server.102/b14220/backrec.htm

Backup and Recovery concepts -- Wikipedia: The Free Encyclopedia November 25 2008 <http://en.wikipedia.org/wiki/Backup_and_Recovery>

Backup and Recovery Overview and Configuration in Oracle9i <http://

pd.acm.org/sks_course.cfm?crs=66137_eng>