Oracle Database Backup and Recovery Basics 10g
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What is Backup and Recovery?
In general, backup and recovery refers to the various strategies and procedures involved in protecting your database against data loss and reconstructing the database after any kind of data loss.Physical Backups and Logical Backups
A backup is a copy of data from your database that can be used to reconstruct that data. Backups can be divided into physical backups and logical backups.See also: Oracle Database Utilities for more details about
importing and exporting data using Oracle export and import
utilities.
Physical backups are backups of the physical files used in storing and recovering your database, such as datafiles, control files, and archived redo logs. Ultimately, every physical backup is a copy of files storing database information to some other location, whether on disk or some offline storage such as tape.
Logical backups contain logical data (for example, tables or stored procedures) exported from a database with an Oracle export utility and stored in a binary file, for later re-importing into a database using the corresponding Oracle import utility.. Physical backups are the foundation of any sound backup and recovery strategy. Logical backups are a useful supplement to physical backups in many circumstances but are not sufficient protection against data loss without physical backups.
Unless otherwise specified, the term 'backup' as used in the backup and recovery documentation refers to physical backups, and to backup part or all of your database is to take some kind of physcial backup. The focus in the backup and recovery documentation set will be almost exclusively on physical backups.
Errors and Failures Requiring Recovery from Backup
While there are several types of problem that can halt the normal operation of an Oracle database or affect database I/O operations, only two typically require DBA intervention and media recovery: media failure, and user errors.Other failures may require DBA intervention to restart the database (after an instance failure) or allocate more disk space (after statement failure due to, for instance, a full datafile) but these situations will not generally cause data loss or require recovery from backup.
User Error
User errors occur when, either due to an error in application logic or a manual mis-step, data in your database is changed or deleted incorrectly. Data loss due to user error includes such missteps as dropping important tables or deleting or changing the contents of a table. While user training a nd careful management of privileges can prevent most user errors, your backup strategy determines how gracefully you recover the lost data when user error does cause data loss.Media Failure
A media failure is the failure of a read or write of a disk file required to run the database, due to a physical problem with the disk such as a head crash. Any database file can be vulnerable to a media failure. The appropriate recovery from a media failure depends on the files affected and the types of backup available.