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| Re: BACKUP AND RECOVERY [message #13543 is a reply to message #13540] |
Fri, 16 July 2004 04:02  |
Rahul Priyadarshy
Messages: 19
Registered: July 2004
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Junior Member |
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A backup is a representative copy of data. This copy can include important parts of a database such
as the control file, redo logs, and datafiles. A backup protects data from application error and acts as
a safeguard against unexpected data loss, by providing a way to restore original data.
Backups are divided into physical backups and logical backups. Physical backups are copies of
physical database files. The phrase “backup and recovery” usually refers to the transfer of copied files
from one location to another, along with the various operations performed on these files. In contrast,
logical backups contain data that is exported using SQL commands and stored in a binary file.
Logical backups are used to supplement physical backups.
Restoring a physical backup means reconstructing it and making it available to the Oracle server. To
recover a restored backup, data is updated using redo records from the transaction log.
The transaction log records changes made to the database after the backup was taken.
Oracle performs crash recovery and instance recovery automatically after an instance failure.
In the case of media failure, a database administrator (DBA) must initiate a recovery operation.
Recovering a backup involves two distinct operations: rolling the backup forward to a more recent
time by applying redo data, and rolling back all changes made in uncommitted transactions to their
original state.
In general, recovery refers to the various operations involved in restoring, rolling forward, and rolling
back a backup. Backup and recovery refers to the various strategies and operations involved in
protecting the database against data loss and reconstructing the database should
loss occur.
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