Database Reference
In-Depth Information
Logical failures - this includes failures that corrupt data, failures of software (such as
bugs) and application failures corrupt data.
Networking failures - These are errors where one component cannot talk to another
component. This can lead to a number of problems.
User errors - These are errors where the user accidently or purposely corrupts data.
Disasters - Things like earthquakes, tornadoes, and flooding happen from time to time
and you have to be prepared for failures on a more massive scale.
When considering an overall backup and recovery architecture, you need to consider
each of these kinds of failures and how to recover from them. Each type of failure requires
a different approach when trying to protect from and mitigate the results of that failure.
We will discuss these things in a number of places in this topic.
Physical and Logical Backups
There are two different kinds of Oracle backup and recovery. The first is a physical backup
and the second is a logical backup. A physical backup involves backing up the physical files
of the database to some backup medium, such as another disk or a tape drive.
The logical backup extracts the data from the database and stores it in a separate backup
file. Thus, the physical component of the database is not backed up, only the data and meta
data needed to reconstruct the database if the logical backup should need to be used to
restore the database.
In general the logical backup is of less use than a physical backup. This is because the
recovery variations available with physical backups are generally greater than with logical
backups. Another benefit of physical backups over logical backups is that large logical back-
ups will usually take longer to restore than a physical backup from the same database.
Other benefits of physical backups are that they can be done in a consistent manner and
they provide the ability to restore the database to any given point in time that is required.
Logical backups do not provide this point-in-time recovery functionality.
Tools for Backup and Recovery
There are different ways of performing backup and recovery of an Oracle database. The most
common tools that you will find in use are:
RMAN - Perhaps the most commonly used tool, RMAN is a free tool provided by Oracle
that performs physical backups of the Oracle database. RMAN is easy to implement and use.
Oracle Data Pump - Oracle Data Pump is a method of performing logical backups of the
Oracle Database.
Oracle Flashback features - Oracle Database provides a number of features that revolve
around its Flashback Database functionality. These flashback features include the following:
Flashback Database
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Flashback Query
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Flashback Version Query
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Flashback Transaction Query
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