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Don Burleson Blog 









Oracle Database Backup and Recovery

Oracle Application Server Tips by Burleson Consulting

Whether you are working on a development system or a production system, you need to take precautions to protect your valuable work from external problems such as power outages or server crashes.  In the case of a production system, a company in many cases has bet it?s continued existence on Oracle software.  The Oracle database has built its reputation as a powerful data management system that can safely maintain the data entrusted to it.   The Oracle Application Server 10g continues in that vein with a robust capability to recover from external or internal problems.  Chapter 9 discussed High Availability solutions that could reduce or eliminate application server down time.  In this chapter we discuss methods to backup the application server and if necessary restore from a backup.   

Types of Problems

Before discussion methods of backing up and restoring the application server, we need to discuss that type of problems that the system could encounter and how they affect the application server.  I have divided these problems up into two types, internal and external.  An external problem happens outside the application server or within the application server code itself.  Internal problems happen within the user application running in the application server. 

External Problems

Most system crashes are the result of human error.  An operator makes a change and the effect cascades to the point of crashing the entire system.  The second most common cause of system crashes is equipment failures. 

Equipment Failures

In the not too distant past, one of the basic tasks of a DBA was to recover data files from disk failures.  With the rapid adoption of RAID systems, many DBAs have never had to perform this task.  As discussed in chapter 9, you can create an array of application server so that any equipment related failure would not stop the application server from servicing user request.  This is the basis for using multiple inexpensive commodity servers to produce fault tolerant systems.  Still, even though the application server is still running, an operator must recover the failed node and place it back into operation. 

Server Crashes

A crash is the sudden failure of a system.  It may be caused by the loss of power, equipment failure, or a software problem such as a memory leak.  The primary problem with a system crash is that data in memory is lost before it can be saved.  The Oracle Application Server 10g and the Oracle database (to include the Metadata Repository database) can normally self-recover from a server crash, however, the user application may not.

User Error

This is the most common problem that administrators must deal with and many times it is the hardest to recover from if not prepared.  The development team spends the last three days working late at night to prepare the application upgrade for deployment into the production system.  A tired developer accidentally deletes a critical application file.  If (as commonly happens) the team has not backed up the development system, they may not be able to recover that critical file.  In many companies, the development system will require daily backups while the production system may need only occasional backups.  It all depends on when the system changes.

Another common error is deleting the wrong data.  This can be a user error and the failure of some type of automation such as a nightly script. 

SQL> delete from transactions where tans_date > SYSDATE ?7;

In the above example, if the user was trying to delete all transactions older than 7 days, he just made a mistake.  Instead he deleted all transactions younger than 7 days.  If the operator realizes his mistake before committing, the database can roll back the delete.  If the user commits or logs off (implicit commit) then the deleted data must be recovered.  Another form of user error is incomplete automation of task.  A company implements a nightly script that processes the daily transactions and then truncates the transaction table.  The process fails (maybe for something simple like a database link being unavailable) and the second part kicks in and truncates the table causing the loss of that days receipts. 

Site Disaster

A site disaster is the total loss of the system site, from earthquake or fire for example.  In this case, backups and/or failover systems must be maintain off site at a location that will not be effected by the disaster that strikes the main site.  Failover systems are discussed in chapter 9. 

Internal Problems

Internal problems happen within the user application and involve programming practices that insure persistent data is properly maintained and updated to reflect the application data in memory.  This was discussed briefly in chapter 7, but is beyond the scope of this book.  The Oracle Application Server 10g has a number of features that assist with internal problems such as OC4J islands that maintain state across instances, but these features (chapter 9) are designed to support the loss of an application server instance not to compensate for poor programming of the user applications. 

Between external and internal problems, there will come a time when you will need to recover the application server or database.  Oracle provides a robust set of tools to insure data protection but you have to use them.  I am always amazed when I visit a new client and find that they have no backup strategy and in many case are not running their database in archivelog mode.  My philosophy is that if your data is worth being in an Oracle product, it is worth implementing the tools to protect it.

This is an excerpt from "Oracle 10g Application Server Administration Handbook" by Don Burleson and John Garmany.

If you like Oracle tuning, you may enjoy the new book "Oracle Tuning: The Definitive Reference", over 900 pages of BC's favorite tuning tips & scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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