Why Database Recovery Techniques are important?
Database are prone to failures due to inconsistency, network failure, errors or any accidental damage. Reliable database recovery techniques are highly important to bring a database back into a working state after a failure. Recovery includes the procedures of restoring database to the earlier and previously existing condition. Data Base Management Systems must include easy and quick techniques for the user or DBA to find and recover the failed or deleted data. The techniques provided by Oracle are reliable and efficient enough to maintain and bring the database to the same condition.
Some of the techniques available to the database user can be used to recover data are:
In this technique, two directories named shadow and current directories are created. Initially both the directories are considered to be same. Here the old record is not updated but rather a new record is created and the pointer of the current directory is changed to the newly created record. As soon as this operation is completed, the shadow directory is deleted and the current directory becomes visible.
One of the most famous mechanism, this is utilized by making periodic backup copies of database. Backup copies are created at periodic intervals without any disturbance in the functioning of database. This copy saves some portions of the database. Backup technique is used when a backup copy is available to the database as per the user request.
It is highly regarded set of modules that is responsible for restoring the database to the correct state if any anomaly occurs. It basically uses log files as well as backup copies for the purpose of recovery. It uses a collection of modules to recover the database entries.
A checkpoint in DBMS is defined as a pointer to the database and the log file. The method of checkpoints is used to limit the search and subsequent processing in log files. Checkpoints act as schedules that help in writing all the logs in a DBMS to the main memory. By this facility we are able to find the time when the failure has occurred. Finally transactions are undone if the transaction was active at the same time at which it was destroyed.
The logging facilities are stored in the database systems to keep track of the database changes occurring in a particular session. As the DBMS is aware of the fact that these log files are very important to recover data, multiple copies are always created. To avoid these log files from failure these are stored in offline storage. Then earlier files are archived but the most recent ones are always kept online in this method. Online files can be accessed frequently for recovery.
If you are looking forward to a career in Database Management, knowledge of the above mentioned techniques is a great advantage. In case the DB records are lost, failed or damaged in a database you can always rely on any of these database recovery techniques.
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