Analysis and Discussion on Oracle Database Restoration

Oracle is still quite common, So I studied Oracle Database restoration and shared it with you here. I hope it will be useful to you. When we use a database, we always hope that the database content is reliable and correct, but due to computer system faults, hardware faults, software faults, network faults, process faults and system faults) the operation of the database system is affected, the correctness of the data in the database is affected, or even the database is damaged, so that all or part of the data in the database is lost.

Therefore, when the above fault occurs, we hope to reconstruct the complete database, which is called Oracle database recovery. The recovery process can be roughly divided into the recovery (Restore) and recovery (Restore) processes. Oracle Database recovery can be divided into the following two types:

Instance fault consistency recovery

If an instance fails unexpectedly, such as power failure or background process failure, or the shutdoum abort statement is unexpectedly issued, the instance must be restored. The instance restores the Oracle database to the transaction consistency state before the fault. If an instance fault is found in the online backup, the media must be restored. In other cases, Oracle will automatically perform instance recovery when new instances are assembled and opened at the next database startup. If needed, the instance is automatically restarted from the assembly status to the open status, which is handled:
1. Roll Forward to learn about the data not recorded in the recovery data file. This data is recorded in online logs, including restoring the content of the rollback segment.
2. Roll Back uncommitted transactions and regenerate the operation specified by the rollback segment in step 1.
3. Release the resources that are being processed by the firm at the time of the fault.
4. resolves any outstanding distributed transactions that are being committed in a phase at the time of failure.

Recovery from media faults or inconsistent file errors

A media fault occurs when a file or part of a file or disk cannot be read or written. File errors generally refer to file inconsistencies caused by accidental file deletion or accidents. Databases in this state are inconsistent, and DBAs need to manually recover the database. There are two types of recovery, which are determined by the database running archiving and backup methods.

1. All lost modifications can be restored when the media is completely restored. Generally, a database backup is required and the database is running in the archive state and there are available archive logs. For different types of errors, different types of full recovery can be used, which determines the availability of file destruction and database.

2. Incomplete media recovery refers to media recovery when full media recovery is impossible or not required. Restructured the damaged database to restore a transaction consistency state before a media fault or before a user error. Incomplete media recovery has different types of use, depending on the need for incomplete media recovery. The following types are available: undo, time-based, and modification-based Incomplete recovery.

CANCEL-based recovery: in some cases, incomplete media recovery must be controlled, and DBA can CANCEL the operation at the specified point. The recovery Location Based on revocation is online or archived in one or more log groups. It has been damaged by media faults and cannot be used in the recovery process. Therefore, media recovery must be controlled, as a result, the recovery operation is aborted after the latest and undamaged log groups are used for data files.

Restoration Based on TIME and modification (SCN): If the DBA wants to restore to a specified point in the past, it is an ideal incomplete media restoration, generally, it occurs before a specific operation is restored and before a data table is deleted. The preceding section describes Oracle Database restoration.

1. How to completely uninstall Oracle
2. Classic description of the Oracle SMON Process
3. Oracle routine for beginners
4. Two Methods for Oracle data comparison
5. A brief summary of Oracle Learning Process