Introduction to Oracle database backup and recovery

■ Xinmei, Ningbo Electric Power Bureau

Database Backup is the premise and basis for data recovery. If there is no data backup, it will be difficult to recover in the event of database problems or disasters. Common Oracle Database faults include statement faults, user process faults, instance faults, user errors, and media faults. The recovery depends on the backup. As a DBA, it is the responsibility to maintain the recoverability of the database from the following three aspects: (1) Minimize the number of database failures, so that the database can maintain maximum availability; (2) when the database inevitably fails, the recovery time should be minimized to maximize the recovery efficiency; (3) when the database fails, make sure that as little data as possible is lost or there is no loss at all, so that the data has the maximum recoverability. Next I will take Oracle8i as an example to discuss the backup and recovery of the database.

Oracle Database Backup recovery methods and features

Oracle Database Backup is divided into physical backup and logical backup. Physical backup is a copy of database files. Physical backup can be classified into cold backup and Hot Backup Based on the status of data during Backup; Export/Import) the tool is used for logical backup.

Export backup can extract data and database definitions and save the data as a binary file in Oracle's internal format. Import is used for reverse operations. The export backup mechanism cannot provide time point recovery. Because it adopts the query table method, the speed is slow. When exporting/importing data, you must pay attention to character set issues, which are prone to errors; for databases with a large amount of data, the export/import operation may fail.

Cold backup is a physical backup of data files after the database is normally shut down. When the database is closed, all data files, control files, parameter files, password files, and redo log files of the database are copied to the backup media. These files maintain a complete image when data is disabled.

Hot Backup (also known as online backup) is a physical backup of data when the database runs in archivelog mode and is enabled. If you do not use oracle rman for hot backup, you can set each tablespace to the backup state, copy the corresponding data file, and then restore the tablespace to the normal state. Databases can use backup files and archive logs for full or incomplete recovery, and can be recovered to any point in time.

Comparison of features of the preceding backup methods

Method	Type	Recovery features
Export	Logic	Any database object can be restored to its export status.
Cold backup	Physical	The database can be restored to the state when it is disabled.
Hot Backup	Physical	The database can be restored to any time point. Oracle Database recovery Manager Recovery Manager (RMAN) is an Oracle application tool that allows DBAs to conveniently perform backup and recovery tasks on databases. It is different from other backup methods, it provides DBA centralized control over enterprise database backup and recovery operations. RMAN supports backing up databases, tablespaces, data files, control files, and archive files. It stores scripts for routine backup and provides block-Based Incremental backup, only Backup blocks that have changed since one backup can shorten the backup and recovery time, check the backup validity, and detect Bad blocks during the backup process, and record the relevant information to the dynamic view. It can be integrated with the scheduled function of the operating system for automatic backup. It supports Oracle Parallel Server backup and recovery. No additional redo logs are generated during the backup process, data File Reading is not restricted, and the system performance is not affected. APIs are provided to use third-party media management tools to ensure the speed and reliability of backup storage devices. The actual physical backup copy will be stored on the specified storage system, which can be a tape or disk. RMAN writes all the backup data to the backup set or image copy file in Oracle-specific format and reads it using the RMAN application tool. Oracle utility RMAN provides DBAs with a centralized backup management and recovery control mechanism for managing multiple Oracle databases, which greatly reduces DBA workload, it can be freed from the hassle of backing up data and reprocessing data. The database not only implements online tape backup, but also enables centralized management of backup on different machines, which correspondingly improves the security of system operation.