Media recovery requires a control file, data files (typically restored from backup), and online and archived redo log files containing changes since the time the data files were backed up. Any database transactions in the archived redo log files not reflected in the data files are applied to the data files, bringing them to a transaction-consistent state before the database is opened. If you restore the archived redo log files and data files, then you must perform media recovery before you can open the database. The advantage of making inconsistent backups is that you can back up your database while the database is open for updates. The online redo log files must be archived and then backed up with the data files to ensure recoverability.ĭespite the name, an inconsistent backup is as robust a form of backup as a consistent backup. Open database backups are inconsistent because the online redo log files contain changes not yet applied to the data files. If the database is in ARCHIVELOG mode, then you can make inconsistent backups that are recoverable using archived redo log files. When you restore your data files from a consistent backup, you can open the database immediately. All committed changes in the online redo log files are written to the data files during the shut down process, so the data files are in a transaction-consistent state. To make a consistent backup, your database must have been shut down cleanly and remain closed for the duration of the backup. Oracle Database Backup and Recovery User's Guide discusses the flashback features of Oracle Database at greater length.Ī backup is either consistent or inconsistent. You can use all of the features while your database is available. None of the preceding features requires advance preparation such as creating logical exports to allow for retrieval of your lost data. The first two features operate at the logical level, whereas the last feature operates at the physical level. Oracle Flashback Database, which enables you to revert the entire database to a past point in time Oracle Flashback Drop, which enables you to retrieve deleted (dropped) database tables Oracle Flashback Table, which enables you to revert a table to its contents at a time in the recent past This section introduces the following flashback features: The flashback features enable you to reverse the effects of unwanted database changes without restoring data files from backup or performing media recovery. The Oracle Database flashback features provide a range of physical and logical data recovery tools as efficient, easy-to-use alternatives to physical and logical backups. An effective backup strategy must be based on physical backups. Logical backups, such as exporting database objects such as tables or tablespaces, are a useful supplement to physical backups, but cannot protect your whole database. RMAN optimizes performance and space consumption during backup with file multiplexing and backup set compression, and integrates with leading tape and storage media products. RMAN is designed to work intimately with the server, providing block-level corruption detection during backup and restore. Oracle Recovery Manager (RMAN), a command-line and Enterprise Manager-based tool, is the method preferred by Oracle for efficiently backing up and recovering your Oracle database. The backup mechanisms work at the physical level to protect against file damage, such as the accidental deletion of a data file or the failure of a disk drive. With these files you can reconstruct your database. The files protected by the backup and recovery facilities built into Oracle Enterprise Manager Database Control (Database Control) include data files, control files, server parameter files, and archived redo log files. The focus in Oracle Database backup and recovery is on the physical backup of database files, which permits you to reconstruct your database.
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