Availability and Recovery - New Flashback Features
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Oracle Database 10g offers some new features associated with flashback query. The first is Flashback Database, which allows you to flash back the entire database to a specific point in time. The second feature is Flashback Drop, which allows you to undrop an object in the Oracle Database 10g database. We will also look at flashback version query, which allows you to look at a set of changes that have occurred in the database between two sets of times. Also, Oracle Database 10g allows you to configure a tablespace for guaranteed retention, ensuring that the undo in the tablespace will be retained. The following sections discuss these features in more detail.
Flashback Database
Flashback query is a very powerful feature in Oracle Database that was introduced in Oracle9i and enhanced in Oracle9i Release 2. Now, Oracle Database 10g offers even more functionality in the form of Flashback Database. Flashback Database allows you to flash back the entire database to a specific point in time. This can be useful to resolve problems such as logical data corruption that might be caused by wayward application code. Also, Flashback Database can help in the resolution of user errors that might cause the loss or unintentional change in data (we all know that never happens!).
NOTE -- Flashback Database is not a means of recovering the database in the event of some physical loss, or recovering from some form of physical corruption.
One of the principle benefits of Flashback Database is that it can be a much faster method of recovering data than other recovery methods (e.g., via tablespace point-in-time recovery or logical backups or Log Miner). Let’s look in a bit more detail at the architecture associated with Flashback Database, and then look at how to use Oracle Database 10g’s Flashback Database.
Flashback Database Architecture
Flashback Database involves some new Oracle Database 10g architectural components that you will want to be aware of: Flashback Database logs, and RVWR, one of the new Oracle Database 10g background processes.
Flashback Database Logs - A Flashback Database log is a new kind of log file that contains the before image of Oracle database blocks. The Flashback Database logs must be created in the database recovery area (and thus a flashback recovery area must be configured). Flashback logs are not archived, as are database redo logs, and they are not used for physical database recovery.
The RVWR Background Process - When Flashback Database is enabled, a new background process, RVWR, is started. This process is responsible to write Flashback Database data to the Flashback Database logs.
 This chapter is from Oracle Database 10g New Features, by Robert Freeman (McGraw-Hill/Osborne, 2004, ISBN: 0072229470). Check it out at your favorite bookstore today. Buy this book now.
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