5.2. An Overview of the Flashback Database

The Flashback Database is new to Oracle 10g. As mentioned previously, this feature builds upon the flash query capability that was first introduced in Oracle 9i. Now Flashback technology has been greatly extended, which includes flashback database, flashback query, flashback version query, flashback transaction query, flashback table, and flashback drop. There is one main difference with these flashback technologies and the new Oracle 10g Flashback Database: The Flashback Database relies on "before" images in the flashback logs, but traditional flashback technology relies on the undo data.

The Flashback Database allows you to flash the entire database back to a specific point-in-time. This is extremely useful to recover from errors such as truncating a large table, an incomplete batch job, or a dropped user. Flashback Database recovery is also the best choice for most logical corruptions such as a bad complex transaction that gets propagated throughout the database.

Real World Scenario: Limitations with the Flashback Database

Flashback Database recovery has some limitations that can impact the use of this valuable tool. User errors or logical corruptions are often the most difficult recovery processes because impact to the database is often not clearly known. These types of failures by themselves are where the Flashback Database is the most effective.

However, Flashback Database recovery cannot recover through some cases that are common occurrences in a lot of situations such as resizing a datafile to a smaller size or a deleted data-file. In these cases, Flashback Database recovery can be used with traditional incomplete recovery for an efficient recovery solution.

In the case of a deleted or resized datafile, the datafile would need to be restored with traditional methods to a point-in-time prior to the deletion or resizing of the datafile. Then you could use Flashback Database recovery to recover the rest of the database.


One major technological benefit of the Flashback Database is that it allows you to reverse user errors or logical corruption much quicker than performing a traditional incomplete recovery or using the Oracle Log Miner utility. The reason the Flashback Database recovery is much quicker than traditional recovery operations is due to the fact that recovery is no longer impacted by the size of the database. The mean time to recovery (MTTR) for traditional recovery is dependent on the size of the datafiles and archive logs that need to be restored and applied. Using Flashback Database recovery, recovery time is proportional to the number of changes that need to be backed out of the recovery process, not the size of datafiles and archive logs. This makes the Flashback Database recovery process the most efficient recovery process in most user error or logical corruption situations.

The Flashback Database architecture consists of the recovery writer RVWR background process and Flashback Database logs. When the Flashback Database is enabled, the RVWR process is started. Flashback Database logs are a new type of log file that contain a "before" image of physical database blocks. The RVWR writes the Flashback Database logs in the flash recovery area. Writing Flashback Database logs requires the flash recovery area to be enabled. The flash recovery area is a prerequisite to the Flashback Database because the Flashback Database logs are written to the flash recovery area. Figure 5.1 shows a diagram of the main components of the Flashback Database architecture.

Figure 5.1. Flashback Database architecture

The Flashback Database is a nice substitute for incomplete recovery for logical corruption and user errors. However, there are some limitations to the Flashback Database that you should be aware of:

  • Media failure cannot be resolved with the Flashback Database. You will still need to restore datafiles and recover archived redo logs to recover from media failure.

  • Resizing datafiles to a smaller size, also called shrinking datafiles, cannot be undone with the Flashback Database.

  • You cannot use the Flashback Database if the control file has been restored or recreated.

  • Dropping a tablespace and recovery through RESETLOGS cannot be performed.

  • You cannot flash back the database to an SCN prior to the earliest available SCN in the flashback logs.

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