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Database level: The Flashback Database feature allows you to restore an entire database to a point in time, thus undoing all changes since that time. For example, you can restore a dropped schema or an erroneously truncated table. Flashback Database mainly uses flashback logs to retrieve older versions of the data blocks; it also relies, to a much smaller extent, on archived redo logs to completely recover a database without restoring data files and performing traditional media recovery. As you can see, Oracle s Flashback technology employs a variety of techniques. The row-level Flashback techniques and Flashback Table use undo data and are discussed in 6. Flashback Drop and Flashback Database rely on the new concept of a Recycle Bin and Flashback log data, respectively, to undo errors at various levels. We will focus on these latter two techniques in this chapter.

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Therefore, the term type information is often used instead of metadata In this book, I will use the more comprehensive term metadata, unless I really mean metadata describing types only In that case, I will use the more precise term type information..

Unlike traditional recovery techniques, the primary use of Flashback techniques isn t to recover from a media loss, but to recover from human errors. For example, you may accidentally change the wrong set of data or drop a table. Or you may just want to query historical data and perform change analysis. In some extreme cases, you may want to revert the entire database to a previous point in time.

If you have a damaged disk drive, or if there is physical corruption (not logical corruption due to application or user errors) in your database, you must still use the traditional methods of restoring backups and using archived redo logs to perform the recovery.

Traditionally, the only way to recover from human error was to employ traditional backup and restore techniques. The process of restoring the database files and then rolling forward through all the redo logs could often involve significant downtime, however, and Flashback technology offers you a much more efficient and much faster way to recover from logical errors, in most cases while the database is still online and available to users. Furthermore, Flashback techniques allow you to selectively restore certain objects. With traditional techniques, you have no choice but to recover the entire database.

here are times you may want to enter some input or perform an action without having to use the Enter key. A while back, I encountered this problem when I needed to view the numerical output of ballistic equations. I wanted to be able to increment or decrement an input value and recalculate the results by pressing just one key. I came up with a script that would do this, and display both the changed input value and the new results calculated from it. The example script here, while interesting, is just a simple demonstration of how to process instant response. My script accomplished its task quite well. The following script is a simplified version that calculates and displays the values for a projectile s trajectory. The user can set the launch angle and the firing velocity in the manner described. The script will then display the projectile s distance, maximum height, and duration of flight. First we initialize some variables and, because we will alter the terminal settings, we save the current settings so that we can restore them later.

The Flashback Drop feature provides a means to recover an accidentally dropped table (or index) without the loss of any recent transactions. Most experienced DBAs will have experienced situations where a production table has been accidentally dropped, or the wrong table truncated. It takes seconds to perform DROP TABLE and your SQL prompt comes back very quickly but its consequences can be dire. Unfortunately, you aren t required to confirm your choice to drop a table before the table is gone! In Oracle Database 10g, when you drop a table, Oracle doesn t get rid of it immediately. It lists the table, and any dependent objects, in the Recycle Bin (more on this shortly) and retains it for as long as possible. If you quickly realize a mistake has been made, you can use the following simple command to immediately restore your lost table: SQL> FLASHBACK TABLE table_name TO BEFORE DROP;

One of the best ways to avoid accidentally dropping a table is to use the new prompt variables in SQL*Plus, so your database name and username appear as part of the prompt. I explain this in 12.

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