5.1. An Overview of Flashback Technologies

Oracle Flashback Technologies were first developed in Oracle 9i with the advent of the Flashback Query. In Oracle 10g, there has been a significant extension of this technology. This chapter focuses on one specific Flashback Technology—the Oracle Flashback Database—but it is important to have a general understanding of all the Flashback Technologies and where these technologies are best used. This understanding will enable you to put the benefits of each of these technologies into context. The new Oracle 10g Flashback Technologies consist of the following:

• Flashback Database

• Flashback Drop

• Flashback Versions Query

• Flashback Transaction Query

• Flashback Table

Chapter 6, "Recovering from User Errors," will discuss Flashback Drop, Flashback Versions Query, Flashback Transaction Query, and Flashback Table in detail. It is important to note that all the flashback technologies, with the exception of the Flashback Database, are based on undo data. The Flashback Database is best used as a replacement for incomplete recovery of a complete database. The main benefit of the Oracle Flashback Database over incomplete database recovery is that the Flashback Database is much quicker and more efficient. The Flashback Database is not based on undo data but on flashback logs.

Flashback Drop, Flashback Versions Query, Flashback Transactions Query, and Flashback Table are best used to recover individual objects or rows within an object. The Flashback Drop provides a virtual Recycle Bin that allows a dropped object to be restored. The Flashback Versions Query and Flashback Transaction Query are designed to identify and allow you to fix rows of data that need to be reverted to a previous state. Flashback Table is designed to recover individual tables or groups of tables from errors such as when the table is updated with the wrong WHERE clause.

The Flashback Technologies, with the exception of the Flashback Database, are designed so that end users can repair their own errors. This reduces the need for the DBA to be involved in every recovery activity. The Flashback Database and sometimes the Flashback Table is a DBA activity because of their global impact to the database. The Flashback Database is best suited to recover from errors such as truncating a large table, an incomplete batch job, or a dropped user. The next sections will explain the Flashback Database in detail and show you how to use it.