Flashback Query Benefits (368)

This section lists some of the benefits of using Flashback Query.
■ Application Transparency
Packaged applications, like report generation tools that only do queries, can run in
Flashback Query mode by using logon triggers. Applications can run
transparently without requiring changes to code. All the constraints that the
application needs to be satisfied are guaranteed to hold good, because there is a
consistent version of the database as of the Flashback Query time.
■ Application Performance
If an application requires recovery actions, it can do so by saving SCNs and
flashing back to those SCNs. This is a lot easier and faster than saving data sets
and restoring them later, which would be required if the application were to do
explicit versioning. Using Flashback Query, there are no costs for logging that
would be incurred by explicit versioning.
■ Online Operation
Flashback Query is an online operation. Concurrent DMLs and queries from other
sessions are allowed while an object is queried inside Flashback Query.The speed
of these operations is unaffected. Moreover, different sessions can flash back to
different Flashback times or SCNs on the same object concurrently. The speed of
the Flashback Query itself depends on the amount of undo that needs to be
applied, which is proportional to how far back in time the query goes.
■ Easy Manageability
There is no additional management on the part of the user, except setting the
appropriate retention interval, having the right privileges, and so on. No
additional logging has to be turned on, because past versions are constructed
automatically, as needed.

閃回查詢的優勢
1. 應用透明
2. 提高應用效能
與先轉存再恢復相比更容易更方便
3. 聯機操作
在想同的表上其他會話也可以閃回
4. 易於管理
出了有足夠的許可權外 , 無需其他的附加要求

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