Database Reference
In-Depth Information
If you have been working through this topic chapter by chap-
ter, you should have a pretty firm grasp of Oracle backup and
recovery methods available through RMAN. For the most
part, RMAN works in the physical realm. It provides recovery from physical problems
such as physical block corruption, failed hardware, missing files, and so on. It is vital for a
database administrator to be able to recover from these types of problems, and RMAN is
definitely the tool for the job.
But database administrators must also have tools to deal with
logical corruption
in the
database. Logical corruption, for the most part, is synonymous with the term
user error
.
Rather than having a physical problem with your database, you have a problem with the
data in your database. Here are some examples:
■
A developer accidentally drops a table.
■
A programming bug causes data updates to populate the wrong records.
■
The DBA is purging data and accidentally deletes the wrong rows.
■
An inadvertent table
TRUNCATE
takes place.
Logical corruption is far more common than physical corruption. And although RMAN
could certainly be used to recover from logical corruption, a full-blown recovery effort is
time-consuming and generally involves database downtime.
In these situations, Flashback technology provides the solution. It allows dropped objects
to be recovered. It allows queries to view data as it existed at a point in time in the past, and
it allows queries to view a history of changes made to data. It even allows returning the entire
database to a point in time or system change number (SCN). Having a thorough understand-
ing of the many Flashback options will not only help you pass your OCP exam; it will help
you to be a better DBA.
This chapter offers a detailed explanation of the functionality provided by Flashback
technology as it exists in Oracle Database 12
c
(Oracle 12
c
).
Initially, we will provide a brief overview of Flashback functionality and where it fits in
the database administrator's arsenal. We will also examine Automatic Undo Management, the
cornerstone upon which key Flashback technologies rely. Next, we will examine the various
Flashback options:
Flashback Drop and the Recycle Bin
■
Flashback Query
■
Flashback Version Query
■
Flashback Transaction
■
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