Beginning Oracle Database 11g Administration From Novice to Professional

CHAPTER 13 RECOVERY 283
Flashback Technology
The information contained in the undo segments can be used to reconstruct prior versions
of the data. The amount of information available in the undo segments is governed
by the size of the undo segments and by the setting. The default value of
the setting is only 900 seconds (15 minutes)—you should increase it to a
more appropriate value. Also make sure that the undo segments are fairly large.
Note The more advanced flashback features such as Flashback Transaction Query, Flashback Table, and
Flashback Database are available only with the Enterprise Edition of Oracle Database 11g.
Flashback Query
If data in a table is inadvertently changed, the prior values of the data items can be obtained
by using the undo segments, and suitable SQL statements can be constructed to correct the
data, as in the following example.
First, let’s increase the salary of employee 101 by $1,000: