Oracle Flashback Query lets you view and repair historical data. You can perform
queries on the database as of a certain wall clock time or user-specified system change
number (SCN).

Flashback Query uses Oracle＇s multiversion read-consistency capabilities to restore
data by applying undo as needed. Oracle Database 10g automatically tunes a
parameter called the undo retention period. The undo retention period indicates the
amount of time that must pass before old undo information—that is, undo information
for committed transactions—can be overwritten. The database collects usage statistics
and tunes the undo retention period based on these statistics and on undo tablespace
size.

Using Flashback Query, you can query the database as it existed this morning,
yesterday, or last week. The speed of this operation depends only on the amount of
data being queried and the number of changes to the data that need to be backed out.
You can query the history of a given row or a transaction. Using undo data stored in
the database, you can view all versions of a row and revert to a previous version of
that row. Flashback Transaction Query history lets you examine changes to the
database at the transaction level.

You can audit the rows of a table and get information about the transactions that
changed the rows and the times when it was changed. With the transaction ID, you
can do transaction mining through LogMiner to get complete information about the
transaction.

Oracle闪回查询I
1. 利用回闪查询，用户可以查看某一行的历史信息
用户可以查看某一数据行的历史版本，并进行任意的恢复
用户还可以使用回闪事务查询在事务级查看数据库变化的历史情况
2. 用户能够对数据行进行监控，了解哪些事务对数据进行了修改，以及修改是何时发生的。
用户可以在 LogMiner 中通过事务 ID 获得与该事务完整的信息