Overview of Oracle Flashback Query I (366)

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閃回查詢I
1. 利用回閃查詢，使用者可以檢視某一行的歷史資訊
使用者可以檢視某一資料行的歷史版本，並進行任意的恢復
使用者還可以使用回閃事務查詢在事務級檢視資料庫變化的歷史情況
2. 使用者能夠對資料行進行監控，瞭解哪些事務對資料進行了修改，以及修改是何時發生的。
使用者可以在 LogMiner 中透過事務 ID 獲得與該事務完整的資訊

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