ANBOB™

从9i开始oracle提供了一个很强大的flashback,10G更是对闪回做了加强，闪加数据变的更加简单，各种闪回又是如何实现呢的？是redo log?undo log?flashback log?recyclebin?

Flashback Table, Flashback Query, Flashback Transaction Query and Flashback Version
Query all rely on undo data, records of the effects of each update to an Oracle database
and values overwritten in the update. Used primarily for such purposes as providing
read consistency for SQL queries and rolling back transactions, these undo records
contain the information required to reconstruct data as it stood at a past time and all
changes since that time.

Flashback Drop is built around a mechanism called the Recycle Bin, which Oracle
uses to manage dropped database objects until the space they occupied is needed to
store new data.

At the physical level, Oracle Flashback Database provides a more efficient direct
alternative to database point-in-time recovery. If you have datafiles which merely have
unwanted changes, then you can use Flashback Database to cause your current
datafiles revert to their contents at a past time. The end product is much like the result
of a point-in-time recovery, but is generally much faster because it does not require
restoring datafiles from backup, and requires only limited application of redo
compared to media recovery.

Flashback Database uses flashback logs to access past versions of data blocks, as well
as some information from the archived redo log. Flashback Database requires that you
configure a flash recovery area for your database, because the flashback logs can only
be stored there. Flashback logging is not enabled by default. Space used for flashback
logs is managed automatically by the database, and balanced against space required
for other files in the flash recovery area.

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