A flashback archive
guarantees the capture of all changes to customer data.
Therefore, all DDL operations which would invalidate the
history data are not allowed for tables with flashback
archiving enabled. These operations include:
-
Dropping the
table
-
Truncating the
table
-
Renaming the
table
-
Dropping or removing columns of the table
In the flashback
archive, there is a column mapping table which is used to
map columns in the history table to columns in the original
table.
SYS AS
SYSDBA @ orcl SQL> SELECT * FROM
lutz.SYS_FBA_DDL_COLMAP_60849;
STARTSCN
ENDSCN XID O COLUMN_NAME TYPE
HISTORICAL_COLUMN_NAME
---------- ------ --- - -----------
------ -------------------------
910480
COL1 NUMBER
COL1
910480
COL2 NUMBER
COL2
% The internal
tables in the flashback archive cannot be dropped
directly. They are automatically dropped with a
DROP FLASHBACK ARCHIVE statement.
%
Dropping a flashback archive does not drop the tablespaces
used by it. They could also contain other data!
What's new about UNDO
and transactions in 11g?
Optimized UNDO BACKUP
with RMAN
Prior to Oracle database 11g, RMAN
always backed up all undo
with a full backup, including undo for
committed transactions. However, in 11g, RMAN is able to
skip undo information for transactions which
have already committed and which the undo_retention
time has exceeded. RMAN can do this because the committed
undo is not needed for a recovery operation. This makes
backups of the undo tablespace a lot faster, though it does
not have any impact on flashback operations.
%
BACKUP UNDO OPTIMIZATION is an RMAN feature which is
enabled by DEFAULT and cannot be switched
off
Conclusion
As of Oracle 10g, DBAs were unable to
apply undo on a whole transaction, despite advances in
reading data from past points, and manually viewing undo sql
with flashback table. 11g does bring the DBA the
ability to flashback transaction. Furthermore, using
flashback data archive allows for UNDO data to no longer be
time consuming by using dedicated tablespaces. Due to
increasing regulation of customer data in various
organizations, flashback data archive offers automated
transaction tracking over large spans of time. To
ensure a seamless process, in 11g startup FBDA is used
automatically as a background process for flashback data
archiver. Furthermore, in 11g RMAN has also been
improved when it comes to backing up, and undo commands.
New 11g features covered
in this chapter:
and include the URL for the page.
