You stated that "The whole export will be read into undo segments". You
further stated that setting consistent=y makes "the whole export
'repeatable'". These statements are mis-information.
An export, with or without consistent=y, does not consume previously
unused undo space. (In fact, individual tables are always exported
consistently regardless of the setting). Undo will be read as needed to
create a read-consistent view of the data, just as they would for any
transaction. If there is very little update activity in the database,
then very little undo will need to be read.
I just started up a database and began a consistent=y export.
The export file is over 3 GB in size so far (still running).
select begin_time, end_time, undoblks from v$undostat;
BEGIN_TIME END_TIME UNDOBLKS ------------------- ------------------- ---------- 2005/09/28 10:14:11 2005/09/28 10:23:06 3 2005/09/28 10:04:11 2005/09/28 10:14:11 18
Gogala, Mladen wrote:
Unfortunately, it's not a misinformation. With "consistent=y", you will have
SET TRANSACTION READ ONLY as the first statement in the export. What does this statement do you can read for yourself in the manual. It wasn't an overuse of sarcasm.
As far as logical backup goes, I would tend not to disagree, but it has nothing to do with CONSISTENT=YES. This "read consistent export" can only
ensure consistency with respect to certain point in time if it builds a
read-consistent image of the database with respect to that point in time.
You have three guesses to guess which structures are used for building
such a consistent image.
So Mark, please read the fine manual before you accuse me of being overly sarcastic.
-- Mladen Gogala Ext. 121
-- Mark Bole http://www.bincomputing.com
-- //www.freelists.org/webpage/oracle-l
