In simple terms, the undo tablespace has the "before" image of changes,
and the redo log files have the "after" image of changes.
When a user issues an insert, update or delete statement, the previous
contents of each affected row are copied to the undo tablespace. The
new values are written to the redo log files. At regular intervals, one
of Oracle's background processes picks up these changes from the redo
log files and writes them to the actual tables and indexes.
If the database is running in archivelog mode, then after these changes
get copied from the on-line redo log files to the actual tables and
indexes, the on-line redo log file gets copied to the archived redo log
destination before the on-line redo log file gets re-used for later
changes.
-----Original Message-----
From: Rajavardhan
[mailto:oracledba-ezmlmshield-x21101155.[Email address protected]
Sent: Friday, June 29, 2007 5:00 AM
To: LazyDBA Discussion
Subject: difference between undo table space and redolog
Hi
Gurus
Can some give clear info on
Undo tablespace and redolog files
Thanks & Regards
V.Rajavardhan Reddy
Software Engineer
GSS America Infotech Ltd.
Block B, 3'rd Floor,
Cyber Gateway,
Hi-Tech City,
Hyderabad.
Tel:- 040-40028700
Fax:- 040-40028703
Visit us: http://www.gssamerica.com
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