Guest

• Dec 29th, 2005

 

Rollback segments are used to

1. get data blocks to the original state when user issues a 'rollback' statement
2. give consistent data to a user, hiding uncommitted changes made by other users/sessions
3. to undo uncommitted changes during database recovery. After applying all changes recorded in the redo logs, Oracle uses rollback segments to undo uncommitted changes. Since rollback segments are stored in the database buffers, they are automatically protected by the redo log.

vijay

• Jun 15th, 2007

 

Transaction rollback:  Suppose if you  are updating the data, now you want to rollback so the old image will read from rollback segments.  You are old image from rollback segment.

Transaction Recovery:  Suppose you are updating the data,now the instance failed,  so the uncommited data has to be rolled back, so it will rollback from undo segments if the data is protected by redo logs.

Read consistency:  Suppose you are updating the data, so lock will held for that table,now other users query means it has to old data before you commit, so that data will read from rollback segements.  It is nothing but read consistency

Mohammed Abdul Afroze

• Sep 18th, 2007

 

Rollback Segment Stores Undo Information and are used for the following purposes.

1. To undo the previous command
2. For read consistency and
3. For crash recovery.