TRAINING (ORA-7) - Undo Management and Undo Tablespace

Undo Management and Undo Tablespace

Undo data is:
- A copy of original, pre modified data
- Captured for every transaction that changes data
- Retained at least until the transaction is ended
- Used to support:
Rollback operations
Read-consistent and flashback queries
Recovery from failed transactions


Monitoring Undo: Undo usually requires little management. Areas to monitor include:
- Undo tablespace free space
- “Snapshot too old” error


Administration of undo:

- Issue
     > Undo tablespace space errors
- Solution
     > Size the undo tablespace properly
     > Ensure large transactions commit periodically

- Issue
     > “Snapshot too old” errors
- Solution
     > Configure an appropriate undo retention interval
     > Size the undo tablespace properly
     > Consider guaranteeing undo retention