Manually managing undo data

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Managing Undo Data

Managing Undo Data Automatic Undo Management The Oracle server automatically manages the creation, allocation, and tuning of undo segments. Manual Undo Management You manually manage the creation, allocation, and tuning of undo segments. It was the only method available prior to Oracle9i. Information about manual undo management can be found in “Appendix B: Manually Managing Undo Data.”

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Manually Managing Undo Data (Rollback Segments)

Allocation of a Rollback Segment When a transaction begins, a rollback segment must be assigned to this transaction. A transaction can request a specific rollback segment using the following command: SET TRANSACTION USE ROLLBACK SEGMENT rollback_segment If no such request is made, the Oracle server chooses the rollback segment with the fewest transactions and assigns it to the transaction. Using Extents Transactions use extents of a rollback segment in a sequential, circular fashion, moving from one to the next after the current extent is full.

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