Undo Space Acquisition and Management (299)

When you open the database, the instance attempts to acquire one or more undo
tablespaces. You determine whether to operate in automatic undo management mode
or manual undo management mode at instance startup using the UNDO_MANAGEMENT
initialization parameter. The supported values are AUTO or MANUAL. If AUTO, then the
instance is started in automatic undo management mode. The default value is MANUAL.
■ If you use the undo tablespace method, then you are using automatic undo
management mode. This is recommended.
■ If you use the rollback segment method of managing undo space, then you are
using manual undo management mode.

回滾表空間的獲取和管理
1. 當開啟資料庫時 , 例項需要獲取一個或多個回滾表空間
2. 如果使用者正使用撤銷表空間 , 那麼資料庫就執行在自動撤銷管理模式下 . Oracle 建議採用此種模式.
3. 如果使用者正使用回滾段管理撤銷空間,那麼資料庫就執行在手工撤銷管理模式下 .

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