Overview

The biggest difference between Astore and Ustore lies in whether the latest data and historical data are stored separately. Astore does not perform separated storage. Ustore only separates data, but does not separate indexes.

Astore Advantages

Astore does not have rollback segments, but Ustore does. For Ustore, the rollback segment is very important. If the rollback segment is damaged, data will be lost or even the database cannot be started. In addition, redo and undo operations are required during Ustore restoration. For Astore, because it does not have a rollback segment, old data is stored in the original files. Therefore, when the database crashes, complex restoration is not performed like that performed by a Ustore database.
Besides, the error "Snapshot Too Old" is not frequently reported, because old data is directly recorded in data files instead of rollback segments.
The rollback can be completed quickly because data is not deleted.

Rollback is complex. During transaction rollback, the modifications made by the transaction must be undone, the inserted records must be deleted, and the updated records must be rolled back. In addition, a large number of redo logs are generated during the rollback.
WAL in Astore is simpler than that in Ustore. Only data file changes need to be recorded in WALs. Rollback segment changes do not need to be recorded.
The recycle bin (flashback DROP and flashback TRUNCATE) function is supported.