Overview

Updated on 2024-07-04 GMT+08:00

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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, rollback segments are very important. If rollback segments are damaged, data will be lost or even the database cannot be started. In addition, redo and undo operations are required for Ustore restoration. For Astore, it does not have a rollback segment, therefore, old data is stored in the original files, whose restoration is not as complex as that of Ustore.
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 operation can be completed quickly since no data needs to be deleted. However, the rollback operation is complex, because the modifications and the inserted records must be deleted, and the updated records must be undone. In addition, a large number of redo logs are generated during 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.

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