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 Example: Restart 

You need to restart the database because it has crashed. The database instance is recovered from the last savepoint .

The following diagram shows how different transactions are handled during a restart.

 

Transaction

Required recovery measures

T1

No recovery measures required.
Changes made by transaction T1 were recorded fully at the last savepoint that was carried out before the crash.

T2, T3

No recovery measures required.
However, any modifications made before the most recent savepoint must be reversed. The redo tasks therefore evaluate the relevant
undo log files.

T5

No recovery measures required.
The changes made by T5 were rolled back before the crash and are not yet stored in the data area.

T4, T6

The log reader creates the redo log files and the corresponding entries in the redo list. The redo tasks import the required redo log entries for these transactions.

 

 

 

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