Background documentationExample: Restart Locate this document in the navigation structure

 

A power outage has occurred and you have to restart the database. During the restart, the database system restores the database starting from the time of the last savepoint.

This graphic is explained in the accompanying text.

Status of the Transactions at the Time of System Failure

How the Database System Handles Transactions During a Restart

Transaction

What Does the Database System Do?

T1

Nothing

The changes by transaction T1 were completely written to the data area by the last savepoint before the system failure.

T2, T3

The database system rolls back the changes made before the savepoint. To do this, it evaluates the corresponding undo log files.

T5

Nothing

The database system had already rolled back the changes by T5 before the system failure (ROLLBACK). These changes were never written to the data area through a savepoint.

T4, T6

The database system imports the required redo log entries for these transactions and repeats the transactions (ROLL FORWARD).

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