A restart has to be performed because of a system failure. The database system restores the database instance starting from the time of the last savepoint.
The following figure shows how the database system handles the transactions for a restart.
Status of the transactions at the time of a system failure
Handling the transactions during a restart
Transaction |
Required Action |
T1 |
None The changes to transaction T1 were saved completely by the last savepoint before the failure. |
T2, T3 |
None The changes made before the savepoint have to be rolled back. The redo tasks evaluate the corresponding undo log files. |
T5 |
None The changes from T5 were rolled back before the system breakdown and have not yet been saved in the data area. |
T4, T6 |
The log reader creates the redo log files and corresponding entries in the redo list. The redo tasks import the necessary redo log entries. |