User Guide

SAP AG November 2002
Savepoint on Restart
Savepoints [Page 149] are also written during a restart [Page 146] (redo of a redo).
In this case, the items of the log reader [Page
50] and the state of all open redo transactions
are saved to the data area [Page 131], and reused for the next restart.
In this way, a terminated restart can be started again.
Example: Restart
The database crashed.
For the subsequent restart [Page
146], the database instance is recovered starting from the
time of the last savepoint [Page 149].
No recovery measures are required for transactions T1 and T5. The changes for transaction
T1 were recorded in full by the last savepoint. The changes for T5 were rolled back before the
crash, and are not yet stored in the data area.
For transactions T4 and T6, the log reader [Page
50] creates redo log files [Page 50] and
relevant entries in the redo list [Page
51]. The redo tasks [Page 51] import the required redo
log entries for these transactions.
No recovery measures are required for transactions T2 and T3. However, the modifications
made before the savepoint must be reversed. The redo tasks therefore evaluate the relevant
undo log files [Page
48].
User Manual: SAP DB 52