Restart or Recovery 
The
log concept for the SAP DB database system includes the import of the required log entries, if the database instance is restarted or recovered.
The
redo log manager ensures that the required log entries are made available and processed in the correct, time-based sequence.
transaction, the available redo log entries are stored by the log reader in a redo log file.
Transactions for which a redo is actually required are stored by the log reader in a redo list.
The redo tasks evaluate the redo list, and import the required redo and undo log entries for each transaction they find.
See also:
Example: Restart