User Guide

SAP AG November 2002

• The redo log manager can cancel any of the tasks it starts.

At the end of an action, the redo log manager collects all error messages, and may then

terminate the restart [Page

146] or recovery, if required.

• The redo log manager generates the redo list [Page

51]

Log Reader

The log reader is an active component during a restart or recovery [Page 49]. The log reader

is a server task [Page 16].

Actions

From the data that was stored at the time of the last savepoint [Page 149], the log reader

determines the transaction file [Page

152], and uses this transaction file to re-generate the

transaction list [Page 152].

The log reader determines the required information from redo log management [Page 45] or

from the backup manager, so that all the redo log entries [Page

44] written since the last

savepoint can be made available.

• If transactions [Page

152] in the transaction list are marked as ended at the time of the

savepoint, the log reader enters these transactions in the redo list [Page 51] immediately.

• The log reader creates a redo log file [Page

50] for each further transaction found in the

redo log entries.

• COMMIT transactions

If a COMMIT [Page

129] is found for the whole transaction, the log reader enters the

transaction in the redo list.

• ROLLBACK transactions

If a ROLLBACK [Page

147] is found for the whole transaction, the log reader enters the

transaction in the redo list.

• ROLLBACK in subtransactions

If a ROLLBACK is found within a transaction, the log reader removes the corresponding

log entries from the redo log file. This means that these log entries are not processed

unnecessarily.

• Uncompleted transactions

If uncompleted transactions are found after all redo log entries are read, the log reader

flags these transactions with a ROLLBACK and enters them in the redo list. These

transactions are then treated as ROLLBACK transactions.

For information on the further processing of the transactions, see Redo Tasks [Page

51].