Redo log entries for transactions are written and managed in redo log management.
In very special situations, you can deactivate redo log management temporarily.
Redo log entries are always written when a user task carries out a modifying transaction.
1. The user task that carries out a transaction reserves main memory space in the log queue and writes the redo log entry for its transaction to a log page in this reserved area.
2. The user task releases the reserved area of the log queue for processing by the log writer. It tells the log writer if it wants to wait for the corresponding log page from the log queue to be written to the log area. This is always a requirement for COMMIT and ROLLBACKprocesses.
3. The log writer reads the redo log entries from the log queue.
4. The log writer writes the redo log entries to the log area as a log page.
5. If the user task is waiting for the redo log entry to be written, the log writer alerts the user task as soon as the redo log entry has been written and tells it the log sequence number.
In the log area, redo log management also stores and regularly updates the database parameters and other internal information that controls the logging.
Redo log management also plays a part in the following situations:
· During a log backup, redo log management ascertains if any entries from the log area have to be saved, and if so how many.
· Redo log management also displays information on waiting times and the type of access used to access the entries in the log queue.
See also:
Using Log Entries at Restart or Recovery