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 Log Writer 

The log writer is an active component of redo log management. It belongs to the user kernel thread. The log writer’s job is to write log pages from the log queue into the log area.

The log writer is activated in the following situations:

·        A log page is full

·        COMMIT or ROLLBACK transactions

After the log writer has written log pages to the log area, it alerts the user tasks that have been waiting to write their redo log entries.

The log writer regularly checks the status of the log area. When the log area is full, the log writer locks the log queue. This means that all the transactions that want to add redo log entries to the log queue are stopped.

When the database system is started, the log writer is initialized using permanently stored, internal configuration information. The configuration information is written to the log area at regular intervals, particularly at savepoints.

When the automatic log backup is activated, the log writer ensures that the redo log entries from the log area are backed up automatically. When a certain number of log entries have been written, the administrative information is copied to the log area, and savepoints are requested, if required. This shortens the restart time, if a restart is required.

 

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