Explanation:
The background process DBWn writes all the data from the write list that is part of the buffer cache, to the data files. Whenever a checkpoint is triggered, the LGWR and DBWn process start writing the data from their corresponding buffers to the physical files and the CKPT process updates the checkpoint SCN values in the data file headers and the control file.
Reference:
Oracle 9i Net Services Administrator’s Guide
Oracle 9i Net Services Reference Guide
Oracle 9i Recovery Manager Reference
Oracle 9i Backup and Recovery Concepts

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