Explanation:
The CKRT process handles two things in Oracle: it signals to DBWR that dirty buffers must be written to disk, and also writes log sequence numbers to datafile headers and the control file. It does not, however, write dirty buffers to disk – DBWR does that. It also doesn’t write redo log information to disk, only LGWR does that. Finally, it does not read data from disk into memory for user processes – the server process performs this task.
Reference:
Oracle 9i: Administrator’s Guide
Oracle 9i: Concepts

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