Q

CKPT explained

Can you explain what CKPT does? I am not clear if this process writes the data file header directly, or if it passes to DBWn the SCN, and DBWn writes the data file's header. The same thing about control files and redo log online. Thanks a lot.

The Checkpoint process (CKPT) is responsible for performing a checkpoint. When a checkpoint occurs, all changed blocks are written from the database buffer cache to the database datafiles. When CKPT performs a checkpoint, it signals DBWn to wake up and write to the datafiles. CKPT does not write changed data to the datafiles. However, CKPT does update the datafile headers to signify the SCN when the checkpoint was performed. Oracle uses the SCN in the datafile header to know if recovery is needed on the datafile in a failure situation. CKPT also updates the control files to indicate the last time a checkpoint was performed.

This was first published in May 2005
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