This is one background process that you can’t ignore for Oracle Certification Exam (1z0 062). Below are important points on CKPT from certification point of view:
- When checkpoint occurs, Oracle Database must update the headers of all datafiles to record the details of the checkpoint.
- The CKPT process doesn’t write blocks to disk; DBWn always perform that work
- When log switch happens, checkpoint is called
- Checkpoint is the position in the log file, from which instance recovery begins in case of crash!
The below parameters decides checkpoint interval:
Types of checkpoints:
As per Jonathan Lewis, below link has various types of checkpoints:
Check point priority:
As per Jonathan Lewis:
The checkpoints started by “alter system checkpoint” are high priority and synchronous – so you wait for the checkpoint to complete and you will see dirty buffers being copied to disc, and both start and end of background checkpoint will be incremented. The checkpoint started by “alter system switch logfile” is (in all but very old – possibly pre 8.1 – databases) a low priority checkpoint which is asynchronous, so your session returns immediately, the background start is recorded, but no action need be taken, but over a period of time you will see buffers written.
If you have N log files and do N-1 switches you’ll see Oracle suddenly very desperate to catch up (at least a bit) on the background checkpoints because of the “unable to switch logfile checkpoint not complete” problem that appears.