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Lesson 7What is CKPT?
Objective Learn what causes a Checkpoint.

What causes checkpoint

What is a checkpoint?

You need to know that the data in your database is good and that the instance is giving you all the information you need. This is why checkpoints were created.
The CKPT process is a coordinator process. CKPT works with the DBWR and LGWR processes to make sure that all the modified database buffers are written to disk and that the headers of the control files and redo log files are marked as current. At the end of a checkpoint, you know that all the modified buffers in the data buffer cache and the redo log buffer have been written to disk. This coordination is diagrammed below.

Checkpoint process
Checkpoint process

What causes a checkpoint?

You can force a checkpoint by issuing commands from SQL*Plus or Oracle SQL Developer, for example:
> alter system checkpoint local

> alter system checkpoint global

In other cases checkpoint events are automatically processed by normal events such as:
  1. When a redo log file fills, the LGWR switches to another redo log file
  2. If you have set LOG_CHECKPOINT_TIMEOUT (an init.ora parameter) and the specified interval has lapsed
  3. If you have set LOG_CHECKPOINT_INTERVAL (an init.ora parameter) and the specified number of disk block have been written to the redo log files
  4. During a normal instance shutdown
  5. If you take a tablespace off line
  6. If an online backup is started
The next lesson explores database physical files.

lgwr ckpt - Quiz

Click the Quiz link below to test your understanding of LGWR, ARCH, and DBWR.
lgwr ckpt - Quiz lgwr ckpt - Quiz