CKPTINTVL and its effect on checkpoints

If the RTO_SERVER_RESTART configuration parameter is not on, the CKPTINTVL configuration parameter specifies the frequency, in seconds, at which the database server checks to determine whether a checkpoint is needed.

When the RTO_SERVER_RESTART configuration parameter is on, the database server ignores the CKPTINTVL configuration parameter. Instead, the server automatically triggers checkpoints in order to maintain the RTO_SERVER_RESTART policy.

The database server can skip a checkpoint if all data is physically consistent when the checkpoint interval expires.

Checkpoints also occur in either of these circumstances:
  • Whenever the physical log becomes 75 percent full
  • If a high number of dirty partitions exist, even if the physical log is not 75 percent full.
    This occurs because when the database server checks if the physical log is 75 percent full, the server also checks if the following condition is true:
    (Physical Log Pages Used + Number of Dirty Partitions) >= 
    (Physical Log Size * 9) /10)

    A partition, which represents one page going into the physical log during checkpoint processing and has a page that maintains information (such as the number of rows and number of data pages) about the partition, becomes dirty when the partition is updated.

If you set CKPTINTVL to a long interval, you can use physical-log capacity to trigger checkpoints based on actual database activity instead of an arbitrary time unit. However, a long checkpoint interval can increase the time needed for recovery in the event of a failure. Depending on your throughput and data-availability requirements, you can choose an initial checkpoint interval of 5, 10, or 15 minutes, with the understanding that checkpoints might occur more often, depending on physical-logging activity.

The database server writes a message to the message log to note the time that it completes a checkpoint. To read these messages, use onstat -m.


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