When a failed Secondary server is back in service and connected to Primary, HotStandby continues sending the Primary transaction log file contents to the Secondary node in an automated process that is known as HotStandby database catchup.

You can tune the performance of the database catchup by adjusting how much time the server spends on catchup, as opposed to servicing current client database queries. The catchup time is controlled with the HotStandby.CatchupSpeedRate parameter, which defines in percentages the time the server spends on catchup. For example:

If HotStandby.CatchupSpeedRate is assigned a value of 90, the server spends approximately 90% of its time on catchup and about 10% of its time responding to user queries.

The higher the HotStandby.CatchupSpeedRate value is, the faster the catchup. However, a higher catchup rate also affects other activities, such as user queries. By default, HotStandby.CatchupSpeedRate is set to 50.