When a failed secondary server is back in service and connected to the primary server, HotStandby (HSB) continues sending the primary server transaction log file contents to the secondary server in an automated process that is known as HSB 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 (as a percentage) the time the server spends on catchup, see CatchupSpeedRate.
For example:
[HotStandby] CatchupSpeedRate = 90
In this example, 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, the faster the catchup. However, a higher catchup rate also affects other activities, such as user queries.