Start and Stop the Performance Monitor
The Performance Monitor provides three ways to monitor the database performance: immediate monitoring, scheduled monitoring, and manual refresh.
The settings on the General tab in Preferences window determine whether the monitoring process begins immediately or at a scheduled time. The monitoring continues to collect the statistics at the refresh interval until you stop the monitoring or until the scheduled end time.
To start the monitoring processing for collecting the database performance statistics
Click 
To stop the monitoring process
Click 
The manual refresh of the statistics collects the statistics immediately and only collects them once.