Oracle recommends keeping an Always-On Monitoring instance running at all times regardless of whether Enterprise Manager is up or down. By telling the Always-On Monitoring to turn off notifications, you can have it run in the background while Enterprise Manager is up. During Enterprise Manager downtime, whether planned or unplanned, you can issue an emsctl command to tell Always-On Monitoring to restart notifications. The primary advantage to having Always-On Monitoring running at all times is that it will stay up to date with any changes made to your Enterprise Manager installation. Always-On Monitoring keeps itself in sync with Enterprise Manager by periodically running a synchronization job. This job runs every 24 hours by default, however the job execution time can be changed to meet the needs of your monitored environment.

You may also run Always-On Monitoring only when needed instead of having it run constantly in the background. However, doing so will require Always-On Monitoring to synchronize with the Enterprise Manager OMS. Depending on the size of your Enterprise Manager deployment, synchronization may take 10-15 minutes in order to obtain current information on all Enterprise Manager targets and metrics.