A customer manages the scheduled outages from a third party server using the ReST API in order to create and maintain the maintenance windows for the monitored machines.
There are about 1500 different definitions on poll-outages.xml.
Doing a Java Flight Recorder on that server, I figured out that the most popular methods on that installation are related with checking scheduled outages.
The OpenNMS server is polling more than 25000 services and collecting data from around 7000 devices. Also, the configuration packages for Pollerd, Collectd and Threshold have all those 1500 scheduled outages associated.
The consequence of this is that the CPU of the OpenNMS server is above 70% all the time (considering that the CPU count according with /proc/cpuinfo is 32, OpenNMS has 16GB of Heap Size and the server has 96GB of RAM).