The current event defintion for event uei.opennms.org/nodes/pathOutage doesn't allow to reduce the events on a single critical path:
<event-label>OpenNMS-defined node event: pathOutage</event-label>
<p>The state of node %parm[nodelabel]% is unknown
because the critical path to the node is down.</p>
<p>This event is generated when node outage processing
determines that the critical path IP address/service for
this node is not responding..</p>
%parm[nodelabel]% path outage. Critical path =
<alarm-data reduction-key="%uei%:%dpname%:%nodeid%" alarm-type="3" auto-clean="false"/>
That means, if a critical path is down, users will show an alarm for every nodes behind this critical path.
Also, there's no corresponding clear event, so users will have to clear all these alarms manualy.
Changing the reduction key to the following would allow event reduction on a single path outage:
<alarm-data reduction-key="%uei%:%parm[criticalPathIp]%:%parm[criticalPathServiceName]%" alarm-type="3" auto-clean="false"/>