After accessing the Foglight Management Server (FMS) Administration -> Rules & Notifications -> Rule Diagnostics dashboard, the FMS begins to Alarm with "Catalyst Memory Usage Check" or "Catalyst Garbage Collector Check" alarms, including emails for "FSM: Memory usage monitor".
The Rule Diagnostics dashboard must load information on all Rules and Rulettes (instances of a rule per scoped topology object). This can cause excessive memory usage, and if your FMS is operating near the limits of it's allocated JVM heap, can cause these sorts of memory errors.
The memory will be held active as long as the user session is active.
Increase the JVM heap allocation in foglight.config as detailed in the Foglight Performance and Tuning Field Guide
The memory should be released to the JVM once the user session logs out, so logging out of the web console will cease the alarms and emails.
Enhancement request FGL-12529 has been submitted to Development for consideration in a future release of Foglight 5