From time to time, we run into a memory problem that is not related to Java Heap but Native Memory. Let's imagine the situation where we have a running container that is restarted once per day. We look at Prometheus/Grafana to check the reason behind this issue. However, we don't spot any problem with Java Heap size (exported via JMX) and start blaming our container scheduler to do any inconvenient operations with our containers :). The real problem can be hidden a bit deeper — in Native Memory.
Do you use any native memory allocator in your code or do you use any library that stores its internal state outside the Java Heap? It could be whatever third-party code that tries to minimize GC, such as I/O libraries or databases/caches keeping data in memory inside your process.