private void addAgentLevelHistogram(Map<String, Histogram> agentHistogramMap, String agentId, TimeHistogram histogram) {
            Histogram agentHistogram = agentHistogramMap.get(agentId);
            if (agentHistogram == null) {
                agentHistogram = new Histogram(application.getServiceType());
                agentHistogramMap.put(agentId, agentHistogram);
            }
            agentHistogram.add(histogram);
        }
this class is a collection of
applicationHistogram
agentHistogram
applicationTimeHistogram
agentTimeHistogram

@author emeroad
web/src/main/java/com/navercorp/pinpoint/web/applicationmap/histogram/NodeHistogram.java