public void addTimeHistogram(TimeHistogram timeHistogram) {
        TimeHistogram find = this.timeHistogramMap.get(timeHistogram.getTimeStamp());
        if (find == null) {
            find = new TimeHistogram(agentId.getServiceType(), timeHistogram.getTimeStamp());
            this.timeHistogramMap.put(timeHistogram.getTimeStamp(), find);
        }
        find.add(timeHistogram);
    }
to uniquely identify a host from UI, we can use things like hostname, agentId, endpoint, etc
web/src/main/java/com/navercorp/pinpoint/web/applicationmap/rawdata/AgentHistogram.java