@Override
    public void in(TopN topN) {
        TopNWorker worker = workers.get(topN.getClass());
        if (worker != null) {
            worker.in(topN);
        }
    }
TopN is a special process, which hold a certain size of windows, and cache all top N records, save to the persistence
in low frequency.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/worker/TopNStreamProcessor.java