@Override
  public boolean requestDelayedFlush(HRegion r, long delay) {
    synchronized (regionsInQueue) {
      if (!regionsInQueue.containsKey(r)) {
        // This entry has some delay
        FlushRegionEntry fqe = new FlushRegionEntry(r, null, FlushLifeCycleTracker.DUMMY);
        fqe.requeue(delay);
        this.regionsInQueue.put(r, fqe);
        this.flushQueue.add(fqe);
        r.incrementFlushesQueuedCount();
        return true;
      }
      return false;
    }
  }
Return the FlushType if we're above the low watermark
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreFlusher.java