private int getPrefetchingQueueCountInternal() {
    return consumerGroupIdToSubscriptionBroker.values().stream()
        .map(SubscriptionBroker::getPrefetchingQueueCount)
        .reduce(0, Integer::sum);
  }
@return {@code true} if drop broker success, {@code false} otherwise
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/subscription/agent/SubscriptionBrokerAgent.java