public static SubscriptionPollResponseCache getInstance() {
    return SubscriptionPollResponseCache.SubscriptionEventBinaryCacheHolder.INSTANCE;
  }
This class is used to control memory usage of cache {@link SubscriptionPollResponse} in {@link
CachedSubscriptionPollResponse}.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/subscription/event/cache/SubscriptionPollResponseCache.java