public Optional<Long> getSubscriptionTime(final String topic) {
    return shouldRecordSubscriptionCreationTime()
        ? Optional.ofNullable(topicNameToSubscriptionCreationTime.get(topic))
        : Optional.empty();
  }
Get the consumers subscribing the given topic in this group.

@param topic The topic name.
@return The set of consumer IDs subscribing the given topic in this group. If no consumer is
    subscribing the topic, return an empty set.
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/subscription/meta/consumer/ConsumerGroupMeta.java