FrankYang0529 commented on code in PR #17444:
URL: https://github.com/apache/kafka/pull/17444#discussion_r1820720961
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group-coordinator/src/main/java/org/apache/kafka/coordinator/group/Utils.java:
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@@ -235,4 +238,20 @@ public static ApiMessage
messageOrNull(ApiMessageAndVersion apiMessageAndVersion
return apiMessageAndVersion.message();
}
}
+
+ public static long hashSubscriptionMetadata(Map<String, TopicMetadata>
subscriptionMetadata) {
Review Comment:
I would like to add some implementation detail about the "cache" in
GroupMetadataManager, so we don't waste resource to store unsubscribed topics
or recalculate a topic hash with same value.
1. Only compute topic hash which is subscribed by a group. That means we
will compute topic hash in `GroupMetadataManager#subscribeGroupToTopic` when
it's first time subscribed by one of groups. Also, the hash value will be
removed in `GroupMetadataManager#unsubscribeGroupFromTopic` if there is no
group subscribes it.
2. In `GroupMetadataManager#onNewMetadataImage`, we only recalculate topic
hash which is in `topicsDelta.changedTopics()`.
3. In `GroupMetadataManager#consumerGroupHeartbeat`, if the metadata is
expired, we will rebuild topic hash map which is subscribed by the group from
the cache. So we don't recalculate it here.
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