chia7712 commented on code in PR #17444:
URL: https://github.com/apache/kafka/pull/17444#discussion_r1820684694
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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:
hi @dajac
@FrankYang0529 and I discussed this offline, and we could tier the hash by
topic to address both reduced space usage and computation:
1. The coordinator will maintain an in-memory cache `Map<UUID, Integer>`
where the key is the topic UUID and the value is the hash based on 'name +
partitions + racks'.
2. `ModernGroup#subscribedTopicMetadata` will be changed from `<String,
TopicMetadata>` to `<String, Integer>`.
3. The cache will be updated whenever a group needs to calculate the hash
for an uncached topic or when new metadata brings a topic change.
Advantages of this approach:
1. We can replace `TopicMetadata` with an `integer`, saving space.
2. We can reuse cached hashes, reducing computation."
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