dajac commented on code in PR #17444:
URL: https://github.com/apache/kafka/pull/17444#discussion_r1820753168
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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:
Why not using a single hash? The issue is that we don't always know which
topics have changed (e.g. after a coordinator failover) so we have to recompute
the cache anyway.
> 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'.
If we store a hash per topic, it should be stored by topic name because
member subscribe by topic name and we must also catch the topic recreation.
> 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.
Could you elaborate on how this will work?
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