chia7712 commented on code in PR #17444:
URL: https://github.com/apache/kafka/pull/17444#discussion_r1817881509
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group-coordinator/src/main/java/org/apache/kafka/coordinator/group/modern/TopicMetadata.java:
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@@ -41,10 +41,25 @@ public class TopicMetadata {
*/
private final int numPartitions;
+ /**
+ * Map of every partition Id to a set of its rack Ids, if they exist.
+ * If rack information is unavailable for all partitions, this is an empty
map.
+ */
+ private final Map<Integer, Set<String>> partitionRacks;
Review Comment:
> Ideally, assignors should generate deterministic results, so it doesn't
trigger useless rebalance.
I don't think this is easy to follow. For instance, assignors typically loop
through members, topics, or partitions to calculate the assignment, but we
don't enforce a specific order for these objects in the input.
> For metadata change, there are two cases can trigger group rebalance:
The rack of a partition can change if the partition is moved from node_a in
rack_a to node_b in rack_b.
> Finally, we can set a new value in ModernGroup. When above cases are
detected in GroupMetadataManager#onNewMetadataImage, we set the value to true.
In new consumer group heartbeat, we don't need to calculate subscription
metadata, we can check the value and calculate a new target assignment
directly. After we gets new target assignment, we set the value back to false.
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