[GitHub] [kafka] rajinisivaram commented on a diff in pull request #12990: KAFKA-14451: Rack-aware consumer partition assignment for RangeAssignor (KIP-881)

["rajinisivaram (via GitHub)" <gi...@apache.org>]

rajinisivaram commented on code in PR #12990:
URL: https://github.com/apache/kafka/pull/12990#discussion_r1112011199


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clients/src/main/java/org/apache/kafka/clients/consumer/RangeAssignor.java:
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@@ -63,9 +76,19 @@
  * <li><code>I0: [t0p0, t0p1, t1p0, t1p1]</code>
  * <li><code>I1: [t0p2, t1p2]</code>
  * </ul>
+ * <p>
+ * Rack-aware assignment is used if both consumer and partition replica racks are available and
+ * some partitions have replicas only on a subset of racks. We attempt to match consumer racks with
+ * partition replica racks on a best-effort basis, prioritizing balanced assignment over rack alignment.
+ * Topics with equal partition count and same set of subscribers prioritize co-partitioning guarantee
+ * over rack alignment. In this case, aligning partition replicas of these topics on the same racks
+ * will improve locality for consumers. For example, if partitions 0 of all topics have a replica on
+ * rack 'a', partition 1 on rack 'b' etc., partition 0 of all topics can be assigned to a consumer
+ * on rack 'a', partition 1 to a consumer on rack 'b' and so on.

Review Comment:
   Yes, that is correct. 



##########
clients/src/main/java/org/apache/kafka/clients/consumer/RangeAssignor.java:
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@@ -76,43 +99,185 @@ private Map<String, List<MemberInfo>> consumersPerTopic(Map<String, Subscription
         Map<String, List<MemberInfo>> topicToConsumers = new HashMap<>();
         for (Map.Entry<String, Subscription> subscriptionEntry : consumerMetadata.entrySet()) {

Review Comment:
   Done.



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