Re: [PR] KAFKA-16587: Add subscription model information to group state [kafka]

["dongnuo123 (via GitHub)" <gi...@apache.org>]

dongnuo123 commented on code in PR #15785:
URL: https://github.com/apache/kafka/pull/15785#discussion_r1586420616


##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/consumer/ConsumerGroup.java:
##########
@@ -966,6 +979,53 @@ private static void maybeUpdateSubscribedTopicNames(
         }
     }
 
+    /**
+     * Updates the subscription count.
+     *
+     * @param oldMember             The old member.
+     * @param newMember             The new member.
+     *
+     * @return Copy of the map of topics to the count of number of subscribers.
+     */
+    public Map<String, Integer> computeSubscribedTopicNames(
+        ConsumerGroupMember oldMember,
+        ConsumerGroupMember newMember
+    ) {
+        Map<String, Integer> subscribedTopicNames = new HashMap<>(this.subscribedTopicNames);
+        maybeUpdateSubscribedTopicNames(
+            subscribedTopicNames,
+            oldMember,
+            newMember
+        );
+        return subscribedTopicNames;
+    }
+
+    /**
+     * Compute the subscription type of the consumer group.
+     *
+     * @param subscribedTopicNames      A map of topic names to the count of members subscribed to each topic.
+     *
+     * @return {@link SubscriptionType#HOMOGENEOUS} if all members are subscribed to exactly the same topics;
+     *         otherwise, {@link SubscriptionType#HETEROGENEOUS}.
+     */
+    public static SubscriptionType subscriptionType(
+        Map<String, Integer> subscribedTopicNames
+    ) {
+        if (subscribedTopicNames.isEmpty()) {
+            return HOMOGENEOUS;
+        }
+
+        // Take the subscriber count of the first topic as the reference.
+        int referenceCount = subscribedTopicNames.values().iterator().next();

Review Comment:
   Do we need to check if referenceCount is equal to member count?



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