showuon commented on a change in pull request #10509:
URL: https://github.com/apache/kafka/pull/10509#discussion_r625598009



##########
File path: 
clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractStickyAssignor.java
##########
@@ -163,127 +159,180 @@ private boolean allSubscriptionsEqual(Set<String> 
allTopics,
      */
     private Map<String, List<TopicPartition>> constrainedAssign(Map<String, 
Integer> partitionsPerTopic,
                                                                 Map<String, 
List<TopicPartition>> consumerToOwnedPartitions) {
-        SortedSet<TopicPartition> unassignedPartitions = 
getTopicPartitions(partitionsPerTopic);
+        if (log.isDebugEnabled()) {
+            log.debug("performing constrained assign. partitionsPerTopic: {}, 
consumerToOwnedPartitions: {}",
+                partitionsPerTopic, consumerToOwnedPartitions);
+        }
 
         Set<TopicPartition> allRevokedPartitions = new HashSet<>();
 
-        // Each consumer should end up in exactly one of the below
-        // the consumers not yet at capacity
+        // the consumers not yet at expected capacity
         List<String> unfilledMembers = new LinkedList<>();
-        // the members with exactly maxQuota partitions assigned
-        Queue<String> maxCapacityMembers = new LinkedList<>();
-        // the members with exactly minQuota partitions assigned
-        Queue<String> minCapacityMembers = new LinkedList<>();
 
         int numberOfConsumers = consumerToOwnedPartitions.size();
-        int minQuota = (int) Math.floor(((double) unassignedPartitions.size()) 
/ numberOfConsumers);
-        int maxQuota = (int) Math.ceil(((double) unassignedPartitions.size()) 
/ numberOfConsumers);
+        int totalPartitionsCount = 
partitionsPerTopic.values().stream().reduce(0, Integer::sum);
+
+        int minQuota = (int) Math.floor(((double) totalPartitionsCount) / 
numberOfConsumers);
+        int maxQuota = (int) Math.ceil(((double) totalPartitionsCount) / 
numberOfConsumers);
+        // the expected number of members with maxQuota assignment
+        int numExpectedMaxCapacityMembers = totalPartitionsCount % 
numberOfConsumers;
+        // the number of members with exactly maxQuota partitions assigned
+        int numMaxCapacityMembers = 0;
 
-        // initialize the assignment map with an empty array of size minQuota 
for all members
+        // initialize the assignment map with an empty array of size maxQuota 
for all members
         Map<String, List<TopicPartition>> assignment = new HashMap<>(
-            
consumerToOwnedPartitions.keySet().stream().collect(Collectors.toMap(c -> c, c 
-> new ArrayList<>(minQuota))));
+            
consumerToOwnedPartitions.keySet().stream().collect(Collectors.toMap(c -> c, c 
-> new ArrayList<>(maxQuota))));
 
+        List<TopicPartition> assignedPartitions = new ArrayList<>();
         // Reassign as many previously owned partitions as possible
         for (Map.Entry<String, List<TopicPartition>> consumerEntry : 
consumerToOwnedPartitions.entrySet()) {
             String consumer = consumerEntry.getKey();
             List<TopicPartition> ownedPartitions = consumerEntry.getValue();
 
             List<TopicPartition> consumerAssignment = assignment.get(consumer);
-            int i = 0;
-            // assign the first N partitions up to the max quota, and mark the 
remaining as being revoked
-            for (TopicPartition tp : ownedPartitions) {
-                if (i < maxQuota) {
-                    consumerAssignment.add(tp);
-                    unassignedPartitions.remove(tp);
-                } else {
-                    allRevokedPartitions.add(tp);
-                }
-                ++i;
-            }
 
             if (ownedPartitions.size() < minQuota) {
+                // the expected assignment size is more than consumer have 
now, so keep all the owned partitions
+                // and put this member into unfilled member list
+                if (ownedPartitions.size() > 0) {
+                    consumerAssignment.addAll(ownedPartitions);
+                    assignedPartitions.addAll(ownedPartitions);
+                }
                 unfilledMembers.add(consumer);
+            } else if (ownedPartitions.size() >= maxQuota && 
numMaxCapacityMembers < numExpectedMaxCapacityMembers) {
+                // consumer owned the "maxQuota" of partitions or more, and 
we're still under the number of expected max capacity members
+                // so keep "maxQuota" of the owned partitions, and revoke the 
rest of the partitions
+                numMaxCapacityMembers++;
+                List<TopicPartition> maxQuotaPartitions = 
ownedPartitions.subList(0, maxQuota);
+                consumerAssignment.addAll(maxQuotaPartitions);
+                assignedPartitions.addAll(maxQuotaPartitions);
+                allRevokedPartitions.addAll(ownedPartitions.subList(maxQuota, 
ownedPartitions.size()));
             } else {
-                // It's possible for a consumer to be at both min and max 
capacity if minQuota == maxQuota
-                if (consumerAssignment.size() == minQuota)
-                    minCapacityMembers.add(consumer);
-                if (consumerAssignment.size() == maxQuota)
-                    maxCapacityMembers.add(consumer);
+                // consumer owned at least "minQuota" of partitions but we're 
already at the allowed number of max capacity members

Review comment:
       Yes, this could happen, and just updated. Also the renaming is better. 
Thanks.




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