dajac commented on code in PR #15717:
URL: https://github.com/apache/kafka/pull/15717#discussion_r1572314707


##########
jmh-benchmarks/src/main/java/org/apache/kafka/jmh/assignor/ServerSideAssignorBenchmark.java:
##########
@@ -0,0 +1,266 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.jmh.assignor;
+
+import org.apache.kafka.common.Uuid;
+import org.apache.kafka.coordinator.group.assignor.AssignmentMemberSpec;
+import org.apache.kafka.coordinator.group.assignor.AssignmentSpec;
+import org.apache.kafka.coordinator.group.assignor.GroupAssignment;
+import org.apache.kafka.coordinator.group.assignor.MemberAssignment;
+import org.apache.kafka.coordinator.group.assignor.PartitionAssignor;
+import org.apache.kafka.coordinator.group.assignor.RangeAssignor;
+import org.apache.kafka.coordinator.group.assignor.SubscribedTopicDescriber;
+import org.apache.kafka.coordinator.group.assignor.UniformAssignor;
+import org.apache.kafka.coordinator.group.consumer.SubscribedTopicMetadata;
+import org.apache.kafka.coordinator.group.consumer.TopicMetadata;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Threads;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+
+@State(Scope.Benchmark)
+@Fork(value = 1)
+@Warmup(iterations = 5)
+@Measurement(iterations = 5)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+public class ServerSideAssignorBenchmark {
+
+    public enum AssignorType {
+        RANGE(new RangeAssignor()),
+        UNIFORM(new UniformAssignor());
+
+        private final PartitionAssignor assignor;
+
+        AssignorType(PartitionAssignor assignor) {
+            this.assignor = assignor;
+        }
+
+        public PartitionAssignor assignor() {
+            return assignor;
+        }
+    }
+
+    /**
+     * The subscription pattern followed by the members of the group.
+     *
+     * A subscription model is considered homogenous if all the members of the 
group
+     * are subscribed to the same set of topics, it is heterogeneous otherwise.
+     */
+    public enum SubscriptionModel {
+        HOMOGENEOUS, HETEROGENEOUS
+    }
+
+    /**
+     * The assignment type is decided based on whether all the members are 
assigned partitions
+     * for the first time (full), or incrementally when a rebalance is 
triggered.
+     */
+    public enum AssignmentType {
+        FULL, INCREMENTAL
+    }
+
+    @Param({"100", "500", "1000", "5000", "10000"})
+    private int memberCount;
+
+    @Param({"5", "10", "50"})
+    private int partitionsToMemberRatio;
+
+    @Param({"10", "100", "1000"})
+    private int topicCount;
+
+    @Param({"true", "false"})
+    private boolean isRackAware;
+
+    @Param({"HOMOGENEOUS", "HETEROGENEOUS"})
+    private SubscriptionModel subscriptionModel;
+
+    @Param({"RANGE", "UNIFORM"})
+    private AssignorType assignorType;
+
+    @Param({"FULL", "INCREMENTAL"})
+    private AssignmentType assignmentType;
+
+    private PartitionAssignor partitionAssignor;
+
+    private static final int NUMBER_OF_RACKS = 3;
+
+    private AssignmentSpec assignmentSpec;
+
+    private SubscribedTopicDescriber subscribedTopicDescriber;
+
+    private final List<Uuid> allTopicIds = new ArrayList<>(topicCount);
+
+    @Setup(Level.Trial)
+    public void setup() {
+        Map<Uuid, TopicMetadata> topicMetadata = createTopicMetadata();
+        subscribedTopicDescriber = new SubscribedTopicMetadata(topicMetadata);
+
+        createAssignmentSpec();
+
+        partitionAssignor = assignorType.assignor();
+
+        if (assignmentType == AssignmentType.INCREMENTAL) {
+            simulateIncrementalRebalance(topicMetadata);
+        }
+    }
+
+    private Map<Uuid, TopicMetadata> createTopicMetadata() {
+        Map<Uuid, TopicMetadata> topicMetadata = new HashMap<>();
+        int partitionsPerTopicCount = (memberCount * partitionsToMemberRatio) 
/ topicCount;
+
+        Map<Integer, Set<String>> partitionRacks = isRackAware ?
+            mkMapOfPartitionRacks(partitionsPerTopicCount) :
+            Collections.emptyMap();
+
+        for (int i = 0; i < topicCount; i++) {
+            Uuid topicUuid = Uuid.randomUuid();
+            String topicName = "topic" + i;
+            allTopicIds.add(topicUuid);
+            topicMetadata.put(topicUuid, new TopicMetadata(
+                topicUuid,
+                topicName,
+                partitionsPerTopicCount,
+                partitionRacks
+            ));
+        }
+
+        return topicMetadata;
+    }
+
+    private void createAssignmentSpec() {
+        Map<String, AssignmentMemberSpec> members = new HashMap<>();
+
+        // In the rebalance case, we will add the last member as a trigger.
+        // This is done to keep the total members count consistent with the 
input.
+        int numberOfMembers = 
assignmentType.equals(AssignmentType.INCREMENTAL) ? memberCount - 1 : 
memberCount;
+
+        if (subscriptionModel.equals(SubscriptionModel.HOMOGENEOUS)) {
+            for (int i = 0; i < numberOfMembers; i++) {
+                addMemberSpec(members, i, new HashSet<>(allTopicIds));
+            }
+        } else {
+            // Check minimum topics requirement
+            if (topicCount < 5) {
+                throw new IllegalArgumentException("At least 5 topics are 
recommended for effective bucketing.");
+            }
+
+            // Adjust bucket count based on member count when member count < 5
+            int bucketCount = Math.min(5, numberOfMembers);
+            int bucketSizeTopics = (int) Math.ceil((double) topicCount / 
bucketCount);
+            int bucketSizeMembers = (int) Math.ceil((double) numberOfMembers / 
bucketCount);
+
+            // Define buckets for each member and assign topics from the same 
bucket
+            for (int bucket = 0; bucket < bucketCount; bucket++) {
+                int memberStartIndex = bucket * bucketSizeMembers;
+                int memberEndIndex = Math.min((bucket + 1) * 
bucketSizeMembers, numberOfMembers);
+
+                int topicStartIndex = bucket * bucketSizeTopics;
+                int topicEndIndex = Math.min((bucket + 1) * bucketSizeTopics, 
topicCount);
+
+                Set<Uuid> bucketTopics = new 
HashSet<>(allTopicIds.subList(topicStartIndex, topicEndIndex));
+
+                // Assign topics to each member in the current bucket
+                for (int i = memberStartIndex; i < memberEndIndex; i++) {
+                    addMemberSpec(members, i, new HashSet<>(bucketTopics));
+                }
+            }
+        }
+
+        this.assignmentSpec = new AssignmentSpec(members);
+    }
+
+    private Optional<String> rackId(int index) {
+        return isRackAware ? Optional.of("rack" + index % NUMBER_OF_RACKS) : 
Optional.empty();
+    }
+
+    private void addMemberSpec(
+        Map<String, AssignmentMemberSpec> members,
+        int memberIndex,
+        Set<Uuid> subscribedTopicIds
+    ) {
+        String memberId = "member" + memberIndex;
+        Optional<String> rackId = rackId(memberIndex);
+
+        members.put(memberId, new AssignmentMemberSpec(
+            Optional.empty(),
+            rackId,
+            subscribedTopicIds,
+            Collections.emptyMap()
+        ));
+    }
+
+    private static Map<Integer, Set<String>> mkMapOfPartitionRacks(int 
numPartitions) {
+        Map<Integer, Set<String>> partitionRacks = new 
HashMap<>(numPartitions);
+        for (int i = 0; i < numPartitions; i++) {
+            partitionRacks.put(i, new HashSet<>(Arrays.asList("rack" + i % 
NUMBER_OF_RACKS, "rack" + (i + 1) % NUMBER_OF_RACKS)));
+        }
+        return partitionRacks;
+    }
+
+    private void simulateIncrementalRebalance(Map<Uuid, TopicMetadata> 
topicMetadata) {
+        GroupAssignment initialAssignment = 
partitionAssignor.assign(assignmentSpec, subscribedTopicDescriber);
+        Map<String, MemberAssignment> members = initialAssignment.members();
+
+        Map<String, AssignmentMemberSpec> updatedMembers = new HashMap<>();
+        members.forEach((memberId, memberAssignment) -> {
+            AssignmentMemberSpec memberSpec = 
assignmentSpec.members().get(memberId);
+            updatedMembers.put(memberId, new AssignmentMemberSpec(
+                memberSpec.instanceId(),
+                memberSpec.rackId(),
+                memberSpec.subscribedTopicIds(),
+                memberAssignment.targetPartitions()
+            ));
+        });
+
+        Optional<String> rackId = rackId(memberCount - 1);
+        updatedMembers.put("newMember", new AssignmentMemberSpec(
+            Optional.empty(),
+            rackId,
+            topicMetadata.keySet(),

Review Comment:
   I don't fully understand this one. Intuitively, I thought that we would use 
the last bucket to respect the topology of the group. Is there a reason not to 
do it? One way would be to reuse the subscribed topics of the last member in 
`members`. Would it work?



##########
jmh-benchmarks/src/main/java/org/apache/kafka/jmh/assignor/TargetAssignmentBuilderBenchmark.java:
##########
@@ -0,0 +1,202 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.jmh.assignor;
+
+import org.apache.kafka.common.Uuid;
+import org.apache.kafka.coordinator.group.assignor.AssignmentMemberSpec;
+import org.apache.kafka.coordinator.group.assignor.AssignmentSpec;
+import org.apache.kafka.coordinator.group.assignor.GroupAssignment;
+import org.apache.kafka.coordinator.group.assignor.MemberAssignment;
+import org.apache.kafka.coordinator.group.assignor.PartitionAssignor;
+import org.apache.kafka.coordinator.group.assignor.UniformAssignor;
+import org.apache.kafka.coordinator.group.consumer.Assignment;
+import org.apache.kafka.coordinator.group.consumer.ConsumerGroupMember;
+import org.apache.kafka.coordinator.group.consumer.SubscribedTopicMetadata;
+import org.apache.kafka.coordinator.group.consumer.TargetAssignmentBuilder;
+import org.apache.kafka.coordinator.group.consumer.TopicMetadata;
+import org.apache.kafka.coordinator.group.consumer.VersionedMetadata;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Threads;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+
+@State(Scope.Benchmark)
+@Fork(value = 1)
+@Warmup(iterations = 5)
+@Measurement(iterations = 5)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+public class TargetAssignmentBuilderBenchmark {
+
+    @Param({"100", "500", "1000", "5000", "10000"})
+    private int memberCount;
+
+    @Param({"5", "10", "50"})
+    private int partitionsToMemberRatio;
+
+    @Param({"10", "100", "1000"})
+    private int topicCount;
+
+    private static final String GROUP_ID = "benchmark-group";
+
+    private static final int GROUP_EPOCH = 0;
+
+    private PartitionAssignor partitionAssignor;
+
+    private Map<String, TopicMetadata> subscriptionMetadata = 
Collections.emptyMap();
+
+    private TargetAssignmentBuilder targetAssignmentBuilder;
+
+    private AssignmentSpec assignmentSpec;
+
+    private final List<String> allTopicNames = new ArrayList<>(topicCount);
+
+    private final List<Uuid> allTopicIds = new ArrayList<>(topicCount);
+
+    @Setup(Level.Trial)
+    public void setup() {
+        // For this benchmark we will use the Uniform Assignor
+        // and a group that has a homogeneous subscription model.
+        partitionAssignor = new UniformAssignor();
+
+        subscriptionMetadata = generateMockSubscriptionMetadata();
+        Map<String, ConsumerGroupMember> members = generateMockMembers();
+        Map<String, Assignment> existingTargetAssignment = 
generateMockInitialTargetAssignment();
+
+        // Add a new member to trigger a rebalance.
+        Set<String> subscribedTopics = new 
HashSet<>(subscriptionMetadata.keySet());
+
+        ConsumerGroupMember newMember = new 
ConsumerGroupMember.Builder("new-member")
+            .setSubscribedTopicNames(new ArrayList<>(subscribedTopics))

Review Comment:
   Could we use `allTopicNames` instead of creating a set to create an list?



##########
jmh-benchmarks/src/main/java/org/apache/kafka/jmh/assignor/ServerSideAssignorBenchmark.java:
##########
@@ -0,0 +1,266 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.jmh.assignor;
+
+import org.apache.kafka.common.Uuid;
+import org.apache.kafka.coordinator.group.assignor.AssignmentMemberSpec;
+import org.apache.kafka.coordinator.group.assignor.AssignmentSpec;
+import org.apache.kafka.coordinator.group.assignor.GroupAssignment;
+import org.apache.kafka.coordinator.group.assignor.MemberAssignment;
+import org.apache.kafka.coordinator.group.assignor.PartitionAssignor;
+import org.apache.kafka.coordinator.group.assignor.RangeAssignor;
+import org.apache.kafka.coordinator.group.assignor.SubscribedTopicDescriber;
+import org.apache.kafka.coordinator.group.assignor.UniformAssignor;
+import org.apache.kafka.coordinator.group.consumer.SubscribedTopicMetadata;
+import org.apache.kafka.coordinator.group.consumer.TopicMetadata;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Threads;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+
+@State(Scope.Benchmark)
+@Fork(value = 1)
+@Warmup(iterations = 5)
+@Measurement(iterations = 5)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+public class ServerSideAssignorBenchmark {
+
+    public enum AssignorType {
+        RANGE(new RangeAssignor()),
+        UNIFORM(new UniformAssignor());
+
+        private final PartitionAssignor assignor;
+
+        AssignorType(PartitionAssignor assignor) {
+            this.assignor = assignor;
+        }
+
+        public PartitionAssignor assignor() {
+            return assignor;
+        }
+    }
+
+    /**
+     * The subscription pattern followed by the members of the group.
+     *
+     * A subscription model is considered homogenous if all the members of the 
group
+     * are subscribed to the same set of topics, it is heterogeneous otherwise.
+     */
+    public enum SubscriptionModel {
+        HOMOGENEOUS, HETEROGENEOUS
+    }
+
+    /**
+     * The assignment type is decided based on whether all the members are 
assigned partitions
+     * for the first time (full), or incrementally when a rebalance is 
triggered.
+     */
+    public enum AssignmentType {
+        FULL, INCREMENTAL
+    }
+
+    @Param({"100", "500", "1000", "5000", "10000"})
+    private int memberCount;
+
+    @Param({"5", "10", "50"})
+    private int partitionsToMemberRatio;
+
+    @Param({"10", "100", "1000"})
+    private int topicCount;
+
+    @Param({"true", "false"})
+    private boolean isRackAware;
+
+    @Param({"HOMOGENEOUS", "HETEROGENEOUS"})
+    private SubscriptionModel subscriptionModel;
+
+    @Param({"RANGE", "UNIFORM"})
+    private AssignorType assignorType;
+
+    @Param({"FULL", "INCREMENTAL"})
+    private AssignmentType assignmentType;
+
+    private PartitionAssignor partitionAssignor;
+
+    private static final int NUMBER_OF_RACKS = 3;
+
+    private AssignmentSpec assignmentSpec;
+
+    private SubscribedTopicDescriber subscribedTopicDescriber;
+
+    private final List<Uuid> allTopicIds = new ArrayList<>(topicCount);
+
+    @Setup(Level.Trial)
+    public void setup() {
+        Map<Uuid, TopicMetadata> topicMetadata = createTopicMetadata();
+        subscribedTopicDescriber = new SubscribedTopicMetadata(topicMetadata);
+
+        createAssignmentSpec();
+
+        partitionAssignor = assignorType.assignor();
+
+        if (assignmentType == AssignmentType.INCREMENTAL) {
+            simulateIncrementalRebalance(topicMetadata);
+        }
+    }
+
+    private Map<Uuid, TopicMetadata> createTopicMetadata() {
+        Map<Uuid, TopicMetadata> topicMetadata = new HashMap<>();
+        int partitionsPerTopicCount = (memberCount * partitionsToMemberRatio) 
/ topicCount;
+
+        Map<Integer, Set<String>> partitionRacks = isRackAware ?
+            mkMapOfPartitionRacks(partitionsPerTopicCount) :
+            Collections.emptyMap();
+
+        for (int i = 0; i < topicCount; i++) {
+            Uuid topicUuid = Uuid.randomUuid();
+            String topicName = "topic" + i;
+            allTopicIds.add(topicUuid);
+            topicMetadata.put(topicUuid, new TopicMetadata(
+                topicUuid,
+                topicName,
+                partitionsPerTopicCount,
+                partitionRacks
+            ));
+        }
+
+        return topicMetadata;
+    }
+
+    private void createAssignmentSpec() {
+        Map<String, AssignmentMemberSpec> members = new HashMap<>();
+
+        // In the rebalance case, we will add the last member as a trigger.
+        // This is done to keep the total members count consistent with the 
input.
+        int numberOfMembers = 
assignmentType.equals(AssignmentType.INCREMENTAL) ? memberCount - 1 : 
memberCount;
+
+        if (subscriptionModel.equals(SubscriptionModel.HOMOGENEOUS)) {
+            for (int i = 0; i < numberOfMembers; i++) {
+                addMemberSpec(members, i, new HashSet<>(allTopicIds));
+            }
+        } else {
+            // Check minimum topics requirement
+            if (topicCount < 5) {
+                throw new IllegalArgumentException("At least 5 topics are 
recommended for effective bucketing.");
+            }
+
+            // Adjust bucket count based on member count when member count < 5
+            int bucketCount = Math.min(5, numberOfMembers);

Review Comment:
   Should we define a const for `5`?



##########
jmh-benchmarks/src/main/java/org/apache/kafka/jmh/assignor/TargetAssignmentBuilderBenchmark.java:
##########
@@ -0,0 +1,202 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.jmh.assignor;
+
+import org.apache.kafka.common.Uuid;
+import org.apache.kafka.coordinator.group.assignor.AssignmentMemberSpec;
+import org.apache.kafka.coordinator.group.assignor.AssignmentSpec;
+import org.apache.kafka.coordinator.group.assignor.GroupAssignment;
+import org.apache.kafka.coordinator.group.assignor.MemberAssignment;
+import org.apache.kafka.coordinator.group.assignor.PartitionAssignor;
+import org.apache.kafka.coordinator.group.assignor.UniformAssignor;
+import org.apache.kafka.coordinator.group.consumer.Assignment;
+import org.apache.kafka.coordinator.group.consumer.ConsumerGroupMember;
+import org.apache.kafka.coordinator.group.consumer.SubscribedTopicMetadata;
+import org.apache.kafka.coordinator.group.consumer.TargetAssignmentBuilder;
+import org.apache.kafka.coordinator.group.consumer.TopicMetadata;
+import org.apache.kafka.coordinator.group.consumer.VersionedMetadata;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Threads;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+
+@State(Scope.Benchmark)
+@Fork(value = 1)
+@Warmup(iterations = 5)
+@Measurement(iterations = 5)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+public class TargetAssignmentBuilderBenchmark {
+
+    @Param({"100", "500", "1000", "5000", "10000"})
+    private int memberCount;
+
+    @Param({"5", "10", "50"})
+    private int partitionsToMemberRatio;
+
+    @Param({"10", "100", "1000"})
+    private int topicCount;
+
+    private static final String GROUP_ID = "benchmark-group";
+
+    private static final int GROUP_EPOCH = 0;
+
+    private PartitionAssignor partitionAssignor;
+
+    private Map<String, TopicMetadata> subscriptionMetadata = 
Collections.emptyMap();
+
+    private TargetAssignmentBuilder targetAssignmentBuilder;
+
+    private AssignmentSpec assignmentSpec;
+
+    private final List<String> allTopicNames = new ArrayList<>(topicCount);
+
+    private final List<Uuid> allTopicIds = new ArrayList<>(topicCount);
+
+    @Setup(Level.Trial)
+    public void setup() {
+        // For this benchmark we will use the Uniform Assignor
+        // and a group that has a homogeneous subscription model.
+        partitionAssignor = new UniformAssignor();
+
+        subscriptionMetadata = generateMockSubscriptionMetadata();
+        Map<String, ConsumerGroupMember> members = generateMockMembers();
+        Map<String, Assignment> existingTargetAssignment = 
generateMockInitialTargetAssignment();
+
+        // Add a new member to trigger a rebalance.
+        Set<String> subscribedTopics = new 
HashSet<>(subscriptionMetadata.keySet());
+
+        ConsumerGroupMember newMember = new 
ConsumerGroupMember.Builder("new-member")
+            .setSubscribedTopicNames(new ArrayList<>(subscribedTopics))
+            .build();
+
+        targetAssignmentBuilder = new TargetAssignmentBuilder(GROUP_ID, 
GROUP_EPOCH, partitionAssignor)
+            .withMembers(members)
+            .withSubscriptionMetadata(subscriptionMetadata)
+            .withTargetAssignment(existingTargetAssignment)
+            .addOrUpdateMember(newMember.memberId(), newMember);
+    }
+
+    private Map<String, ConsumerGroupMember> generateMockMembers() {
+        Map<String, ConsumerGroupMember> members = new HashMap<>();
+
+        for (int i = 0; i < memberCount - 1; i++) {
+            Set<String> subscribedTopics;
+            subscribedTopics = new HashSet<>(allTopicNames);
+
+            ConsumerGroupMember member = new 
ConsumerGroupMember.Builder("member" + i)
+                .setSubscribedTopicNames(new ArrayList<>(subscribedTopics))

Review Comment:
   Could we also use `allTopicNames` directly here?



##########
jmh-benchmarks/src/main/java/org/apache/kafka/jmh/assignor/TargetAssignmentBuilderBenchmark.java:
##########
@@ -0,0 +1,202 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.jmh.assignor;
+
+import org.apache.kafka.common.Uuid;
+import org.apache.kafka.coordinator.group.assignor.AssignmentMemberSpec;
+import org.apache.kafka.coordinator.group.assignor.AssignmentSpec;
+import org.apache.kafka.coordinator.group.assignor.GroupAssignment;
+import org.apache.kafka.coordinator.group.assignor.MemberAssignment;
+import org.apache.kafka.coordinator.group.assignor.PartitionAssignor;
+import org.apache.kafka.coordinator.group.assignor.UniformAssignor;
+import org.apache.kafka.coordinator.group.consumer.Assignment;
+import org.apache.kafka.coordinator.group.consumer.ConsumerGroupMember;
+import org.apache.kafka.coordinator.group.consumer.SubscribedTopicMetadata;
+import org.apache.kafka.coordinator.group.consumer.TargetAssignmentBuilder;
+import org.apache.kafka.coordinator.group.consumer.TopicMetadata;
+import org.apache.kafka.coordinator.group.consumer.VersionedMetadata;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Threads;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+
+@State(Scope.Benchmark)
+@Fork(value = 1)
+@Warmup(iterations = 5)
+@Measurement(iterations = 5)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+public class TargetAssignmentBuilderBenchmark {
+
+    @Param({"100", "500", "1000", "5000", "10000"})
+    private int memberCount;
+
+    @Param({"5", "10", "50"})
+    private int partitionsToMemberRatio;
+
+    @Param({"10", "100", "1000"})
+    private int topicCount;
+
+    private static final String GROUP_ID = "benchmark-group";
+
+    private static final int GROUP_EPOCH = 0;
+
+    private PartitionAssignor partitionAssignor;
+
+    private Map<String, TopicMetadata> subscriptionMetadata = 
Collections.emptyMap();
+
+    private TargetAssignmentBuilder targetAssignmentBuilder;
+
+    private AssignmentSpec assignmentSpec;
+
+    private final List<String> allTopicNames = new ArrayList<>(topicCount);
+
+    private final List<Uuid> allTopicIds = new ArrayList<>(topicCount);
+
+    @Setup(Level.Trial)
+    public void setup() {
+        // For this benchmark we will use the Uniform Assignor
+        // and a group that has a homogeneous subscription model.
+        partitionAssignor = new UniformAssignor();
+
+        subscriptionMetadata = generateMockSubscriptionMetadata();
+        Map<String, ConsumerGroupMember> members = generateMockMembers();
+        Map<String, Assignment> existingTargetAssignment = 
generateMockInitialTargetAssignment();
+
+        // Add a new member to trigger a rebalance.
+        Set<String> subscribedTopics = new 
HashSet<>(subscriptionMetadata.keySet());
+
+        ConsumerGroupMember newMember = new 
ConsumerGroupMember.Builder("new-member")
+            .setSubscribedTopicNames(new ArrayList<>(subscribedTopics))
+            .build();
+
+        targetAssignmentBuilder = new TargetAssignmentBuilder(GROUP_ID, 
GROUP_EPOCH, partitionAssignor)
+            .withMembers(members)
+            .withSubscriptionMetadata(subscriptionMetadata)
+            .withTargetAssignment(existingTargetAssignment)
+            .addOrUpdateMember(newMember.memberId(), newMember);
+    }
+
+    private Map<String, ConsumerGroupMember> generateMockMembers() {
+        Map<String, ConsumerGroupMember> members = new HashMap<>();
+
+        for (int i = 0; i < memberCount - 1; i++) {
+            Set<String> subscribedTopics;
+            subscribedTopics = new HashSet<>(allTopicNames);

Review Comment:
   nit: You can combine these two into one line.



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