dajac commented on code in PR #14182: URL: https://github.com/apache/kafka/pull/14182#discussion_r1315500509
########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/GeneralUniformAssignmentBuilder.java: ########## @@ -0,0 +1,31 @@ +/* + * 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.coordinator.group.assignor; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +public class GeneralUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(GeneralUniformAssignmentBuilder.class); Review Comment: nit: `log` -> `LOG` as this is a constant. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/GeneralUniformAssignmentBuilder.java: ########## @@ -0,0 +1,31 @@ +/* + * 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.coordinator.group.assignor; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +public class GeneralUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(GeneralUniformAssignmentBuilder.class); + + @Override + protected GroupAssignment buildAssignment() { + return null; + Review Comment: nit: We can remove this empty line. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); + private final AssignmentSpec assignmentSpec; + private final SubscribedTopicDescriber subscribedTopicDescriber; + // List of topics subscribed to by all members. + private final Set<Uuid> subscriptionIds; + private final RackInfo rackInfo; + // Count of members to receive an extra partition beyond the minimum quota, + // to account for the distribution of the remaining partitions. + private int remainingMembersToGetAnExtraPartition; + // Map of members to the remaining number of partitions needed to meet the minimum quota, + // including members eligible for an extra partition. + private final Map<String, Integer> potentiallyUnfilledMembers; + // Members mapped to the remaining number of partitions needed to meet the full quota. + // Full quota = minQuota + one extra partition (if applicable). + private Map<String, Integer> unfilledMembers; + private List<TopicIdPartition> unassignedPartitions; + private final Map<String, MemberAssignment> newAssignment; + // Tracks the current owner of each partition when using rack-aware strategy. + // Current refers to the existing assignment. + private final Map<TopicIdPartition, String> currentPartitionOwners; + // Indicates if a rack aware assignment can be done. + // True if racks are defined for both members and partitions. + boolean useRackAwareStrategy; + + OptimizedUniformAssignmentBuilder(AssignmentSpec assignmentSpec, SubscribedTopicDescriber subscribedTopicDescriber) { + this.assignmentSpec = assignmentSpec; + this.subscribedTopicDescriber = subscribedTopicDescriber; + this.subscriptionIds = new HashSet<>(assignmentSpec.members().values().iterator().next().subscribedTopicIds()); + this.rackInfo = new RackInfo(assignmentSpec, subscribedTopicDescriber, subscriptionIds); + this.potentiallyUnfilledMembers = new HashMap<>(); + this.unfilledMembers = new HashMap<>(); + this.newAssignment = new HashMap<>(); + this.useRackAwareStrategy = rackInfo.useRackStrategy; Review Comment: nit: Do we need to define `useRackAwareStrategy` as an attribute if we can get it from `rackInfo.useRackStrategy`? We could perhaps have a method instead. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); + private final AssignmentSpec assignmentSpec; + private final SubscribedTopicDescriber subscribedTopicDescriber; + // List of topics subscribed to by all members. + private final Set<Uuid> subscriptionIds; + private final RackInfo rackInfo; + // Count of members to receive an extra partition beyond the minimum quota, + // to account for the distribution of the remaining partitions. + private int remainingMembersToGetAnExtraPartition; + // Map of members to the remaining number of partitions needed to meet the minimum quota, + // including members eligible for an extra partition. + private final Map<String, Integer> potentiallyUnfilledMembers; + // Members mapped to the remaining number of partitions needed to meet the full quota. + // Full quota = minQuota + one extra partition (if applicable). + private Map<String, Integer> unfilledMembers; + private List<TopicIdPartition> unassignedPartitions; + private final Map<String, MemberAssignment> newAssignment; + // Tracks the current owner of each partition when using rack-aware strategy. + // Current refers to the existing assignment. + private final Map<TopicIdPartition, String> currentPartitionOwners; + // Indicates if a rack aware assignment can be done. + // True if racks are defined for both members and partitions. + boolean useRackAwareStrategy; + + OptimizedUniformAssignmentBuilder(AssignmentSpec assignmentSpec, SubscribedTopicDescriber subscribedTopicDescriber) { + this.assignmentSpec = assignmentSpec; + this.subscribedTopicDescriber = subscribedTopicDescriber; + this.subscriptionIds = new HashSet<>(assignmentSpec.members().values().iterator().next().subscribedTopicIds()); Review Comment: I suppose that we assume that we cannot get here if members is empty. Is this correct? ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/UniformAssignor.java: ########## @@ -0,0 +1,288 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.apache.kafka.common.Uuid; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; +import java.util.stream.Collectors; +import java.util.stream.IntStream; + +/** + * The Uniform Assignor distributes Kafka topic partitions among group members for balanced assignment. + * The assignor employs two different strategies based on the nature of topic + * subscriptions across the group members: + * <ul> + * <li> + * <b> Optimized Uniform Assignment Builder: </b> This strategy is used when all members have subscribed + * to the same set of topics. + * </li> + * <li> + * <b> General Uniform Assignment Builder: </b> This strategy is used when members have varied topic + * subscriptions. + * </li> + * </ul> + * + * The appropriate strategy is automatically chosen based on the current members' topic subscriptions. + * + * @see OptimizedUniformAssignmentBuilder + * @see GeneralUniformAssignmentBuilder + */ +public class UniformAssignor implements PartitionAssignor { + private static final Logger log = LoggerFactory.getLogger(UniformAssignor.class); + public static final String UNIFORM_ASSIGNOR_NAME = "uniform"; + + @Override + public String name() { + return UNIFORM_ASSIGNOR_NAME; + } + + /** + * Perform the group assignment given the current members and + * topic metadata. + * + * @param assignmentSpec The member assignment spec. + * @param subscribedTopicDescriber The topic and cluster metadata describer {@link SubscribedTopicDescriber}. + * @return The new assignment for the group. + */ + @Override + public GroupAssignment assign( + AssignmentSpec assignmentSpec, + SubscribedTopicDescriber subscribedTopicDescriber + ) throws PartitionAssignorException { + AbstractAssignmentBuilder assignmentBuilder; + if (assignmentSpec.members().isEmpty()) + return new GroupAssignment(Collections.emptyMap()); + + if (allSubscriptionsEqual(assignmentSpec.members())) { + log.debug("Detected that all members are subscribed to the same set of topics, invoking the " + + "optimized assignment algorithm"); + assignmentBuilder = new OptimizedUniformAssignmentBuilder(assignmentSpec, subscribedTopicDescriber); + } else { + assignmentBuilder = new GeneralUniformAssignmentBuilder(); + log.debug("Detected that all members are subscribed to a different set of topics, invoking the " + + "general assignment algorithm"); + } + + return assignmentBuilder.buildAssignment(); + } + + /** + * Determines if all members are subscribed to the same list of topic IDs. + * + * @param members A map of member identifiers to their respective {@code AssignmentMemberSpec}. + * Assumes the map is non-empty. + * @return true if all members have the same subscription list of topic IDs, + * false otherwise. + */ + private boolean allSubscriptionsEqual(Map<String, AssignmentMemberSpec> members) { + Set<Uuid> firstSubscriptionSet = new HashSet<>(members.values().iterator().next().subscribedTopicIds()); + for (AssignmentMemberSpec memberSpec : members.values()) { + Set<Uuid> currentSubscriptionSet = new HashSet<>(memberSpec.subscribedTopicIds()); Review Comment: Is using an HashSet necessary here? We could perhaps use `firstSubscriptionSet.containsAll(memberSpec.subscribedTopicIds())`. Would it work? ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/consumer/SubscribedTopicMetadata.java: ########## @@ -68,12 +68,17 @@ public int numPartitions(Uuid topicId) { * @param topicId Uuid corresponding to the partition's topic. * @param partition Partition Id within the topic. * @return The set of racks corresponding to the replicas of the topics partition. - * If the topic Id does not exist, an empty set is returned + * If the topic Id does not exist or no partition rack information is available, an empty set is returned. */ @Override public Set<String> racksForPartition(Uuid topicId, int partition) { TopicMetadata topic = this.topicMetadata.get(topicId); - return topic == null ? Collections.emptySet() : topic.partitionRacks().get(partition); + if (topic == null) { Review Comment: nit: Could we keep the previous code and use `getOrDefault` instead of `get`? The code would be more concise... ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/RangeAssignor.java: ########## @@ -89,16 +93,17 @@ public MemberWithRemainingAssignments(String memberId, int remaining) { private Map<Uuid, List<String>> membersPerTopic(final AssignmentSpec assignmentSpec, final SubscribedTopicDescriber subscribedTopicDescriber) { Map<Uuid, List<String>> membersPerTopic = new HashMap<>(); Map<String, AssignmentMemberSpec> membersData = assignmentSpec.members(); - + // Only add topic Ids to the map if they are present in the topic metadata. membersData.forEach((memberId, memberMetadata) -> { Collection<Uuid> topics = memberMetadata.subscribedTopicIds(); for (Uuid topicId : topics) { if (subscribedTopicDescriber.numPartitions(topicId) == -1) { - throw new PartitionAssignorException("Member is subscribed to a non-existent topic"); + log.warn("Members are subscribed to topic " + topicId + " which doesn't exist in the topic metadata."); Review Comment: Shouldn't we keep what we had here? ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); + private final AssignmentSpec assignmentSpec; + private final SubscribedTopicDescriber subscribedTopicDescriber; + // List of topics subscribed to by all members. + private final Set<Uuid> subscriptionIds; + private final RackInfo rackInfo; + // Count of members to receive an extra partition beyond the minimum quota, + // to account for the distribution of the remaining partitions. + private int remainingMembersToGetAnExtraPartition; + // Map of members to the remaining number of partitions needed to meet the minimum quota, + // including members eligible for an extra partition. + private final Map<String, Integer> potentiallyUnfilledMembers; + // Members mapped to the remaining number of partitions needed to meet the full quota. + // Full quota = minQuota + one extra partition (if applicable). + private Map<String, Integer> unfilledMembers; + private List<TopicIdPartition> unassignedPartitions; + private final Map<String, MemberAssignment> newAssignment; + // Tracks the current owner of each partition when using rack-aware strategy. + // Current refers to the existing assignment. + private final Map<TopicIdPartition, String> currentPartitionOwners; + // Indicates if a rack aware assignment can be done. + // True if racks are defined for both members and partitions. + boolean useRackAwareStrategy; + + OptimizedUniformAssignmentBuilder(AssignmentSpec assignmentSpec, SubscribedTopicDescriber subscribedTopicDescriber) { + this.assignmentSpec = assignmentSpec; + this.subscribedTopicDescriber = subscribedTopicDescriber; + this.subscriptionIds = new HashSet<>(assignmentSpec.members().values().iterator().next().subscribedTopicIds()); + this.rackInfo = new RackInfo(assignmentSpec, subscribedTopicDescriber, subscriptionIds); + this.potentiallyUnfilledMembers = new HashMap<>(); + this.unfilledMembers = new HashMap<>(); + this.newAssignment = new HashMap<>(); + this.useRackAwareStrategy = rackInfo.useRackStrategy; + // Without rack-aware strategy, tracking current owners of unassigned partitions is unnecessary + // as all sticky partitions are retained until a member meets its quota. + this.currentPartitionOwners = useRackAwareStrategy ? new HashMap<>() : Collections.emptyMap(); + } + + /** + * Here's the step-by-step breakdown of the assignment process: + * + * <li> Compute the quotas of partitions for each member based on the total partitions and member count.</li> + * <li> For existing assignments, retain partitions based on the determined quota and member's rack compatibility.</li> + * <li> If a partition's rack mismatches with its owner, track it for future use.</li> + * <li> Identify members that haven't fulfilled their partition quota or are eligible to receive extra partitions.</li> + * <li> Derive the unassigned partitions by taking the difference between total partitions and the sticky assignments.</li> + * <li> Depending on members needing extra partitions, select members from the potentially unfilled list + * and add them to the unfilled list.</li> + * <li> Proceed with a round-robin assignment adhering to rack awareness. + * For each unassigned partition, locate the first compatible member from the unfilled list.</li> + * <li> If no rack-compatible member is found, revert to the tracked current owner. + * If that member can't accommodate the partition due to quota limits, resort to a generic round-robin assignment.</li> + * */ + @Override + protected GroupAssignment buildAssignment() throws PartitionAssignorException{ + int totalPartitionsCount = 0; + // Removes the current topic from subscriptionIds if the topic doesn't exist in the topic metadata. + for (Uuid topicId : subscriptionIds) { + int partitionCount = subscribedTopicDescriber.numPartitions(topicId); + if (partitionCount == -1) { + IllegalStateException illegalStateException = + new IllegalStateException("The topic " + topicId + " seems to be in an invalid state."); + + throw new PartitionAssignorException( + "Members are subscribed to topic " + topicId + " which doesn't exist in the topic metadata.", + illegalStateException + ); + } else { + totalPartitionsCount += partitionCount; + } + } + + if (subscriptionIds.isEmpty()) { + log.info("The subscription list is empty, returning an empty assignment"); + return new GroupAssignment(Collections.emptyMap()); + } + + // The minimum required quota that each member needs to meet for a balanced assignment. + // This is the same for all members. + int numberOfMembers = assignmentSpec.members().size(); + final int minQuota = totalPartitionsCount / numberOfMembers; + remainingMembersToGetAnExtraPartition = totalPartitionsCount % numberOfMembers; + + assignmentSpec.members().keySet().forEach(memberId -> + newAssignment.put(memberId, new MemberAssignment(new HashMap<>()) + )); + + Set<TopicIdPartition> allAssignedStickyPartitions = computeAssignedStickyPartitions(minQuota); + unassignedPartitions = computeUnassignedPartitions(allAssignedStickyPartitions); + unfilledMembers = computeUnfilledMembers(); + + if (!unassignedPartitionsCountEqualsRemainingAssignmentsCount()) { + throw new PartitionAssignorException("Number of available partitions is not equal to the total requirement"); + } + + if (useRackAwareStrategy) rackAwareRoundRobinAssignment(); + unassignedPartitionsRoundRobinAssignment(); + + return new GroupAssignment(newAssignment); + } + + /** + * Retrieves a set of partitions that were currently assigned to members and will be retained in the new assignment, + * by ensuring that the partitions are still relevant based on current topic metadata and subscriptions. + * If rack awareness is enabled, it ensures that a partition's rack matches the member's rack. + * + * <p> For each member, it: + * <ul> + * <li> Finds the valid current assignment considering topic subscriptions and metadata.</li> + * <li> If current assignments exist, retains up to the minimum quota of assignments.</li> + * <li> If there are members that should get an extra partition, + * assigns the next partition after the retained ones.</li> + * <li> For members with assignments not exceeding the minimum quota, + * it identifies them as potentially unfilled members and tracks the remaining quota.</li> + * </ul> + * + * @return A set containing all the sticky partitions that have been retained in the new assignment. + */ + private Set<TopicIdPartition> computeAssignedStickyPartitions(Integer minQuota) { + Set<TopicIdPartition> allAssignedStickyPartitions = new HashSet<>(); + + assignmentSpec.members().forEach((memberId, assignmentMemberSpec) -> { + // Remove all the topics that aren't in the subscriptions or the topic metadata anymore. + // If rack awareness is enabled, only add partitions if the members rack matches the partitions rack. + List<TopicIdPartition> validCurrentAssignment = validCurrentAssignment( + memberId, + assignmentMemberSpec.assignedPartitions() + ); + + int currentAssignmentSize = validCurrentAssignment.size(); + int remaining = minQuota - currentAssignmentSize; + + if (currentAssignmentSize > 0) { + int retainedPartitionsCount = min(currentAssignmentSize, minQuota); + IntStream.range(0, retainedPartitionsCount).forEach(i -> { + newAssignment.get(memberId) + .targetPartitions() + .computeIfAbsent(validCurrentAssignment.get(i).topicId(), __ -> new HashSet<>()) + .add(validCurrentAssignment.get(i).partition()); + allAssignedStickyPartitions.add(validCurrentAssignment.get(i)); + }); + + // The extra partition is located at the last index from the previous step. + if (remaining < 0 && remainingMembersToGetAnExtraPartition > 0) { + newAssignment.get(memberId) + .targetPartitions() + .computeIfAbsent(validCurrentAssignment.get(retainedPartitionsCount).topicId(), __ -> new HashSet<>()) + .add(validCurrentAssignment.get(retainedPartitionsCount).partition()); + allAssignedStickyPartitions.add(validCurrentAssignment.get(retainedPartitionsCount)); + remainingMembersToGetAnExtraPartition--; + } + } + + if (remaining >= 0) { + potentiallyUnfilledMembers.put(memberId, remaining); + } + + }); + + return allAssignedStickyPartitions; + } + + /** + * Filters the current assignment of partitions for a given member. + * + * If a partition is assigned to a member not subscribed to its topic or + * if the rack-aware strategy is to be used but there is a mismatch, + * the partition is excluded from the valid assignment and stored for future consideration. + * + * @param memberId The Id of the member whose assignment is being validated. + * @param assignedPartitions The partitions currently assigned to the member. + * + * @return List of valid partitions after applying the filters. + */ + private List<TopicIdPartition> validCurrentAssignment( + String memberId, + Map<Uuid, Set<Integer>> assignedPartitions + ) { + List<TopicIdPartition> validCurrentAssignmentList = new ArrayList<>(); + assignedPartitions.forEach((topicId, currentAssignment) -> { + if (subscriptionIds.contains(topicId)) { + currentAssignment.forEach(partition -> { + TopicIdPartition topicIdPartition = new TopicIdPartition(topicId, partition); + if (useRackAwareStrategy && rackInfo.racksMismatch(memberId, topicIdPartition)) { + currentPartitionOwners.put(topicIdPartition, memberId); + } else { + validCurrentAssignmentList.add(topicIdPartition); + } + }); + } + else { + log.debug("The topic " + topicId + " is no longer present in the subscribed topics list"); + } + }); + + return validCurrentAssignmentList; + } + + /** + * This method iterates over the unassigned partitions and attempts to allocate them + * to members while considering their rack affiliations. + */ + private void rackAwareRoundRobinAssignment() { + Queue<String> roundRobinMembers = new LinkedList<>(unfilledMembers.keySet()); + + // Sort partitions in ascending order by number of potential members with matching racks. + // Partitions with no potential members aren't included in this list. + List<TopicIdPartition> sortedPartitions = rackInfo.sortPartitionsByRackMembers(unassignedPartitions); + + sortedPartitions.forEach(partition -> { + boolean assigned = false; + for (int i = 0; i < roundRobinMembers.size() && !assigned; i++) { + String memberId = roundRobinMembers.poll(); + Integer remainingPartitionCount = unfilledMembers.getOrDefault(memberId, 0); + + if (remainingPartitionCount > 0 && !rackInfo.racksMismatch(memberId, partition)) { + assignPartitionToMember(memberId, partition); + assigned = true; + unassignedPartitions.remove(partition); + } + + // Only re-add to the end of the queue if it's still in the unfilledMembers map + if (unfilledMembers.containsKey(memberId)) { + roundRobinMembers.add(memberId); + } + } + }); + } + + /** + * Allocates the unassigned partitions to available members. + * + * If the rack-aware strategy is enabled, partitions are attempted to be assigned back to their current owners first. + * + * If a partition couldn't be assigned to its current owner due to quotas or + * if the rack-aware strategy is not enabled, the partitions are allocated to members in a round-robin fashion.</p> Review Comment: nit: We can remove `</p>`. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); + private final AssignmentSpec assignmentSpec; Review Comment: Could we please add javadoc to all the attributes? We have been doing this for all the new code in this module so we should continue. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); + private final AssignmentSpec assignmentSpec; + private final SubscribedTopicDescriber subscribedTopicDescriber; + // List of topics subscribed to by all members. + private final Set<Uuid> subscriptionIds; + private final RackInfo rackInfo; + // Count of members to receive an extra partition beyond the minimum quota, + // to account for the distribution of the remaining partitions. + private int remainingMembersToGetAnExtraPartition; + // Map of members to the remaining number of partitions needed to meet the minimum quota, + // including members eligible for an extra partition. + private final Map<String, Integer> potentiallyUnfilledMembers; + // Members mapped to the remaining number of partitions needed to meet the full quota. + // Full quota = minQuota + one extra partition (if applicable). + private Map<String, Integer> unfilledMembers; + private List<TopicIdPartition> unassignedPartitions; + private final Map<String, MemberAssignment> newAssignment; + // Tracks the current owner of each partition when using rack-aware strategy. + // Current refers to the existing assignment. + private final Map<TopicIdPartition, String> currentPartitionOwners; + // Indicates if a rack aware assignment can be done. + // True if racks are defined for both members and partitions. + boolean useRackAwareStrategy; + + OptimizedUniformAssignmentBuilder(AssignmentSpec assignmentSpec, SubscribedTopicDescriber subscribedTopicDescriber) { + this.assignmentSpec = assignmentSpec; + this.subscribedTopicDescriber = subscribedTopicDescriber; + this.subscriptionIds = new HashSet<>(assignmentSpec.members().values().iterator().next().subscribedTopicIds()); + this.rackInfo = new RackInfo(assignmentSpec, subscribedTopicDescriber, subscriptionIds); + this.potentiallyUnfilledMembers = new HashMap<>(); + this.unfilledMembers = new HashMap<>(); + this.newAssignment = new HashMap<>(); + this.useRackAwareStrategy = rackInfo.useRackStrategy; + // Without rack-aware strategy, tracking current owners of unassigned partitions is unnecessary + // as all sticky partitions are retained until a member meets its quota. + this.currentPartitionOwners = useRackAwareStrategy ? new HashMap<>() : Collections.emptyMap(); + } + + /** + * Here's the step-by-step breakdown of the assignment process: + * + * <li> Compute the quotas of partitions for each member based on the total partitions and member count.</li> + * <li> For existing assignments, retain partitions based on the determined quota and member's rack compatibility.</li> + * <li> If a partition's rack mismatches with its owner, track it for future use.</li> + * <li> Identify members that haven't fulfilled their partition quota or are eligible to receive extra partitions.</li> + * <li> Derive the unassigned partitions by taking the difference between total partitions and the sticky assignments.</li> + * <li> Depending on members needing extra partitions, select members from the potentially unfilled list + * and add them to the unfilled list.</li> + * <li> Proceed with a round-robin assignment adhering to rack awareness. + * For each unassigned partition, locate the first compatible member from the unfilled list.</li> + * <li> If no rack-compatible member is found, revert to the tracked current owner. + * If that member can't accommodate the partition due to quota limits, resort to a generic round-robin assignment.</li> + * */ + @Override + protected GroupAssignment buildAssignment() throws PartitionAssignorException{ + int totalPartitionsCount = 0; + // Removes the current topic from subscriptionIds if the topic doesn't exist in the topic metadata. + for (Uuid topicId : subscriptionIds) { + int partitionCount = subscribedTopicDescriber.numPartitions(topicId); + if (partitionCount == -1) { + IllegalStateException illegalStateException = + new IllegalStateException("The topic " + topicId + " seems to be in an invalid state."); Review Comment: I think that we should directly throw the IllegalStateException. It is a bit weird to construct it to wrap it in another one right away. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/UniformAssignor.java: ########## @@ -0,0 +1,288 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.apache.kafka.common.Uuid; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; +import java.util.stream.Collectors; +import java.util.stream.IntStream; + +/** + * The Uniform Assignor distributes Kafka topic partitions among group members for balanced assignment. + * The assignor employs two different strategies based on the nature of topic + * subscriptions across the group members: + * <ul> + * <li> + * <b> Optimized Uniform Assignment Builder: </b> This strategy is used when all members have subscribed + * to the same set of topics. + * </li> + * <li> + * <b> General Uniform Assignment Builder: </b> This strategy is used when members have varied topic + * subscriptions. + * </li> + * </ul> + * + * The appropriate strategy is automatically chosen based on the current members' topic subscriptions. + * + * @see OptimizedUniformAssignmentBuilder + * @see GeneralUniformAssignmentBuilder + */ +public class UniformAssignor implements PartitionAssignor { + private static final Logger log = LoggerFactory.getLogger(UniformAssignor.class); + public static final String UNIFORM_ASSIGNOR_NAME = "uniform"; + + @Override + public String name() { + return UNIFORM_ASSIGNOR_NAME; + } + + /** + * Perform the group assignment given the current members and + * topic metadata. + * + * @param assignmentSpec The member assignment spec. + * @param subscribedTopicDescriber The topic and cluster metadata describer {@link SubscribedTopicDescriber}. + * @return The new assignment for the group. + */ + @Override + public GroupAssignment assign( + AssignmentSpec assignmentSpec, + SubscribedTopicDescriber subscribedTopicDescriber + ) throws PartitionAssignorException { + AbstractAssignmentBuilder assignmentBuilder; + if (assignmentSpec.members().isEmpty()) + return new GroupAssignment(Collections.emptyMap()); + + if (allSubscriptionsEqual(assignmentSpec.members())) { + log.debug("Detected that all members are subscribed to the same set of topics, invoking the " + + "optimized assignment algorithm"); + assignmentBuilder = new OptimizedUniformAssignmentBuilder(assignmentSpec, subscribedTopicDescriber); + } else { + assignmentBuilder = new GeneralUniformAssignmentBuilder(); + log.debug("Detected that all members are subscribed to a different set of topics, invoking the " + + "general assignment algorithm"); + } + + return assignmentBuilder.buildAssignment(); + } + + /** + * Determines if all members are subscribed to the same list of topic IDs. + * + * @param members A map of member identifiers to their respective {@code AssignmentMemberSpec}. + * Assumes the map is non-empty. + * @return true if all members have the same subscription list of topic IDs, + * false otherwise. + */ + private boolean allSubscriptionsEqual(Map<String, AssignmentMemberSpec> members) { + Set<Uuid> firstSubscriptionSet = new HashSet<>(members.values().iterator().next().subscribedTopicIds()); + for (AssignmentMemberSpec memberSpec : members.values()) { + Set<Uuid> currentSubscriptionSet = new HashSet<>(memberSpec.subscribedTopicIds()); + if (!firstSubscriptionSet.equals(currentSubscriptionSet)) { + return false; + } + } + return true; + } + + /** + * The assignment builder is used to construct the final assignment in a series of steps that + * are determined by the type of subscriptions. + * + * There are common methods present that are used by any type of assignment strategy. + */ + protected static abstract class AbstractAssignmentBuilder { + protected abstract GroupAssignment buildAssignment(); + + /** + * Determines if rack-aware assignment is appropriate based on the provided rack information. + * + * @param memberRacks Racks where members are located. + * @param partitionRacks Racks where partitions are located. + * @param racksPerPartition Map of partitions to their associated racks. + * + * @return {@code true} if rack-aware assignment should be applied; {@code false} otherwise. + */ + protected boolean useRackAwareAssignment( + Set<String> memberRacks, + Set<String> partitionRacks, + Map<TopicIdPartition, Set<String>> racksPerPartition + ) { + if (memberRacks.isEmpty() || Collections.disjoint(memberRacks, partitionRacks)) + return false; + else { + return !racksPerPartition.values().stream().allMatch(partitionRacks::equals); + } + } + + /** + * Constructs a list of {@code TopicIdPartition} for each topic Id based on its partition count. + * + * @param allTopicIds The list of subscribed topic Ids. + * @param subscribedTopicDescriber Utility to fetch the partition count for a given topic. + * + * @return List of generated {@code TopicIdPartition} for all provided topic Ids. + */ + protected List<TopicIdPartition> allTopicIdPartitions( + List<Uuid> allTopicIds, + SubscribedTopicDescriber subscribedTopicDescriber + ) { + List<TopicIdPartition> allTopicIdPartitions = new ArrayList<>(); + allTopicIds.forEach(topic -> + IntStream.range(0, subscribedTopicDescriber.numPartitions((topic))) + .forEach(i -> allTopicIdPartitions.add(new TopicIdPartition(topic, i)) + ) + ); + + return allTopicIdPartitions; + } + + /** + * Represents the rack information of members and partitions along with utility methods + * to facilitate rack-aware assignment strategies for a given consumer group. + */ + protected class RackInfo { + /** + * Map of every member to its rack. + */ + protected final Map<String, String> memberRacks; + /** + * Map of every partition to a list of its racks. + */ + protected final Map<TopicIdPartition, Set<String>> partitionRacks; + /** + * Number of members with the same rack as the partition. + */ + private final Map<TopicIdPartition, Integer> numMembersWithSameRackByPartition; + protected final boolean useRackStrategy; Review Comment: nit: javadoc. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); + private final AssignmentSpec assignmentSpec; + private final SubscribedTopicDescriber subscribedTopicDescriber; + // List of topics subscribed to by all members. + private final Set<Uuid> subscriptionIds; + private final RackInfo rackInfo; + // Count of members to receive an extra partition beyond the minimum quota, + // to account for the distribution of the remaining partitions. + private int remainingMembersToGetAnExtraPartition; + // Map of members to the remaining number of partitions needed to meet the minimum quota, + // including members eligible for an extra partition. + private final Map<String, Integer> potentiallyUnfilledMembers; + // Members mapped to the remaining number of partitions needed to meet the full quota. + // Full quota = minQuota + one extra partition (if applicable). + private Map<String, Integer> unfilledMembers; + private List<TopicIdPartition> unassignedPartitions; + private final Map<String, MemberAssignment> newAssignment; + // Tracks the current owner of each partition when using rack-aware strategy. + // Current refers to the existing assignment. + private final Map<TopicIdPartition, String> currentPartitionOwners; + // Indicates if a rack aware assignment can be done. + // True if racks are defined for both members and partitions. + boolean useRackAwareStrategy; + + OptimizedUniformAssignmentBuilder(AssignmentSpec assignmentSpec, SubscribedTopicDescriber subscribedTopicDescriber) { + this.assignmentSpec = assignmentSpec; + this.subscribedTopicDescriber = subscribedTopicDescriber; + this.subscriptionIds = new HashSet<>(assignmentSpec.members().values().iterator().next().subscribedTopicIds()); + this.rackInfo = new RackInfo(assignmentSpec, subscribedTopicDescriber, subscriptionIds); + this.potentiallyUnfilledMembers = new HashMap<>(); + this.unfilledMembers = new HashMap<>(); + this.newAssignment = new HashMap<>(); + this.useRackAwareStrategy = rackInfo.useRackStrategy; + // Without rack-aware strategy, tracking current owners of unassigned partitions is unnecessary + // as all sticky partitions are retained until a member meets its quota. + this.currentPartitionOwners = useRackAwareStrategy ? new HashMap<>() : Collections.emptyMap(); + } + + /** + * Here's the step-by-step breakdown of the assignment process: + * + * <li> Compute the quotas of partitions for each member based on the total partitions and member count.</li> + * <li> For existing assignments, retain partitions based on the determined quota and member's rack compatibility.</li> + * <li> If a partition's rack mismatches with its owner, track it for future use.</li> + * <li> Identify members that haven't fulfilled their partition quota or are eligible to receive extra partitions.</li> + * <li> Derive the unassigned partitions by taking the difference between total partitions and the sticky assignments.</li> + * <li> Depending on members needing extra partitions, select members from the potentially unfilled list + * and add them to the unfilled list.</li> + * <li> Proceed with a round-robin assignment adhering to rack awareness. + * For each unassigned partition, locate the first compatible member from the unfilled list.</li> + * <li> If no rack-compatible member is found, revert to the tracked current owner. + * If that member can't accommodate the partition due to quota limits, resort to a generic round-robin assignment.</li> + * */ + @Override + protected GroupAssignment buildAssignment() throws PartitionAssignorException{ + int totalPartitionsCount = 0; + // Removes the current topic from subscriptionIds if the topic doesn't exist in the topic metadata. + for (Uuid topicId : subscriptionIds) { + int partitionCount = subscribedTopicDescriber.numPartitions(topicId); + if (partitionCount == -1) { + IllegalStateException illegalStateException = + new IllegalStateException("The topic " + topicId + " seems to be in an invalid state."); + + throw new PartitionAssignorException( + "Members are subscribed to topic " + topicId + " which doesn't exist in the topic metadata.", + illegalStateException + ); + } else { + totalPartitionsCount += partitionCount; + } + } + + if (subscriptionIds.isEmpty()) { + log.info("The subscription list is empty, returning an empty assignment"); + return new GroupAssignment(Collections.emptyMap()); + } + + // The minimum required quota that each member needs to meet for a balanced assignment. + // This is the same for all members. + int numberOfMembers = assignmentSpec.members().size(); Review Comment: Could this be final as well? ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); Review Comment: nit: `log` -> `LOG`. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/UniformAssignor.java: ########## @@ -0,0 +1,288 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.apache.kafka.common.Uuid; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; +import java.util.stream.Collectors; +import java.util.stream.IntStream; + +/** + * The Uniform Assignor distributes Kafka topic partitions among group members for balanced assignment. + * The assignor employs two different strategies based on the nature of topic + * subscriptions across the group members: + * <ul> + * <li> + * <b> Optimized Uniform Assignment Builder: </b> This strategy is used when all members have subscribed + * to the same set of topics. + * </li> + * <li> + * <b> General Uniform Assignment Builder: </b> This strategy is used when members have varied topic + * subscriptions. + * </li> + * </ul> + * + * The appropriate strategy is automatically chosen based on the current members' topic subscriptions. + * + * @see OptimizedUniformAssignmentBuilder + * @see GeneralUniformAssignmentBuilder + */ +public class UniformAssignor implements PartitionAssignor { + private static final Logger log = LoggerFactory.getLogger(UniformAssignor.class); + public static final String UNIFORM_ASSIGNOR_NAME = "uniform"; + + @Override + public String name() { + return UNIFORM_ASSIGNOR_NAME; + } + + /** + * Perform the group assignment given the current members and + * topic metadata. + * + * @param assignmentSpec The member assignment spec. + * @param subscribedTopicDescriber The topic and cluster metadata describer {@link SubscribedTopicDescriber}. + * @return The new assignment for the group. + */ + @Override + public GroupAssignment assign( + AssignmentSpec assignmentSpec, + SubscribedTopicDescriber subscribedTopicDescriber + ) throws PartitionAssignorException { + AbstractAssignmentBuilder assignmentBuilder; + if (assignmentSpec.members().isEmpty()) + return new GroupAssignment(Collections.emptyMap()); + + if (allSubscriptionsEqual(assignmentSpec.members())) { + log.debug("Detected that all members are subscribed to the same set of topics, invoking the " + + "optimized assignment algorithm"); + assignmentBuilder = new OptimizedUniformAssignmentBuilder(assignmentSpec, subscribedTopicDescriber); + } else { + assignmentBuilder = new GeneralUniformAssignmentBuilder(); + log.debug("Detected that all members are subscribed to a different set of topics, invoking the " + + "general assignment algorithm"); + } + + return assignmentBuilder.buildAssignment(); + } + + /** + * Determines if all members are subscribed to the same list of topic IDs. + * + * @param members A map of member identifiers to their respective {@code AssignmentMemberSpec}. + * Assumes the map is non-empty. + * @return true if all members have the same subscription list of topic IDs, + * false otherwise. + */ + private boolean allSubscriptionsEqual(Map<String, AssignmentMemberSpec> members) { + Set<Uuid> firstSubscriptionSet = new HashSet<>(members.values().iterator().next().subscribedTopicIds()); + for (AssignmentMemberSpec memberSpec : members.values()) { + Set<Uuid> currentSubscriptionSet = new HashSet<>(memberSpec.subscribedTopicIds()); + if (!firstSubscriptionSet.equals(currentSubscriptionSet)) { + return false; + } + } + return true; + } + + /** + * The assignment builder is used to construct the final assignment in a series of steps that + * are determined by the type of subscriptions. + * + * There are common methods present that are used by any type of assignment strategy. + */ + protected static abstract class AbstractAssignmentBuilder { + protected abstract GroupAssignment buildAssignment(); + + /** + * Determines if rack-aware assignment is appropriate based on the provided rack information. + * + * @param memberRacks Racks where members are located. + * @param partitionRacks Racks where partitions are located. + * @param racksPerPartition Map of partitions to their associated racks. + * + * @return {@code true} if rack-aware assignment should be applied; {@code false} otherwise. + */ + protected boolean useRackAwareAssignment( + Set<String> memberRacks, + Set<String> partitionRacks, + Map<TopicIdPartition, Set<String>> racksPerPartition + ) { + if (memberRacks.isEmpty() || Collections.disjoint(memberRacks, partitionRacks)) + return false; + else { + return !racksPerPartition.values().stream().allMatch(partitionRacks::equals); + } + } + + /** + * Constructs a list of {@code TopicIdPartition} for each topic Id based on its partition count. + * + * @param allTopicIds The list of subscribed topic Ids. + * @param subscribedTopicDescriber Utility to fetch the partition count for a given topic. + * + * @return List of generated {@code TopicIdPartition} for all provided topic Ids. + */ + protected List<TopicIdPartition> allTopicIdPartitions( + List<Uuid> allTopicIds, + SubscribedTopicDescriber subscribedTopicDescriber + ) { + List<TopicIdPartition> allTopicIdPartitions = new ArrayList<>(); + allTopicIds.forEach(topic -> + IntStream.range(0, subscribedTopicDescriber.numPartitions((topic))) + .forEach(i -> allTopicIdPartitions.add(new TopicIdPartition(topic, i)) + ) + ); + + return allTopicIdPartitions; + } + + /** + * Represents the rack information of members and partitions along with utility methods + * to facilitate rack-aware assignment strategies for a given consumer group. + */ + protected class RackInfo { + /** + * Map of every member to its rack. + */ + protected final Map<String, String> memberRacks; + /** + * Map of every partition to a list of its racks. + */ + protected final Map<TopicIdPartition, Set<String>> partitionRacks; + /** + * Number of members with the same rack as the partition. + */ + private final Map<TopicIdPartition, Integer> numMembersWithSameRackByPartition; + protected final boolean useRackStrategy; + + /** + * Constructs rack information based on assignment specification and subscribed topics. + * + * @param assignmentSpec The current assignment specification. + * @param subscribedTopicDescriber Topic and partition metadata of the subscribed topics. + * @param topicIds List of topic Ids. + */ + public RackInfo( + AssignmentSpec assignmentSpec, + SubscribedTopicDescriber subscribedTopicDescriber, + Set<Uuid> topicIds + ) { + Map<String, List<String>> membersByRack = new HashMap<>(); + assignmentSpec.members().forEach((memberId, assignmentMemberSpec) -> + assignmentMemberSpec.rackId().filter(r -> !r.isEmpty()).ifPresent( + rackId -> membersByRack.computeIfAbsent(rackId, __ -> new ArrayList<>()).add(memberId) + ) + ); + + Set<String> allPartitionRacks; + Map<TopicIdPartition, Set<String>> partitionRacks; + List<TopicIdPartition> topicIdPartitions = allTopicIdPartitions(new ArrayList<>(topicIds), subscribedTopicDescriber); Review Comment: nit: Do we really need to create the ArrayList here? ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/UniformAssignor.java: ########## @@ -0,0 +1,288 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.apache.kafka.common.Uuid; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; +import java.util.stream.Collectors; +import java.util.stream.IntStream; + +/** + * The Uniform Assignor distributes Kafka topic partitions among group members for balanced assignment. + * The assignor employs two different strategies based on the nature of topic + * subscriptions across the group members: + * <ul> + * <li> + * <b> Optimized Uniform Assignment Builder: </b> This strategy is used when all members have subscribed + * to the same set of topics. + * </li> + * <li> + * <b> General Uniform Assignment Builder: </b> This strategy is used when members have varied topic + * subscriptions. + * </li> + * </ul> + * + * The appropriate strategy is automatically chosen based on the current members' topic subscriptions. + * + * @see OptimizedUniformAssignmentBuilder + * @see GeneralUniformAssignmentBuilder + */ +public class UniformAssignor implements PartitionAssignor { + private static final Logger log = LoggerFactory.getLogger(UniformAssignor.class); Review Comment: nit: `log` -> `LOG`. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/UniformAssignor.java: ########## @@ -0,0 +1,288 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.apache.kafka.common.Uuid; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; +import java.util.stream.Collectors; +import java.util.stream.IntStream; + +/** + * The Uniform Assignor distributes Kafka topic partitions among group members for balanced assignment. + * The assignor employs two different strategies based on the nature of topic + * subscriptions across the group members: + * <ul> + * <li> + * <b> Optimized Uniform Assignment Builder: </b> This strategy is used when all members have subscribed + * to the same set of topics. + * </li> + * <li> + * <b> General Uniform Assignment Builder: </b> This strategy is used when members have varied topic + * subscriptions. + * </li> + * </ul> + * + * The appropriate strategy is automatically chosen based on the current members' topic subscriptions. + * + * @see OptimizedUniformAssignmentBuilder + * @see GeneralUniformAssignmentBuilder + */ +public class UniformAssignor implements PartitionAssignor { + private static final Logger log = LoggerFactory.getLogger(UniformAssignor.class); + public static final String UNIFORM_ASSIGNOR_NAME = "uniform"; + + @Override + public String name() { + return UNIFORM_ASSIGNOR_NAME; + } + + /** + * Perform the group assignment given the current members and + * topic metadata. + * + * @param assignmentSpec The member assignment spec. + * @param subscribedTopicDescriber The topic and cluster metadata describer {@link SubscribedTopicDescriber}. + * @return The new assignment for the group. + */ + @Override + public GroupAssignment assign( + AssignmentSpec assignmentSpec, + SubscribedTopicDescriber subscribedTopicDescriber + ) throws PartitionAssignorException { + AbstractAssignmentBuilder assignmentBuilder; + if (assignmentSpec.members().isEmpty()) + return new GroupAssignment(Collections.emptyMap()); + + if (allSubscriptionsEqual(assignmentSpec.members())) { + log.debug("Detected that all members are subscribed to the same set of topics, invoking the " + + "optimized assignment algorithm"); + assignmentBuilder = new OptimizedUniformAssignmentBuilder(assignmentSpec, subscribedTopicDescriber); + } else { + assignmentBuilder = new GeneralUniformAssignmentBuilder(); + log.debug("Detected that all members are subscribed to a different set of topics, invoking the " + + "general assignment algorithm"); + } + + return assignmentBuilder.buildAssignment(); + } + + /** + * Determines if all members are subscribed to the same list of topic IDs. + * + * @param members A map of member identifiers to their respective {@code AssignmentMemberSpec}. + * Assumes the map is non-empty. + * @return true if all members have the same subscription list of topic IDs, + * false otherwise. + */ + private boolean allSubscriptionsEqual(Map<String, AssignmentMemberSpec> members) { + Set<Uuid> firstSubscriptionSet = new HashSet<>(members.values().iterator().next().subscribedTopicIds()); + for (AssignmentMemberSpec memberSpec : members.values()) { + Set<Uuid> currentSubscriptionSet = new HashSet<>(memberSpec.subscribedTopicIds()); + if (!firstSubscriptionSet.equals(currentSubscriptionSet)) { + return false; + } + } + return true; + } + + /** + * The assignment builder is used to construct the final assignment in a series of steps that + * are determined by the type of subscriptions. + * + * There are common methods present that are used by any type of assignment strategy. + */ + protected static abstract class AbstractAssignmentBuilder { + protected abstract GroupAssignment buildAssignment(); + + /** + * Determines if rack-aware assignment is appropriate based on the provided rack information. + * + * @param memberRacks Racks where members are located. + * @param partitionRacks Racks where partitions are located. + * @param racksPerPartition Map of partitions to their associated racks. + * + * @return {@code true} if rack-aware assignment should be applied; {@code false} otherwise. + */ + protected boolean useRackAwareAssignment( Review Comment: nit: Could this method be static? ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); + private final AssignmentSpec assignmentSpec; + private final SubscribedTopicDescriber subscribedTopicDescriber; + // List of topics subscribed to by all members. + private final Set<Uuid> subscriptionIds; + private final RackInfo rackInfo; + // Count of members to receive an extra partition beyond the minimum quota, + // to account for the distribution of the remaining partitions. + private int remainingMembersToGetAnExtraPartition; + // Map of members to the remaining number of partitions needed to meet the minimum quota, + // including members eligible for an extra partition. + private final Map<String, Integer> potentiallyUnfilledMembers; + // Members mapped to the remaining number of partitions needed to meet the full quota. + // Full quota = minQuota + one extra partition (if applicable). + private Map<String, Integer> unfilledMembers; + private List<TopicIdPartition> unassignedPartitions; + private final Map<String, MemberAssignment> newAssignment; + // Tracks the current owner of each partition when using rack-aware strategy. + // Current refers to the existing assignment. + private final Map<TopicIdPartition, String> currentPartitionOwners; + // Indicates if a rack aware assignment can be done. + // True if racks are defined for both members and partitions. + boolean useRackAwareStrategy; + + OptimizedUniformAssignmentBuilder(AssignmentSpec assignmentSpec, SubscribedTopicDescriber subscribedTopicDescriber) { + this.assignmentSpec = assignmentSpec; + this.subscribedTopicDescriber = subscribedTopicDescriber; + this.subscriptionIds = new HashSet<>(assignmentSpec.members().values().iterator().next().subscribedTopicIds()); + this.rackInfo = new RackInfo(assignmentSpec, subscribedTopicDescriber, subscriptionIds); + this.potentiallyUnfilledMembers = new HashMap<>(); + this.unfilledMembers = new HashMap<>(); + this.newAssignment = new HashMap<>(); + this.useRackAwareStrategy = rackInfo.useRackStrategy; + // Without rack-aware strategy, tracking current owners of unassigned partitions is unnecessary + // as all sticky partitions are retained until a member meets its quota. + this.currentPartitionOwners = useRackAwareStrategy ? new HashMap<>() : Collections.emptyMap(); + } + + /** + * Here's the step-by-step breakdown of the assignment process: + * + * <li> Compute the quotas of partitions for each member based on the total partitions and member count.</li> + * <li> For existing assignments, retain partitions based on the determined quota and member's rack compatibility.</li> + * <li> If a partition's rack mismatches with its owner, track it for future use.</li> + * <li> Identify members that haven't fulfilled their partition quota or are eligible to receive extra partitions.</li> + * <li> Derive the unassigned partitions by taking the difference between total partitions and the sticky assignments.</li> + * <li> Depending on members needing extra partitions, select members from the potentially unfilled list + * and add them to the unfilled list.</li> + * <li> Proceed with a round-robin assignment adhering to rack awareness. + * For each unassigned partition, locate the first compatible member from the unfilled list.</li> + * <li> If no rack-compatible member is found, revert to the tracked current owner. + * If that member can't accommodate the partition due to quota limits, resort to a generic round-robin assignment.</li> + * */ + @Override + protected GroupAssignment buildAssignment() throws PartitionAssignorException{ + int totalPartitionsCount = 0; + // Removes the current topic from subscriptionIds if the topic doesn't exist in the topic metadata. Review Comment: This comment is incorrect as the implementation fails if the topic does not exist. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); + private final AssignmentSpec assignmentSpec; + private final SubscribedTopicDescriber subscribedTopicDescriber; + // List of topics subscribed to by all members. + private final Set<Uuid> subscriptionIds; + private final RackInfo rackInfo; + // Count of members to receive an extra partition beyond the minimum quota, + // to account for the distribution of the remaining partitions. + private int remainingMembersToGetAnExtraPartition; + // Map of members to the remaining number of partitions needed to meet the minimum quota, + // including members eligible for an extra partition. + private final Map<String, Integer> potentiallyUnfilledMembers; + // Members mapped to the remaining number of partitions needed to meet the full quota. + // Full quota = minQuota + one extra partition (if applicable). + private Map<String, Integer> unfilledMembers; + private List<TopicIdPartition> unassignedPartitions; + private final Map<String, MemberAssignment> newAssignment; + // Tracks the current owner of each partition when using rack-aware strategy. + // Current refers to the existing assignment. + private final Map<TopicIdPartition, String> currentPartitionOwners; + // Indicates if a rack aware assignment can be done. + // True if racks are defined for both members and partitions. + boolean useRackAwareStrategy; + + OptimizedUniformAssignmentBuilder(AssignmentSpec assignmentSpec, SubscribedTopicDescriber subscribedTopicDescriber) { + this.assignmentSpec = assignmentSpec; + this.subscribedTopicDescriber = subscribedTopicDescriber; + this.subscriptionIds = new HashSet<>(assignmentSpec.members().values().iterator().next().subscribedTopicIds()); + this.rackInfo = new RackInfo(assignmentSpec, subscribedTopicDescriber, subscriptionIds); + this.potentiallyUnfilledMembers = new HashMap<>(); + this.unfilledMembers = new HashMap<>(); + this.newAssignment = new HashMap<>(); + this.useRackAwareStrategy = rackInfo.useRackStrategy; + // Without rack-aware strategy, tracking current owners of unassigned partitions is unnecessary + // as all sticky partitions are retained until a member meets its quota. + this.currentPartitionOwners = useRackAwareStrategy ? new HashMap<>() : Collections.emptyMap(); + } + + /** + * Here's the step-by-step breakdown of the assignment process: + * + * <li> Compute the quotas of partitions for each member based on the total partitions and member count.</li> + * <li> For existing assignments, retain partitions based on the determined quota and member's rack compatibility.</li> + * <li> If a partition's rack mismatches with its owner, track it for future use.</li> + * <li> Identify members that haven't fulfilled their partition quota or are eligible to receive extra partitions.</li> + * <li> Derive the unassigned partitions by taking the difference between total partitions and the sticky assignments.</li> + * <li> Depending on members needing extra partitions, select members from the potentially unfilled list + * and add them to the unfilled list.</li> + * <li> Proceed with a round-robin assignment adhering to rack awareness. + * For each unassigned partition, locate the first compatible member from the unfilled list.</li> + * <li> If no rack-compatible member is found, revert to the tracked current owner. + * If that member can't accommodate the partition due to quota limits, resort to a generic round-robin assignment.</li> + * */ Review Comment: nit: There is an space between the `*`. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/common/TopicIdPartition.java: ########## @@ -0,0 +1,74 @@ +/* Review Comment: We already have the very same class in the `metadata` module. I wonder if we should move that one to `server-common` module so that we could reuse it here. It could land in the `common` package over there. What do you think? ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/UniformAssignor.java: ########## @@ -0,0 +1,288 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.apache.kafka.common.Uuid; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; +import java.util.stream.Collectors; +import java.util.stream.IntStream; + +/** + * The Uniform Assignor distributes Kafka topic partitions among group members for balanced assignment. + * The assignor employs two different strategies based on the nature of topic + * subscriptions across the group members: + * <ul> + * <li> + * <b> Optimized Uniform Assignment Builder: </b> This strategy is used when all members have subscribed + * to the same set of topics. + * </li> + * <li> + * <b> General Uniform Assignment Builder: </b> This strategy is used when members have varied topic + * subscriptions. + * </li> + * </ul> + * + * The appropriate strategy is automatically chosen based on the current members' topic subscriptions. + * + * @see OptimizedUniformAssignmentBuilder + * @see GeneralUniformAssignmentBuilder + */ +public class UniformAssignor implements PartitionAssignor { + private static final Logger log = LoggerFactory.getLogger(UniformAssignor.class); + public static final String UNIFORM_ASSIGNOR_NAME = "uniform"; + + @Override + public String name() { + return UNIFORM_ASSIGNOR_NAME; + } + + /** + * Perform the group assignment given the current members and + * topic metadata. + * + * @param assignmentSpec The member assignment spec. + * @param subscribedTopicDescriber The topic and cluster metadata describer {@link SubscribedTopicDescriber}. + * @return The new assignment for the group. + */ + @Override + public GroupAssignment assign( + AssignmentSpec assignmentSpec, + SubscribedTopicDescriber subscribedTopicDescriber + ) throws PartitionAssignorException { + AbstractAssignmentBuilder assignmentBuilder; + if (assignmentSpec.members().isEmpty()) + return new GroupAssignment(Collections.emptyMap()); + + if (allSubscriptionsEqual(assignmentSpec.members())) { + log.debug("Detected that all members are subscribed to the same set of topics, invoking the " + + "optimized assignment algorithm"); + assignmentBuilder = new OptimizedUniformAssignmentBuilder(assignmentSpec, subscribedTopicDescriber); + } else { + assignmentBuilder = new GeneralUniformAssignmentBuilder(); + log.debug("Detected that all members are subscribed to a different set of topics, invoking the " + + "general assignment algorithm"); + } + + return assignmentBuilder.buildAssignment(); + } + + /** + * Determines if all members are subscribed to the same list of topic IDs. + * + * @param members A map of member identifiers to their respective {@code AssignmentMemberSpec}. + * Assumes the map is non-empty. + * @return true if all members have the same subscription list of topic IDs, + * false otherwise. + */ + private boolean allSubscriptionsEqual(Map<String, AssignmentMemberSpec> members) { + Set<Uuid> firstSubscriptionSet = new HashSet<>(members.values().iterator().next().subscribedTopicIds()); + for (AssignmentMemberSpec memberSpec : members.values()) { + Set<Uuid> currentSubscriptionSet = new HashSet<>(memberSpec.subscribedTopicIds()); + if (!firstSubscriptionSet.equals(currentSubscriptionSet)) { + return false; + } + } + return true; + } + + /** + * The assignment builder is used to construct the final assignment in a series of steps that + * are determined by the type of subscriptions. + * + * There are common methods present that are used by any type of assignment strategy. + */ + protected static abstract class AbstractAssignmentBuilder { Review Comment: Is there a reason to have this abstract class here? Personally, I find it a bit weird as the concrete classes are not defined in this class. How about extracting it? ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); + private final AssignmentSpec assignmentSpec; + private final SubscribedTopicDescriber subscribedTopicDescriber; + // List of topics subscribed to by all members. + private final Set<Uuid> subscriptionIds; + private final RackInfo rackInfo; + // Count of members to receive an extra partition beyond the minimum quota, + // to account for the distribution of the remaining partitions. + private int remainingMembersToGetAnExtraPartition; + // Map of members to the remaining number of partitions needed to meet the minimum quota, + // including members eligible for an extra partition. + private final Map<String, Integer> potentiallyUnfilledMembers; + // Members mapped to the remaining number of partitions needed to meet the full quota. + // Full quota = minQuota + one extra partition (if applicable). + private Map<String, Integer> unfilledMembers; + private List<TopicIdPartition> unassignedPartitions; + private final Map<String, MemberAssignment> newAssignment; + // Tracks the current owner of each partition when using rack-aware strategy. + // Current refers to the existing assignment. + private final Map<TopicIdPartition, String> currentPartitionOwners; + // Indicates if a rack aware assignment can be done. + // True if racks are defined for both members and partitions. + boolean useRackAwareStrategy; + + OptimizedUniformAssignmentBuilder(AssignmentSpec assignmentSpec, SubscribedTopicDescriber subscribedTopicDescriber) { + this.assignmentSpec = assignmentSpec; + this.subscribedTopicDescriber = subscribedTopicDescriber; + this.subscriptionIds = new HashSet<>(assignmentSpec.members().values().iterator().next().subscribedTopicIds()); + this.rackInfo = new RackInfo(assignmentSpec, subscribedTopicDescriber, subscriptionIds); + this.potentiallyUnfilledMembers = new HashMap<>(); + this.unfilledMembers = new HashMap<>(); + this.newAssignment = new HashMap<>(); + this.useRackAwareStrategy = rackInfo.useRackStrategy; + // Without rack-aware strategy, tracking current owners of unassigned partitions is unnecessary + // as all sticky partitions are retained until a member meets its quota. + this.currentPartitionOwners = useRackAwareStrategy ? new HashMap<>() : Collections.emptyMap(); + } + + /** + * Here's the step-by-step breakdown of the assignment process: + * + * <li> Compute the quotas of partitions for each member based on the total partitions and member count.</li> + * <li> For existing assignments, retain partitions based on the determined quota and member's rack compatibility.</li> + * <li> If a partition's rack mismatches with its owner, track it for future use.</li> + * <li> Identify members that haven't fulfilled their partition quota or are eligible to receive extra partitions.</li> + * <li> Derive the unassigned partitions by taking the difference between total partitions and the sticky assignments.</li> + * <li> Depending on members needing extra partitions, select members from the potentially unfilled list + * and add them to the unfilled list.</li> + * <li> Proceed with a round-robin assignment adhering to rack awareness. + * For each unassigned partition, locate the first compatible member from the unfilled list.</li> + * <li> If no rack-compatible member is found, revert to the tracked current owner. + * If that member can't accommodate the partition due to quota limits, resort to a generic round-robin assignment.</li> + * */ + @Override + protected GroupAssignment buildAssignment() throws PartitionAssignorException{ + int totalPartitionsCount = 0; + // Removes the current topic from subscriptionIds if the topic doesn't exist in the topic metadata. + for (Uuid topicId : subscriptionIds) { + int partitionCount = subscribedTopicDescriber.numPartitions(topicId); + if (partitionCount == -1) { + IllegalStateException illegalStateException = + new IllegalStateException("The topic " + topicId + " seems to be in an invalid state."); + + throw new PartitionAssignorException( + "Members are subscribed to topic " + topicId + " which doesn't exist in the topic metadata.", + illegalStateException + ); + } else { + totalPartitionsCount += partitionCount; + } + } + + if (subscriptionIds.isEmpty()) { + log.info("The subscription list is empty, returning an empty assignment"); + return new GroupAssignment(Collections.emptyMap()); + } + + // The minimum required quota that each member needs to meet for a balanced assignment. + // This is the same for all members. + int numberOfMembers = assignmentSpec.members().size(); + final int minQuota = totalPartitionsCount / numberOfMembers; + remainingMembersToGetAnExtraPartition = totalPartitionsCount % numberOfMembers; + + assignmentSpec.members().keySet().forEach(memberId -> + newAssignment.put(memberId, new MemberAssignment(new HashMap<>()) + )); + + Set<TopicIdPartition> allAssignedStickyPartitions = computeAssignedStickyPartitions(minQuota); + unassignedPartitions = computeUnassignedPartitions(allAssignedStickyPartitions); + unfilledMembers = computeUnfilledMembers(); + + if (!unassignedPartitionsCountEqualsRemainingAssignmentsCount()) { + throw new PartitionAssignorException("Number of available partitions is not equal to the total requirement"); + } + + if (useRackAwareStrategy) rackAwareRoundRobinAssignment(); + unassignedPartitionsRoundRobinAssignment(); + + return new GroupAssignment(newAssignment); + } + + /** + * Retrieves a set of partitions that were currently assigned to members and will be retained in the new assignment, + * by ensuring that the partitions are still relevant based on current topic metadata and subscriptions. + * If rack awareness is enabled, it ensures that a partition's rack matches the member's rack. + * + * <p> For each member, it: + * <ul> + * <li> Finds the valid current assignment considering topic subscriptions and metadata.</li> + * <li> If current assignments exist, retains up to the minimum quota of assignments.</li> + * <li> If there are members that should get an extra partition, + * assigns the next partition after the retained ones.</li> + * <li> For members with assignments not exceeding the minimum quota, + * it identifies them as potentially unfilled members and tracks the remaining quota.</li> + * </ul> + * + * @return A set containing all the sticky partitions that have been retained in the new assignment. + */ + private Set<TopicIdPartition> computeAssignedStickyPartitions(Integer minQuota) { Review Comment: nit: We should use `int` here. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignmentBuilder.java: ########## @@ -0,0 +1,393 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.stream.IntStream; + +import static java.lang.Math.min; + +/** + * Assigns partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * The order of priority of properties during the assignment will be: + * balance > rack matching (when applicable) > stickiness. + */ +public class OptimizedUniformAssignmentBuilder extends UniformAssignor.AbstractAssignmentBuilder { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignmentBuilder.class); + private final AssignmentSpec assignmentSpec; + private final SubscribedTopicDescriber subscribedTopicDescriber; + // List of topics subscribed to by all members. + private final Set<Uuid> subscriptionIds; + private final RackInfo rackInfo; + // Count of members to receive an extra partition beyond the minimum quota, + // to account for the distribution of the remaining partitions. + private int remainingMembersToGetAnExtraPartition; + // Map of members to the remaining number of partitions needed to meet the minimum quota, + // including members eligible for an extra partition. + private final Map<String, Integer> potentiallyUnfilledMembers; + // Members mapped to the remaining number of partitions needed to meet the full quota. + // Full quota = minQuota + one extra partition (if applicable). + private Map<String, Integer> unfilledMembers; + private List<TopicIdPartition> unassignedPartitions; + private final Map<String, MemberAssignment> newAssignment; + // Tracks the current owner of each partition when using rack-aware strategy. + // Current refers to the existing assignment. + private final Map<TopicIdPartition, String> currentPartitionOwners; + // Indicates if a rack aware assignment can be done. + // True if racks are defined for both members and partitions. + boolean useRackAwareStrategy; + + OptimizedUniformAssignmentBuilder(AssignmentSpec assignmentSpec, SubscribedTopicDescriber subscribedTopicDescriber) { + this.assignmentSpec = assignmentSpec; + this.subscribedTopicDescriber = subscribedTopicDescriber; + this.subscriptionIds = new HashSet<>(assignmentSpec.members().values().iterator().next().subscribedTopicIds()); + this.rackInfo = new RackInfo(assignmentSpec, subscribedTopicDescriber, subscriptionIds); + this.potentiallyUnfilledMembers = new HashMap<>(); + this.unfilledMembers = new HashMap<>(); + this.newAssignment = new HashMap<>(); + this.useRackAwareStrategy = rackInfo.useRackStrategy; + // Without rack-aware strategy, tracking current owners of unassigned partitions is unnecessary + // as all sticky partitions are retained until a member meets its quota. + this.currentPartitionOwners = useRackAwareStrategy ? new HashMap<>() : Collections.emptyMap(); + } + + /** + * Here's the step-by-step breakdown of the assignment process: + * + * <li> Compute the quotas of partitions for each member based on the total partitions and member count.</li> + * <li> For existing assignments, retain partitions based on the determined quota and member's rack compatibility.</li> + * <li> If a partition's rack mismatches with its owner, track it for future use.</li> + * <li> Identify members that haven't fulfilled their partition quota or are eligible to receive extra partitions.</li> + * <li> Derive the unassigned partitions by taking the difference between total partitions and the sticky assignments.</li> + * <li> Depending on members needing extra partitions, select members from the potentially unfilled list + * and add them to the unfilled list.</li> + * <li> Proceed with a round-robin assignment adhering to rack awareness. + * For each unassigned partition, locate the first compatible member from the unfilled list.</li> + * <li> If no rack-compatible member is found, revert to the tracked current owner. + * If that member can't accommodate the partition due to quota limits, resort to a generic round-robin assignment.</li> + * */ + @Override + protected GroupAssignment buildAssignment() throws PartitionAssignorException{ + int totalPartitionsCount = 0; + // Removes the current topic from subscriptionIds if the topic doesn't exist in the topic metadata. + for (Uuid topicId : subscriptionIds) { + int partitionCount = subscribedTopicDescriber.numPartitions(topicId); + if (partitionCount == -1) { + IllegalStateException illegalStateException = + new IllegalStateException("The topic " + topicId + " seems to be in an invalid state."); + + throw new PartitionAssignorException( + "Members are subscribed to topic " + topicId + " which doesn't exist in the topic metadata.", + illegalStateException + ); + } else { + totalPartitionsCount += partitionCount; + } + } + + if (subscriptionIds.isEmpty()) { + log.info("The subscription list is empty, returning an empty assignment"); + return new GroupAssignment(Collections.emptyMap()); + } + + // The minimum required quota that each member needs to meet for a balanced assignment. + // This is the same for all members. + int numberOfMembers = assignmentSpec.members().size(); + final int minQuota = totalPartitionsCount / numberOfMembers; + remainingMembersToGetAnExtraPartition = totalPartitionsCount % numberOfMembers; + + assignmentSpec.members().keySet().forEach(memberId -> + newAssignment.put(memberId, new MemberAssignment(new HashMap<>()) + )); + + Set<TopicIdPartition> allAssignedStickyPartitions = computeAssignedStickyPartitions(minQuota); + unassignedPartitions = computeUnassignedPartitions(allAssignedStickyPartitions); + unfilledMembers = computeUnfilledMembers(); + + if (!unassignedPartitionsCountEqualsRemainingAssignmentsCount()) { + throw new PartitionAssignorException("Number of available partitions is not equal to the total requirement"); + } + + if (useRackAwareStrategy) rackAwareRoundRobinAssignment(); + unassignedPartitionsRoundRobinAssignment(); + + return new GroupAssignment(newAssignment); + } + + /** + * Retrieves a set of partitions that were currently assigned to members and will be retained in the new assignment, + * by ensuring that the partitions are still relevant based on current topic metadata and subscriptions. + * If rack awareness is enabled, it ensures that a partition's rack matches the member's rack. + * + * <p> For each member, it: + * <ul> + * <li> Finds the valid current assignment considering topic subscriptions and metadata.</li> + * <li> If current assignments exist, retains up to the minimum quota of assignments.</li> + * <li> If there are members that should get an extra partition, + * assigns the next partition after the retained ones.</li> + * <li> For members with assignments not exceeding the minimum quota, + * it identifies them as potentially unfilled members and tracks the remaining quota.</li> + * </ul> + * + * @return A set containing all the sticky partitions that have been retained in the new assignment. + */ + private Set<TopicIdPartition> computeAssignedStickyPartitions(Integer minQuota) { + Set<TopicIdPartition> allAssignedStickyPartitions = new HashSet<>(); + + assignmentSpec.members().forEach((memberId, assignmentMemberSpec) -> { + // Remove all the topics that aren't in the subscriptions or the topic metadata anymore. + // If rack awareness is enabled, only add partitions if the members rack matches the partitions rack. + List<TopicIdPartition> validCurrentAssignment = validCurrentAssignment( + memberId, + assignmentMemberSpec.assignedPartitions() + ); + + int currentAssignmentSize = validCurrentAssignment.size(); + int remaining = minQuota - currentAssignmentSize; + + if (currentAssignmentSize > 0) { + int retainedPartitionsCount = min(currentAssignmentSize, minQuota); + IntStream.range(0, retainedPartitionsCount).forEach(i -> { + newAssignment.get(memberId) + .targetPartitions() + .computeIfAbsent(validCurrentAssignment.get(i).topicId(), __ -> new HashSet<>()) + .add(validCurrentAssignment.get(i).partition()); + allAssignedStickyPartitions.add(validCurrentAssignment.get(i)); + }); + + // The extra partition is located at the last index from the previous step. + if (remaining < 0 && remainingMembersToGetAnExtraPartition > 0) { + newAssignment.get(memberId) + .targetPartitions() + .computeIfAbsent(validCurrentAssignment.get(retainedPartitionsCount).topicId(), __ -> new HashSet<>()) + .add(validCurrentAssignment.get(retainedPartitionsCount).partition()); Review Comment: nit: This code is duplicated. Should we have an helper method for it? ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/RangeAssignor.java: ########## @@ -49,6 +51,8 @@ * </ol> */ public class RangeAssignor implements PartitionAssignor { + private static final Logger log = LoggerFactory.getLogger(RangeAssignor.class); Review Comment: nit: `log` -> `LOG`. ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/UniformAssignor.java: ########## @@ -0,0 +1,288 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.coordinator.group.common.TopicIdPartition; +import org.apache.kafka.common.Uuid; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; +import java.util.stream.Collectors; +import java.util.stream.IntStream; + +/** + * The Uniform Assignor distributes Kafka topic partitions among group members for balanced assignment. + * The assignor employs two different strategies based on the nature of topic + * subscriptions across the group members: + * <ul> + * <li> + * <b> Optimized Uniform Assignment Builder: </b> This strategy is used when all members have subscribed + * to the same set of topics. + * </li> + * <li> + * <b> General Uniform Assignment Builder: </b> This strategy is used when members have varied topic + * subscriptions. + * </li> + * </ul> + * + * The appropriate strategy is automatically chosen based on the current members' topic subscriptions. + * + * @see OptimizedUniformAssignmentBuilder + * @see GeneralUniformAssignmentBuilder + */ +public class UniformAssignor implements PartitionAssignor { + private static final Logger log = LoggerFactory.getLogger(UniformAssignor.class); + public static final String UNIFORM_ASSIGNOR_NAME = "uniform"; + + @Override + public String name() { + return UNIFORM_ASSIGNOR_NAME; + } + + /** + * Perform the group assignment given the current members and + * topic metadata. + * + * @param assignmentSpec The member assignment spec. + * @param subscribedTopicDescriber The topic and cluster metadata describer {@link SubscribedTopicDescriber}. + * @return The new assignment for the group. + */ + @Override + public GroupAssignment assign( + AssignmentSpec assignmentSpec, + SubscribedTopicDescriber subscribedTopicDescriber + ) throws PartitionAssignorException { + AbstractAssignmentBuilder assignmentBuilder; + if (assignmentSpec.members().isEmpty()) + return new GroupAssignment(Collections.emptyMap()); + + if (allSubscriptionsEqual(assignmentSpec.members())) { + log.debug("Detected that all members are subscribed to the same set of topics, invoking the " + + "optimized assignment algorithm"); + assignmentBuilder = new OptimizedUniformAssignmentBuilder(assignmentSpec, subscribedTopicDescriber); + } else { + assignmentBuilder = new GeneralUniformAssignmentBuilder(); + log.debug("Detected that all members are subscribed to a different set of topics, invoking the " + + "general assignment algorithm"); + } + + return assignmentBuilder.buildAssignment(); + } + + /** + * Determines if all members are subscribed to the same list of topic IDs. + * + * @param members A map of member identifiers to their respective {@code AssignmentMemberSpec}. + * Assumes the map is non-empty. + * @return true if all members have the same subscription list of topic IDs, + * false otherwise. + */ + private boolean allSubscriptionsEqual(Map<String, AssignmentMemberSpec> members) { + Set<Uuid> firstSubscriptionSet = new HashSet<>(members.values().iterator().next().subscribedTopicIds()); + for (AssignmentMemberSpec memberSpec : members.values()) { + Set<Uuid> currentSubscriptionSet = new HashSet<>(memberSpec.subscribedTopicIds()); + if (!firstSubscriptionSet.equals(currentSubscriptionSet)) { + return false; + } + } + return true; + } + + /** + * The assignment builder is used to construct the final assignment in a series of steps that + * are determined by the type of subscriptions. + * + * There are common methods present that are used by any type of assignment strategy. + */ + protected static abstract class AbstractAssignmentBuilder { + protected abstract GroupAssignment buildAssignment(); + + /** + * Determines if rack-aware assignment is appropriate based on the provided rack information. + * + * @param memberRacks Racks where members are located. + * @param partitionRacks Racks where partitions are located. + * @param racksPerPartition Map of partitions to their associated racks. + * + * @return {@code true} if rack-aware assignment should be applied; {@code false} otherwise. + */ + protected boolean useRackAwareAssignment( + Set<String> memberRacks, + Set<String> partitionRacks, + Map<TopicIdPartition, Set<String>> racksPerPartition + ) { + if (memberRacks.isEmpty() || Collections.disjoint(memberRacks, partitionRacks)) + return false; + else { + return !racksPerPartition.values().stream().allMatch(partitionRacks::equals); + } + } + + /** + * Constructs a list of {@code TopicIdPartition} for each topic Id based on its partition count. + * + * @param allTopicIds The list of subscribed topic Ids. + * @param subscribedTopicDescriber Utility to fetch the partition count for a given topic. + * + * @return List of generated {@code TopicIdPartition} for all provided topic Ids. + */ + protected List<TopicIdPartition> allTopicIdPartitions( Review Comment: ditto. -- This is an automated message from the Apache Git Service. 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