rreddy-22 commented on code in PR #14182: URL: https://github.com/apache/kafka/pull/14182#discussion_r1316793219
########## 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: I believe it's easier to understand since allTopicIdPartitions is a method that returns this list which is used later on no? -- This is an automated message from the Apache Git Service. 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