rreddy-22 commented on code in PR #13443: URL: https://github.com/apache/kafka/pull/13443#discussion_r1189235728
########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/RangeAssignor.java: ########## @@ -0,0 +1,228 @@ +/* + * 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.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collection; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; + +import static java.lang.Math.min; + +/** + * This Range Assignor inherits properties of both the range assignor and the sticky assignor. + * The properties are as follows: + * <ol> + * <li> Each member must get at least one partition from every topic that it is subscribed to. The only exception is when + * the number of subscribed members is greater than the number of partitions for that topic. (Range) </li> + * <li> Partitions should be assigned to members in a way that facilitates the join operation when required. (Range) + * This can only be done if every member is subscribed to the same topics and the topics are co-partitioned. + * Two streams are co-partitioned if the following conditions are met: + * <ul> + * <li> The keys must have the same schemas. </li> + * <li> The topics involved must have the same number of partitions. </li> + * </ul> + * </li> + * <li> Members should retain as much of their previous assignment as possible to reduce the number of partition movements during reassignment. (Sticky) </li> + * </ol> + */ +public class RangeAssignor implements PartitionAssignor { + private static final Logger log = LoggerFactory.getLogger(RangeAssignor.class); + + public static final String RANGE_ASSIGNOR_NAME = "range"; + + @Override + public String name() { + return RANGE_ASSIGNOR_NAME; + } + + /** + * Pair of memberId and remaining partitions to meet the quota. + */ + private static class MemberWithRemainingAssignments { + /** + * Member Id. + */ + private final String memberId; + /** + * Number of partitions required to meet the assignment quota. + */ + private final Integer remaining; + + public MemberWithRemainingAssignments(String memberId, Integer remaining) { + this.memberId = memberId; + this.remaining = remaining; + } + } + + /** + * @return Map of topicIds to a list of members subscribed to them. + */ + private Map<Uuid, List<String>> membersPerTopic(final AssignmentSpec assignmentSpec) { + Map<Uuid, List<String>> membersPerTopic = new HashMap<>(); + Map<String, AssignmentMemberSpec> membersData = assignmentSpec.members(); + + membersData.forEach((memberId, memberMetadata) -> { + Collection<Uuid> topics = memberMetadata.subscribedTopicIds(); + for (Uuid topicId: topics) { + // Only topics that are present in both the subscribed topics list and the topic metadata should be considered for assignment. + if (assignmentSpec.topics().containsKey(topicId)) { + membersPerTopic + .computeIfAbsent(topicId, k -> new ArrayList<>()) + .add(memberId); + } else { + log.warn("Member " + memberId + " subscribed to topic " + topicId + " which doesn't exist in the topic metadata"); + } + } + }); + + return membersPerTopic; + } + + /** + * <p> The algorithm includes the following steps: + * <ol> + * <li> Generate a map of members per topic using the given member subscriptions.</li> + * <li> Generate a list of members called potentially unfilled members, which consists of members that have not met the minimum required quota of partitions for the assignment AND + * get a list called assigned sticky partitions per topic, which has the partitions that will be retained in the new assignment.</li> + * <li> Generate a list of unassigned partitions by calculating the difference between the total partitions for the topic and the assigned (sticky) partitions. </li> + * <li> Find members from the potentially unfilled members list that haven't met the total required quota + * i.e. minRequiredQuota + 1, if the member is designated to receive one of the excess partitions OR minRequiredQuota otherwise. </li> + * <li> Assign partitions to them in ranges from the unassigned partitions per topic + * based on the remaining partitions value. </li> + * </ol> + * </p> + */ + @Override + public GroupAssignment assign(final AssignmentSpec assignmentSpec) throws PartitionAssignorException { + Map<String, MemberAssignment> newAssignment = new HashMap<>(); + + // Step 1 + Map<Uuid, List<String>> membersPerTopic = membersPerTopic(assignmentSpec); + + membersPerTopic.forEach((topicId, membersForTopic) -> { + + AssignmentTopicMetadata topicData = assignmentSpec.topics().get(topicId); + int numPartitionsForTopic = topicData.numPartitions(); + int minRequiredQuota = numPartitionsForTopic / membersForTopic.size(); + // Each member can get only ONE extra partition per topic after receiving the minimum quota. + int numMembersWithExtraPartition = numPartitionsForTopic % membersForTopic.size(); + + // Idle members case : When the number of members subscribed to a topic is greater than the total number of partitions, + // all members get assigned via the "extra partitions" logic since minRequiredQuota = 0. + + // Step 2 + Set<Integer> assignedStickyPartitionsForTopic = new HashSet<>(); + List<MemberWithRemainingAssignments> potentiallyUnfilledMembers = new ArrayList<>(); + + for (String memberId : membersForTopic) { + Set<Integer> assignedPartitionsForTopic = assignmentSpec.members().get(memberId) + .assignedPartitions().getOrDefault(topicId, Collections.emptySet()); + + int currentAssignmentSize = assignedPartitionsForTopic.size(); + List<Integer> currentAssignmentListForTopic = new ArrayList<>(assignedPartitionsForTopic); + + // If there were partitions from this topic that were previously assigned to this member present, retain as much as possible. + // We need to retain: + // 1) currentSize number of partitions (when currentSize < required) OR Review Comment: okay I wont use variable names again -- This is an automated message from the Apache Git Service. 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