rreddy-22 commented on code in PR #14182: URL: https://github.com/apache/kafka/pull/14182#discussion_r1290765488
########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/OptimizedUniformAssignor.java: ########## @@ -0,0 +1,396 @@ +/* + * 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.Iterator; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.Queue; +import java.util.Set; + +import static java.lang.Math.min; + +/** + * Assigns Kafka partitions to members of a consumer group ensuring a balanced distribution with + * considerations for sticky assignments and rack-awareness. + * + * <p> Here's the step-by-step breakdown of the assignment process: + * + * <ul> + * <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> If a partition's rack mismatches with its member, track it with its prior owner.</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 previous owner. + * If that member can't accommodate the partition due to quota limits, resort to a generic round-robin assignment.</li> + * </ul> + */ +public class OptimizedUniformAssignor extends UniformAssignor { + private static final Logger log = LoggerFactory.getLogger(OptimizedUniformAssignor.class); + // List of topics subscribed to by all members. + private final List<Uuid> subscriptionList; + private final AssignmentSpec assignmentSpec; + private final SubscribedTopicDescriber subscribedTopicDescriber; + private final RackInfo rackInfo; + // The minimum required quota that each member needs to meet for a balanced assignment. + // This is the same for all members. + private final int minQuota; + // Count of members expected to receive an extra partition beyond the minimum quota, + // to account for the distribution of the remaining partitions. + private int expectedNumMembersWithExtraPartition; + // Map of members to their remaining partitions needed to meet the minimum quota, + // including members eligible for an extra partition. + private final Map<String, Integer> potentiallyUnfilledMembers; + // Members mapped to the number of partitions they still need to meet the full quota. + // Full quota = minQuota + one extra partition (if applicable). + private Map<String, Integer> unfilledMembers; + // Partitions that still need to be assigned. + private List<TopicIdPartition> unassignedPartitions; + private final Map<String, MemberAssignment> newAssignment; + // Tracks the previous owner of each partition when using rack-aware strategy. + private final Map<TopicIdPartition, String> partitionToPrevOwner; + // Indicates if a rack aware assignment can be done. + // True if racks are defined for both members and partitions. + boolean useRackAwareStrategy; + + OptimizedUniformAssignor(AssignmentSpec assignmentSpec, SubscribedTopicDescriber subscribedTopicDescriber) { + this.subscribedTopicDescriber = subscribedTopicDescriber; + this.assignmentSpec = assignmentSpec; + + subscriptionList = new ArrayList<>(assignmentSpec.members().values().iterator().next().subscribedTopicIds()); + + int totalPartitionsCount = 0; + // Removes the current topic from subscriptionList if the topic doesn't exist in the topic metadata. + Iterator<Uuid> iterator = subscriptionList.iterator(); + while (iterator.hasNext()) { + Uuid topicId = iterator.next(); + int partitionCount = subscribedTopicDescriber.numPartitions(topicId); + if (partitionCount == -1) { + log.warn("Members are subscribed to topic " + topicId + " which doesn't exist in the topic metadata."); + iterator.remove(); + } else { + totalPartitionsCount += partitionCount; + } + } + + RackInfo rackInfo = new RackInfo(assignmentSpec, subscribedTopicDescriber, subscriptionList); + this.rackInfo = rackInfo; + + // Without rack-aware strategy, tracking previous owners of unassigned partitions is unnecessary + // as all sticky partitions are retained until a member meets its quota. + if (rackInfo.memberRacks.isEmpty() || rackInfo.partitionRacks.isEmpty()) { + this.useRackAwareStrategy = false; + partitionToPrevOwner = Collections.emptyMap(); + } else { + this.useRackAwareStrategy = true; + partitionToPrevOwner = new HashMap<>(); + } + + int numberOfMembers = assignmentSpec.members().size(); + minQuota = (int) Math.floor(((double) totalPartitionsCount) / numberOfMembers); + expectedNumMembersWithExtraPartition = totalPartitionsCount % numberOfMembers; + + potentiallyUnfilledMembers = new HashMap<>(); + unfilledMembers = new HashMap<>(); + newAssignment = new HashMap<>(); Review Comment: Any computations required to initialise the global attributes are done in this constructor, similar to the other existing assignors -- This is an automated message from the Apache Git Service. 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