rreddy-22 commented on code in PR #13443: URL: https://github.com/apache/kafka/pull/13443#discussion_r1152313744
########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/ServerSideStickyRangeAssignor.java: ########## @@ -0,0 +1,268 @@ +/* + * 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. + */ + +/** + * <p>The Server Side Sticky Range Assignor inherits properties of both the range assignor and the sticky assignor. + * Properties are :- + * <ul> + * <li> 1) Each consumer must get at least one partition per topic that it is subscribed to whenever the number of consumers is + * less than or equal to the number of partitions for that topic. (Range) </li> + * <li> 2) Partitions should be assigned to consumers in a way that facilitates join operations where required. (Range) </li> + * This can only be done if the topics are co-partitioned in the first place + * Co-partitioned:- + * Two streams are co-partitioned if the following conditions are met:- + * ->The keys must have the same schemas + * ->The topics involved must have the same number of partitions + * <li> 3) Consumers should retain as much as their previous assignment as possible. (Sticky) </li> + * </ul> + * </p> + * + * <p>The algorithm works mainly in 5 steps described below + * <ul> + * <li> 1) Get a map of the consumersPerTopic created using the member subscriptions.</li> + * <li> 2) Get a list of consumers (potentiallyUnfilled) that have not met the minimum required quota for assignment AND + * get a list of sticky partitions that we want to retain in the new assignment.</li> + * <li> 3) Add consumers from potentiallyUnfilled to Unfilled if they haven't met the total required quota = minQuota + (if necessary) extraPartition </li> + * <li> 4) Get a list of available partitions by calculating the difference between total partitions and assigned sticky partitions </li> + * <li> 5) Iterate through unfilled consumers and assign partitions from available partitions </li> + * </ul> + * </p> + * + */ +package org.apache.kafka.coordinator.group.assignor; + + +import org.apache.kafka.common.Uuid; + +import java.util.List; +import java.util.Map; +import java.util.Set; +import java.util.ArrayList; +import java.util.HashSet; +import java.util.HashMap; +import java.util.Collections; + +import static java.lang.Math.min; + +public class ServerSideStickyRangeAssignor implements PartitionAssignor { + + public static final String RANGE_ASSIGNOR_NAME = "range-sticky"; + + @Override + public String name() { + return RANGE_ASSIGNOR_NAME; + } + + protected static <K, V> void putList(Map<K, List<V>> map, K key, V value) { + List<V> list = map.computeIfAbsent(key, k -> new ArrayList<>()); + list.add(value); + } + + protected static <K, V> void putSet(Map<K, Set<V>> map, K key, V value) { + Set<V> set = map.computeIfAbsent(key, k -> new HashSet<>()); + set.add(value); + } + + static class Pair<T, U> { + private final T first; + private final U second; + + public Pair(T first, U second) { + this.first = first; + this.second = second; + } + + public T getFirst() { + return first; + } + + public U getSecond() { + return second; + } + + @Override + public String toString() { + return "(" + first + ", " + second + ")"; + } + } + + // Returns a map of the list of consumers per Topic (keyed by topicId) + private Map<Uuid, List<String>> consumersPerTopic(AssignmentSpec assignmentSpec) { + Map<Uuid, List<String>> mapTopicsToConsumers = new HashMap<>(); + Map<String, AssignmentMemberSpec> membersData = assignmentSpec.members; + + for (Map.Entry<String, AssignmentMemberSpec> memberEntry : membersData.entrySet()) { + String memberId = memberEntry.getKey(); + AssignmentMemberSpec memberMetadata = memberEntry.getValue(); + List<Uuid> topics = new ArrayList<>(memberMetadata.subscribedTopics); + for (Uuid topicId: topics) { + putList(mapTopicsToConsumers, topicId, memberId); + } + } + return mapTopicsToConsumers; + } + + private Map<Uuid, List<Integer>> getAvailablePartitionsPerTopic(AssignmentSpec assignmentSpec, Map<Uuid, Set<Integer>> assignedStickyPartitionsPerTopic) { + Map<Uuid, List<Integer>> availablePartitionsPerTopic = new HashMap<>(); + Map<Uuid, AssignmentTopicMetadata> topicsMetadata = assignmentSpec.topics; + // Iterate through the topics map provided in assignmentSpec + for (Map.Entry<Uuid, AssignmentTopicMetadata> topicMetadataEntry : topicsMetadata.entrySet()) { + Uuid topicId = topicMetadataEntry.getKey(); + availablePartitionsPerTopic.put(topicId, new ArrayList<>()); + int numPartitions = topicsMetadata.get(topicId).numPartitions; + // since the loop iterates from 0 to n, the partitions will be in ascending order within the list of available partitions per topic + Set<Integer> assignedStickyPartitionsForTopic = assignedStickyPartitionsPerTopic.get(topicId); + for (int i = 0; i < numPartitions; i++) { + if (assignedStickyPartitionsForTopic == null || !assignedStickyPartitionsForTopic.contains(i)) { + availablePartitionsPerTopic.get(topicId).add(i); + } + } + } + return availablePartitionsPerTopic; + } + + @Override + public GroupAssignment assign(AssignmentSpec assignmentSpec) throws PartitionAssignorException { + Map<String, Map<Uuid, Set<Integer>>> membersWithNewAssignmentPerTopic = new HashMap<>(); + // Step 1 + Map<Uuid, List<String>> consumersPerTopic = consumersPerTopic(assignmentSpec); + // Step 2 + Map<Uuid, List<Pair<String, Integer>>> unfilledConsumersPerTopic = new HashMap<>(); + Map<Uuid, Set<Integer>> assignedStickyPartitionsPerTopic = new HashMap<>(); + + for (Map.Entry<Uuid, List<String>> topicEntry : consumersPerTopic.entrySet()) { + Uuid topicId = topicEntry.getKey(); + // For each topic we have a temporary list of consumers stored in potentiallyUnfilledConsumers. + // The list is populated with consumers that satisfy one of the two conditions :- + // 1) Consumers that have the minimum required number of partitions .i.e numPartitionsPerConsumer BUT they could be assigned an extra partition later on. + // In this case we add the consumer to the unfilled consumers map iff an extra partition needs to be assigned to it. + // 2) Consumers that don't have the minimum required partitions, so irrespective of whether they get an extra partition or not they get added to the unfilled map later. + List<Pair<String, Integer>> potentiallyUnfilledConsumers = new ArrayList<>(); + List<String> consumersForTopic = topicEntry.getValue(); + + AssignmentTopicMetadata topicData = assignmentSpec.topics.get(topicId); + int numPartitionsForTopic = topicData.numPartitions; + int numPartitionsPerConsumer = numPartitionsForTopic / consumersForTopic.size(); + // Each consumer can get only one extra partition per topic after receiving the minimum quota = numPartitionsPerConsumer + int numConsumersWithExtraPartition = numPartitionsForTopic % consumersForTopic.size(); + + for (String memberId: consumersForTopic) { + // Size of the older assignment, this will be 0 when assign is called for the first time. + // The older assignment is required when a reassignment occurs to ensure stickiness. + int currentAssignmentSize = 0; + List<Integer> currentAssignmentListForTopic = new ArrayList<>(); + // Convert the set to a list first and sort the partitions in numeric order since we want the same partition numbers from each topic + // to go to the same consumer in case of co-partitioned topics. + Set<Integer> currentAssignmentSetForTopic = assignmentSpec.members.get(memberId).currentAssignmentPerTopic.get(topicId); + // We want to make sure that the currentAssignment is not null to avoid a null pointer exception + if (currentAssignmentSetForTopic != null) { + currentAssignmentListForTopic = new ArrayList<>(currentAssignmentSetForTopic); Review Comment: We need the order of the partitions to be guaranteed and sorted when we're retaining the prev assignment, that's why we had to convert it to a list first. -- This is an automated message from the Apache Git Service. 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