aliehsaeedii commented on code in PR #18652: URL: https://github.com/apache/kafka/pull/18652#discussion_r1930298932
########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/assignor/StickyTaskAssignor.java: ########## @@ -0,0 +1,401 @@ +/* + * 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.streams.assignor; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.Comparator; +import java.util.HashMap; +import java.util.HashSet; +import java.util.Iterator; +import java.util.Map; +import java.util.Objects; +import java.util.Optional; +import java.util.Set; +import java.util.stream.Collectors; + +public class StickyTaskAssignor implements TaskAssignor { + + public static final String STICKY_ASSIGNOR_NAME = "sticky"; + private static final Logger log = LoggerFactory.getLogger(StickyTaskAssignor.class); + // helper data structures: + private TaskPairs taskPairs; + Map<TaskId, Member> activeTaskToPrevMember; + Map<TaskId, Set<Member>> standbyTaskToPrevMember; + Map<String, ProcessState> processIdToState; + int allTasks; + int totalCapacity; + int tasksPerMember; + + @Override + public String name() { + return STICKY_ASSIGNOR_NAME; + } + + @Override + public GroupAssignment assign(final GroupSpec groupSpec, final TopologyDescriber topologyDescriber) throws TaskAssignorException { + initialize(groupSpec, topologyDescriber); + //active + Set<TaskId> activeTasks = toTaskIds(groupSpec, topologyDescriber, true); + assignActive(activeTasks); + //standby + final int numStandbyReplicas = + groupSpec.assignmentConfigs().isEmpty() ? 0 + : Integer.parseInt(groupSpec.assignmentConfigs().get("numStandbyReplicas")); + if (numStandbyReplicas > 0) { + Set<TaskId> statefulTasks = toTaskIds(groupSpec, topologyDescriber, false); + assignStandby(statefulTasks, numStandbyReplicas); + } + return buildGroupAssignment(groupSpec.members().keySet()); + } + + private Set<TaskId> toTaskIds(final GroupSpec groupSpec, final TopologyDescriber topologyDescriber, final boolean isActive) { + Set<TaskId> ret = new HashSet<>(); + for (String subtopology : groupSpec.subtopologies()) { + if (isActive || topologyDescriber.isStateful(subtopology)) { + int numberOfPartitions = topologyDescriber.numTasks(subtopology); + for (int i = 0; i < numberOfPartitions; i++) { + ret.add(new TaskId(subtopology, i)); + } + } + } + return ret; + } + + private void initialize(final GroupSpec groupSpec, final TopologyDescriber topologyDescriber) { + allTasks = 0; + for (String subtopology : groupSpec.subtopologies()) { + int numberOfPartitions = topologyDescriber.numTasks(subtopology); + allTasks += numberOfPartitions; + } + totalCapacity = groupSpec.members().size(); + tasksPerMember = computeTasksPerMember(allTasks, totalCapacity); + taskPairs = new TaskPairs(allTasks * (allTasks - 1) / 2); + processIdToState = new HashMap<>(); + activeTaskToPrevMember = new HashMap<>(); + standbyTaskToPrevMember = new HashMap<>(); + for (Map.Entry<String, AssignmentMemberSpec> memberEntry : groupSpec.members().entrySet()) { + final String memberId = memberEntry.getKey(); + final String processId = memberEntry.getValue().processId(); + final Member member = new Member(processId, memberId); + final AssignmentMemberSpec memberSpec = memberEntry.getValue(); + processIdToState.putIfAbsent(processId, new ProcessState(processId)); + processIdToState.get(processId).addMember(memberId); + // prev active tasks + for (Map.Entry<String, Set<Integer>> entry : memberSpec.activeTasks().entrySet()) { + Set<Integer> partitionNoSet = entry.getValue(); + for (int partitionNo : partitionNoSet) { + activeTaskToPrevMember.put(new TaskId(entry.getKey(), partitionNo), member); + } + } + // prev standby tasks + for (Map.Entry<String, Set<Integer>> entry : memberSpec.standbyTasks().entrySet()) { + Set<Integer> partitionNoSet = entry.getValue(); + for (int partitionNo : partitionNoSet) { + TaskId taskId = new TaskId(entry.getKey(), partitionNo); + standbyTaskToPrevMember.putIfAbsent(taskId, new HashSet<>()); + standbyTaskToPrevMember.get(taskId).add(member); + } + } + } + } + + private GroupAssignment buildGroupAssignment(final Set<String> members) { + final Map<String, MemberAssignment> memberAssignments = new HashMap<>(); + final Map<String, Set<TaskId>> activeTasksAssignments = activeTasksAssignments(); + final Map<String, Set<TaskId>> standbyTasksAssignments = standbyTasksAssignments(); + for (String memberId : members) { + Map<String, Set<Integer>> activeTasks = new HashMap<>(); + if (activeTasksAssignments.containsKey(memberId)) { + activeTasks = toCompactedTaskIds(activeTasksAssignments.get(memberId)); + } + Map<String, Set<Integer>> standByTasks = new HashMap<>(); + if (standbyTasksAssignments.containsKey(memberId)) { + standByTasks = toCompactedTaskIds(standbyTasksAssignments.get(memberId)); + } + memberAssignments.put(memberId, new MemberAssignment(activeTasks, standByTasks, new HashMap<>())); + } + return new GroupAssignment(memberAssignments); + } + + private Map<String, Set<TaskId>> standbyTasksAssignments() { + return processIdToState.entrySet().stream() + .flatMap(entry -> entry.getValue().assignedStandbyTasksByMember().entrySet().stream()) + .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (set1, set2) -> { + set1.addAll(set2); + return set1; + })); + } + + private Map<String, Set<TaskId>> activeTasksAssignments() { + return processIdToState.entrySet().stream() + .flatMap(entry -> entry.getValue().assignedActiveTasksByMember().entrySet().stream()) + .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (set1, set2) -> { + set1.addAll(set2); + return set1; + })); + } + + private Map<String, Set<Integer>> toCompactedTaskIds(final Set<TaskId> taskIds) { + Map<String, Set<Integer>> ret = new HashMap<>(); + for (TaskId taskId : taskIds) { + ret.putIfAbsent(taskId.subtopologyId(), new HashSet<>()); + ret.get(taskId.subtopologyId()).add(taskId.partition()); + } + return ret; + } + + private void assignActive(final Set<TaskId> activeTasks) { + // 1. re-assigning existing active tasks to clients that previously had the same active tasks + for (Iterator<TaskId> it = activeTasks.iterator(); it.hasNext();) { + final TaskId task = it.next(); + final Member prevMember = activeTaskToPrevMember.get(task); + if (prevMember != null && hasUnfulfilledQuota(prevMember)) { + processIdToState.get(prevMember.processId).addTask(prevMember.memberId, task, true); + updateHelpers(prevMember, task, true); + it.remove(); + } + } + // 2. re-assigning tasks to clients that previously have seen the same task (as standby task) + for (Iterator<TaskId> it = activeTasks.iterator(); it.hasNext();) { + final TaskId task = it.next(); + final Set<Member> prevMembers = standbyTaskToPrevMember.get(task); + if (prevMembers != null && !prevMembers.isEmpty()) { + final Member prevMember = findMemberWithLeastLoad(prevMembers, task, true); + if (prevMember != null && hasUnfulfilledQuota(prevMember)) { + processIdToState.get(prevMember.processId).addTask(prevMember.memberId, task, true); + updateHelpers(prevMember, task, true); + it.remove(); + } + } + } + // 3. assign any remaining unassigned tasks + for (Iterator<TaskId> it = activeTasks.iterator(); it.hasNext();) { + final TaskId task = it.next(); + final Member member = findMemberWithLeastLoad(task); + if (member != null) { + processIdToState.get(member.processId).addTask(member.memberId, task, true); + it.remove(); + updateHelpers(member, task, true); + } + } + } + + private void maybeUpdateTasksPerMember(final int activeTasksNo) { + if (activeTasksNo == tasksPerMember) { + totalCapacity--; + allTasks -= activeTasksNo; + tasksPerMember = computeTasksPerMember(allTasks, totalCapacity); + } + } + + private Member findMemberWithLeastLoad(final Set<Member> members, TaskId taskId, final boolean returnSameMember) { + Set<Member> rightPairs = members.stream() + .filter(member -> taskPairs.hasNewPair(taskId, processIdToState.get(member.processId).assignedTasks())) + .collect(Collectors.toSet()); + if (rightPairs.isEmpty()) { + rightPairs = members; + } + Optional<ProcessState> processWithLeastLoad = rightPairs.stream() + .map(member -> processIdToState.get(member.processId)) + .min(Comparator.comparingDouble(ProcessState::load)); + assert processWithLeastLoad.isPresent(); + // if the same exact former member is needed + if (returnSameMember) { + return standbyTaskToPrevMember.get(taskId).stream() + .filter(standby -> standby.processId.equals(processWithLeastLoad.get().processId())) + .findFirst() + .orElseGet(() -> memberWithLeastLoad(processWithLeastLoad.get())); + } + return memberWithLeastLoad(processWithLeastLoad.get()); + } + + private Member findMemberWithLeastLoad(final TaskId taskId) { + Set<Member> allMembers = processIdToState.entrySet().stream() + .flatMap(entry -> entry.getValue().memberToTaskCounts().keySet().stream() + .map(memberId -> new Member(entry.getKey(), memberId))) + .collect(Collectors.toSet()); + return findMemberWithLeastLoad(allMembers, taskId, false); + } + + private Member findMemberWithLeastLoad(final TaskId taskId, final Set<String> processes) { + Set<Member> allMembers = processes.stream() + .flatMap(processId -> processIdToState.get(processId).memberToTaskCounts().keySet().stream() + .map(memberId -> new Member(processId, memberId))) + .collect(Collectors.toSet()); + return findMemberWithLeastLoad(allMembers, taskId, false); + } + + private Member memberWithLeastLoad(final ProcessState processWithLeastLoad) { + Optional<String> memberWithLeastLoad = processWithLeastLoad.memberToTaskCounts().entrySet().stream() + .min(Map.Entry.comparingByValue()) + .map(Map.Entry::getKey); + return memberWithLeastLoad.map(memberId -> new Member(processWithLeastLoad.processId(), memberId)).orElse(null); + } + + private boolean hasUnfulfilledQuota(final Member member) { + return processIdToState.get(member.processId).memberToTaskCounts().get(member.memberId) < tasksPerMember; + } + + private void assignStandby(final Set<TaskId> standbyTasks, final int numStandbyReplicas) { + for (TaskId task : standbyTasks) { + for (int i = 0; i < numStandbyReplicas; i++) { + final Set<String> availableProcesses = findAllowedProcesses(task); + if (availableProcesses.isEmpty()) { + log.warn("Unable to assign " + (numStandbyReplicas - i) + + " of " + numStandbyReplicas + " standby tasks for task [" + task + "]. " + + "There is not enough available capacity. You should " + + "increase the number of threads and/or application instances " + + "to maintain the requested number of standby replicas."); + break; + } + Member standby = null; + // prev active task + Member prevMember = activeTaskToPrevMember.get(task); + if (prevMember != null && availableProcesses.contains(prevMember.processId) && isLoadBalanced(prevMember.processId) + && taskPairs.hasNewPair(task, processIdToState.get(prevMember.processId).assignedTasks())) { + standby = prevMember; + } + // prev standby tasks + if (standby == null) { + final Set<Member> prevMembers = standbyTaskToPrevMember.get(task); + if (prevMembers != null && !prevMembers.isEmpty()) { + prevMembers.removeIf(member -> !availableProcesses.contains(member.processId)); + prevMember = findMemberWithLeastLoad(prevMembers, task, true); + if (prevMember != null && isLoadBalanced(prevMember.processId)) { + standby = prevMember; + } + } + } + // others + if (standby == null) { + standby = findMemberWithLeastLoad(task, availableProcesses); + } + processIdToState.get(standby.processId).addTask(standby.memberId, task, false); + updateHelpers(standby, task, false); + } + } + } + + private boolean isLoadBalanced(final String processId) { + final ProcessState process = processIdToState.get(processId); + return process.hasCapacity() || isLeastLoadedProcess(process.load()); + } + + private boolean isLeastLoadedProcess(final double load) { Review Comment: Very good question @bbejeck I think currently, we don't consider task type ([here](https://github.com/apache/kafka/blob/a8f6fc9cc4cf1db27f90145296d9d597995081ba/streams/src/main/java/org/apache/kafka/streams/processor/assignment/assignors/StickyTaskAssignor.java#L337-L341)). Do you confirm it? That would also be a good point for further discussion. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: jira-unsubscr...@kafka.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
