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Posted to jira@kafka.apache.org by GitBox <gi...@apache.org> on 2022/02/12 20:56:50 UTC
[GitHub] [kafka] cadonna commented on a change in pull request #10851: KAFKA-6718 / Rack aware standby task assignor
cadonna commented on a change in pull request #10851:
URL: https://github.com/apache/kafka/pull/10851#discussion_r805203233
##########
File path: streams/src/main/java/org/apache/kafka/streams/processor/internals/assignment/ClientTagAwareStandbyTaskAssignor.java
##########
@@ -0,0 +1,289 @@
+/*
+ * 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.streams.processor.internals.assignment;
+
+import org.apache.kafka.streams.processor.TaskId;
+import org.apache.kafka.streams.processor.internals.assignment.AssignorConfiguration.AssignmentConfigs;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+
+import static org.apache.kafka.streams.processor.internals.assignment.TaskAssignmentUtils.computeTasksToRemainingStandbys;
+import static org.apache.kafka.streams.processor.internals.assignment.TaskAssignmentUtils.pollClientAndMaybeAssignRemainingStandbyTasks;
+import static org.apache.kafka.streams.processor.internals.assignment.TaskAssignmentUtils.shouldBalanceLoad;
+
+/**
+ * Distributes standby tasks over different tag dimensions.
+ * Only tags specified via {@link AssignmentConfigs#rackAwareAssignmentTags} are taken into account.
+ * Standby task distribution is on a best-effort basis. For example, if there's not enough capacity on the clients
+ * with different tag dimensions compared to an active and corresponding standby task,
+ * in that case, the algorithm will fall back to distributing tasks on least-loaded clients.
+ */
+class ClientTagAwareStandbyTaskAssignor implements StandbyTaskAssignor {
+ private static final Logger log = LoggerFactory.getLogger(ClientTagAwareStandbyTaskAssignor.class);
+
+ @Override
+ public boolean assign(final Map<UUID, ClientState> clients,
+ final Set<TaskId> allTaskIds,
+ final Set<TaskId> statefulTaskIds,
+ final AssignorConfiguration.AssignmentConfigs configs) {
+ final int numStandbyReplicas = configs.numStandbyReplicas;
+ final Set<String> rackAwareAssignmentTags = new HashSet<>(configs.rackAwareAssignmentTags);
+
+ final Map<TaskId, Integer> tasksToRemainingStandbys = computeTasksToRemainingStandbys(
+ numStandbyReplicas,
+ allTaskIds
+ );
+
+ final Map<String, Set<String>> tagKeyToValues = new HashMap<>();
+ final Map<TagEntry, Set<UUID>> tagEntryToClients = new HashMap<>();
+
+ fillClientsTagStatistics(clients, tagEntryToClients, tagKeyToValues);
+
+ final ConstrainedPrioritySet standbyTaskClientsByTaskLoad = new ConstrainedPrioritySet(
+ (client, t) -> !clients.get(client).hasAssignedTask(t),
+ client -> clients.get(client).assignedTaskLoad()
+ );
+
+ final Map<TaskId, Integer> pendingStandbyTaskToNumberRemainingStandbys = new HashMap<>();
+ final Map<TaskId, UUID> pendingStandbyTaskToClientId = new HashMap<>();
+
+ for (final TaskId statefulTaskId : statefulTaskIds) {
+ for (final Map.Entry<UUID, ClientState> entry : clients.entrySet()) {
+ final UUID clientId = entry.getKey();
+ final ClientState clientState = entry.getValue();
+
+ if (clientState.activeTasks().contains(statefulTaskId)) {
+ final int numberOfRemainingStandbys = assignStandbyTasksForActiveTask(
+ standbyTaskClientsByTaskLoad,
+ numStandbyReplicas,
+ statefulTaskId,
+ clientId,
+ rackAwareAssignmentTags,
+ clients,
+ tasksToRemainingStandbys,
+ tagKeyToValues,
+ tagEntryToClients
+ );
+
+ if (numberOfRemainingStandbys > 0) {
+ pendingStandbyTaskToNumberRemainingStandbys.put(statefulTaskId, numberOfRemainingStandbys);
Review comment:
Would it be possible to decrement the numbers in `tasksToRemainingStandbys` to maintain the remaining standbys to distribute instead of using `pendingStandbyTaskToNumberRemainingStandbys`?
##########
File path: streams/src/main/java/org/apache/kafka/streams/processor/internals/assignment/ClientTagAwareStandbyTaskAssignor.java
##########
@@ -0,0 +1,289 @@
+/*
+ * 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.streams.processor.internals.assignment;
+
+import org.apache.kafka.streams.processor.TaskId;
+import org.apache.kafka.streams.processor.internals.assignment.AssignorConfiguration.AssignmentConfigs;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+
+import static org.apache.kafka.streams.processor.internals.assignment.TaskAssignmentUtils.computeTasksToRemainingStandbys;
+import static org.apache.kafka.streams.processor.internals.assignment.TaskAssignmentUtils.pollClientAndMaybeAssignRemainingStandbyTasks;
+import static org.apache.kafka.streams.processor.internals.assignment.TaskAssignmentUtils.shouldBalanceLoad;
+
+/**
+ * Distributes standby tasks over different tag dimensions.
+ * Only tags specified via {@link AssignmentConfigs#rackAwareAssignmentTags} are taken into account.
+ * Standby task distribution is on a best-effort basis. For example, if there's not enough capacity on the clients
+ * with different tag dimensions compared to an active and corresponding standby task,
+ * in that case, the algorithm will fall back to distributing tasks on least-loaded clients.
+ */
+class ClientTagAwareStandbyTaskAssignor implements StandbyTaskAssignor {
+ private static final Logger log = LoggerFactory.getLogger(ClientTagAwareStandbyTaskAssignor.class);
+
+ @Override
+ public boolean assign(final Map<UUID, ClientState> clients,
+ final Set<TaskId> allTaskIds,
+ final Set<TaskId> statefulTaskIds,
+ final AssignorConfiguration.AssignmentConfigs configs) {
+ final int numStandbyReplicas = configs.numStandbyReplicas;
+ final Set<String> rackAwareAssignmentTags = new HashSet<>(configs.rackAwareAssignmentTags);
+
+ final Map<TaskId, Integer> tasksToRemainingStandbys = computeTasksToRemainingStandbys(
+ numStandbyReplicas,
+ allTaskIds
+ );
+
+ final Map<String, Set<String>> tagKeyToValues = new HashMap<>();
+ final Map<TagEntry, Set<UUID>> tagEntryToClients = new HashMap<>();
+
+ fillClientsTagStatistics(clients, tagEntryToClients, tagKeyToValues);
+
+ final ConstrainedPrioritySet standbyTaskClientsByTaskLoad = new ConstrainedPrioritySet(
+ (client, t) -> !clients.get(client).hasAssignedTask(t),
+ client -> clients.get(client).assignedTaskLoad()
+ );
+
+ final Map<TaskId, Integer> pendingStandbyTaskToNumberRemainingStandbys = new HashMap<>();
+ final Map<TaskId, UUID> pendingStandbyTaskToClientId = new HashMap<>();
+
+ for (final TaskId statefulTaskId : statefulTaskIds) {
+ for (final Map.Entry<UUID, ClientState> entry : clients.entrySet()) {
+ final UUID clientId = entry.getKey();
+ final ClientState clientState = entry.getValue();
+
+ if (clientState.activeTasks().contains(statefulTaskId)) {
+ final int numberOfRemainingStandbys = assignStandbyTasksForActiveTask(
+ standbyTaskClientsByTaskLoad,
+ numStandbyReplicas,
+ statefulTaskId,
+ clientId,
+ rackAwareAssignmentTags,
+ clients,
+ tasksToRemainingStandbys,
+ tagKeyToValues,
+ tagEntryToClients
+ );
+
+ if (numberOfRemainingStandbys > 0) {
+ pendingStandbyTaskToNumberRemainingStandbys.put(statefulTaskId, numberOfRemainingStandbys);
+ pendingStandbyTaskToClientId.put(statefulTaskId, clientId);
+ }
+ }
+ }
+ }
+
+ if (!pendingStandbyTaskToNumberRemainingStandbys.isEmpty()) {
+ assignPendingStandbyTasksToLeastLoadedClients(clients,
+ numStandbyReplicas,
+ rackAwareAssignmentTags,
+ standbyTaskClientsByTaskLoad,
+ pendingStandbyTaskToNumberRemainingStandbys,
+ pendingStandbyTaskToClientId);
+ }
+
+ // returning false, because standby task assignment will never require a follow-up probing rebalance.
+ return false;
+ }
+
+ private static void assignPendingStandbyTasksToLeastLoadedClients(final Map<UUID, ClientState> clients,
+ final int numStandbyReplicas,
+ final Set<String> rackAwareAssignmentTags,
+ final ConstrainedPrioritySet standbyTaskClientsByTaskLoad,
+ final Map<TaskId, Integer> pendingStandbyTaskToNumberRemainingStandbys,
+ final Map<TaskId, UUID> pendingStandbyTaskToClientId) {
+ // We need to re offer all the clients to find the least loaded ones
+ standbyTaskClientsByTaskLoad.offerAll(clients.keySet());
+
+ for (final Entry<TaskId, Integer> pendingStandbyTaskAssignmentEntry : pendingStandbyTaskToNumberRemainingStandbys.entrySet()) {
+ final TaskId activeTaskId = pendingStandbyTaskAssignmentEntry.getKey();
+ final UUID clientId = pendingStandbyTaskToClientId.get(activeTaskId);
+
+ final int numberOfRemainingStandbys = pollClientAndMaybeAssignRemainingStandbyTasks(
+ clients,
+ pendingStandbyTaskToNumberRemainingStandbys,
+ standbyTaskClientsByTaskLoad,
+ activeTaskId
+ );
+
+ if (numberOfRemainingStandbys > 0) {
+ log.warn("Unable to assign {} of {} standby tasks for task [{}] with client tags [{}]. " +
+ "There is not enough available capacity. You should " +
+ "increase the number of application instances " +
+ "on different client tag dimensions " +
+ "to maintain the requested number of standby replicas. " +
+ "Rack awareness is configured with [{}] tags.",
+ numberOfRemainingStandbys, numStandbyReplicas, activeTaskId,
+ clients.get(clientId).clientTags(), rackAwareAssignmentTags);
+ }
+ }
+ }
+
+ @Override
+ public boolean isAllowedTaskMovement(final ClientState source, final ClientState destination) {
+ final Map<String, String> sourceClientTags = source.clientTags();
+ final Map<String, String> destinationClientTags = destination.clientTags();
+
+ for (final Entry<String, String> sourceClientTagEntry : sourceClientTags.entrySet()) {
+ if (!sourceClientTagEntry.getValue().equals(destinationClientTags.get(sourceClientTagEntry.getKey()))) {
+ return false;
+ }
+ }
+
+ return true;
+ }
+
+ private static void fillClientsTagStatistics(final Map<UUID, ClientState> clientStates,
+ final Map<TagEntry, Set<UUID>> tagEntryToClients,
+ final Map<String, Set<String>> tagKeyToValues) {
+ for (final Entry<UUID, ClientState> clientStateEntry : clientStates.entrySet()) {
+ final UUID clientId = clientStateEntry.getKey();
+ final ClientState clientState = clientStateEntry.getValue();
+
+ clientState.clientTags().forEach((tagKey, tagValue) -> {
+ tagKeyToValues.computeIfAbsent(tagKey, ignored -> new HashSet<>()).add(tagValue);
+ tagEntryToClients.computeIfAbsent(new TagEntry(tagKey, tagValue), ignored -> new HashSet<>()).add(clientId);
+ });
+ }
+ }
+
+ private static int assignStandbyTasksForActiveTask(final ConstrainedPrioritySet standbyTaskClientsByTaskLoad,
+ final int numStandbyReplicas,
+ final TaskId activeTaskId,
+ final UUID activeTaskClient,
+ final Set<String> rackAwareAssignmentTags,
+ final Map<UUID, ClientState> clientStates,
+ final Map<TaskId, Integer> tasksToRemainingStandbys,
+ final Map<String, Set<String>> tagKeyToValues,
+ final Map<TagEntry, Set<UUID>> tagEntryToClients) {
+
+ final Set<UUID> usedClients = new HashSet<>();
+
+ standbyTaskClientsByTaskLoad.offerAll(clientStates.keySet());
+
+ int numRemainingStandbys = tasksToRemainingStandbys.get(activeTaskId);
+
+ usedClients.add(activeTaskClient);
+
+ final Set<UUID> clientsOnAlreadyUsedTagDimensions = new HashSet<>();
+
+ while (numRemainingStandbys > 0) {
+ clientsOnAlreadyUsedTagDimensions.addAll(
+ findClientsOnUsedTagDimensions(
+ usedClients,
+ rackAwareAssignmentTags,
+ clientStates,
+ tagEntryToClients,
+ tagKeyToValues
+ )
+ );
+
+ final UUID polledClient = standbyTaskClientsByTaskLoad.poll(
+ activeTaskId, uuid -> !clientsOnAlreadyUsedTagDimensions.contains(uuid)
+ );
+
+ if (polledClient == null) {
+ break;
+ }
+
+ final ClientState standbyTaskClient = clientStates.get(polledClient);
+
+ if (shouldBalanceLoad(clientStates.values(), standbyTaskClient)) {
Review comment:
I see what you want to do. However, the capacity is the number of consumers on the Streams client, i.e., the number of stream threads running on the Streams client. With this check, you only allow to assign standby tasks to clients that have less tasks assigned as stream threads running. That is actually rather an unlikely case. Normally, you have more tasks assigned to a Streams client than the number of stream threads running on the client.
I would keep it simple and ignore the balance for now.
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