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Posted to jira@kafka.apache.org by GitBox <gi...@apache.org> on 2021/07/14 10:55:09 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_r669496452
##########
File path: streams/src/main/java/org/apache/kafka/streams/processor/internals/assignment/HighAvailabilityTaskAssignor.java
##########
@@ -51,12 +57,12 @@ public boolean assign(final Map<UUID, ClientState> clients,
final SortedSet<TaskId> statefulTasks = new TreeSet<>(statefulTaskIds);
final TreeMap<UUID, ClientState> clientStates = new TreeMap<>(clients);
- assignActiveStatefulTasks(clientStates, statefulTasks);
+ final Map<TaskId, UUID> statefulTasksClientMappings = assignActiveStatefulTasks(clientStates, statefulTasks);
Review comment:
As far as I can see, this map is only used in `ClientTagAwareStandbyTaskAssignor` and it is only used to iterate over pairs (taskId, uuid). That can also be accomplished by iterating over the client states and for each client state iterate over the assigned active tasks. I do not think that we need to modify the signature of `assignActiveStatefulTasks()`. Or am I missing something?
##########
File path: streams/src/main/java/org/apache/kafka/streams/processor/internals/assignment/StandbyTaskAssignor.java
##########
@@ -0,0 +1,39 @@
+/*
+ * 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 java.util.Map;
+import java.util.TreeMap;
+import java.util.UUID;
+
+abstract class StandbyTaskAssignor {
+ protected final AssignmentConfigs configs;
+
+ StandbyTaskAssignor(final AssignmentConfigs configs) {
+ this.configs = configs;
+ }
+
+ abstract void assignStandbyTasks(final Map<TaskId, UUID> statefulTasksWithClients,
+ final TreeMap<UUID, ClientState> clientStates);
Review comment:
I think it should be `SortedMap` instead of `TreeMap`. I also saw that we sometimes missed to use `SortedMap` instead of `TreeMap` in some signatures. It needs to be a sorted map because the assignments should be stable otherwise it could happen that we compute different assignments for the same input which could lead to unnecessary state migrations.
##########
File path: streams/src/main/java/org/apache/kafka/streams/processor/internals/assignment/ClientTagAwareStandbyTaskAssignor.java
##########
@@ -0,0 +1,212 @@
+/*
+ * 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.Optional;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.UUID;
+import java.util.function.Function;
+
+import static java.util.stream.Collectors.toMap;
+
+/**
+ * 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 are not enough clients available
+ * on 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 extends StandbyTaskAssignor {
+ private static final Logger log = LoggerFactory.getLogger(ClientTagAwareStandbyTaskAssignor.class);
+
+ ClientTagAwareStandbyTaskAssignor(final AssignmentConfigs configs) {
+ super(configs);
+ }
+
+ @Override
+ public void assignStandbyTasks(final Map<TaskId, UUID> statefulTasksWithClients,
+ final TreeMap<UUID, ClientState> clientStates) {
+ final int numStandbyReplicas = configs.numStandbyReplicas;
+ final Set<String> rackAwareAssignmentTags = new HashSet<>(configs.rackAwareAssignmentTags);
+
+ final StandbyTaskDistributor standbyTaskDistributor = new StandbyTaskDistributor(
+ numStandbyReplicas,
+ clientStates,
+ rackAwareAssignmentTags,
+ statefulTasksWithClients
+ );
+
+ statefulTasksWithClients.forEach(standbyTaskDistributor::assignStandbyTasksForActiveTask);
+ }
+
+ @Override
+ public boolean isValidTaskMovement(final TaskMovementAttempt taskMovementAttempt) {
+ final Map<String, String> sourceClientTags = taskMovementAttempt.sourceClient().clientTags();
+ final Map<String, String> destinationClientTags = taskMovementAttempt.destinationClient().clientTags();
+
+ for (final Entry<String, String> sourceClientTagEntry : sourceClientTags.entrySet()) {
+ if (!sourceClientTagEntry.getValue().equals(destinationClientTags.get(sourceClientTagEntry.getKey()))) {
+ return false;
+ }
+ }
+
+ return true;
+ }
+
+ private static final class StandbyTaskDistributor {
Review comment:
Why do we need this internal class? Wouldn't it be simpler to structure the code with methods directly under `ClientTagAwareStandbyTaskAssignor`?
##########
File path: streams/src/main/java/org/apache/kafka/streams/processor/internals/assignment/DefaultStandbyTaskAssignor.java
##########
@@ -0,0 +1,78 @@
+/*
+ * 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.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.UUID;
+
+import static java.util.stream.Collectors.toMap;
+
+class DefaultStandbyTaskAssignor extends StandbyTaskAssignor {
+ private static final Logger log = LoggerFactory.getLogger(DefaultStandbyTaskAssignor.class);
+
+ public DefaultStandbyTaskAssignor(final AssignorConfiguration.AssignmentConfigs configs) {
+ super(configs);
+ }
+
+ @Override
+ public void assignStandbyTasks(final Map<TaskId, UUID> statefulTasksWithClients,
+ final TreeMap<UUID, ClientState> clientStates) {
+ final int numStandbyReplicas = configs.numStandbyReplicas;
+ final Set<TaskId> statefulTasks = statefulTasksWithClients.keySet();
+ final Map<TaskId, Integer> tasksToRemainingStandbys = statefulTasks.stream()
+ .collect(
+ toMap(
+ task -> task,
+ t -> numStandbyReplicas
+ )
+ );
Review comment:
```suggestion
final Map<TaskId, Integer> tasksToRemainingStandbys =
statefulTasks.stream().collect(Collectors.toMap(task -> task, t -> numStandbyReplicas));
```
##########
File path: streams/src/main/java/org/apache/kafka/streams/processor/internals/assignment/HighAvailabilityTaskAssignor.java
##########
@@ -51,12 +57,12 @@ public boolean assign(final Map<UUID, ClientState> clients,
final SortedSet<TaskId> statefulTasks = new TreeSet<>(statefulTaskIds);
final TreeMap<UUID, ClientState> clientStates = new TreeMap<>(clients);
- assignActiveStatefulTasks(clientStates, statefulTasks);
+ final Map<TaskId, UUID> statefulTasksClientMappings = assignActiveStatefulTasks(clientStates, statefulTasks);
assignStandbyReplicaTasks(
clientStates,
- statefulTasks,
- configs.numStandbyReplicas
+ statefulTasksClientMappings,
+ configs
);
Review comment:
I was wondering whether we can simply standby assignment if `configs.numStandbyReplicas == 0`. Here or as first step in the method body of `assignStandbyReplicaTasks()`. In this way we can remove `NoopStandbyTaskAssignor`.
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