kafka RoundRobinAssignor 源码

  • 2022-10-20
  • 浏览 (524)

kafka RoundRobinAssignor 代码

文件路径:/clients/src/main/java/org/apache/kafka/clients/consumer/RoundRobinAssignor.java

/*
 * 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.clients.consumer;

import org.apache.kafka.clients.consumer.internals.AbstractPartitionAssignor;
import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.utils.CircularIterator;
import org.apache.kafka.common.utils.Utils;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.SortedSet;
import java.util.TreeSet;

/**
 * <p>The round robin assignor lays out all the available partitions and all the available consumers. It
 * then proceeds to do a round robin assignment from partition to consumer. If the subscriptions of all consumer
 * instances are identical, then the partitions will be uniformly distributed. (i.e., the partition ownership counts
 * will be within a delta of exactly one across all consumers.)
 *
 * <p>For example, suppose there are two consumers <code>C0</code> and <code>C1</code>, two topics <code>t0</code> and <code>t1</code>,
 * and each topic has 3 partitions, resulting in partitions <code>t0p0</code>, <code>t0p1</code>, <code>t0p2</code>,
 * <code>t1p0</code>, <code>t1p1</code>, and <code>t1p2</code>.
 *
 * <p>The assignment will be:
 * <ul>
 * <li><code>C0: [t0p0, t0p2, t1p1]</code>
 * <li><code>C1: [t0p1, t1p0, t1p2]</code>
 * </ul>
 *
 * <p>When subscriptions differ across consumer instances, the assignment process still considers each
 * consumer instance in round robin fashion but skips over an instance if it is not subscribed to
 * the topic. Unlike the case when subscriptions are identical, this can result in imbalanced
 * assignments. For example, we have three consumers <code>C0</code>, <code>C1</code>, <code>C2</code>,
 * and three topics <code>t0</code>, <code>t1</code>, <code>t2</code>, with 1, 2, and 3 partitions, respectively.
 * Therefore, the partitions are <code>t0p0</code>, <code>t1p0</code>, <code>t1p1</code>, <code>t2p0</code>, <code>t2p1</code>, <code>t2p2</code>.
 * <code>C0</code> is subscribed to <code>t0</code>;
 * <code>C1</code> is subscribed to <code>t0</code>, <code>t1</code>;
 * and <code>C2</code> is subscribed to <code>t0</code>, <code>t1</code>, <code>t2</code>.
 *
 * <p>That assignment will be:
 * <ul>
 * <li><code>C0: [t0p0]</code>
 * <li><code>C1: [t1p0]</code>
 * <li><code>C2: [t1p1, t2p0, t2p1, t2p2]</code>
 * </ul>
 *
 * Since the introduction of static membership, we could leverage <code>group.instance.id</code> to make the assignment behavior more sticky.
 * For example, we have three consumers with assigned <code>member.id</code> <code>C0</code>, <code>C1</code>, <code>C2</code>,
 * two topics <code>t0</code> and <code>t1</code>, and each topic has 3 partitions, resulting in partitions <code>t0p0</code>,
 * <code>t0p1</code>, <code>t0p2</code>, <code>t1p0</code>, <code>t1p1</code>, and <code>t1p2</code>. We choose to honor
 * the sorted order based on ephemeral <code>member.id</code>.
 *
 * <p>The assignment will be:
 * <ul>
 * <li><code>C0: [t0p0, t1p0]</code>
 * <li><code>C1: [t0p1, t1p1]</code>
 * <li><code>C2: [t0p2, t1p2]</code>
 * </ul>
 *
 * After one rolling bounce, group coordinator will attempt to assign new <code>member.id</code> towards consumers,
 * for example <code>C0</code> -&gt; <code>C5</code> <code>C1</code> -&gt; <code>C3</code>, <code>C2</code> -&gt; <code>C4</code>.
 *
 * <p>The assignment could be completely shuffled to:
 * <ul>
 * <li><code>C3 (was C1): [t0p0, t1p0] (before was [t0p1, t1p1])</code>
 * <li><code>C4 (was C2): [t0p1, t1p1] (before was [t0p2, t1p2])</code>
 * <li><code>C5 (was C0): [t0p2, t1p2] (before was [t0p0, t1p0])</code>
 * </ul>
 *
 * This issue could be mitigated by the introduction of static membership. Consumers will have individual instance ids
 * <code>I1</code>, <code>I2</code>, <code>I3</code>. As long as
 * 1. Number of members remain the same across generation
 * 2. Static members' identities persist across generation
 * 3. Subscription pattern doesn't change for any member
 *
 * <p>The assignment will always be:
 * <ul>
 * <li><code>I0: [t0p0, t1p0]</code>
 * <li><code>I1: [t0p1, t1p1]</code>
 * <li><code>I2: [t0p2, t1p2]</code>
 * </ul>
 */
public class RoundRobinAssignor extends AbstractPartitionAssignor {
    public static final String ROUNDROBIN_ASSIGNOR_NAME = "roundrobin";

    @Override
    public Map<String, List<TopicPartition>> assign(Map<String, Integer> partitionsPerTopic,
                                                    Map<String, Subscription> subscriptions) {
        Map<String, List<TopicPartition>> assignment = new HashMap<>();
        List<MemberInfo> memberInfoList = new ArrayList<>();
        for (Map.Entry<String, Subscription> memberSubscription : subscriptions.entrySet()) {
            assignment.put(memberSubscription.getKey(), new ArrayList<>());
            memberInfoList.add(new MemberInfo(memberSubscription.getKey(),
                                              memberSubscription.getValue().groupInstanceId()));
        }

        CircularIterator<MemberInfo> assigner = new CircularIterator<>(Utils.sorted(memberInfoList));

        for (TopicPartition partition : allPartitionsSorted(partitionsPerTopic, subscriptions)) {
            final String topic = partition.topic();
            while (!subscriptions.get(assigner.peek().memberId).topics().contains(topic))
                assigner.next();
            assignment.get(assigner.next().memberId).add(partition);
        }
        return assignment;
    }

    private List<TopicPartition> allPartitionsSorted(Map<String, Integer> partitionsPerTopic,
                                                     Map<String, Subscription> subscriptions) {
        SortedSet<String> topics = new TreeSet<>();
        for (Subscription subscription : subscriptions.values())
            topics.addAll(subscription.topics());

        List<TopicPartition> allPartitions = new ArrayList<>();
        for (String topic : topics) {
            Integer numPartitionsForTopic = partitionsPerTopic.get(topic);
            if (numPartitionsForTopic != null)
                allPartitions.addAll(AbstractPartitionAssignor.partitions(topic, numPartitionsForTopic));
        }
        return allPartitions;
    }

    @Override
    public String name() {
        return ROUNDROBIN_ASSIGNOR_NAME;
    }

}

相关信息

kafka 源码目录

相关文章

kafka CommitFailedException 源码

kafka Consumer 源码

kafka ConsumerConfig 源码

kafka ConsumerGroupMetadata 源码

kafka ConsumerInterceptor 源码

kafka ConsumerPartitionAssignor 源码

kafka ConsumerRebalanceListener 源码

kafka ConsumerRecord 源码

kafka ConsumerRecords 源码

kafka CooperativeStickyAssignor 源码

0  赞