org.apache.kafka.clients.consumer.ConsumerPartitionAssignor Maven / Gradle / Ivy
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* 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 java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Optional;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.apache.kafka.common.Cluster;
import org.apache.kafka.common.Configurable;
import org.apache.kafka.common.KafkaException;
import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.utils.Utils;
/**
* This interface is used to define custom partition assignment for use in
* {@link org.apache.kafka.clients.consumer.KafkaConsumer}. Members of the consumer group subscribe
* to the topics they are interested in and forward their subscriptions to a Kafka broker serving
* as the group coordinator. The coordinator selects one member to perform the group assignment and
* propagates the subscriptions of all members to it. Then {@link #assign(Cluster, GroupSubscription)} is called
* to perform the assignment and the results are forwarded back to each respective members
*
* In some cases, it is useful to forward additional metadata to the assignor in order to make
* assignment decisions. For this, you can override {@link #subscriptionUserData(Set)} and provide custom
* userData in the returned Subscription. For example, to have a rack-aware assignor, an implementation
* can use this user data to forward the rackId belonging to each member.
*/
public interface ConsumerPartitionAssignor {
/**
* Return serialized data that will be included in the {@link Subscription} sent to the leader
* and can be leveraged in {@link #assign(Cluster, GroupSubscription)} ((e.g. local host/rack information)
*
* @param topics Topics subscribed to through {@link org.apache.kafka.clients.consumer.KafkaConsumer#subscribe(java.util.Collection)}
* and variants
* @return nullable subscription user data
*/
default ByteBuffer subscriptionUserData(Set topics) {
return null;
}
/**
* Perform the group assignment given the member subscriptions and current cluster metadata.
* @param metadata Current topic/broker metadata known by consumer
* @param groupSubscription Subscriptions from all members including metadata provided through {@link #subscriptionUserData(Set)}
* @return A map from the members to their respective assignments. This should have one entry
* for each member in the input subscription map.
*/
GroupAssignment assign(Cluster metadata, GroupSubscription groupSubscription);
/**
* Callback which is invoked when a group member receives its assignment from the leader.
* @param assignment The local member's assignment as provided by the leader in {@link #assign(Cluster, GroupSubscription)}
* @param metadata Additional metadata on the consumer (optional)
*/
default void onAssignment(Assignment assignment, ConsumerGroupMetadata metadata) {
}
/**
* Indicate which rebalance protocol this assignor works with;
* By default it should always work with {@link RebalanceProtocol#EAGER}.
*/
default List supportedProtocols() {
return Collections.singletonList(RebalanceProtocol.EAGER);
}
/**
* Return the version of the assignor which indicates how the user metadata encodings
* and the assignment algorithm gets evolved.
*/
default short version() {
return (short) 0;
}
/**
* Unique name for this assignor (e.g. "range" or "roundrobin" or "sticky"). Note, this is not required
* to be the same as the class name specified in {@link ConsumerConfig#PARTITION_ASSIGNMENT_STRATEGY_CONFIG}
* @return non-null unique name
*/
String name();
final class Subscription {
private final List topics;
private final ByteBuffer userData;
private final List ownedPartitions;
private Optional groupInstanceId;
public Subscription(List topics, ByteBuffer userData, List ownedPartitions) {
this.topics = topics;
this.userData = userData;
this.ownedPartitions = ownedPartitions;
this.groupInstanceId = Optional.empty();
}
public Subscription(List topics, ByteBuffer userData) {
this(topics, userData, Collections.emptyList());
}
public Subscription(List topics) {
this(topics, null, Collections.emptyList());
}
public List topics() {
return topics;
}
public ByteBuffer userData() {
return userData;
}
public List ownedPartitions() {
return ownedPartitions;
}
public void setGroupInstanceId(Optional groupInstanceId) {
this.groupInstanceId = groupInstanceId;
}
public Optional groupInstanceId() {
return groupInstanceId;
}
@Override
public String toString() {
return "Subscription(" +
"topics=" + topics +
(userData == null ? "" : ", userDataSize=" + userData.remaining()) +
", ownedPartitions=" + ownedPartitions +
", groupInstanceId=" + (groupInstanceId.map(String::toString).orElse("null")) +
")";
}
}
final class Assignment {
private List partitions;
private ByteBuffer userData;
public Assignment(List partitions, ByteBuffer userData) {
this.partitions = partitions;
this.userData = userData;
}
public Assignment(List partitions) {
this(partitions, null);
}
public List partitions() {
return partitions;
}
public ByteBuffer userData() {
return userData;
}
@Override
public String toString() {
return "Assignment(" +
"partitions=" + partitions +
(userData == null ? "" : ", userDataSize=" + userData.remaining()) +
')';
}
}
final class GroupSubscription {
private final Map subscriptions;
public GroupSubscription(Map subscriptions) {
this.subscriptions = subscriptions;
}
public Map groupSubscription() {
return subscriptions;
}
@Override
public String toString() {
return "GroupSubscription(" +
"subscriptions=" + subscriptions +
")";
}
}
final class GroupAssignment {
private final Map assignments;
public GroupAssignment(Map assignments) {
this.assignments = assignments;
}
public Map groupAssignment() {
return assignments;
}
@Override
public String toString() {
return "GroupAssignment(" +
"assignments=" + assignments +
")";
}
}
/**
* The rebalance protocol defines partition assignment and revocation semantics. The purpose is to establish a
* consistent set of rules that all consumers in a group follow in order to transfer ownership of a partition.
* {@link ConsumerPartitionAssignor} implementors can claim supporting one or more rebalance protocols via the
* {@link ConsumerPartitionAssignor#supportedProtocols()}, and it is their responsibility to respect the rules
* of those protocols in their {@link ConsumerPartitionAssignor#assign(Cluster, GroupSubscription)} implementations.
* Failures to follow the rules of the supported protocols would lead to runtime error or undefined behavior.
*
* The {@link RebalanceProtocol#EAGER} rebalance protocol requires a consumer to always revoke all its owned
* partitions before participating in a rebalance event. It therefore allows a complete reshuffling of the assignment.
*
* {@link RebalanceProtocol#COOPERATIVE} rebalance protocol allows a consumer to retain its currently owned
* partitions before participating in a rebalance event. The assignor should not reassign any owned partitions
* immediately, but instead may indicate consumers the need for partition revocation so that the revoked
* partitions can be reassigned to other consumers in the next rebalance event. This is designed for sticky assignment
* logic which attempts to minimize partition reassignment with cooperative adjustments.
*/
enum RebalanceProtocol {
EAGER((byte) 0), COOPERATIVE((byte) 1);
private final byte id;
RebalanceProtocol(byte id) {
this.id = id;
}
public byte id() {
return id;
}
public static RebalanceProtocol forId(byte id) {
switch (id) {
case 0:
return EAGER;
case 1:
return COOPERATIVE;
default:
throw new IllegalArgumentException("Unknown rebalance protocol id: " + id);
}
}
}
/**
* Get a list of configured instances of {@link org.apache.kafka.clients.consumer.ConsumerPartitionAssignor}
* based on the class names/types specified by {@link org.apache.kafka.clients.consumer.ConsumerConfig#PARTITION_ASSIGNMENT_STRATEGY_CONFIG}
*/
static List getAssignorInstances(List assignorClasses, Map configs) {
List assignors = new ArrayList<>();
// a map to store assignor name -> assignor class name
Map assignorNameMap = new HashMap<>();
if (assignorClasses == null)
return assignors;
for (Object klass : assignorClasses) {
// first try to get the class if passed in as a string
if (klass instanceof String) {
try {
klass = Class.forName((String) klass, true, Utils.getContextOrKafkaClassLoader());
} catch (ClassNotFoundException classNotFound) {
throw new KafkaException(klass + " ClassNotFoundException exception occurred", classNotFound);
}
}
if (klass instanceof Class) {
Object assignor = Utils.newInstance((Class) klass);
if (assignor instanceof Configurable)
((Configurable) assignor).configure(configs);
if (assignor instanceof ConsumerPartitionAssignor) {
String assignorName = ((ConsumerPartitionAssignor) assignor).name();
if (assignorNameMap.containsKey(assignorName)) {
throw new KafkaException("The assignor name: '" + assignorName + "' is used in more than one assignor: " +
assignorNameMap.get(assignorName) + ", " + assignor.getClass().getName());
}
assignorNameMap.put(assignorName, assignor.getClass().getName());
assignors.add((ConsumerPartitionAssignor) assignor);
} else {
throw new KafkaException(klass + " is not an instance of " + ConsumerPartitionAssignor.class.getName());
}
} else {
throw new KafkaException("List contains element of type " + klass.getClass().getName() + ", expected String or Class");
}
}
return assignors;
}
}