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The admin client allows users to instruct the controller to attempt to elect the preferred replica on a given set of topic partitions. In addition to preferred replica leader elections the controller also supports three other types of elections. In this proposal we modify the “PreferredLeaderElection” RPC to also support unclean leader election. The new RPC also makes it possible to easily add new type of elections in the future.
Public Interfaces
Network protocol
Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.
A public interface is any change to the following:
Binary log format
The network protocol and api behavior
Any class in the public packages under clientsConfiguration, especially client configuration
org/apache/kafka/common/serialization
org/apache/kafka/common
org/apache/kafka/common/errors
org/apache/kafka/clients/producer
org/apache/kafka/clients/consumer (eventually, once stable)
Monitoring
Command line tools and arguments
- Anything else that will likely break existing users in some way when they upgrade
Proposed Changes
Code Block | ||
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| ||
{
"apiKey": 43,
"type": "request",
"name": "ElectLeadersRequest",
"validVersions": "0-1",
"fields": [
{ "name": "TopicPartitions", "type": "[]TopicPartitions", "versions": "0+", "nullableVersions": "0+",
"about": "The topic partitions to elect leaders.",
"fields": [
{ "name": "Topic", "type": "string", "versions": "0+",
"about": "The name of a topic." },
{ "name": "PartitionId", "type": "[]int32", "versions": "0",
"about": "The partitions of this topic whose preferred leader should be elected." },
{ "name": "Partitions", "type": "[]Partitions", "versions": "1+",
"about": "The partitions of this topic whose leader should be elected.",
"fields": [
{ "name": "PartitionId", "type": "int32", "versions": "1+",
"about": "The partition id." },
{ "name": "ElectionType", "type": "int8", "versions": "1+",
"about": "Type of elections to conduct for the partition. A value of '0' elects the preferred leader. A value of '1' elects an unclean leader if there are no in-sync leaders." }
]
}
]
},
{ "name": "TimeoutMs", "type": "int32", "versions": "0+", "default": "60000",
"about": "The time in ms to wait for the election to complete." }
]
} |
AdminClient Abstract Class
A new method will be added to the AdminClient abstract class to support this new version of the RPC.
Code Block | ||
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package org.apache.kafka.clients.admin;
public abstract class AdminClient ... {
...
/**
* Attempt to elect a new leader for each of the topic partition in {@code partitionElections}. The type of elections supported are
* document in the {@link TopicPartitionElection} type.
*
* If {@code partitionElections} is null, then attempt to elect the preferred replica for all of the partitions.
*
* @param partitionElections The partitions and the type of elections to conduct.
* @param options The options to use when electing the leaders.
* @return The ElectLeadersResult.
*/
public abstract ElectLeadersResult electLeaders(
Collection<TopicPartitionElection> partitionElections,
ElectLeadersOptions options);
} |
TopicPartitionElection Class
Code Block |
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package org.apache.kafka.common;
public final class TopicPartitionElection {
public static enum ElectionType {
PREFERRED((byte) 0), UNCLEANED((byte) 1);
public final byte value;
ElectionType(byte value) {
this.value = value;
}
}
public final TopicPartition topicPartition;
public final ElectionType electionType;
...
} |
Admin Command
The command kafka-preferred-replica.election.{sh,bat} will be deprecated and the following command will be added.
Code Block |
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$ bin/kafka-leader-election.sh --help
This tool attempts to elect a new leader for a set of topic partitions. The type of elections supported are preferred replicas and unclean replica.
Option Description
------ -----------
--admin.config <String: config file> Admin client config properties file to
pass to the admin client when --
bootstrap-server is given.
--bootstrap-server <String: host:port> A host name and port for the broker to
connect to, in the form host:port.
Multiple comma-separated URLs can be
given. REQUIRED unless --zookeeper
is given.
--help Print usage information.
--path-to-json-file <String: list of The JSON file with the list of
partitions for which replica partitions for which leader election
leader election needs to be should be done. Supported elections
triggered> are 0 for preferred and 1 for uncleaned.
If an election is not specified,
preferred is the default. This is an
example format.
{"partitions":
[{"topic": "foo", "partition": 1},
{"topic": "foobar", "partition": 2, "election": 1}]
}
Defaults to all existing partitions |
Proposed Changes
In addition to the protocol and client changes enumerated above the Controller will be extended to allow unclean leader election requests to come from the admin client. Currently the controller only support preferred leader elections from the admin client. Unclean leader election can only be enabled through either a topic configuration change or a broker configuration Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.
Compatibility, Deprecation, and Migration Plan
- What impact (if any) will there be on existing users?
- If we are changing behavior how will we phase out the older behavior?
- If we need special migration tools, describe them here.
- When will we remove the existing behavior?
Rejected Alternatives
If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.