THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Status
Current state: Under DiscussionAccepted
Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]
JIRAJIRA:
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PR: https://github.com/apache/kafka/pull/6686
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
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The admin client allows users to instruct the controller to attempt to elect the preferred replica as leader 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
One of those other election types is what we call unclean leader election. For the user to enable and trigger unclean leader election they need to either modify the topic configuration or the broker configuration. We believe that this is potentially a dangerous configuration that could lead to data loss. Specially if the user forgets to disable unclean leader election after it completes. Being able to trigger unclean leader election once for a given partition is a much safer mechanism.
In this proposal we modify the “PreferredLeaderElection” RPC to support unclean leader election in addition to preferred leader election. The new RPC definition also makes it possible to easily add new type of elections in the future.
Public Interfaces
Network protocol
Request
Added a top level property called ElectionType with supported values of 0 and 1.
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{
"apiKey": 43,
"type": "request",
"name": "ElectLeadersRequest",
"validVersions": "0-1",
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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": "TopicElectionType", "type": "stringint8", "versions": "01+", "about": "TheType name of aelections topic." }, { "name": "PartitionId", "type": "[]int32", "versions": "0", "about": "The partitions of this topic whose preferred leader should be electedto conduct for the partition. A value of '0' elects the preferred replica. A value of '1' elects the first live replica if there are no in-sync replica." }, { "name": "PartitionsTopicPartitions", "type": "[]PartitionsTopicPartitions", "versions": "10+", "nullableVersions": "0+", "about": "The partitions of this topic whosepartitions leaderto shouldelect be electedleaders.", "fields": [ { "name": "PartitionIdTopic", "type": "int32string", "versions": "10+", "about": "The name partitionof a idtopic." }, { "name": "ElectionTypePartitionId", "type": "int8[]int32", "versions": "10+", "about": "TypeThe partitions of electionsthis topic towhose conductleader forshould thebe partitionelected." 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." } ] }, { "name] } |
Response
Added a top level property called ErrorCode for returning errors that apply to all the topic partitions. The current implementation is using this to return cluster authorization errors.
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{ "apiKey": 43, "type": "TimeoutMsresponse", "typename": "int32ElectLeadersResponse", "versionsvalidVersions": "0+-1", "fields": [ { "name": "ThrottleTimeMs", "type": "int32", "defaultversions": "600000+", "about": "The timeduration in ms to wait for the election to completemilliseconds for which the request was throttled due to a quota violation, or zero if the request did not violate any quota." }, { ] } |
AdminClient Abstract Class
A new method will be added to the AdminClient abstract class to support this new version of the RPC.
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package org.apache.kafka.clients.admin; public abstract class AdminClient ... {"name": "ErrorCode", "type": "int16", "versions": "1+", "ignorable": false, ... "about": /** * 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. *"The top level response error code." }, { "name": "ReplicaElectionResults", "type": "[]ReplicaElectionResult", "versions": "0+", "about": "The election results, or an empty array if the requester did not have permission and the request asks for all partitions.", "fields": [ * 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 "name": "Topic", "type": "string", "versions": "0+", "entityType": "topicName", "about": "The topic name" }, { "name": "PartitionResult", "type": "[]PartitionResult", "versions": "0+", "about": "The results for each partition", "fields": [ { "name": "PartitionId", "type": "int32", The options to use when electing the leaders. * @return"versions": "0+", "about": "The partition id" }, { "name": "ErrorCode", "type": "int16", "versions": "0+", "about": "The ElectLeadersResult. result error, or zero if */ there was public abstract ElectLeadersResult electLeaders(no error."}, { "name": "ErrorMessage", Collection<TopicPartitionElection> partitionElections, "type": "string", "versions": "0+", "nullableVersions": "0+", ElectLeadersOptions options); } |
TopicPartitionElection Class
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package org.apache.kafka.common; public final class TopicPartitionElection { public static enum ElectionType { "about": "The result message, or null if there was no error."} PREFERRED((byte) 0), UNCLEANED((byte) 1); public final byte value; ElectionType(byte value) { this.value = value; } }]} ]} ] } |
AdminClient Abstract Class
A new method will be added to the AdminClient abstract class to support this new version of the RPC.
When the partition parameter is null the controller will attempt the election type on all of partitions that are legible for election. This means that the RPC will only return success or failure on partition that eligible for election as oppose to all of the partitions in the cluster as the previous implemented behaved.
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package org.apache.kafka.clients.admin; public abstract class AdminClient ... { ... public/** final TopicPartition topicPartition; * ... public final ElectionType electionType; * @deprecated Since 2.4.. } |
Admin Command
The command kafka-preferred-replica-election.{sh,bat} will be deprecated and the following command will be added.
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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. Option0. Use {@link #electLeaders}. */ @Deprecated public abstract ElectPreferredLeadersResult electPreferredLeaders(Collection<TopicPartition> partitions, Description ------ ElectPreferredLeadersOptions options); /** ----------- --admin.config <String: config file> Admin client config properties file to * ... * * @param electionType The type of election. * @param partitions The partitions for which to conduct passelections. to the admin client when* -- @param options The options to use when electing the leaders. * @return bootstrap-server is given. --bootstrap-server <String: host:port> A host name and port for the brokerThe toElectLeadersResult. */ public abstract ElectLeadersResult electLeaders( ElectionType electionType, Set<TopicPartition> partitions, connect to, in the form host:port. ElectLeadersOptions options); } |
ElectLeaderResult Class
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final public ElectLeadersResult { ... public KafkaFuture<Map<TopicPartition, Optional<Throwable>>> partitions() { ... } public KafkFuture<Void> all() { Multiple comma-separated URLs can be... } } |
ElectionType Enumeration
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package org.apache.kafka.common; public enum ElectionType { PREFERRED((byte) 0), UNCLEAN((byte) 1); public final byte value; ElectionType(byte value) { this.value = value; } } |
Admin Command
The command kafka-preferred-replica-election.{sh,bat} will be deprecated and the following command will be added.
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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. Optiongiven. REQUIRED unless --zookeeper is given. --help Print usage information. Description ---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> ----------- --admin.config <String: config file> Admin client config properties file to pass to the admin are 0 for preferredclient and 1 for uncleaned. when --bootstrap-server is given. --all-topic-partitions Perform election on all of the topic partitions. Not allowed if If an election is not specified, --topic, --partition or --path-to-json-file is specified. --bootstrap-server <String: host:port> A host name and port for the broker to preferred is the default. This is an connect to, in the example formatform host:port. {"partitions": Multiple comma-separated URLs can be [{"topic": "foo", "partition": 1},given. REQUIRED unless --zookeeper {"topic": "foobar", "partition": 2, "election": 1}] is given. --election-type <String: election> Type of election to attempt. Possible values are "preferred" } for preferred election or "unclean" for unclean election. Defaults to all existing partitions REQUIRED. --topic <String: topic> Name of topic for which to perform an election. REQUIRED if --partition is specified. Not allowed if --path-to-json-file or --all-topic-partitions is specified. --partition <Integer: partition id> Partition id for which to perform an election. REQUIRED if --topic is specified. Not allowed if --path-to-json-file or --all-topic-partitions is specified. --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 unclean. If an election is not specified, preferred is the default. This is an example format. {"partitions": [{"topic": "foo", "partition": 1}, {"topic": "foobar", "partition": 2}] } Not allowed if --all-topic-partitions, --topic or --partition flags are specified. |
Metrics
The following metrics were added:
- kafka.server:type=DelayedOperationPurgatory,name=NumDelayedOperations,delayedOperation=ElectLeader
- kafka.server:type=DelayedOperationPurgatory,name=PurgatorySize,delayedOperation=ElectLeader
While the following metrics were removed:
- kafka.server:type=DelayedOperationPurgatory,name=NumDelayedOperations,delayedOperation=ElectPreferredLeader
- kafka.server:type=DelayedOperationPurgatory,name=PurgatorySize,delayedOperation=ElectPreferredLeader
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 supports preferred leader election from the admin client. Unclean leader election can only be enabled through either a topic configuration change or a broker configuration change.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 supports preferred leader election from the admin client. Unclean leader election can only be enabled through either a topic configuration change or a broker configuration change.
When performing unclean leader election on a topic partition through the admin client the "unclean leader election" topic configuration and broker configuration will be ignored. In the code this will result is code similar to the one below:
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uncleanElectionFromAdminClient || logConfigs(partition.topic).uncleanLeaderElectionEnable.booleanValue() |
Compatibility, Deprecation, and Migration Plan
- The kafka-preferred-replica-elections.{sh,bat} scripts will be deprecated.
- The electPreferredLeaders method in AdminClient will be deprecated.
- The DelayedOperationPurgatory metrics ElectPreferredLeader were replaced with ElectLeader
Rejected Alternatives
Not applicable.