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The group coordinator has to determine which assignment strategy must be used for the group. The group's members may not have exactly the same assignors at any given point in time - e.g. they may migrate from an assignor to another one for instance. The group coordinator will chose the assignor as follow:

A client side assignor is used if possible. This means that a client side assignor must be supported by all the members. If multiple are, it will respect the precedence defined by the members when they advertise their supported client side assignors.
A The server side assignor is used if any member specified oneotherwise. If multiple server side assignors are specified in the group, the group coordinator uses the most common one. The client side assignor is used otherwise. The If a member does not provide an assignor, the group coordinator will use the assignor which is supported by all the members in the group and, if multiple are, it will respect the precedence defined by the members when they advertise their supposed default to the first one in group.consumer.assignors.

Server Side Mode

The server side assignor is pluggable and the client can choose the one that it wants to use by providing its name in the heartbeat request. If the selected assignor does not exist, the group coordinator will reject the heartbeat with an UNSUPPORTED_ASSIGNOR error. The list of supported assignors will be configured in the broker configuration.

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Code Block

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{
  "apiKey": TBD,
  "type": "request",
  "listeners": ["zkBroker", "broker"],
  "name": "ConsumerGroupHeartbeatRequest",
  "validVersions": "0",
  "flexibleVersions": "0+",
  "fields": [
      { "name": "GroupId", "type": "string", "versions": "0+", "entityType": "groupId",
        "about": "The group identifier." },
      { "name": "MemberId", "type": "string", "versions": "0+",
        "about": "The member id generated by the server. The member id must be kept during the entire lifetime of the member." },
      { "name": "MemberEpoch", "type": "int32", "versions": "0+", "default": "-1",
        "about": "The current member epoch; 0 to join the group; -1 to leave the group." },
      { "name": "InstanceId", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
        "about": "null if not provided or if it didn't change since the last heartbeat; the instance Id otherwise." },
      { "name": "RackId", "type": "string", "versions": "0+",  "nullableVersions": "0+", "default": "null",
        "about": "null if not provided or if it didn't change since the last heartbeat; the rack ID of consumer otherwise." },
      { "name": "RebalanceTimeoutMs", "type": "int32", "versions": "0+", "default": -1,
        "about": "-1 if it didn't chance since the last heartbeat; the maximum time in milliseconds that the coordinator will wait on the member to revoke its partitions otherwise." },
      { "name": "SubscribedTopicIds", "type": "[]uuid", "versions": "0+", "nullableVersions": "0+", "default": "null",
        "about": "null if it didn't change since the last heartbeat; the subscribed topic ids otherwise." },
      { "name": "SubscribedTopicRegex", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
        "about": "null if it didn't change since the last heartbeat; the subscribed topic regex otherwise" },
      { "name": "ServerAssignor", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
        "about": "null if not used or if it didn't change since the last heartbeat; the server side assignor to use otherwise." }, 
      { "name": "ClientAssignors", "type": "[]Assignor", "versions": "0+", "nullableVersions": "0+", "default": "null",
        "about": "null if not used or if it didn't change since the last heartbeat; the list of client-side assignors otherwise.", "fields": [
          { "name": "Name", "type": "string", "versions": "0+",
            "about": "The name of the assignor." },
          { "name": "MinimumVersion", "type": "int16", "versions": "0+",
            "about": "The minimum supported version for the metadata." },
          { "name": "MaximumVersion", "type": "int16", "versions": "0+",
            "about": "The maximum supported version for the metadata." },
          { "name": "Reason", "type": "int8", "versions": "0+",
            "about": "The reason of the metadata update." }, 
          { "name": "MetadataVersion", "type": "int16", "versions": "0+",
            "about": "The version of the metadata." },
          { "name": "MetadataBytes", "type": "bytes", "versions": "0+",
            "about": "The metadata." }
      ]},
      { "name": "TopicPartitions", "type": "[]TopicPartitionTopicPartitions", "versions": "0+", "nullableVersions": "0+", "default": "null",
        "about": "null if it didn't change since the last heartbeat; the partitions owned by the member.", "fields": [
          { "name": "TopicId", "type": "uuid", "versions": "0+",
            "about": "The topic ID." },
          { "name": "Partitions", "type": "[]int32", "versions": "0+",
            "about": "The partitions." }
      ]}
  ]
}

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Code Block

language	js
linenumbers	true

{
  "apiKey": TBD,
  "type": "response",
  "name": "ConsumerGroupHeartbeatResponse",
  "validVersions": "0",
  "flexibleVersions": "0+",
  // Supported errors:
  // - GROUP_AUTHORIZATION_FAILED
  // - NOT_COORDINATOR
  // - COORDINATOR_NOT_AVAILABLE
  // - COORDINATOR_LOAD_IN_PROGRESS
  // - INVALID_REQUEST
  // - UNKNOWN_MEMBER_ID
  // - FENCED_MEMBER_EPOCH
  // - UNSUPPORTED_ASSIGNOR
  "fields": [
    { "name": "ThrottleTimeMs", "type": "int32", "versions": "0+",
      "about": "The duration in milliseconds for which the request was throttled due to a quota violation, or zero if the request did not violate any quota." },
    { "name": "ErrorCode", "type": "int16", "versions": "0+",
      "about": "The top-level error code, or 0 if there was no error" },
    { "name": "ErrorMessage", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "The top-level error message, or null if there was no error." },
    { "name": "MemberEpoch", "type": "int32", "versions": "0+",
      "about": "The member epoch." },
    { "name": "ShouldComputeAssignment", "type": "bool", "versions": "0+",
      "about": "True if the member should compute the assignment for the group." },
    { "name": "HeartbeatIntervalMs", "type": "int32", "versions": "0+",
      "about": "The heartbeat interval in milliseconds." }, 
    { "name": "Assignment", "type": "Assignment", "versions": "0+", "nullableVersions": "0+", "default": "null",
	  "about": "null if not provided; the assignment otherwise.", "fields": [
        { "name": "Error", "type": "int8", "versions": "0+",
          "about": "The assigned error." },
        { "name": "AssignedTopicPartitions", "type": "[]TopicPartitionTopicPartitions", "versions": "0+",
          "about": "The partitions assigned to the member that can be used immediately." },
        { "name": "PendingTopicPartitions", "type": "[]TopicPartitionTopicPartitions", "versions": "0+",
          "about": "The partitions assigned to the member that cannot be used because they are not released by their former owners yet." },
        { "name": "MetadataVersion", "type": "int16", "versions": "0+",
          "about": "The version of the metadata." },
        { "name": "MetadataBytes", "type": "bytes", "versions": "0+",
          "about": "The assigned metadata." }
	]}
  ],
  "commonStructs": [
    { "name": "TopicPartitions", "versions": "0+", "fields": [
        { "name": "TopicId", "type": "uuid", "versions": "0+",
          "about": "The topic ID." },
        { "name": "Partitions", "type": "[]int32", "versions": "0+",
          "about": "The partitions." }
    ]}
  ]
}

...

Code Block

language	js
linenumbers	true

{
  "apiKey": 71,
  "type": "response",
  "name": "ConsumerGroupDescribeResponse",
  "validVersions": "0",
  "flexibleVersions": "0+",
  // Supported errors: 
  // - GROUP_AUTHORIZATION_FAILED
  // - NOT_COORDINATOR
  // - COORDINATOR_NOT_AVAILABLE
  // - COORDINATOR_LOAD_IN_PROGRESS
  // - INVALID_REQUEST
  // - INVALID_GROUP_ID
  // - GROUP_ID_NOT_FOUND
  "fields": [
    { "name": "ThrottleTimeMs", "type": "int32", "versions": "0+",
      "about": "The duration in milliseconds for which the request was throttled due to a quota violation, or zero if the request did not violate any quota." },
    { "name": "Groups", "type": "[]DescribedGroup", "versions": "0+",
      "about": "Each described group.",
      "fields": [
        { "name": "ErrorCode", "type": "int16", "versions": "0+",
          "about": "The describe error, or 0 if there was no error." },
        { "name": "ErrorMessage", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
          "about": "The top-level error message, or null if there was no error." }
        { "name": "GroupId", "type": "string", "versions": "0+", "entityType": "groupId",
          "about": "The group ID string." },
        { "name": "GroupState", "type": "string", "versions": "0+",
          "about": "The group state string, or the empty string." },
        { "name": "GroupEpoch", "type": "int32", "versions": "0+",
          "about": "The group epoch." },
        { "name": "AssignmentEpoch", "type": "int32", "versions": "0+",
          "about": "The assignment epoch." },
        { "name": "AssignorName", "type": "string", "versions": "0+",
          "about": "The selected assignor." },
        { "name": "Members", "type": "[]Member", "versions": "0+",
          "about": "The members.",
          "fields": [
          { "name": "MemberId", "type": "uuid", "versions": "0+",
            "about": "The member ID." },
          { "name": "InstanceId", "type": "string", "versions": "0+",  "nullableVersions": "0+", "default": "null", 
            "about": "The member instance ID." },
          { "name": "RackId", "type": "string", "versions": "0+",  "nullableVersions": "0+", "default": "null", 
            "about": "The member rack ID." },
          { "name": "MemberEpoch", "type": "int32", "versions": "0+",
            "about": "The current member epoch." },
          { "name": "ClientId", "type": "string", "versions": "0+",
            "about": "The client ID." },
          { "name": "ClientHost", "type": "string", "versions": "0+",
            "about": "The client host." },
          { "name": "ClientHostSubscribedTopicIds", "type": "string[]uuid", "versions": "0+",
            "about": "The clientsubscribed topic hostIDs." },
          { "name": "SubscribedTopicIdsSubscribedTopicRegex", "type": "[]uuidstring", "versions": "0+", "nullableVersions": "0+", "default": "null",
            "about": "Thethe subscribed topic IDs regex otherwise or null of not provided." },
              { "name": "Assignment", "type": "Assignment", "versions": "0+",
            "about": "The current assignment.",
            "fields": [
            { "name": "Partitions", "type": "[]TopicPartitionTopicPartitions", "versions": "0+",
              "about": "The assigned topic-partitions to the member.",
              "fields": [
                { "name": "TopicId", "type": "uuid", "versions": "0+",
                  "about": "The topic ID." },
                { "name": "Partitions", "type": "[]int32", "versions": "0+",
                  "about": "The partitions." }
              ]},
            { "name": "Version", "type": "int32", "versions": "0+",
              "about": "The assignor metadata version." }
            { "name": "Metadata", "type": "bytes", "versions": "0+",
              "about": "The assignor metadata bytes." }
          ]},
          { "name": "TargetAssignment", "type": "Assignment", "versions": "0+",
            "about": "The target assignment.",
            "fields": [
            { "name": "Partitions", "type": "[]TopicPartitionTopicPartitions", "versions": "0+",
              "about": "The assigned topic-partitions to the member.",
              "fields": [
                { "name": "TopicId", "type": "uuid", "versions": "0+",
                  "about": "The topic ID." },
                { "name": "Partitions", "type": "[]int32", "versions": "0+",
                  "about": "The partitions." }
              ]},
            { "name": "Version", "type": "int32", "versions": "0+",
              "about": "The assignor metadata version." }
            { "name": "Metadata", "type": "bytes", "versions": "0+",
              "about": "The assignor metadata bytes." }
          ]},
      { "name": "AuthorizedOperations", "type": "int32", "versions": "3+", "default": "-2147483648",
        "about": "32-bit bitfield to represent authorized operations for this group." }
    ]}
  ]
}

...

Code Block

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linenumbers	true

{
  "apiKey": 9,
  "type": "request",
  "listeners": ["zkBroker", "broker"],
  "name": "OffsetFetchRequest",
  // In version 0, the request read offsets from ZK.
  //
  // Starting in version 1, the broker supports fetching offsets from the internal __consumer_offsets topic.
  //
  // Starting in version 2, the request can contain a null topics array to indicate that offsets
  // for all topics should be fetched. It also returns a top level error code
  // for group or coordinator level errors.
  //
  // Version 3, 4, and 5 are the same as version 2.
  //
  // Version 6 is the first flexible version.
  //
  // Version 7 is adding the require stable flag.
  //
  // Version 8 is adding support for fetching offsets for multiple groups at a time
  //
  // Version 9 adds GenerationIdOrMemberEpoch, MemberId and TopicId fields (KIP-848).
  "validVersions": "0-9",
  "flexibleVersions": "6+",
  "fields": [
    { "name": "GroupId", "type": "string", "versions": "0-7", "entityType": "groupId",
      "about": "The group to fetch offsets for." },
    // New fields.
    { "name": "GenerationIdOrMemberEpoch", "type": "int32", "versions": "9+", "default": "-1", "ignorable": true,
      "about": "The generation of the group." },
    { "name": "MemberId", "type": "string", "versions": "9+", "ignorable": true,
        "about": "The member ID assigned by the group coordinator." },
    // End of new fields.
    { "name": "Topics", "type": "[]OffsetFetchRequestTopic", "versions": "0-7", "nullableVersions": "2-7",
      "about": "Each topic we would like to fetch offsets for, or null to fetch offsets for all topics.", "fields": [
      { "name": "Name", "type": "string", "versions": "0-7", "entityType": "topicName",
        "about": "The topic name."},
      { "name": "PartitionIndexes", "type": "[]int32", "versions": "0-7",
        "about": "The partition indexes we would like to fetch offsets for." }
    ]},
    { "name": "Groups", "type": "[]OffsetFetchRequestGroup", "versions": "8+",
      "about": "Each group we would like to fetch offsets for", "fields": [
      { "name": "groupId", "type": "string", "versions": "8+", "entityType": "groupId",
        "about": "The group ID."},
      { "name": "Topics", "type": "[]OffsetFetchRequestTopics", "versions": "8+", "nullableVersions": "8+",
        "about": "Each topic we would like to fetch offsets for, or null to fetch offsets for all topics.", "fields": [
        // Updated field.
        { "name": "Name", "type": "string", "versions": "8+", "nullableVersions": "9+", "default": "null", "entityType": "topicName",
          "about": "The topic name."},
        // New field.
        { "name": "TopicId", "type": "uuid", "versions": "9+", "about": "The unique topic ID" },
        { "name": "PartitionIndexes", "type": "[]int32", "versions": "8+",
          "about": "The partition indexes we would like to fetch offsets for." }
      ]}
    ]},
    { "name": "RequireStable", "type": "bool", "versions": "7+", "default": "false",
      "about": "Whether broker should hold on returning unstable offsets but set a retriable error code for the partitions."}
  ]
}

...

The MemberId and the GenerationIdOrMemberEpoch are verified. STALE_MEMBER_EPOCH, UNKNOWN_MEMBER_ID or ILLEGAL_GENERATION is returned accordingly.

The admin client is not expected to provide the MemberId nor the GenerationIdOrMemberEpoch.

Response Schema

Code Block

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{
  "apiKey": 9,
  "type": "response",
  "name": "OffsetFetchResponse",
  // Version 1 is the same as version 0.
  //
  // Version 2 adds a top-level error code.
  //
  // Version 3 adds the throttle time.
  //
  // Starting in version 4, on quota violation, brokers send out responses before throttling.
  //
  // Version 5 adds the leader epoch to the committed offset.
  //
  // Version 6 is the first flexible version.
  //
  // Version 7 adds pending offset commit as new error response on partition level.
  //
  // Version 8 is adding support for fetching offsets for multiple groups
  //
  // Version 9 adds TopicId field and can return STALE_MEMBER_EPOCH, UNKNOWN_MEMBER_ID,
  // ILLEGAL_GENERATION, and UNKNOWN_TOPIC_ID errors.
  "validVersions": "0-8",
  "flexibleVersions": "6+",
  "fields": [
    { "name": "ThrottleTimeMs", "type": "int32", "versions": "3+", "ignorable": true,
      "about": "The duration in milliseconds for which the request was throttled due to a quota violation, or zero if the request did not violate any quota." },
    { "name": "Topics", "type": "[]OffsetFetchResponseTopic", "versions": "0-7",
      "about": "The responses per topic.", "fields": [
      { "name": "Name", "type": "string", "versions": "0-7", "entityType": "topicName",
        "about": "The topic name." },
      { "name": "Partitions", "type": "[]OffsetFetchResponsePartition", "versions": "0-7",
        "about": "The responses per partition", "fields": [
        { "name": "PartitionIndex", "type": "int32", "versions": "0-7",
          "about": "The partition index." },
        { "name": "CommittedOffset", "type": "int64", "versions": "0-7",
          "about": "The committed message offset." },
        { "name": "CommittedLeaderEpoch", "type": "int32", "versions": "5-7", "default": "-1",
          "ignorable": true, "about": "The leader epoch." },
        { "name": "Metadata", "type": "string", "versions": "0-7", "nullableVersions": "0-7",
          "about": "The partition metadata." },
        { "name": "ErrorCode", "type": "int16", "versions": "0-7",
          "about": "The error code, or 0 if there was no error." }
      ]}
    ]},
    { "name": "ErrorCode", "type": "int16", "versions": "2-7", "default": "0", "ignorable": true,
      "about": "The top-level error code, or 0 if there was no error." },
    { "name": "Groups", "type": "[]OffsetFetchResponseGroup", "versions": "8+",
      "about": "The responses per group id.", "fields": [
      { "name": "groupId", "type": "string", "versions": "8+", "entityType": "groupId",
        "about": "The group ID." },
      { "name": "Topics", "type": "[]OffsetFetchResponseTopics", "versions": "8+",
        "about": "The responses per topic.", "fields": [
        { "name": "Name", "type": "string", "versions": "8+", "nullableVersions": "9+", "default": "null", "entityType": "topicName",
          "about": "The topic name."},
        { "name": "TopicId", "type": "uuid", "versions": "9+", "about": "The unique topic ID" },
        { "name": "Partitions", "type": "[]OffsetFetchResponsePartitions", "versions": "8+",
          "about": "The responses per partition", "fields": [
          { "name": "PartitionIndex", "type": "int32", "versions": "8+",
            "about": "The partition index." },
          { "name": "CommittedOffset", "type": "int64", "versions": "8+",
            "about": "The committed message offset." },
          { "name": "CommittedLeaderEpoch", "type": "int32", "versions": "8+", "default": "-1",
            "ignorable": true, "about": "The leader epoch." },
          { "name": "Metadata", "type": "string", "versions": "8+", "nullableVersions": "8+",
            "about": "The partition metadata." },
          { "name": "ErrorCode", "type": "int16", "versions": "8+",
            "about": "The partition-level error code, or 0 if there was no error." }
        ]}
      ]},
      { "name": "ErrorCode", "type": "int16", "versions": "8+", "default": "0",
        "about": "The group-level error code, or 0 if there was no error." }
    ]}
  ]
}

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Code Block

language	java
linenumbers	true

package org.apache.kafka.server.group.consumer;

public interface PartitionAssignor {

    class AssignmentSpec {
        /**
         * The members keyed by member id.
         */
        Map<String, AssignmentMemberSpec> members;

        /**
         * The topics' metadata keyed by topic id
         */
        Map<Uuid, AssignmentTopicMetadata> topics;
    }

    class AssignmentMemberSpec {
        /**
         * The instance ID if provided.
         */
        Optional<String> instanceId;

        /**
         * The rack ID if provided.
         */
        Optional<String> rackId;

        /**
         * The set of topics that the member is subscribed to.
         */
        List<String>Collection<String> subscribedTopics;

        /**
         * The current target partitions of the member.
         */
        List<TopicPartition>Collection<TopicPartition> targetPartitions;
    }

    class AssignmentTopicMetadata {
        /**
         * The topic name.
         */
        String topicName;

        /**
		 * The number of partitions.
		 */
		int numPartitions; 
    }

    class GroupAssignment {
        /**
         * The member assignments keyed by member id.
         */
        Map<String, MemberAssignment> members;
    }

    class MemberAssignment {
        /**
         * The target partitions assigned to this member.
         */
        List<TopicPartition>Collection<TopicPartition> targetPartitions;
    }

    /**
     * Unique name for this assignor.
     */
    String name();

    /**
     * Perform the group assignment given the current members and
     * topic metadata.
     *
     * @param assignmentSpec The assignment spec.
     * @return The new assignment for the group.
     */
    GroupAssignment assign(AssignmentSpec assignmentSpec) throws PartitionAssignorException;
}

...

Name	Type	Default	Doc
group.coordinator.threads	int	1	The number of threads used to run the state machines.
group.consumer.session.timeout.ms	int	45s	The timeout to detect client failures when using the consumer group protocol.
group.consumer.min.session.timeout.ms	int	45s	The minimum session timeout.
group.consumer.max.session.timeout.ms	int	60s	The maximum session timeout.
group.consumer.heartbeat.interval.ms	int	5s	The heartbeat interval given to the members.
group.consumer.min.heartbeat.interval.ms	int	5s	The minimum heartbeat interval.
group.consumer.max.heartbeat.interval.ms	int	15s	The maximum heartbeat interval.
group.consumer.max.size	int	MaxValue	The maximum number of consumers that a single consumer group can accommodate.
group.consumer.assignors	Listlist	range, uniform	The server side assignors as a list of full class names. The first one in the list is considered as the default assignor to be used in the case where the consumer does not specify an assignor.

Group Configurations

New dynamic group properties.

...

Code Block

language	java
linenumbers	true

package org.apache.kafka.clients.consumer;
  
public interface PartitionAssignor {

    class Metadata {
        /**
         * The metadata version.
         */
        int version;

        /**
         * The metadata bytes.
         */
        ByteBuffer bytes;
    }

    class AssignmentSpec {
        /**
         * The members keyed by member id.
         */
        Map<String, AssignmentMemberSpec> members;

        /**
         * The topics' metadata keyed by topic id
         */
        Map<Uuid, AssignmentTopicMetadata> topics;
    }

    class AssignmentMemberSpec {
        /**
         * The instance ID if provided.
         */
        Optional<String> instanceId;

        /**
         * The rack ID if provided.
         */
        Optional<String> rackId;

        /**
         * The set of topics that the member is subscribed to.
         */
        List<String>Collection<String> subscribedTopics;

   		/**
		 * The reason reported by the member.
		 */
		byte reason;  

		/**
		 * The metadata reported by the member.
		 */
        Metadata metadata;

        /**
         * The current target partitions of the member.
         */
        List<TopicPartition>Collection<TopicPartition> targetPartitions;
    }

    class AssignmentTopicMetadata {
        /**
         * The topic name.
         */
        String topicName;

        /**
		 * The number of partitions.
		 */
		int numPartitions; 
    }

    class GroupAssignment {
        /**
         * The assignment error.
         */
		byte error;

        /**
         * The member assignments keyed by member id.
         */
        Map<String, MemberAssignment> members;
    }

    class MemberAssignment {
        /**
         * The target partitions assigned to this member.
         */
        List<TopicPartition>Collection<TopicPartition> targetPartitions;

 		/**
		 * The metadata.
		 */
		Metadata metadata;
    }

	class AssignorMetadata {
   		/**
		 * The reason reported by the assignor.
		 */
		byte reason; 

 		/**
		 * The metadata reported by the assignor.
		 */
		Metadata metadata;
    }

    /**
     * Unique name for this assignor.
     */
    String name();

    /**
     * The minimum version.
     */
    int minimumVersion();

    /**
     * The maximum version.
     */
    int maximumVersion();

    /**
     * Return assignor metadata that will be sent to the assignor.
     */
    AssignorMetadata metadata();

    /**
     * Perform the group assignment given the current members and
     * topic metadata.
     *
     * @param assignmentSpec The assignment spec.
     * @return The new assignment for the group.
     */
    GroupAssignment assign(AssignmentSpec assignmentSpec);

    /**
     * Callback which is invoked when the member received a new assignment 
     * from the assignor/group coordinator. This is called once per epoch
     * and contains the target partitions for this members. This means that
     * partitions may not be assigned to the member yet. The rebalance
     * listener must be used to know this.
     * 
     * @param byte The error reported by the assignor.
     * @param assignment The assignment computed by the assignor.
     * @param consumerGroupMetadata The group metadata.
     */
    void onAssignment(byte error, MemberAssignment assignment, ConsumerGroupMetadata consumerGroupMetadata);
}

...

Name	Type	Default	Doc
group.protocol	enum	generic	A flag which indicates if the new protocol should be used or not. It could be: generic or consumer
group.remote.assignor	string	uniformnull	The server side assignor to use. It cannot be used in conjunction with group.local.assignor. `null` means that the choice of the assignor is left to the group coordinator.
group.local.assignors	list	empty	The list of client side (local) assignors as a list of full class names. It cannot be used in conjunction with group.remote.assignor.

...

Group (epoch=2)

A
B

Target Assignment (epoch=2)

A - partitions=[foo-0, foo-1]
B - partitions=[foo-2]

Member Assignment

A - epoch=2, partitions=[foo-0, foo-1], pending-partitions=[]
B - epoch=2, partitions=[foo-2], pending-partitions=[foo-2]

When B heartbeats, he can now gets foo-2.

...

The group coordinator sees that C does not own any partitions any more, so it can transition to epoch 23 and transition to CompletingRebalance. The transition to epoch 23 is important here because the new epoch must be given to the member in the JoinGroup response. This is the new generation of the group for him.

Group (epoch=23)

A (upgraded)
C (CompletingRebalance)

Target Assignment (epoch=23)

A - partitions=[foo-0, foo-1, foo-3]
C - partitions=[foo-2, foo-5, foo-4]

Member Assignment

A - epoch=22, partitions=[foo-0, foo-1], pending-partitions=[]
C - epoch=23, partitions=[foo-2, foo-5, foo-4], pending-partitions=[]

...

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Old Version 79

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Key

Server Side Mode

Response Schema

Group Configurations