Struct GroupMetadata 

pub struct GroupMetadata {
    pub message_version: i16,
    pub group: String,
    pub is_tombstone: bool,
    pub schema_version: i16,
    pub protocol_type: String,
    pub generation: i32,
    pub protocol: String,
    pub leader: String,
    pub current_state_timestamp: i64,
    pub members: Vec<MemberMetadata>,
}

Contains the current state of a consumer group.

It is used by the Group Coordinator Broker to track:

1. which consumer is subscribed to what topic
2. which consumer is assigned of which partition

The metadata are divided into 2 classes:

1. Membership metadata
   • Members registered in this group
   • Current protocol assigned to the group (e.g. partition assignment strategy for consumers)
   • Protocol metadata associated with group members
2. State metadata
   • Consumer group state
   • Generation ID
   • Leader ID

Compared to OffsetCommit, GroupMetadata appears relatively infrequently in __consumer_offsets: this is because it’s usually produced when consumers join or leave groups.

Kafka uses code generation to materialise GroupMetadata into Java code, and this is composed of 2 json definitions, that at compile time get turned into Java Classes: GroupMetadataKey and GroupMetadataValue.

Note: As this data is parsed from a message, each field is marked with (KEY) or (PAYLOAD), depending to what part of the message they were parsed from.

Fields

message_version: i16

(KEY) First 2-bytes integers in the original __consumer_offsets, identifying this data type.

This controls the bespoke binary parser behaviour.

group: String

(KEY) Group that this struct describes.

is_tombstone: bool

(PAYLOAD) Is this from a tombstone message?

If this is true, this struct doesn’t represent group, but the removal of this specific key (i.e. group) from __consumer_offsets.

If you are tracking this data, this can be used as a “can be removed” signal: likely all consumers of this particular group are gone, and something explicitly removed their group membership information.

The removal follows the Log Compaction rules of Kafka.

schema_version: i16

(PAYLOAD) Informs the parser of what data and in which format, the rest of the payload contains.

This controls the bespoke binary parser behaviour.

protocol_type: String

(PAYLOAD) The class (type) of GroupMetadata::protocol used by this group.

Possible values are consumer or connect.

If value is consumer, it indicates that GroupMetadata::protocol will describes the type of ConsumerPartitionAssignor used by the Group Coordinator.

If the value is connect, it indicates that GroupMetadata::protocol will describes the type of ConnectAssignor used by the WorkerCoordinator.

generation: i32

(PAYLOAD) Monotonically increasing integers, changes when group members change.

This is useful when concurrent operations get out of order, and original order has to be determined.

protocol: String

(PAYLOAD) The protocol of GroupMetadata::protocol_type used by this group.

If protocol_type == consumer, this field will contain the identifier of an implementation of ConsumerPartitionAssignor.

If protocol_type == connect, this field will contain the identifier of an implementation of ConnectAssignor.

leader: String

(PAYLOAD) Identifier (ID) of the GroupMetadata::members leader.

This corresponds to the MemberMetadata::id of one of the Self::members.

current_state_timestamp: i64

(PAYLOAD) Timestamp of when this Group State was captured.

This timestamp is produced to __consumer_offsets by the Group Coordinator: to interpret it correctly, its important to know its timezone.

NOTE: The type of this field is controlled by the ts_* feature flags.

members: Vec<MemberMetadata>

(PAYLOAD) Members that are part of this GroupMetadata::group.

Trait Implementations

impl Clone for GroupMetadata

fn clone(&self) -> GroupMetadata

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for GroupMetadata

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for GroupMetadata

fn default() -> GroupMetadata

Returns the “default value” for a type.

impl PartialEq for GroupMetadata

fn eq(&self, other: &GroupMetadata) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for GroupMetadata

impl StructuralPartialEq for GroupMetadata