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什么是协调器
协调器工作原理
协调器的 Rebalance 机制
1 协调器的生命周期
GroupCoordinator 的创建
在 Kafka 启动的时候, 会自动创建并启动 GroupCoordinator
这个 GroupCoordinator 对象创建的时候传入的几个属性需要介绍一下
new GroupCoordinator(config.brokerId, groupConfig, offsetConfig, groupMetadataManager, heartbeatPurgatory, joinPurgatory, time, metrics)
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offsetConfig 相关配置
private[group] def offsetConfig(config: KafkaConfig) = OffsetConfig( maxMetadataSize = config.offsetMetadataMaxSize, loadBufferSize = config.offsetsLoadBufferSize, offsetsRetentionMs = config.offsetsRetentionMinutes * 60L * 1000L, offsetsRetentionCheckIntervalMs = config.offsetsRetentionCheckIntervalMs, offsetsTopicNumPartitions = config.offsetsTopicPartitions, offsetsTopicSegmentBytes = config.offsetsTopicSegmentBytes, offsetsTopicReplicationFactor = config.offsetsTopicReplicationFactor, offsetsTopicCompressionCodec = config.offsetsTopicCompressionCodec, offsetCommitTimeoutMs = config.offsetCommitTimeoutMs, offsetCommitRequiredAcks = config.offsetCommitRequiredAcks )
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groupConfig 相关配置
groupMetadataManager
组元信息管理类
heartbeatPurgatory
心跳监测操作，每一秒执行一次
joinPurgatory
GroupCoordinator 的启动
def startup(enableMetadataExpiration: Boolean = true): Unit = { info("Starting up.") groupManager.startup(enableMetadataExpiration) isActive.set(true) info("Startup complete.") }
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这个启动对于 GroupCoordinator 来说只是给属性isActive标记为了 true, 但是同时呢也调用了GroupMetadataManager.startup
定时清理 Group 元信息
这个 Group 元信息管理类呢启动了一个定时任务, 名字为：delete-expired-group-metadata
每隔 600000ms 的时候就执行一下 清理过期组元信息的操作, 这个 600000ms 时间是代码写死的。
TODO:GroupMetadataManager#cleanupGroupMetadata
GroupCoordinator OnElection
当内部 topic __consumer_offsets 有分区的 Leader 变更的时候,比如触发了 LeaderAndIsr 的请求, 发现分区 Leader 进行了切换。
那么就会执行 GroupCoordinator#OnElection 的接口, 这个接口会把任务丢个一个单线程的调度程序, 专门处理 offset 元数据缓存加载和卸载的。线程名称前缀为group-metadata-manager- ，一个分区一个任务
最终执行的任务内容是：GroupMetadataManager#doLoadGroupsAndOffsets
__consumer_offsets 的 key 有两种消息类型
key version 0: 消费组消费偏移量信息 -> value version 0: [offset, metadata, timestamp]
key version 1: 消费组消费偏移量信息-> value version 1: [offset, metadata, commit_timestamp, expire_timestamp]
key version 2: 消费组的元信息 -> value version 0: [protocol_type, generation, protocol, leader,
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例如 version:3 的 schemaForGroupValue
Version-0
{ protocol_type: STRING, generation: INT32, protocol: NULLABLE_STRING, leader: NULLABLE_STRING, members: ARRAY({ member_id: STRING, client_id: STRING, client_host: STRING, session_timeout: INT32, subscription: BYTES, assignment: BYTES })}
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Version-1
{ protocol_type: STRING, generation: INT32, protocol: NULLABLE_STRING, leader: NULLABLE_STRING, members: ARRAY({ member_id: STRING, client_id: STRING, client_host: STRING, rebalance_timeout: INT32, session_timeout: INT32, subscription: BYTES, assignment: BYTES })}
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Version-2
{ protocol_type: STRING, generation: INT32, protocol: NULLABLE_STRING, leader: NULLABLE_STRING, current_state_timestamp: INT64, members: ARRAY({ member_id: STRING, client_id: STRING, client_host: STRING, rebalance_timeout: INT32, session_timeout: INT32, subscription: BYTES, assignment: BYTES })}
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Version-3
{ protocol_type: STRING, generation: INT32, protocol: NULLABLE_STRING, leader: NULLABLE_STRING, current_state_timestamp: INT64, members: ARRAY({ member_id: STRING, group_instance_id: NULLABLE_STRING, client_id: STRING, client_host: STRING, rebalance_timeout: INT32, session_timeout: INT32, subscription: BYTES, assignment: BYTES })}
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Value 每个版本的 Scheme 如下
private val GROUP_METADATA_VALUE_SCHEMA_V0 = new Schema( new Field(PROTOCOL_TYPE_KEY, STRING), new Field(GENERATION_KEY, INT32), new Field(PROTOCOL_KEY, NULLABLE_STRING), new Field(LEADER_KEY, NULLABLE_STRING), new Field(MEMBERS_KEY, new ArrayOf(MEMBER_METADATA_V0)))
private val GROUP_METADATA_VALUE_SCHEMA_V1 = new Schema( new Field(PROTOCOL_TYPE_KEY, STRING), new Field(GENERATION_KEY, INT32), new Field(PROTOCOL_KEY, NULLABLE_STRING), new Field(LEADER_KEY, NULLABLE_STRING), new Field(MEMBERS_KEY, new ArrayOf(MEMBER_METADATA_V1)))
private val GROUP_METADATA_VALUE_SCHEMA_V2 = new Schema( new Field(PROTOCOL_TYPE_KEY, STRING), new Field(GENERATION_KEY, INT32), new Field(PROTOCOL_KEY, NULLABLE_STRING), new Field(LEADER_KEY, NULLABLE_STRING), new Field(CURRENT_STATE_TIMESTAMP_KEY, INT64), new Field(MEMBERS_KEY, new ArrayOf(MEMBER_METADATA_V2)))
private val GROUP_METADATA_VALUE_SCHEMA_V3 = new Schema( new Field(PROTOCOL_TYPE_KEY, STRING), new Field(GENERATION_KEY, INT32), new Field(PROTOCOL_KEY, NULLABLE_STRING), new Field(LEADER_KEY, NULLABLE_STRING), new Field(CURRENT_STATE_TIMESTAMP_KEY, INT64), new Field(MEMBERS_KEY, new ArrayOf(MEMBER_METADATA_V3)))
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GroupCoordinator onResignation
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