golang kafka sarama 源码解析

• 消费者组重平衡

github.com/!shopify/sarama@v1.27.2/consumer_group.go

func (c *consumerGroup) newSession(ctx context.Context, topics []string, handler ConsumerGroupHandler, retries int) (*consumerGroupSession, error) {// 获取broker组协调器coordinator, err := c.client.Coordinator(c.groupID)if err != nil {if retries <= 0 {return nil, err}return c.retryNewSession(ctx, topics, handler, retries, true)}// 申请加入组// Join consumer groupjoin, err := c.joinGroupRequest(coordinator, topics)if err != nil {_ = coordinator.Close()return nil, err}switch join.Err {case ErrNoError:c.memberID = join.MemberIdcase ErrUnknownMemberId, ErrIllegalGeneration: // reset member ID and retry immediatelyc.memberID = ""return c.newSession(ctx, topics, handler, retries)case ErrNotCoordinatorForConsumer: // retry after backoff with coordinator refreshif retries <= 0 {return nil, join.Err}return c.retryNewSession(ctx, topics, handler, retries, true)// 已经在重平衡期间case ErrRebalanceInProgress: // retry after backoffif retries <= 0 {return nil, join.Err}return c.retryNewSession(ctx, topics, handler, retries, false)default:return nil, join.Err}// 消费者组中的一个消费者作为leader，进行分区方案分配// Prepare distribution plan if we joined as the leadervar plan BalanceStrategyPlanif join.LeaderId == join.MemberId {members, err := join.GetMembers()if err != nil {return nil, err}// 分配分区plan, err = c.balance(members)if err != nil {return nil, err}}// 同步给kafka,只有 leader会带上分区方案// Sync consumer groupgroupRequest, err := c.syncGroupRequest(coordinator, plan, join.GenerationId)if err != nil {_ = coordinator.Close()return nil, err}switch groupRequest.Err {case ErrNoError:case ErrUnknownMemberId, ErrIllegalGeneration: // reset member ID and retry immediatelyc.memberID = ""return c.newSession(ctx, topics, handler, retries)case ErrNotCoordinatorForConsumer: // retry after backoff with coordinator refreshif retries <= 0 {return nil, groupRequest.Err}return c.retryNewSession(ctx, topics, handler, retries, true)case ErrRebalanceInProgress: // retry after backoffif retries <= 0 {return nil, groupRequest.Err}return c.retryNewSession(ctx, topics, handler, retries, false)default:return nil, groupRequest.Err}// Retrieve and sort claimsvar claims map[string][]int32 // topic->partions// 如果有可消费的分区if len(groupRequest.MemberAssignment) > 0 {members, err := groupRequest.GetMemberAssignment()if err != nil {return nil, err}claims = members.Topicsc.userData = members.UserDatafor _, partitions := range claims {sort.Sort(int32Slice(partitions))}}return newConsumerGroupSession(ctx, c, claims, join.MemberId, join.GenerationId, handler)
}

• 消费者拉取消息

func (c *consumer) newBrokerConsumer(broker *Broker) *brokerConsumer {bc := &brokerConsumer{consumer:         c,broker:           broker,input:            make(chan *partitionConsumer),newSubscriptions: make(chan []*partitionConsumer),wait:             make(chan none),subscriptions:    make(map[*partitionConsumer]none),refs:             0,}go withRecover(bc.subscriptionManager)go withRecover(bc.subscriptionConsumer)return bc
}