persist consumer group offset

1. use one follower
2. read write consumer group offset

weed/mq/client/pub_client/scheduler.go

@@ -145,7 +145,7 @@ func (p *TopicPublisher) doPublishToPartition(job *EachPartitionPublishJob) erro
 				Topic:           p.config.Topic.ToPbTopic(),
 				Partition:       job.Partition,
 				AckInterval:     128,
-				FollowerBrokers: job.FollowerBrokers,
+				FollowerBroker:  job.FollowerBroker,
 				PublisherName:   p.config.PublisherName,
 			},
 		},

weed/mq/client/sub_client/connect_to_sub_coordinator.go

@@ -102,11 +102,10 @@ func (sub *TopicSubscriber) onEachPartition(assigned *mq_pb.BrokerPartitionAssig
 					Topic:         sub.ContentConfig.Topic.ToPbTopic(),
 					PartitionOffset: &mq_pb.PartitionOffset{
 						Partition: assigned.Partition,
-						StartTsNs: sub.alreadyProcessedTsNs,
 						StartType: mq_pb.PartitionOffsetStartType_EARLIEST_IN_MEMORY,
 					},
 					Filter: sub.ContentConfig.Filter,
-					FollowerBrokers: assigned.FollowerBrokers,
+					FollowerBroker: assigned.FollowerBroker,
 				},
 			},
 		});err != nil {
@@ -154,7 +153,6 @@ func (sub *TopicSubscriber) onEachPartition(assigned *mq_pb.BrokerPartitionAssig
 				if processErr != nil {
 					return fmt.Errorf("process error: %v", processErr)
 				}
-				sub.alreadyProcessedTsNs = m.Data.TsNs
 				partitionOffsetChan <- m.Data.TsNs
 				if !shouldContinue {
 					return nil

weed/mq/client/sub_client/subscriber.go

@@ -37,7 +37,6 @@ type TopicSubscriber struct {
 	OnCompletionFunc           OnCompletionFunc
 	bootstrapBrokers           []string
 	waitForMoreMessage         bool
-	alreadyProcessedTsNs       int64
 	activeProcessors           map[topic.Partition]*ProcessorState
 	activeProcessorsLock       sync.Mutex
 }
@@ -50,7 +49,6 @@ func NewTopicSubscriber(bootstrapBrokers []string, subscriber *SubscriberConfigu
 		brokerPartitionAssignmentChan: make(chan *mq_pb.BrokerPartitionAssignment, 1024),
 		bootstrapBrokers:              bootstrapBrokers,
 		waitForMoreMessage:            true,
-		alreadyProcessedTsNs:          content.StartTime.UnixNano(),
 		activeProcessors:              make(map[topic.Partition]*ProcessorState),
 	}
 }