[jira] [Commented] (KAFKA-7704) kafka.server.ReplicaFetechManager.MaxLag.Replica metric is reported incorrectly

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    [ https://issues.apache.org/jira/browse/KAFKA-7704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16708142#comment-16708142 ] 

ASF GitHub Bot commented on KAFKA-7704:
---------------------------------------

huxihx opened a new pull request #5998: KAFKA-7704: MaxLag.Replica metric is reported incorrectly
URL: https://github.com/apache/kafka/pull/5998
 
 
   On the follower side, for the empty `LogAppendInfo` retrieved from the leader, fetcherLagStats set the wrong lag for fetcherLagStats due to `nextOffset` is zero in this case where it actually means no lagging, so the lag should be set to 0 if `nextOffset` is 0 or `logAppendInfo.lastOffset` is -1.
   
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   - [ ] Verify design and implementation 
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> kafka.server.ReplicaFetechManager.MaxLag.Replica metric is reported incorrectly
> -------------------------------------------------------------------------------
>
>                 Key: KAFKA-7704
>                 URL: https://issues.apache.org/jira/browse/KAFKA-7704
>             Project: Kafka
>          Issue Type: Bug
>          Components: metrics
>    Affects Versions: 2.1.0
>            Reporter: Yu Yang
>            Priority: Major
>         Attachments: Screen Shot 2018-12-03 at 4.33.35 PM.png
>
>
> We recently deployed kafka 2.1, and noticed a jump in kafka.server.ReplicaFetcherManager.MaxLag.Replica metric. At the same time, there is no under-replicated partitions for the cluster. 
> The initial analysis shows that kafka 2.1.0 does not report metric correctly for topics that have no incoming traffic right now, but had traffic earlier. For those topics, ReplicaFetcherManager will consider the maxLag be the latest offset. 
> For instance, we have a topic named `test_topic`: 
> {code}
> [root@kafkabroker03002:/mnt/kafka/test_topic-0]# ls -l
> total 8
> -rw-rw-r-- 1 kafka kafka 10485760 Dec  4 00:13 00000000099043947579.index
> -rw-rw-r-- 1 kafka kafka        0 Sep 23 03:01 00000000099043947579.log
> -rw-rw-r-- 1 kafka kafka       10 Dec  4 00:13 00000000099043947579.snapshot
> -rw-rw-r-- 1 kafka kafka 10485756 Dec  4 00:13 00000000099043947579.timeindex
> -rw-rw-r-- 1 kafka kafka        4 Dec  4 00:13 leader-epoch-checkpoint
> {code}
> kafka reports ReplicaFetcherManager.MaxLag.Replica be 99043947579
>  !Screen Shot 2018-12-03 at 4.33.35 PM.png|width=720px! 



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