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https://issues.apache.org/jira/browse/HDFS-16402?focusedWorklogId=705862&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-705862
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ASF GitHub Bot logged work on HDFS-16402:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 10/Jan/22 01:52
Start Date: 10/Jan/22 01:52
Worklog Time Spent: 10m
Work Description: tomscut commented on pull request #3839:
URL: https://github.com/apache/hadoop/pull/3839#issuecomment-1008483869
> It's good catch here. Would you mind to add new test to cover this case?
BTW, what is the root cause about NPE here? Thanks.
Thanks @Hexiaoqiao for your review and comments.
The main reason is that the `DatanodeDescriptor#storageMap` cannot find the
storage that DN reports through `lifeline`. As a result, the `NPE` is thrown
in line 460 of the code when the storage is operated.
Here is the scenario we encountered:
1 We add a disk to datanode and reconfig `dfs.datanode.data.dir`.
2 After a while, many values on NN's Web become negative.
3 We found the NPE from the NN log and discovered this issue
[HDFS-14042](https://issues.apache.org/jira/browse/HDFS-14042).
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Issue Time Tracking
-------------------
Worklog Id: (was: 705862)
Time Spent: 40m (was: 0.5h)
> HeartbeatManager may cause incorrect stats
> ------------------------------------------
>
> Key: HDFS-16402
> URL: https://issues.apache.org/jira/browse/HDFS-16402
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: tomscut
> Assignee: tomscut
> Priority: Major
> Labels: pull-request-available
> Attachments: image-2021-12-29-08-25-44-303.png,
> image-2021-12-29-08-25-54-441.png
>
> Time Spent: 40m
> Remaining Estimate: 0h
>
> After reconfig {*}dfs.datanode.data.dir{*}, we found that the stats of the
> Namenode Web became *negative* and there were many NPE in namenode logs. This
> problem has been solved by HDFS-14042.
> !image-2021-12-29-08-25-54-441.png|width=681,height=293!
> !image-2021-12-29-08-25-44-303.png|width=677,height=180!
> However, if *HeartbeatManager#updateHeartbeat* and
> *HeartbeatManager#updateLifeline* throw other exceptions, stats errors can
> also occur. We should ensure that *stats.subtract()* and *stats.add()* are
> transactional.
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