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https://issues.apache.org/jira/browse/HDFS-15160?focusedWorklogId=649577&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-649577
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ASF GitHub Bot logged work on HDFS-15160:
-----------------------------------------

                Author: ASF GitHub Bot
            Created on: 11/Sep/21 11:52
            Start Date: 11/Sep/21 11:52
    Worklog Time Spent: 10m 
      Work Description: Hexiaoqiao merged pull request #3200:
URL: https://github.com/apache/hadoop/pull/3200


   


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Issue Time Tracking
-------------------

    Worklog Id:     (was: 649577)
    Time Spent: 5h 50m  (was: 5h 40m)

> ReplicaMap, Disk Balancer, Directory Scanner and various FsDatasetImpl 
> methods should use datanode readlock
> -----------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-15160
>                 URL: https://issues.apache.org/jira/browse/HDFS-15160
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 3.3.0
>            Reporter: Stephen O'Donnell
>            Assignee: Stephen O'Donnell
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 3.3.1, 3.4.0
>
>         Attachments: HDFS-15160-branch-3.3-001.patch, HDFS-15160.001.patch, 
> HDFS-15160.002.patch, HDFS-15160.003.patch, HDFS-15160.004.patch, 
> HDFS-15160.005.patch, HDFS-15160.006.patch, HDFS-15160.007.patch, 
> HDFS-15160.008.patch, HDFS-15160.branch-3-3.001.patch, 
> image-2020-04-10-17-18-08-128.png, image-2020-04-10-17-18-55-938.png
>
>          Time Spent: 5h 50m
>  Remaining Estimate: 0h
>
> Now we have HDFS-15150, we can start to move some DN operations to use the 
> read lock rather than the write lock to improve concurrence. The first step 
> is to make the changes to ReplicaMap, as many other methods make calls to it.
> This Jira switches read operations against the volume map to use the readLock 
> rather than the write lock.
> Additionally, some methods make a call to replicaMap.replicas() (eg 
> getBlockReports, getFinalizedBlocks, deepCopyReplica) and only use the result 
> in a read only fashion, so they can also be switched to using a readLock.
> Next is the directory scanner and disk balancer, which only require a read 
> lock.
> Finally (for this Jira) are various "low hanging fruit" items in BlockSender 
> and fsdatasetImpl where is it fairly obvious they only need a read lock.
> For now, I have avoided changing anything which looks too risky, as I think 
> its better to do any larger refactoring or risky changes each in their own 
> Jira.



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