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https://issues.apache.org/jira/browse/HDFS-9422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15007908#comment-15007908
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He Liangliang commented on HDFS-9422:
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No, the lock can make NO difference, EXCEPT we move the getDiskReport() call
inside the lock. But we don't need the diff in-sync because latter there will
be double-check in checkAndUpdate which is protected by the lock.
> Unnecessary FsDatasetImpl locking in DirectoryScanner cause periodic datanode
> pauses
> ------------------------------------------------------------------------------------
>
> Key: HDFS-9422
> URL: https://issues.apache.org/jira/browse/HDFS-9422
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: He Liangliang
> Assignee: He Liangliang
> Attachments: HDFS-9422.patch
>
>
> In DirectoryScanner, the scan call hold the global dataset lock for quite
> long time (typically > 5 secs for 500k blocks). This will stuck the client
> which need acquire this lock. For applications like HBase, this will affect
> the latency. In fact, this lock is unnecessary.
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