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From "He Liangliang (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-9422) Unnecessary FsDatasetImpl locking in DirectoryScanner cause periodic datanode pauses
Date Fri, 13 Nov 2015 08:28:10 GMT

     [ https://issues.apache.org/jira/browse/HDFS-9422?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

He Liangliang updated HDFS-9422:
--------------------------------
    Attachment: HDFS-9422.patch

The lock is unnecessary:
1. getFinalizedBlocks is thread safe and the returned block list is a deep copy, so the lock
does not protect any extra shared data
2. the latter checkAndUpdate call is also thread safe and will filter out the false alarm

> 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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