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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7492) If multiple threads call FsVolumeList#checkDirs at the same time, we should only do checkDirs once and give the results to all waiting threads
Date Thu, 17 Sep 2015 18:53:04 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7492?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14803419#comment-14803419
] 

Colin Patrick McCabe commented on HDFS-7492:
--------------------------------------------

[~eclark], also check HDFS-8845 for another improvement in this area.

> If multiple threads call FsVolumeList#checkDirs at the same time, we should only do checkDirs
once and give the results to all waiting threads
> ----------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-7492
>                 URL: https://issues.apache.org/jira/browse/HDFS-7492
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>            Reporter: Colin Patrick McCabe
>            Assignee: Elliott Clark
>            Priority: Minor
>
> checkDirs is called when we encounter certain I/O errors.  It's rare to get just a single
I/O error... normally you start getting many errors when a disk is going bad.  For this reason,
we shouldn't start a new checkDirs scan for each error.  Instead, if multiple threads call
FsVolumeList#checkDirs at around the same time, we should only do checkDirs once and give
the results to all the waiting threads.



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