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From "GAO Rui (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10710) In BlockManager#rescanPostponedMisreplicatedBlocks(), postponed misreplicated block counts should be retrieved with NN lock protection
Date Tue, 09 Aug 2016 07:38:21 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10710?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15413118#comment-15413118
] 

GAO Rui commented on HDFS-10710:
--------------------------------

Thanks for your comment and commit, [~jingzhao]!

> In BlockManager#rescanPostponedMisreplicatedBlocks(), postponed misreplicated block counts
should be retrieved with NN lock protection
> --------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-10710
>                 URL: https://issues.apache.org/jira/browse/HDFS-10710
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>            Reporter: GAO Rui
>            Assignee: GAO Rui
>             Fix For: 2.8.0
>
>         Attachments: HDFS-10710.1.patch
>
>
> In BlockManager#rescanPostponedMisreplicatedBlocks(), start and end block counts should
be get with the protect with lock. Or, log records like "-1 blocks are removed" which indicate
minus blocks are removed could be generated. 
> For example, following scenario:
> 1. thread1 run {{long startPostponedMisReplicatedBlocksCount = getPostponedMisreplicatedBlocksCount();}}
currently  startPostponedMisReplicatedBlocksCount get the value 20.
> 2. before thread1 run {{namesystem.writeLock();}} , thread2 increment postponedMisreplicatedBlocksCount
by 1, so postponedMisreplicatedBlocksCount is 21 now.
> 3. thread1 end the iteration, but no postponed block is removed, so after run {{long
endPostponedMisReplicatedBlocksCount = getPostponedMisreplicatedBlocksCount();}}, endPostponedMisReplicatedBlocksCount
get the value of 21.
> 4. thread 1 generate the log:
> {noformat}
>       LOG.info("Rescan of postponedMisreplicatedBlocks completed in " +
>           (Time.monotonicNow() - startTimeRescanPostponedMisReplicatedBlocks) +
>           " msecs. " + endPostponedMisReplicatedBlocksCount +
>           " blocks are left. " + (startPostponedMisReplicatedBlocksCount -
>           endPostponedMisReplicatedBlocksCount) + " blocks are removed.");
> {noformat}
> Then, we'll get the log record like "-1 blocks are removed."



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