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From "He Xiaoqiao (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8992) Balancer throws NPE
Date Sat, 29 Aug 2015 08:29:45 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8992?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14721015#comment-14721015
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He Xiaoqiao commented on HDFS-8992:
-----------------------------------

Thanks Tsz Wo Nicholas Sze for your comments, there is only one line of stack trace:
{code}
2015-06-29 14:06:35,280 WARN org.apache.hadoop.hdfs.server.balancer.Balancer: Dispatcher thread
failed
java.lang.NullPointerException
{code}

> Balancer throws NPE
> -------------------
>
>                 Key: HDFS-8992
>                 URL: https://issues.apache.org/jira/browse/HDFS-8992
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: balancer & mover
>    Affects Versions: 2.4.1
>            Reporter: He Xiaoqiao
>
> Balancer may throw NPE because the following {{if Statements}}
> {code:java|firstline=705}
>           synchronized (block) {
>             // update locations
>             for (String datanodeUuid : blk.getDatanodeUuids()) {
>               final BalancerDatanode d = datanodeMap.get(datanodeUuid);
>               if (datanode != null) { // not an unknown datanode
>                 block.addLocation(d);
>               }
>             }
>           }
> {code}
> Before moving block, Balancer divides into two step to get all DNs info & some blocks
of DN from NN. Regarding one DN commission after {{getDatanodeReport}} then {{getBlockList}}
and one block's target is above DN just right, It will throw NPE when dispatcher.



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