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https://issues.apache.org/jira/browse/HDFS-12363?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16143387#comment-16143387
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Xiao Chen commented on HDFS-12363:
----------------------------------
{{datanodeManager}} is a final member var that's initialized in the ctor and
referenced earlier in the same method, so it doesn't look null.
The line number is likely due to JIT compiler optimization and / or similar
complications at JVM runtime, which simply marked the first line for a
multi-line NPE.
Since NN lock was released and reacquired, we should handle null for
{{getDatanode}} (since {{getStorageInfo}} is already handled).
> Possible NPE in BlockManager$StorageInfoDefragmenter#scanAndCompactStorages
> ---------------------------------------------------------------------------
>
> Key: HDFS-12363
> URL: https://issues.apache.org/jira/browse/HDFS-12363
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.6.0
> Reporter: Xiao Chen
> Assignee: Xiao Chen
>
> Saw NN going down with NPE below:
> {noformat}
> ERROR org.apache.hadoop.hdfs.server.blockmanagement.BlockManager: Thread
> received Runtime exception.
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$StorageInfoDefragmenter.scanAndCompactStorages(BlockManager.java:3897)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$StorageInfoDefragmenter.run(BlockManager.java:3852)
> at java.lang.Thread.run(Thread.java:745)
> 2017-08-21 22:14:05,303 INFO org.apache.hadoop.util.ExitUtil: Exiting with
> status 1
> 2017-08-21 22:14:05,313 INFO org.apache.hadoop.hdfs.server.namenode.NameNode:
> {noformat}
> In that version, {{BlockManager}} code is:
> {code}
> 3896 try {
> 3897 DatanodeStorageInfo storage = datanodeManager.
> 3898 getDatanode(datanodesAndStorages.get(i)).
> 3899 getStorageInfo(datanodesAndStorages.get(i + 1));
> 3900 if (storage != null) {
> {code}
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