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https://issues.apache.org/jira/browse/HDFS-10512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15353315#comment-15353315
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Wei-Chiu Chuang commented on HDFS-10512:
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Hi [~linyiqun] much appreciate your patch. The patch itself looks good to me.
However, I have been hesitate to give my non-binding +1, because when this
method is being called, a block is corrupt. After this patch, VolumeScanner
will not terminate prematurely, which is good, but it still won't tell NameNode
to mark this replica corrupt. And that's still a really bad thing to have.
Any comments? [~xyao] or other watchers?
Do you think this patch should go in despite we do not know the root cause of
NPE?
This is a really bad bug, which causes pipeline to abort, because it will never
transmit correct block to the downstream pipeline, and pipeline can not
construct three good replicas.
BTW, I have found the root cause of corrupt replica, and I'll file another jira
today, but I still think it would be nice to know what causes NPE.
> VolumeScanner may terminate to due NPE in DataNode.reportBadBlocks
> ------------------------------------------------------------------
>
> Key: HDFS-10512
> URL: https://issues.apache.org/jira/browse/HDFS-10512
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Wei-Chiu Chuang
> Assignee: Yiqun Lin
> Attachments: HDFS-10512.001.patch, HDFS-10512.002.patch
>
>
> VolumeScanner may terminate due to unexpected NullPointerException thrown in
> {{DataNode.reportBadBlocks()}}. This is different from HDFS-8850/HDFS-9190
> I observed this bug in a production CDH 5.5.1 cluster and the same bug still
> persist in upstream trunk.
> {noformat}
> 2016-04-07 20:30:53,830 WARN
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner: Reporting bad
> BP-1800173197-10.204.68.5-1444425156296:blk_1170134484_96468685 on /dfs/dn
> 2016-04-07 20:30:53,831 ERROR
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner: VolumeScanner(/dfs/dn,
> DS-89b72832-2a8c-48f3-8235-48e6c5eb5ab3) exiting because of exception
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.datanode.DataNode.reportBadBlocks(DataNode.java:1018)
> at
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner$ScanResultHandler.handle(VolumeScanner.java:287)
> at
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner.scanBlock(VolumeScanner.java:443)
> at
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner.runLoop(VolumeScanner.java:547)
> at
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner.run(VolumeScanner.java:621)
> 2016-04-07 20:30:53,832 INFO
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner: VolumeScanner(/dfs/dn,
> DS-89b72832-2a8c-48f3-8235-48e6c5eb5ab3) exiting.
> {noformat}
> I think the NPE comes from the volume variable in the following code snippet.
> Somehow the volume scanner know the volume, but the datanode can not lookup
> the volume using the block.
> {code}
> public void reportBadBlocks(ExtendedBlock block) throws IOException{
> BPOfferService bpos = getBPOSForBlock(block);
> FsVolumeSpi volume = getFSDataset().getVolume(block);
> bpos.reportBadBlocks(
> block, volume.getStorageID(), volume.getStorageType());
> }
> {code}
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