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https://issues.apache.org/jira/browse/HDFS-6908?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14310628#comment-14310628
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Abhishek Rai commented on HDFS-6908:
------------------------------------
Thanks Harsh, that sounds reasonable. It gives us a way to avoid having to
live with the FSImageFormatPBSnapshot hack longer term once the proper fix for
this bug is applied.
Thanks
> incorrect snapshot directory diff generated by snapshot deletion
> ----------------------------------------------------------------
>
> Key: HDFS-6908
> URL: https://issues.apache.org/jira/browse/HDFS-6908
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: snapshots
> Reporter: Juan Yu
> Assignee: Juan Yu
> Priority: Critical
> Fix For: 2.6.0
>
> Attachments: HDFS-6908.001.patch, HDFS-6908.002.patch,
> HDFS-6908.003.patch
>
>
> In the following scenario, delete snapshot could generate incorrect snapshot
> directory diff and corrupted fsimage, if you restart NN after that, you will
> get NullPointerException.
> 1. create a directory and create a file under it
> 2. take a snapshot
> 3. create another file under that directory
> 4. take second snapshot
> 5. delete both files and the directory
> 6. delete second snapshot
> incorrect directory diff will be generated.
> Restart NN will throw NPE
> {code}
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.namenode.snapshot.FSImageFormatPBSnapshot$Loader.addToDeletedList(FSImageFormatPBSnapshot.java:246)
> at
> org.apache.hadoop.hdfs.server.namenode.snapshot.FSImageFormatPBSnapshot$Loader.loadDeletedList(FSImageFormatPBSnapshot.java:265)
> at
> org.apache.hadoop.hdfs.server.namenode.snapshot.FSImageFormatPBSnapshot$Loader.loadDirectoryDiffList(FSImageFormatPBSnapshot.java:328)
> at
> org.apache.hadoop.hdfs.server.namenode.snapshot.FSImageFormatPBSnapshot$Loader.loadSnapshotDiffSection(FSImageFormatPBSnapshot.java:192)
> at
> org.apache.hadoop.hdfs.server.namenode.FSImageFormatProtobuf$Loader.loadInternal(FSImageFormatProtobuf.java:254)
> at
> org.apache.hadoop.hdfs.server.namenode.FSImageFormatProtobuf$Loader.load(FSImageFormatProtobuf.java:168)
> at
> org.apache.hadoop.hdfs.server.namenode.FSImageFormat$LoaderDelegator.load(FSImageFormat.java:208)
> at
> org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSImage(FSImage.java:906)
> at
> org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSImage(FSImage.java:892)
> at
> org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSImageFile(FSImage.java:715)
> at
> org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSImage(FSImage.java:653)
> at
> org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:276)
> at
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.loadFSImage(FSNamesystem.java:882)
> at
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.loadFromDisk(FSNamesystem.java:629)
> at
> org.apache.hadoop.hdfs.server.namenode.NameNode.loadNamesystem(NameNode.java:498)
> at
> org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:554)
> {code}
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