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https://issues.apache.org/jira/browse/HDFS-6908?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14310489#comment-14310489
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Harsh J commented on HDFS-6908:
-------------------------------
bq. and since it doesn't fix the corrupt fsimage on disk, the hack will always
be needed to make the namenode work.
When the NN comes up (ensure you also have this bugfix patched on), you can
then invoke a {{dfsadmin -saveNamespace}} to recreate a new, good image.
> 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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