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https://issues.apache.org/jira/browse/HDFS-7884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14352826#comment-14352826
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Brahma Reddy Battula commented on HDFS-7884:
--------------------------------------------
Thanks a lot for your detailed analysis, I also feel same..
Cause : Reader is trying to read using the old block Id But the original
block's gs was modified after appending.
When client is latest and DN have old GS, then only throw exception. Othercase
it should support read according to code.Here we missed the case when DN is
having the lastest GS and client is having the old GS..( GS will not be checked
while getting the replica and initializing the BlockSender)..Hence we need
handle..
> NullPointerException in BlockSender
> -----------------------------------
>
> Key: HDFS-7884
> URL: https://issues.apache.org/jira/browse/HDFS-7884
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Brahma Reddy Battula
> Priority: Blocker
> Attachments: HDFS-7884.patch,
> org.apache.hadoop.hdfs.TestAppendSnapshotTruncate-output.txt
>
>
> {noformat}
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.datanode.BlockSender.<init>(BlockSender.java:264)
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.readBlock(DataXceiver.java:506)
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opReadBlock(Receiver.java:116)
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:71)
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:249)
> at java.lang.Thread.run(Thread.java:745)
> {noformat}
> BlockSender.java:264 is shown below
> {code}
> this.volumeRef = datanode.data.getVolume(block).obtainReference();
> {code}
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