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From "Sean Mackrory (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12151) Hadoop 2 clients cannot writeBlock to Hadoop 3 DataNodes
Date Mon, 17 Jul 2017 22:23:01 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12151?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16090677#comment-16090677
] 

Sean Mackrory commented on HDFS-12151:
--------------------------------------

The problem is in lines added by HDFS-9807. When serving clients from before that feature,
no storage Ids will be provided, but we unconditionally address the first element in the array.
I was able to do a successful rolling upgrade from HDFS 2 -> HDFS 3 by just checking the
length first, and passing in null by default.

> Hadoop 2 clients cannot writeBlock to Hadoop 3 DataNodes
> --------------------------------------------------------
>
>                 Key: HDFS-12151
>                 URL: https://issues.apache.org/jira/browse/HDFS-12151
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: rolling upgrades
>            Reporter: Sean Mackrory
>            Assignee: Sean Mackrory
>
> Trying to write to a Hadoop 3 DataNode with a Hadoop 2 client currently fails. On the
client side it looks like this:
> {code}
>     17/07/14 13:31:58 INFO hdfs.DFSClient: Exception in createBlockOutputStream
>     java.io.EOFException: Premature EOF: no length prefix available
>             at org.apache.hadoop.hdfs.protocolPB.PBHelper.vintPrefixed(PBHelper.java:2280)
>             at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.createBlockOutputStream(DFSOutputStream.java:1318)
>             at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1237)
>             at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:449){code}
> But on the DataNode side there's an ArrayOutOfBoundsException because there aren't any
targetStorageIds:
> {code}
>     java.lang.ArrayIndexOutOfBoundsException: 0
>             at org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:815)
>             at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:173)
>             at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:107)
>             at org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:290)
>             at java.lang.Thread.run(Thread.java:745){code}



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