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https://issues.apache.org/jira/browse/HDFS-4600?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13603592#comment-13603592
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Roman Shaposhnik commented on HDFS-4600:
----------------------------------------
As Colin pointed out -- there are different ways of looking at it. I still
consider the difference between READ and APPEND code path to be artificial and
surprising to the user. Imagine a POSIX open(2) giving you different behavior
based on whether you specified O_APPEND or not.
What I'm worried about here is not a pathological use case of a 2 node cluster
but cases where files are over-replicated (for the purposes of availability)
and can NOT be appended to by default. Of course, given that this can be
controlled on a client side -- this makes it less of a problem.
> HDFS file append failing in multinode cluster
> ---------------------------------------------
>
> Key: HDFS-4600
> URL: https://issues.apache.org/jira/browse/HDFS-4600
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.0.3-alpha
> Reporter: Roman Shaposhnik
> Priority: Minor
> Fix For: 2.0.4-alpha
>
> Attachments: core-site.xml, hdfs-site.xml, X.java
>
>
> NOTE: the following only happens in a fully distributed setup (core-site.xml
> and hdfs-site.xml are attached)
> Steps to reproduce:
> {noformat}
> $ javac -cp /usr/lib/hadoop/client/\* X.java
> $ echo aaaaa > a.txt
> $ hadoop fs -ls /tmp/a.txt
> ls: `/tmp/a.txt': No such file or directory
> $ HADOOP_CLASSPATH=`pwd` hadoop X /tmp/a.txt
> 13/03/13 16:05:14 WARN hdfs.DFSClient: DataStreamer Exception
> java.io.IOException: Failed to replace a bad datanode on the existing
> pipeline due to no more good datanodes being available to try. (Nodes:
> current=[10.10.37.16:50010, 10.80.134.126:50010],
> original=[10.10.37.16:50010, 10.80.134.126:50010]). The current failed
> datanode replacement policy is DEFAULT, and a client may configure this via
> 'dfs.client.block.write.replace-datanode-on-failure.policy' in its
> configuration.
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.findNewDatanode(DFSOutputStream.java:793)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.addDatanode2ExistingPipeline(DFSOutputStream.java:858)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.setupPipelineForAppendOrRecovery(DFSOutputStream.java:964)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:470)
> Exception in thread "main" java.io.IOException: Failed to replace a bad
> datanode on the existing pipeline due to no more good datanodes being
> available to try. (Nodes: current=[10.10.37.16:50010, 10.80.134.126:50010],
> original=[10.10.37.16:50010, 10.80.134.126:50010]). The current failed
> datanode replacement policy is DEFAULT, and a client may configure this via
> 'dfs.client.block.write.replace-datanode-on-failure.policy' in its
> configuration.
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.findNewDatanode(DFSOutputStream.java:793)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.addDatanode2ExistingPipeline(DFSOutputStream.java:858)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.setupPipelineForAppendOrRecovery(DFSOutputStream.java:964)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:470)
> 13/03/13 16:05:14 ERROR hdfs.DFSClient: Failed to close file /tmp/a.txt
> java.io.IOException: Failed to replace a bad datanode on the existing
> pipeline due to no more good datanodes being available to try. (Nodes:
> current=[10.10.37.16:50010, 10.80.134.126:50010],
> original=[10.10.37.16:50010, 10.80.134.126:50010]). The current failed
> datanode replacement policy is DEFAULT, and a client may configure this via
> 'dfs.client.block.write.replace-datanode-on-failure.policy' in its
> configuration.
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.findNewDatanode(DFSOutputStream.java:793)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.addDatanode2ExistingPipeline(DFSOutputStream.java:858)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.setupPipelineForAppendOrRecovery(DFSOutputStream.java:964)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:470)
> {noformat}
> Given that the file actually does get created:
> {noformat}
> $ hadoop fs -ls /tmp/a.txt
> Found 1 items
> -rw-r--r-- 3 root hadoop 6 2013-03-13 16:05 /tmp/a.txt
> {noformat}
> this feels like a regression in APPEND's functionality.
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