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https://issues.apache.org/jira/browse/HDFS-4600?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13603036#comment-13603036
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Tsz Wo (Nicholas), SZE commented on HDFS-4600:
----------------------------------------------
Hi Roman, append and create are different in the sense that there is existing
data in before append. The existing data were already persisted in HDFS
earlier. The replace-datanode-on-failure feature is to prevent data lost. For
append, it makes sure there are enough datanodes to protect the existing data.
It is very useful for slow appender. The feature can be disabled by setting
dfs.client.block.write.replace-datanode-on-failure.enable if it is undesirable.
This JIRA is similar to HDFS-3091.
> 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: Blocker
> 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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