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https://issues.apache.org/jira/browse/HDFS-4996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13712949#comment-13712949
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Hudson commented on HDFS-4996:
------------------------------

SUCCESS: Integrated in Hadoop-trunk-Commit #4112 (See 
[https://builds.apache.org/job/Hadoop-trunk-Commit/4112/])
HDFS-4996. ClientProtocol#metaSave can be made idempotent by overwriting the 
output file instead of appending to it. Contributed by Chris Nauroth. 
(cnauroth: 
http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1504679)
* 
/hadoop/common/trunk/hadoop-common-project/hadoop-common/src/site/apt/CommandsManual.apt.vm
* /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
* 
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
* 
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DFSAdmin.java
* 
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestMetaSave.java

                
> ClientProtocol#metaSave can be made idempotent by overwriting the output file 
> instead of appending to it
> --------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-4996
>                 URL: https://issues.apache.org/jira/browse/HDFS-4996
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 3.0.0, 2.1.0-beta
>            Reporter: Chris Nauroth
>            Assignee: Chris Nauroth
>            Priority: Minor
>         Attachments: HDFS-4996.1.patch, HDFS-4996.2.patch
>
>
> {{ClientProtocol#metaSave}} opens its output file for append.  This prevents 
> the operation from being idempotent, because retries can cause unpredictable 
> side effects (single copy of the output vs. multiple copies).  As discussed 
> on HDFS-4974, the operation could be made idempotent by changing this to open 
> the file for overwrite instead of append.

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