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https://issues.apache.org/jira/browse/HDFS-3107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14148430#comment-14148430
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Plamen Jeliazkov commented on HDFS-3107:
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Attaching a new patch. I have included a separate file called "editsStored" to 
the attachments. This is a binary editLog segment that belongs in 
test/resources directory.
Without that binary file in place we can expect 
TestOfflineEditsViewer.testStored() to fail. I cannot seem to add in a binary 
file to a patch.

Turns out the following tests also needed to be fixed up to account for a new 
FSEditLogOp:
# TestNameNodeRetryCache
# TestRetryCacheWithHA

# I added in [~jingzhao]'s catch for the snapshot check. I now make use of 
INode.isInLatestSnapshot() instead.

> HDFS truncate
> -------------
>
>                 Key: HDFS-3107
>                 URL: https://issues.apache.org/jira/browse/HDFS-3107
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: datanode, namenode
>            Reporter: Lei Chang
>            Assignee: Plamen Jeliazkov
>         Attachments: HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, 
> HDFS-3107.patch, HDFS-3107.patch, HDFS_truncate.pdf, 
> HDFS_truncate_semantics_Mar15.pdf, HDFS_truncate_semantics_Mar21.pdf
>
>   Original Estimate: 1,344h
>  Remaining Estimate: 1,344h
>
> Systems with transaction support often need to undo changes made to the 
> underlying storage when a transaction is aborted. Currently HDFS does not 
> support truncate (a standard Posix operation) which is a reverse operation of 
> append, which makes upper layer applications use ugly workarounds (such as 
> keeping track of the discarded byte range per file in a separate metadata 
> store, and periodically running a vacuum process to rewrite compacted files) 
> to overcome this limitation of HDFS.



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