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https://issues.apache.org/jira/browse/HDFS-3107?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Plamen Jeliazkov updated HDFS-3107:
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Attachment: HDFS-3107.patch
Attaching patch with updated Javadoc.
# Changed ClientProtocol JavaDoc to match what Konstantin pointed out.
# Also added an @return JavaDoc for ClientProtocol.
# Modified the FSDirectory unprotectedTruncate() JavaDoc and comments to remove
any notion of 'schedule block for truncate'. The scheduling logic lives in
FSNamesystem.
More tests to show when dealing with competing appends / creates are necessary.
I'll include some in the next patch.
> 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_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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