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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3107) HDFS truncate
Date Sun, 28 Sep 2014 00:31:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14150830#comment-14150830
] 

Konstantin Shvachko commented on HDFS-3107:
-------------------------------------------

Hi Dhruba, good to hear from you.
The design was actually [outlined on Sept 5|https://issues.apache.org/jira/browse/HDFS-3107?focusedCommentId=14123590&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14123590].
The idea is rather simple. We just formalized it in a document per Colin's request last week.
More reviews is better. So if people need time lets wait until end of day Monday Sept 29.
Hope Roman is OK with that?

> 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,
editsStored
>
>   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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