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Date: Sat, 6 Sep 2014 03:37:31 +0000 (UTC)
From: "Lei Chang (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12546721.1331873581000.8545.1409974651063@Atlassian.JIRA>
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Subject: [jira] [Commented] (HDFS-3107) HDFS truncate
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    [ https://issues.apache.org/jira/browse/HDFS-3107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14124291#comment-14124291 ] 

Lei Chang commented on HDFS-3107:
---------------------------------

Is it compatible with snapshot?

> 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_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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