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Date: Mon, 12 Jan 2015 01:43:35 +0000 (UTC)
From: "Konstantin Shvachko (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12546721.1331873581000.57709.1421027015206@Atlassian.JIRA>
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 <JIRA.12546721.1331873581101@arcas>
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=14273144#comment-14273144 ] 

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

[~wheat9] do you have comments or suggestions on the patch? Or do you have anybody in particular in mind to return from vacation? I mean we cannot wait for everybody as the Hadoop community is pretty big - there is always somebody on vacation.
I don't think we are rushing here. The patch is sitting here from September. People expressed desire to have the snapshot support implemented before committing the feature, which is now also done under HDFS-7056. And went through a series of good review rounds by Jing, Collin, Cos, which improved the implementation substantially. Byron independently tested the feature on a cluster with and without snapshots.

So let's plan to finally commit both issues eod tomorrow Monday. If there are no more comments.

> 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-3107-13.patch, HDFS-3107-14.patch, HDFS-3107-15.patch, HDFS-3107-HDFS-7056-combined.patch, HDFS-3107.008.patch, HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, HDFS_truncate.pdf, HDFS_truncate.pdf, HDFS_truncate.pdf, HDFS_truncate_semantics_Mar15.pdf, HDFS_truncate_semantics_Mar21.pdf, editsStored, editsStored.xml
>
>   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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