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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3107) HDFS truncate
Date Mon, 12 Jan 2015 01:43:35 GMT

    [ 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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