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From "Plamen Jeliazkov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3107) HDFS truncate
Date Tue, 04 Nov 2014 16:46:37 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14196336#comment-14196336
] 

Plamen Jeliazkov commented on HDFS-3107:
----------------------------------------

[~cmccabe],

At the time [~shv] talked about my new patch there was nothing posted yet in HDFS-7056 minus
Konstantin's design doc.
We only uploaded even newer patches yesterday around noon.

Please be careful not to confuse [~shv] and [~cos].
The snapshot support patch (for HDFS-7056) was not ready yet when [~cos] made his comment.

We don't have to commit HDFS-3107 on its own. 
There is the option to treat the combined patch HDFS-3107-&-7056 as the first patch, which
accounts for upgrade and rollback functionality as well as snapshot support, demonstrated
in unit test.
This should address your comment: "My reasoning is that if the first patch breaks rollback,
it's tough to see it getting into trunk."
I am not objecting to do work on a branch but I am unsure it is necessary given the combined
patch seems to meet the support requirements asked for this work.

I'll investigate the FindBugs.

> 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-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_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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