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From "Milind Bhandarkar (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3107) HDFS truncate
Date Tue, 20 Mar 2012 17:45:40 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13233609#comment-13233609

Milind Bhandarkar commented on HDFS-3107:

I must have missed a smiley :-)


After appends were enabled in HDFS, we have seen a lot of cases where a lot of (mainly text,
or even compressed text) datasets were merged using appends.

This is where customers realize their mistake immediately after starting to append, and do
a ctrl-c.

This is very common.

Milind Bhandarkar
Chief Architect, Greenplum Labs,
Data Computing Division, EMC
+1-650-523-3858 (W)
+1-408-666-8483 (C)

> HDFS truncate
> -------------
>                 Key: HDFS-3107
>                 URL: https://issues.apache.org/jira/browse/HDFS-3107
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: data-node, name-node
>            Reporter: Lei Chang
>         Attachments: HDFS_truncate_semantics_Mar15.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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