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Date: Tue, 3 Mar 2015 06:54:05 +0000 (UTC)
From: "Steve Armstrong (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12775193.1423984781000.61249.1425365645150@Atlassian.JIRA>
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 <JIRA.12775193.1423984781117@arcas>
Subject: [jira] [Commented] (HDFS-7800) Improve documentation for
 FileSystem.concat()
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    [ https://issues.apache.org/jira/browse/HDFS-7800?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14344634#comment-14344634 ] 

Steve Armstrong commented on HDFS-7800:
---------------------------------------

Wow, that's a fantastic piece of documentation. Why is this seperate from the javadoc I mentioned (https://hadoop.apache.org/docs/current/api/org/apache/hadoop/fs/FileSystem.html) and if they must be seperate, can the javadoc atleast point to the more detailed url?

> Improve documentation for FileSystem.concat()
> ---------------------------------------------
>
>                 Key: HDFS-7800
>                 URL: https://issues.apache.org/jira/browse/HDFS-7800
>             Project: Hadoop HDFS
>          Issue Type: Task
>    Affects Versions: 2.2.0, 2.6.0
>            Reporter: Steve Armstrong
>         Attachments: HDFS-7800-1.patch
>
>
> This is a documentation request.
> [FileSystem.concat()|https://hadoop.apache.org/docs/current/api/org/apache/hadoop/fs/FileSystem.html] says it will "Concat existing files together". It seems to be a Namenode-only operation though, mapping the data blocks into a single file. This means:
> # The destination must exist
> # The destination must be non-empty
> # The destination must have it's last block exactly full
> # All but the last of the source files must have their last block full
> # All the source file will be deleted by this operation
> HDFS-6641 brought up some of these limitations, but was closed as not a problem. I think the javadoc should be improved so it's clear this function was never intended to work the same as a general purpose file concatenation.


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