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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7800) Improve documentation for FileSystem.concat()
Date Mon, 16 Feb 2015 12:39:11 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7800?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14322715#comment-14322715

Steve Loughran commented on HDFS-7800:

think is is all covered in the Filesystem spec, [http://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/filesystem/filesystem.html]
; if there's something missing can it go there? 

> 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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