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