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https://issues.apache.org/jira/browse/HDFS-5902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13894973#comment-13894973
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Benoit Perroud commented on HDFS-5902:
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[~asanderson]: good feedbacks. Having the same parent makes sense.
Symlinks, append, snapshots etc are features that are not implemented in every
other filesystems, or are they? I mean, shall we keep the set of features to
the smallest common subset, or like rename function add a comment warning about
difference of implementation?
> Atomic Directory Swapping Operation
> -----------------------------------
>
> Key: HDFS-5902
> URL: https://issues.apache.org/jira/browse/HDFS-5902
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: namenode
> Affects Versions: 2.2.0
> Reporter: Benoit Perroud
> Priority: Minor
>
> With snapshots, we can already start to have a consistent view of the data
> over time.
> One missing primitive to do one more step in the direction of a transactional
> FS is the ability to swap atomically two folders:
> {code}
> swapFolders(src, dst)
> {code}
> As of today, we need to:
> 1. move the destination folder to a temporary name,
> 2. rename the source folder in destination's name
> 3. rename the dst folder with the temporary name in the source name.
> This can leads to race conditions where the data is not found.
> An operation inside the namenode achieving folders swapping, with the
> appropriate checks and locking to ensure atomicity, would be really useful to
> perform maintenance tasks like folder compation, format conversion, etc...
> (and lot of other use cases).
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