[jira] [Created] (HDFS-5902) Atomic Directory Swapping Operation

["Benoit Perroud (JIRA)" <ji...@apache.org>]

Benoit Perroud created HDFS-5902:
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             Summary: 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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