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Date: Fri, 2 Nov 2012 23:04:12 +0000 (UTC)
From: "Aaron T. Myers (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-4141) Directory diff in snapshots
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    [ https://issues.apache.org/jira/browse/HDFS-4141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13489819#comment-13489819 ] 

Aaron T. Myers commented on HDFS-4141:
--------------------------------------

Patch looks pretty good to me, and it definitely helps to clear up what exactly a diff is from the latest design doc posted by Suresh. My only suggestion for the code is that both apply2Previous/apply2Current and accessPrevious/accessCurrent are pretty similar to each other, and you could probably reduce some code duplication there.

The current code doesn't actually create a Diff at all, but I assume that will be added in another JIRA. I have just one question for you: how will multiple snapshots of the same directory be handled? My guess is that a single INodeDirectoryWithSnapshot will itself contain a list of Diffs, one per snapshot where files are changed in the directory. Is the plan for those diffs to be relative to each other?
                
> Directory diff in snapshots
> ---------------------------
>
>                 Key: HDFS-4141
>                 URL: https://issues.apache.org/jira/browse/HDFS-4141
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>            Reporter: Tsz Wo (Nicholas), SZE
>            Assignee: Tsz Wo (Nicholas), SZE
>         Attachments: h4141_20121101.patch, h4141_20121102b.patch, h4141_20121102.patch
>
>
> With snapshots, the same directory could have different states, e.g. different sets of children, in different snapshots.  We implement a directory diff algorithm in this JIRA.

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