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https://issues.apache.org/jira/browse/HDFS-13102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16350793#comment-16350793
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Shashikant Banerjee commented on HDFS-13102:
--------------------------------------------

Patch v1 implements a SnapshotSkipList for Directory Diffs. It implements List 
interface for DirectoryDiff and provides a linear view of the list through 
general List API's.

> Implement SnapshotSkipList class to store Multi level DirectoryDiffs
> --------------------------------------------------------------------
>
>                 Key: HDFS-13102
>                 URL: https://issues.apache.org/jira/browse/HDFS-13102
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Shashikant Banerjee
>            Assignee: Shashikant Banerjee
>            Priority: Major
>         Attachments: HDFS-13102.001.patch
>
>
> HDFS-11225 explains an issue where deletion of older snapshots can take a 
> very long time in case the no of snapshot diffs is quite large for 
> directories. For any directory under a snapshot, to construct the children 
> list , it needs to combine all the diffs from that particular snapshot to the 
> last snapshotDiff record and reverseApply to the current children list of the 
> directory on live fs. This can take  a significant time if the no of snapshot 
> diffs are quite large and changes per diff is significant.
> This Jira proposes to store the Directory diffs in a SnapshotSkip list, where 
> we store multi level DirectoryDiffs. At each level, the Directory Diff will 
> be cumulative diff of k snapshot diffs,
> where k is the level of a node in the list. 
>  



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